Merge branch 'master' into fix/lost-and-found-scan-skip

adapters/gotaglib/end_to_end_test.go

@@ -90,7 +90,7 @@ var _ = Describe("Extractor", func() {
 		info.FileInfo = testFileInfo{FileInfo: fileInfo}
 
 		metadata := metadata.New(path, info)
-		return new(metadata.ToMediaFile(1, "folderID"))
+		return new(metadata.ToMediaFile(model.Library{ID: 1}, "folderID"))
 	}
 
 	BeforeEach(func() {

cmd/inspect.go

@@ -1,13 +1,17 @@
 package cmd
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
+	"path/filepath"
 	"strings"
 
 	"github.com/navidrome/navidrome/core"
+	"github.com/navidrome/navidrome/db"
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/persistence"
 	"github.com/pelletier/go-toml/v2"
 	"github.com/spf13/cobra"
 	"gopkg.in/yaml.v3"
@@ -28,7 +32,7 @@ var inspectCmd = &cobra.Command{
 	Long:  "Show file tags as seen by Navidrome",
 	Args:  cobra.MinimumNArgs(1),
 	Run: func(cmd *cobra.Command, args []string) {
-		runInspector(args)
+		runInspector(cmd.Context(), args)
 	},
 }
 
@@ -55,18 +59,24 @@ func prettyMarshal(v any) ([]byte, error) {
 	return []byte(res.String()), nil
 }
 
-func runInspector(args []string) {
+func runInspector(ctx context.Context, args []string) {
 	marshal := marshalers[format]
 	if marshal == nil {
 		log.Fatal("Invalid format", "format", format)
 	}
+	libs := loadLibraries(ctx)
+	matcher := model.NewLibraryMatcher(libs)
 	var out []core.InspectOutput
 	for _, filePath := range args {
 		if !model.IsAudioFile(filePath) {
 			log.Warn("Not an audio file", "file", filePath)
 			continue
 		}
-		output, err := core.Inspect(filePath, 1, "")
+		lib, ok := libraryForFile(matcher, filePath)
+		if !ok && len(libs) > 0 {
+			log.Warn("File is not in any library, using the global PID config", "file", filePath)
+		}
+		output, err := core.Inspect(filePath, lib, "")
 		if err != nil {
 			log.Warn("Unable to process file", "file", filePath, "error", err)
 			continue
@@ -77,3 +87,33 @@ func runInspector(args []string) {
 	data, _ := marshal(out)
 	fmt.Println(string(data))
 }
+
+// loadLibraries reads the libraries, so each file gets its library's PID config. It never creates a DB.
+func loadLibraries(ctx context.Context) model.Libraries {
+	if dbFile, ok := existingDBFile(); !ok {
+		log.Warn(ctx, "No database found, using the global PID config", "path", dbFile)
+		return nil
+	}
+	defer db.Init(ctx)()
+	libs, err := persistence.New(db.Db()).Library().GetAll(ctx)
+	if err != nil {
+		log.Warn(ctx, "Could not load libraries, using the global PID config", err)
+		return nil
+	}
+	for i := range libs {
+		if absPath, err := filepath.Abs(libs[i].Path); err == nil {
+			libs[i].Path = absPath
+		}
+	}
+	return libs
+}
+
+// libraryForFile falls back to the default library with no overrides, which uses the global PID config.
+func libraryForFile(matcher *model.LibraryMatcher, filePath string) (model.Library, bool) {
+	if absPath, err := filepath.Abs(filePath); err == nil {
+		if lib, ok := matcher.FindLibrary(absPath); ok {
+			return lib, true
+		}
+	}
+	return model.Library{ID: model.DefaultLibraryID}, false
+}

cmd/inspect_test.go

@@ -0,0 +1,61 @@
+package cmd
+
+import (
+	"os"
+	"path/filepath"
+
+	"github.com/navidrome/navidrome/conf"
+	"github.com/navidrome/navidrome/conf/configtest"
+	"github.com/navidrome/navidrome/model"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("inspect", func() {
+	Describe("libraryForFile", func() {
+		var matcher *model.LibraryMatcher
+		var root string
+
+		BeforeEach(func() {
+			root = GinkgoT().TempDir()
+			cwd, err := os.Getwd()
+			Expect(err).ToNot(HaveOccurred())
+			matcher = model.NewLibraryMatcher(model.Libraries{
+				{ID: 1, Path: filepath.Join(root, "music")},
+				{ID: 2, Path: filepath.Join(cwd, "loose"), PIDAlbum: "folder"},
+			})
+		})
+
+		It("returns the library that contains an absolute path", func() {
+			lib, ok := libraryForFile(matcher, filepath.Join(root, "music", "album", "track.mp3"))
+			Expect(ok).To(BeTrue())
+			Expect(lib.ID).To(Equal(1))
+		})
+
+		It("resolves a relative path against the working directory", func() {
+			lib, ok := libraryForFile(matcher, filepath.Join("loose", "track.mp3"))
+			Expect(ok).To(BeTrue())
+			Expect(lib.PIDAlbum).To(Equal("folder"))
+		})
+
+		It("falls back to the default library without overrides", func() {
+			lib, ok := libraryForFile(matcher, filepath.Join(root, "elsewhere", "track.mp3"))
+			Expect(ok).To(BeFalse())
+			Expect(lib).To(Equal(model.Library{ID: model.DefaultLibraryID}))
+		})
+	})
+
+	Describe("loadLibraries", func() {
+		BeforeEach(func() {
+			DeferCleanup(configtest.SetupConfig())
+		})
+
+		It("does not create a database when there is none", func() {
+			dbFile := filepath.Join(GinkgoT().TempDir(), "navidrome.db")
+			conf.Server.DbPath = dbFile + "?_journal_mode=WAL"
+
+			Expect(loadLibraries(GinkgoT().Context())).To(BeNil())
+			Expect(dbFile).ToNot(BeAnExistingFile())
+		})
+	})
+})

cmd/root.go

@@ -190,16 +190,20 @@ func schedulePeriodicScan(ctx context.Context) func() error {
 	}
 }
 
-func pidHashChanged(ds model.DataStore) (bool, error) {
-	pidAlbum, err := ds.Property().DefaultGet(context.Background(), consts.PIDAlbumKey, "")
+// librariesWithChangedPID returns the names of the libraries whose effective PID config differs from
+// the one used by their last finished scan
+func librariesWithChangedPID(ctx context.Context, ds model.DataStore) ([]string, error) {
+	libs, err := ds.Library().GetAll(ctx)
 	if err != nil {
-		return false, err
+		return nil, err
 	}
-	pidTrack, err := ds.Property().DefaultGet(context.Background(), consts.PIDTrackKey, "")
-	if err != nil {
-		return false, err
+	var names []string
+	for _, lib := range libs {
+		if lib.PIDChanged() {
+			names = append(names, lib.Name)
+		}
 	}
-	return !strings.EqualFold(pidAlbum, conf.Server.PID.Album) || !strings.EqualFold(pidTrack, conf.Server.PID.Track), nil
+	return names, nil
 }
 
 // runInitialScan runs an initial scan of the music library if needed.
@@ -214,12 +218,12 @@ func runInitialScan(ctx context.Context) func() error {
 		if err != nil {
 			return err
 		}
-		pidHasChanged, err := pidHashChanged(ds)
+		pidChangedLibs, err := librariesWithChangedPID(ctx, ds)
 		if err != nil {
 			return err
 		}
 		scanOnStartup := conf.Server.Scanner.Enabled && conf.Server.Scanner.ScanOnStartup
-		scanNeeded := scanOnStartup || inProgress || fullScanRequired == "1" || pidHasChanged
+		scanNeeded := scanOnStartup || inProgress || fullScanRequired == "1" || len(pidChangedLibs) > 0
 		time.Sleep(2 * time.Second) // Wait 2 seconds before the initial scan
 		if scanNeeded {
 			s := CreateScanner(ctx)
@@ -227,9 +231,9 @@ func runInitialScan(ctx context.Context) func() error {
 			case fullScanRequired == "1":
 				log.Warn(ctx, "Full scan required after migration")
 				_ = ds.Property().Delete(ctx, consts.FullScanAfterMigrationFlagKey)
-			case pidHasChanged:
-				log.Warn(ctx, "PID config changed, performing full scan")
-				fullScanRequired = "1"
+			case len(pidChangedLibs) > 0:
+				// Includes never-scanned libraries. The scanner rescans in full only the ones that need it
+				log.Warn(ctx, "Libraries with a new or changed PID config, scanning", "libraries", pidChangedLibs)
 			case inProgress:
 				log.Warn(ctx, "Resuming interrupted scan")
 			default:

cmd/root_test.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"path"
@@ -9,6 +10,8 @@ import (
 	"github.com/go-chi/chi/v5"
 	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/conf/configtest"
+	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/tests"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
@@ -44,3 +47,30 @@ var _ = Describe("profilerHandler", func() {
 		Entry("with a trailing-slash BasePath", "/music/"),
 	)
 })
+
+var _ = Describe("librariesWithChangedPID", func() {
+	var ds *tests.MockDataStore
+	var libs *tests.MockLibraryRepo
+
+	BeforeEach(func() {
+		DeferCleanup(configtest.SetupConfig())
+		libs = &tests.MockLibraryRepo{}
+		ds = &tests.MockDataStore{MockedLibrary: libs}
+	})
+
+	It("returns only the libraries whose PID config changed", func() {
+		pid := model.Library{}.EffectivePID()
+		libs.SetData(model.Libraries{
+			{ID: 1, Name: "Same", ScannedPIDAlbum: pid.Album, ScannedPIDTrack: pid.Track},
+			{ID: 2, Name: "Changed", PIDAlbum: "folder", ScannedPIDAlbum: pid.Album, ScannedPIDTrack: pid.Track},
+			{ID: 3, Name: "Never scanned"},
+		})
+		Expect(librariesWithChangedPID(GinkgoT().Context(), ds)).To(ConsistOf("Changed", "Never scanned"))
+	})
+
+	It("returns the error from the repository", func() {
+		libs.Err = errors.New("db down")
+		_, err := librariesWithChangedPID(GinkgoT().Context(), ds)
+		Expect(err).To(MatchError("db down"))
+	})
+})

cmd/utils.go

@@ -18,11 +18,16 @@ import (
 	"github.com/navidrome/navidrome/persistence"
 )
 
-// requireExistingDB aborts the command when the database file (DbPath minus DSN
-// params) does not exist.
-func requireExistingDB() {
+// existingDBFile returns the database file (DbPath minus DSN params), and whether it exists.
+func existingDBFile() (string, bool) {
 	path, _, _ := strings.Cut(conf.Server.DbPath, "?")
-	if _, err := os.Stat(path); os.IsNotExist(err) {
+	_, err := os.Stat(path)
+	return path, err == nil
+}
+
+// requireExistingDB aborts the command when the database file does not exist.
+func requireExistingDB() {
+	if path, ok := existingDBFile(); !ok {
 		log.Fatal("No existing database", "path", path)
 	}
 }

consts/consts.go

@@ -156,8 +156,6 @@ const (
 	//DefaultAlbumPID = "album_legacy"
 	DefaultAlbumPID = "musicbrainz_albumid|albumartistid,album,albumversion,releasedate"
 	DefaultTrackPID = "musicbrainz_trackid|albumid,discnumber,tracknumber,title"
-	PIDAlbumKey     = "PIDAlbum"
-	PIDTrackKey     = "PIDTrack"
 )
 
 const (

core/inspect.go

@@ -15,7 +15,7 @@ type InspectOutput struct {
 	MappedTags *model.MediaFile `json:"mappedTags,omitempty"`
 }
 
-func Inspect(filePath string, libraryId int, folderId string) (*InspectOutput, error) {
+func Inspect(filePath string, lib model.Library, folderId string) (*InspectOutput, error) {
 	path, file := filepath.Split(filePath)
 
 	s, err := storage.For(path)
@@ -39,12 +39,22 @@ func Inspect(filePath string, libraryId int, folderId string) (*InspectOutput, e
 		return nil, model.ErrNotFound
 	}
 
-	md := metadata.New(path, tag)
+	md := metadata.New(scannerPath(lib, filePath), tag)
 	result := &InspectOutput{
 		File:       filePath,
 		RawTags:    tags[file].Tags,
-		MappedTags: new(md.ToMediaFile(libraryId, folderId)),
+		MappedTags: new(md.ToMediaFile(lib, folderId)),
 	}
 
 	return result, nil
 }
+
+// scannerPath returns the path the scanner uses for the file (relative to its library), so
+// folder-based PIDs match the DB. Files outside the library keep their absolute path.
+func scannerPath(lib model.Library, filePath string) string {
+	absPath, err := filepath.Abs(filePath)
+	if err != nil || lib.Path == "" {
+		return filePath
+	}
+	return model.LibraryRelativePath(lib.Path, absPath)
+}

core/inspect_test.go

@@ -0,0 +1,45 @@
+package core_test
+
+import (
+	"path/filepath"
+
+	"github.com/navidrome/navidrome/core"
+	"github.com/navidrome/navidrome/model"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Inspect", func() {
+	var fixtures string
+
+	BeforeEach(func() {
+		var err error
+		fixtures, err = filepath.Abs(filepath.Join("tests", "fixtures"))
+		Expect(err).ToNot(HaveOccurred())
+	})
+
+	It("maps the file with the library-relative path the scanner uses", func() {
+		lib := model.Library{ID: 2, Path: filepath.Dir(fixtures), PIDAlbum: "folder"}
+		out, err := core.Inspect(filepath.Join(fixtures, "test.mp3"), lib, "")
+		Expect(err).ToNot(HaveOccurred())
+		Expect(out.MappedTags.Path).To(Equal("fixtures/test.mp3"))
+		Expect(out.MappedTags.LibraryID).To(Equal(2))
+	})
+
+	It("gives the same IDs for relative and absolute paths", func() {
+		lib := model.Library{ID: 2, Path: filepath.Dir(fixtures), PIDAlbum: "folder"}
+		abs, err := core.Inspect(filepath.Join(fixtures, "test.mp3"), lib, "")
+		Expect(err).ToNot(HaveOccurred())
+		rel, err := core.Inspect(filepath.Join("tests", "fixtures", "test.mp3"), lib, "")
+		Expect(err).ToNot(HaveOccurred())
+		Expect(rel.MappedTags.AlbumID).To(Equal(abs.MappedTags.AlbumID))
+		Expect(rel.MappedTags.PID).To(Equal(abs.MappedTags.PID))
+	})
+
+	It("keeps the given path for a file outside the library", func() {
+		filePath := filepath.Join(fixtures, "test.mp3")
+		out, err := core.Inspect(filePath, model.Library{ID: model.DefaultLibraryID}, "")
+		Expect(err).ToNot(HaveOccurred())
+		Expect(out.MappedTags.Path).To(Equal(filePath))
+	})
+})

core/library.go

@@ -2,10 +2,12 @@ package core
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io/fs"
 	"os"
 	"path/filepath"
+	"slices"
 	"strconv"
 	"strings"
 	"time"
@@ -15,6 +17,7 @@ import (
 	"github.com/navidrome/navidrome/core/storage"
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/model/metadata"
 	"github.com/navidrome/navidrome/model/request"
 	"github.com/navidrome/navidrome/server/events"
 	"github.com/navidrome/navidrome/utils/slice"
@@ -200,23 +203,22 @@ func (r *libraryRepositoryWrapper) Update(ctx context.Context, id string, entity
 	}
 
 	pathChanged := originalLib.Path != lib.Path
+	pidChanged := (updatesColumn(cols, "pidAlbum") && originalLib.PIDAlbum != lib.PIDAlbum) ||
+		(updatesColumn(cols, "pidTrack") && originalLib.PIDTrack != lib.PIDTrack)
 
 	err = r.LibraryRepository.Put(ctx, lib, cols...)
 	if err != nil {
 		return r.mapError(err)
 	}
 
-	// Restart watcher and trigger scan if path was updated
-	if pathChanged {
-		if r.watcher != nil {
-			if err := r.watcher.Watch(ctx, lib); err != nil {
-				log.Warn(ctx, "Failed to restart watcher for updated library", "libraryID", lib.ID, "name", lib.Name, "path", lib.Path, err)
-			}
+	if pathChanged && r.watcher != nil {
+		if err := r.watcher.Watch(ctx, lib); err != nil {
+			log.Warn(ctx, "Failed to restart watcher for updated library", "libraryID", lib.ID, "name", lib.Name, "path", lib.Path, err)
 		}
+	}
 
-		if r.scanner != nil {
-			go r.triggerScan(ctx, lib, "updated")
-		}
+	if (pathChanged || pidChanged) && r.scanner != nil {
+		go r.triggerScan(ctx, lib, "updated")
 	}
 
 	// Send library refresh event to all clients
@@ -325,6 +327,15 @@ func (r *libraryRepositoryWrapper) validateLibrary(ctx context.Context, library
 		}
 	}
 
+	library.PIDAlbum = strings.TrimSpace(library.PIDAlbum)
+	library.PIDTrack = strings.TrimSpace(library.PIDTrack)
+	if err := metadata.ValidatePIDSpec(library.PIDAlbum, true); err != nil {
+		validationErrors["pidAlbum"] = err.Error()
+	}
+	if err := metadata.ValidatePIDSpec(library.PIDTrack, false); err != nil {
+		validationErrors["pidTrack"] = err.Error()
+	}
+
 	if len(validationErrors) > 0 {
 		return &rest.ValidationError{Errors: validationErrors}
 	}
@@ -332,6 +343,11 @@ func (r *libraryRepositoryWrapper) validateLibrary(ctx context.Context, library
 	return nil
 }
 
+// updatesColumn reports whether an update with these columns writes col. No columns means all of them.
+func updatesColumn(cols []string, col string) bool {
+	return len(cols) == 0 || slices.Contains(cols, col)
+}
+
 func (r *libraryRepositoryWrapper) validateLibraryPath(ctx context.Context, library *model.Library) error {
 	// Validate path format
 	if !filepath.IsAbs(library.Path) {
@@ -399,11 +415,27 @@ func (s *libraryService) validateLibraryIDs(ctx context.Context, libraryIDs []in
 	return nil
 }
 
+var scanWaitInterval = time.Second
+
 func (r *libraryRepositoryWrapper) triggerScan(ctx context.Context, lib *model.Library, action string) {
+	// Runs in its own goroutine and outlives the HTTP request
+	ctx = context.WithoutCancel(ctx)
+
+	// A running scan loaded the libraries before this change, and would reject a new request
+	for {
+		status, err := r.scanner.Status(ctx)
+		if err != nil || !status.Scanning {
+			break
+		}
+		time.Sleep(scanWaitInterval)
+	}
+
 	log.Info(ctx, fmt.Sprintf("Triggering scan for %s library", action), "libraryID", lib.ID, "name", lib.Name, "path", lib.Path)
 	start := time.Now()
-	warnings, err := r.scanner.ScanAll(ctx, false) // Quick scan for new library
-	if err != nil {
+	warnings, err := r.scanner.ScanAll(ctx, false) // Quick scan: the scanner rescans libraries with a changed PID config in full
+	if errors.Is(err, model.ErrAlreadyScanning) {
+		log.Debug(ctx, "Scan already running, it covers this change", "libraryID", lib.ID, "name", lib.Name)
+	} else if err != nil {
 		log.Error(ctx, fmt.Sprintf("Error scanning %s library", action), "libraryID", lib.ID, "name", lib.Name, err)
 	} else {
 		log.Info(ctx, fmt.Sprintf("Scan completed for %s library", action), "libraryID", lib.ID, "name", lib.Name, "warnings", len(warnings), "elapsed", time.Since(start))

core/library_test.go

@@ -322,6 +322,37 @@ var _ = Describe("Library Service", func() {
 			})
 		})
 
+		Describe("PID validation", func() {
+			pidError := func(err error, field string) string {
+				var validationErr *rest.ValidationError
+				Expect(errors.As(err, &validationErr)).To(BeTrue())
+				return validationErr.Errors[field]
+			}
+
+			It("rejects an unknown attribute in the album PID", func() {
+				_, err := repo.Save(ctx, &model.Library{Name: "Lib", Path: tempDir, PIDAlbum: "albmversion"})
+				Expect(pidError(err, "pidAlbum")).To(ContainSubstring(`unknown attribute "albmversion"`))
+			})
+
+			It("rejects albumid in the album PID", func() {
+				_, err := repo.Save(ctx, &model.Library{Name: "Lib", Path: tempDir, PIDAlbum: "albumid"})
+				Expect(pidError(err, "pidAlbum")).To(ContainSubstring("albumid"))
+			})
+
+			It("rejects an unknown attribute in the track PID", func() {
+				_, err := repo.Save(ctx, &model.Library{Name: "Lib", Path: tempDir, PIDTrack: "nosuchtag"})
+				Expect(pidError(err, "pidTrack")).To(ContainSubstring(`unknown attribute "nosuchtag"`))
+			})
+
+			It("trims spaces", func() {
+				library := &model.Library{Name: "Lib", Path: tempDir, PIDAlbum: " folder ", PIDTrack: "  "}
+				_, err := repo.Save(ctx, library)
+				Expect(err).ToNot(HaveOccurred())
+				Expect(library.PIDAlbum).To(Equal("folder"))
+				Expect(library.PIDTrack).To(BeEmpty())
+			})
+		})
+
 		Describe("Path Validation", func() {
 			Context("Create operation", func() {
 				It("fails when path is not absolute", func() {
@@ -679,6 +710,48 @@ var _ = Describe("Library Service", func() {
 			}, "100ms", "10ms").Should(Equal(0))
 		})
 
+		It("triggers scan when updating the library PID config", func() {
+			libraryRepo.SetData(model.Libraries{{ID: 1, Name: "Library", Path: tempDir}})
+
+			library := model.Library{ID: 1, Name: "Library", Path: tempDir, PIDAlbum: "folder"}
+			Expect(repo.Update(ctx, "1", library)).To(Succeed())
+
+			Eventually(func() int {
+				return scanner.GetScanAllCallCount()
+			}, "1s", "10ms").Should(Equal(1))
+			// A quick scan: the scanner itself rescans this library in full
+			Expect(scanner.GetScanAllCalls()[0].FullScan).To(BeFalse())
+		})
+
+		It("does not trigger scan when the PID fields were not sent", func() {
+			libraryRepo.SetData(model.Libraries{{ID: 1, Name: "Library", Path: tempDir, PIDAlbum: "folder"}})
+
+			// The REST layer decodes a missing pidAlbum as "". Only the sent fields count.
+			library := model.Library{ID: 1, Name: "Renamed", Path: tempDir}
+			Expect(repo.Update(ctx, "1", library, "name", "path")).To(Succeed())
+
+			Consistently(func() int {
+				return scanner.GetScanAllCallCount()
+			}, "100ms", "10ms").Should(Equal(0))
+		})
+
+		It("waits for a running scan before triggering a new one", func() {
+			libraryRepo.SetData(model.Libraries{{ID: 1, Name: "Library", Path: tempDir}})
+			scanner.SetScanning(true)
+
+			library := model.Library{ID: 1, Name: "Library", Path: tempDir, PIDAlbum: "folder"}
+			Expect(repo.Update(ctx, "1", library)).To(Succeed())
+
+			Consistently(func() int {
+				return scanner.GetScanAllCallCount()
+			}, "200ms", "20ms").Should(Equal(0))
+
+			scanner.SetScanning(false)
+			Eventually(func() int {
+				return scanner.GetScanAllCallCount()
+			}, "3s", "20ms").Should(Equal(1))
+		})
+
 		It("does not trigger scan when library creation fails", func() {
 			// Try to create library with invalid data (empty name)
 			library := &model.Library{Path: tempDir}

core/metrics/insights.go

@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"runtime/debug"
+	"slices"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -269,9 +270,13 @@ func (c *insightsCollector) collect(ctx context.Context) []byte {
 	if err != nil {
 		log.Trace(ctx, "Error reading radios count", err)
 	}
-	data.Library.Libraries, err = c.ds.Library().CountAll(ctx)
+	libs, err := c.ds.Library().GetAll(ctx)
 	if err != nil {
-		log.Trace(ctx, "Error reading libraries count", err)
+		log.Trace(ctx, "Error reading libraries", err)
+	}
+	data.Library.Libraries = int64(len(libs))
+	if slices.ContainsFunc(libs, func(lib model.Library) bool { return lib.PIDAlbum != "" || lib.PIDTrack != "" }) {
+		data.Config.HasCustomPID = true
 	}
 	data.Library.ActiveUsers, err = c.ds.User().CountAll(ctx, model.QueryOptions{
 		Filters: squirrel.Gt{"last_access_at": time.Now().Add(-7 * 24 * time.Hour)},

core/playlists/import.go

@@ -78,8 +78,8 @@ func (s *playlists) resolveFolder(ctx context.Context, dir string) (*model.Folde
 	if err != nil {
 		return nil, err
 	}
-	matcher := newLibraryMatcher(libs)
-	lib, ok := matcher.findLibrary(dir)
+	matcher := model.NewLibraryMatcher(libs)
+	lib, ok := matcher.FindLibrary(dir)
 	if !ok {
 		return nil, fmt.Errorf("%w: %s", errNotInLibrary, dir)
 	}

core/playlists/parse_m3u.go

@@ -1,13 +1,11 @@
 package playlists
 
 import (
-	"cmp"
 	"context"
 	"fmt"
 	"io"
 	"net/url"
 	"path/filepath"
-	"slices"
 	"strings"
 	"time"
 
@@ -156,61 +154,9 @@ func (r pathResolution) ToQualifiedString() (string, error) {
 	return fmt.Sprintf("%d:%s", r.libraryID, filepath.ToSlash(relativePath)), nil
 }
 
-// libraryMatcher holds sorted libraries with cleaned paths for efficient path matching.
-type libraryMatcher struct {
-	libraries    model.Libraries
-	cleanedPaths []string
-}
-
-// findLibraryForPath finds which library contains the given absolute path.
-// Returns library ID and path, or 0 and empty string if not found.
-func (lm *libraryMatcher) findLibraryForPath(absolutePath string) (int, string) {
-	lib, ok := lm.findLibrary(absolutePath)
-	if !ok {
-		return 0, ""
-	}
-	return lib.ID, filepath.Clean(lib.Path)
-}
-
-// findLibrary checks if the absolute path is under any of the library paths.
-func (lm *libraryMatcher) findLibrary(absolutePath string) (model.Library, bool) {
-	// Check sorted libraries (longest path first) to find the best match
-	for i, cleanLibPath := range lm.cleanedPaths {
-		// Check if absolutePath is under this library path
-		if strings.HasPrefix(absolutePath, cleanLibPath) {
-			// Ensure it's a proper path boundary (not just a prefix)
-			if len(absolutePath) == len(cleanLibPath) || absolutePath[len(cleanLibPath)] == filepath.Separator {
-				return lm.libraries[i], true
-			}
-		}
-	}
-	return model.Library{}, false
-}
-
-// newLibraryMatcher creates a libraryMatcher with libraries sorted by path length (longest first).
-// This ensures correct matching when library paths are prefixes of each other.
-// Example: /music-classical must be checked before /music
-// Otherwise, /music-classical/track.mp3 would match /music instead of /music-classical
-func newLibraryMatcher(libs model.Libraries) *libraryMatcher {
-	// Sort libraries by path length (descending) to ensure longest paths match first.
-	slices.SortFunc(libs, func(i, j model.Library) int {
-		return cmp.Compare(len(j.Path), len(i.Path)) // Reverse order for descending
-	})
-
-	// Pre-clean all library paths once for efficient matching
-	cleanedPaths := make([]string, len(libs))
-	for i, lib := range libs {
-		cleanedPaths[i] = filepath.Clean(lib.Path)
-	}
-	return &libraryMatcher{
-		libraries:    libs,
-		cleanedPaths: cleanedPaths,
-	}
-}
-
 // pathResolver handles path resolution logic for playlist imports.
 type pathResolver struct {
-	matcher *libraryMatcher
+	matcher *model.LibraryMatcher
 }
 
 // newPathResolver creates a pathResolver with libraries loaded from the datastore.
@@ -219,7 +165,7 @@ func newPathResolver(ctx context.Context, ds model.DataStore) (*pathResolver, er
 	if err != nil {
 		return nil, err
 	}
-	matcher := newLibraryMatcher(libs)
+	matcher := model.NewLibraryMatcher(libs)
 	return &pathResolver{matcher: matcher}, nil
 }
 
@@ -246,14 +192,14 @@ func (r *pathResolver) resolvePath(line string, folder *model.Folder) pathResolu
 // a pathResolution with the library information. Returns an invalid resolution if
 // the path is not found in any library.
 func (r *pathResolver) findInLibraries(absolutePath string) pathResolution {
-	libID, libPath := r.matcher.findLibraryForPath(absolutePath)
-	if libID == 0 {
+	lib, ok := r.matcher.FindLibrary(absolutePath)
+	if !ok {
 		return pathResolution{valid: false}
 	}
 	return pathResolution{
 		absolutePath: absolutePath,
-		libraryPath:  libPath,
-		libraryID:    libID,
+		libraryPath:  filepath.Clean(lib.Path),
+		libraryID:    lib.ID,
 		valid:        true,
 	}
 }
@@ -288,7 +234,7 @@ func (r *pathResolver) resolvePaths(ctx context.Context, folder *model.Folder, l
 // HTTP(S) URLs are stored as-is (gated by EnableM3UExternalAlbumArt).
 // Local paths (file://, absolute, or relative) are resolved to an absolute path
 // and validated against known library boundaries via matcher.
-func resolveImageURL(value string, folder *model.Folder, matcher *libraryMatcher, owner model.User) string {
+func resolveImageURL(value string, folder *model.Folder, matcher *model.LibraryMatcher, owner model.User) string {
 	value = strings.TrimSpace(value)
 	if value == "" {
 		return ""
@@ -308,7 +254,7 @@ func resolveImageURL(value string, folder *model.Folder, matcher *libraryMatcher
 		return ""
 	}
 
-	lib, ok := matcher.findLibrary(localPath)
+	lib, ok := matcher.FindLibrary(localPath)
 	// A playlist without a folder (API upload, or CLI import from outside all libraries) may only use the owner's libraries.
 	if !ok || (folder == nil && !owner.HasLibraryAccess(lib.ID)) {
 		return ""

core/playlists/parse_m3u_test.go

@@ -9,187 +9,6 @@ import (
 	. "github.com/onsi/gomega"
 )
 
-var _ = Describe("libraryMatcher", func() {
-	var ds *tests.MockDataStore
-	var mockLibRepo *tests.MockLibraryRepo
-	ctx := context.Background()
-
-	BeforeEach(func() {
-		tests.SkipOnWindows("path separator bug (#TBD-path-sep-playlists)")
-		mockLibRepo = &tests.MockLibraryRepo{}
-		ds = &tests.MockDataStore{
-			MockedLibrary: mockLibRepo,
-		}
-	})
-
-	// Helper function to create a libraryMatcher from the mock datastore
-	createMatcher := func(ds model.DataStore) *libraryMatcher {
-		libs, err := ds.Library().GetAll(ctx)
-		Expect(err).ToNot(HaveOccurred())
-		return newLibraryMatcher(libs)
-	}
-
-	Describe("Longest library path matching", func() {
-		It("matches the longest library path when multiple libraries share a prefix", func() {
-			// Setup libraries with prefix conflicts
-			mockLibRepo.SetData([]model.Library{
-				{ID: 1, Path: "/music"},
-				{ID: 2, Path: "/music-classical"},
-				{ID: 3, Path: "/music-classical/opera"},
-			})
-
-			matcher := createMatcher(ds)
-
-			// Test that longest path matches first and returns correct library ID
-			testCases := []struct {
-				path            string
-				expectedLibID   int
-				expectedLibPath string
-			}{
-				{"/music-classical/opera/track.mp3", 3, "/music-classical/opera"},
-				{"/music-classical/track.mp3", 2, "/music-classical"},
-				{"/music/track.mp3", 1, "/music"},
-				{"/music-classical/opera/subdir/file.mp3", 3, "/music-classical/opera"},
-			}
-
-			for _, tc := range testCases {
-				libID, libPath := matcher.findLibraryForPath(tc.path)
-				Expect(libID).To(Equal(tc.expectedLibID), "Path %s should match library ID %d, but got %d", tc.path, tc.expectedLibID, libID)
-				Expect(libPath).To(Equal(tc.expectedLibPath), "Path %s should match library path %s, but got %s", tc.path, tc.expectedLibPath, libPath)
-			}
-		})
-
-		It("handles libraries with similar prefixes but different structures", func() {
-			mockLibRepo.SetData([]model.Library{
-				{ID: 1, Path: "/home/user/music"},
-				{ID: 2, Path: "/home/user/music-backup"},
-			})
-
-			matcher := createMatcher(ds)
-
-			// Test that music-backup library is matched correctly
-			libID, libPath := matcher.findLibraryForPath("/home/user/music-backup/track.mp3")
-			Expect(libID).To(Equal(2))
-			Expect(libPath).To(Equal("/home/user/music-backup"))
-
-			// Test that music library is still matched correctly
-			libID, libPath = matcher.findLibraryForPath("/home/user/music/track.mp3")
-			Expect(libID).To(Equal(1))
-			Expect(libPath).To(Equal("/home/user/music"))
-		})
-
-		It("matches path that is exactly the library root", func() {
-			mockLibRepo.SetData([]model.Library{
-				{ID: 1, Path: "/music"},
-				{ID: 2, Path: "/music-classical"},
-			})
-
-			matcher := createMatcher(ds)
-
-			// Exact library path should match
-			libID, libPath := matcher.findLibraryForPath("/music-classical")
-			Expect(libID).To(Equal(2))
-			Expect(libPath).To(Equal("/music-classical"))
-		})
-
-		It("handles complex nested library structures", func() {
-			mockLibRepo.SetData([]model.Library{
-				{ID: 1, Path: "/media"},
-				{ID: 2, Path: "/media/audio"},
-				{ID: 3, Path: "/media/audio/classical"},
-				{ID: 4, Path: "/media/audio/classical/baroque"},
-			})
-
-			matcher := createMatcher(ds)
-
-			testCases := []struct {
-				path            string
-				expectedLibID   int
-				expectedLibPath string
-			}{
-				{"/media/audio/classical/baroque/bach/track.mp3", 4, "/media/audio/classical/baroque"},
-				{"/media/audio/classical/mozart/track.mp3", 3, "/media/audio/classical"},
-				{"/media/audio/rock/track.mp3", 2, "/media/audio"},
-				{"/media/video/movie.mp4", 1, "/media"},
-			}
-
-			for _, tc := range testCases {
-				libID, libPath := matcher.findLibraryForPath(tc.path)
-				Expect(libID).To(Equal(tc.expectedLibID), "Path %s should match library ID %d", tc.path, tc.expectedLibID)
-				Expect(libPath).To(Equal(tc.expectedLibPath), "Path %s should match library path %s", tc.path, tc.expectedLibPath)
-			}
-		})
-	})
-
-	Describe("Edge cases", func() {
-		It("handles empty library list", func() {
-			mockLibRepo.SetData([]model.Library{})
-
-			matcher := createMatcher(ds)
-			Expect(matcher).ToNot(BeNil())
-
-			// Should not match anything
-			libID, libPath := matcher.findLibraryForPath("/music/track.mp3")
-			Expect(libID).To(Equal(0))
-			Expect(libPath).To(BeEmpty())
-		})
-
-		It("handles single library", func() {
-			mockLibRepo.SetData([]model.Library{
-				{ID: 1, Path: "/music"},
-			})
-
-			matcher := createMatcher(ds)
-
-			libID, libPath := matcher.findLibraryForPath("/music/track.mp3")
-			Expect(libID).To(Equal(1))
-			Expect(libPath).To(Equal("/music"))
-		})
-
-		It("handles libraries with special characters in paths", func() {
-			mockLibRepo.SetData([]model.Library{
-				{ID: 1, Path: "/music[test]"},
-				{ID: 2, Path: "/music(backup)"},
-			})
-
-			matcher := createMatcher(ds)
-			Expect(matcher).ToNot(BeNil())
-
-			// Special characters should match literally
-			libID, libPath := matcher.findLibraryForPath("/music[test]/track.mp3")
-			Expect(libID).To(Equal(1))
-			Expect(libPath).To(Equal("/music[test]"))
-		})
-	})
-
-	Describe("Path matching order", func() {
-		It("ensures longest paths match first", func() {
-			mockLibRepo.SetData([]model.Library{
-				{ID: 1, Path: "/a"},
-				{ID: 2, Path: "/ab"},
-				{ID: 3, Path: "/abc"},
-			})
-
-			matcher := createMatcher(ds)
-
-			// Verify that longer paths match correctly (not cut off by shorter prefix)
-			testCases := []struct {
-				path          string
-				expectedLibID int
-			}{
-				{"/abc/file.mp3", 3},
-				{"/ab/file.mp3", 2},
-				{"/a/file.mp3", 1},
-			}
-
-			for _, tc := range testCases {
-				libID, _ := matcher.findLibraryForPath(tc.path)
-				Expect(libID).To(Equal(tc.expectedLibID), "Path %s should match library ID %d", tc.path, tc.expectedLibID)
-			}
-		})
-	})
-})
-
 var _ = Describe("pathResolver", func() {
 	var ds *tests.MockDataStore
 	var mockLibRepo *tests.MockLibraryRepo

db/migrations/20260929221042_add_library_pid_columns.sql

@@ -0,0 +1,18 @@
+-- +goose Up
+-- +goose StatementBegin
+alter table library add column pid_album varchar default '' not null;
+alter table library add column pid_track varchar default '' not null;
+alter table library add column scanned_pid_album varchar default '' not null;
+alter table library add column scanned_pid_track varchar default '' not null;
+
+-- Every library was scanned with the global PID config, so seed it as their scanned config.
+-- This way the upgrade does not trigger a full rescan.
+update library set
+    scanned_pid_album = coalesce((select value from property where id = 'PIDAlbum'), ''),
+    scanned_pid_track = coalesce((select value from property where id = 'PIDTrack'), '');
+
+delete from property where id in ('PIDAlbum', 'PIDTrack');
+-- +goose StatementEnd
+
+-- +goose Down
+SELECT 1;

model/library.go

@@ -1,10 +1,13 @@
 package model
 
 import (
+	"cmp"
 	"context"
+	"strings"
 	"time"
 
 	"github.com/deluan/rest"
+	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/utils/slice"
 )
 
@@ -27,6 +30,38 @@ type Library struct {
 	TotalSize          int64     `json:"totalSize" db:"total_size"`
 	TotalDuration      float64   `json:"totalDuration" db:"total_duration"`
 	DefaultNewUsers    bool      `json:"defaultNewUsers" db:"default_new_users"`
+	PIDAlbum           string    `json:"pidAlbum" db:"pid_album"`
+	PIDTrack           string    `json:"pidTrack" db:"pid_track"`
+	ScannedPIDAlbum    string    `json:"-" db:"scanned_pid_album"`
+	ScannedPIDTrack    string    `json:"-" db:"scanned_pid_track"`
+}
+
+// PIDConfig holds the persistent ID specs used to compute track and album IDs.
+type PIDConfig struct {
+	Track string
+	Album string
+}
+
+// EffectivePID returns the PID specs in effect for this library: its own overrides, falling back to
+// the global config.
+func (l Library) EffectivePID() PIDConfig {
+	return PIDConfig{
+		Track: cmp.Or(l.PIDTrack, conf.Server.PID.Track),
+		Album: cmp.Or(l.PIDAlbum, conf.Server.PID.Album),
+	}
+}
+
+// PIDChanged reports whether the effective PID specs differ from the ones used by the last finished
+// scan of this library. A library that was never scanned counts as changed.
+func (l Library) PIDChanged() bool {
+	pid := l.EffectivePID()
+	return !strings.EqualFold(l.ScannedPIDAlbum, pid.Album) || !strings.EqualFold(l.ScannedPIDTrack, pid.Track)
+}
+
+// NeedsPIDRescan reports whether the library has content imported with an old PID config, so it must be
+// rescanned in full. A library that never finished a scan has nothing to regroup.
+func (l Library) NeedsPIDRescan() bool {
+	return !l.LastScanAt.IsZero() && l.PIDChanged()
 }
 
 const (
@@ -59,6 +94,8 @@ type LibraryRepository interface {
 	// TODO These methods should be moved to a core service
 	ScanBegin(ctx context.Context, id int, fullScan bool) error
 	ScanEnd(ctx context.Context, id int) error
+	// SetScannedPID records the PID specs used by the last finished scan of the library
+	SetScannedPID(ctx context.Context, id int, pid PIDConfig) error
 	ScanInProgress(ctx context.Context) (bool, error)
 	RefreshStats(ctx context.Context, id int) error
 }

model/library_matcher.go

@@ -0,0 +1,57 @@
+package model
+
+import (
+	"cmp"
+	"path/filepath"
+	"slices"
+	"strings"
+)
+
+// LibraryMatcher finds the library that contains an absolute path.
+type LibraryMatcher struct {
+	libraries    Libraries
+	cleanedPaths []string
+}
+
+// NewLibraryMatcher sorts the libraries longest path first, so /music-classical is checked before /music.
+func NewLibraryMatcher(libs Libraries) *LibraryMatcher {
+	libs = slices.Clone(libs)
+	slices.SortFunc(libs, func(i, j Library) int {
+		return cmp.Compare(len(j.Path), len(i.Path))
+	})
+	cleanedPaths := make([]string, len(libs))
+	for i, lib := range libs {
+		cleanedPaths[i] = filepath.Clean(lib.Path)
+	}
+	return &LibraryMatcher{libraries: libs, cleanedPaths: cleanedPaths}
+}
+
+// FindLibrary returns the library whose path contains absolutePath.
+func (lm *LibraryMatcher) FindLibrary(absolutePath string) (Library, bool) {
+	for i, libPath := range lm.cleanedPaths {
+		// A cleaned path only ends with a separator when it is a filesystem root
+		if strings.HasPrefix(absolutePath, libPath) && (len(absolutePath) == len(libPath) ||
+			absolutePath[len(libPath)] == filepath.Separator || strings.HasSuffix(libPath, string(filepath.Separator))) {
+			return lm.libraries[i], true
+		}
+	}
+	return Library{}, false
+}
+
+// LibraryRelativePath rebases an absolute path onto the library root, as the scanner's io/fs sees it
+// (forward slashes). Relative paths, and absolute paths outside the library root, are returned unchanged.
+func LibraryRelativePath(libPath, path string) string {
+	if !filepath.IsAbs(path) {
+		return path
+	}
+	// The library root may be relative (e.g. the default "./music"); it resolves against the same cwd
+	absLib, err := filepath.Abs(libPath)
+	if err != nil {
+		return path
+	}
+	rel, err := filepath.Rel(absLib, path)
+	if err != nil || !filepath.IsLocal(rel) {
+		return path
+	}
+	return filepath.ToSlash(rel)
+}

model/library_matcher_test.go

@@ -0,0 +1,91 @@
+package model_test
+
+import (
+	"os"
+	"path/filepath"
+
+	"github.com/navidrome/navidrome/model"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("LibraryMatcher", func() {
+	// Paths are written Unix-style and converted, so they use the OS separator, as filepath.Abs output does
+	find := func(libs model.Libraries, path string) int {
+		for i := range libs {
+			libs[i].Path = filepath.FromSlash(libs[i].Path)
+		}
+		lib, ok := model.NewLibraryMatcher(libs).FindLibrary(filepath.FromSlash(path))
+		if !ok {
+			return 0
+		}
+		return lib.ID
+	}
+
+	DescribeTable("matches the longest library path",
+		func(libs model.Libraries, path string, expectedID int) {
+			Expect(find(libs, path)).To(Equal(expectedID))
+		},
+		Entry("nested library", model.Libraries{{ID: 1, Path: "/music"}, {ID: 2, Path: "/music-classical"}, {ID: 3, Path: "/music-classical/opera"}}, "/music-classical/opera/subdir/track.mp3", 3),
+		Entry("sibling with a shared prefix", model.Libraries{{ID: 1, Path: "/music"}, {ID: 2, Path: "/music-classical"}}, "/music-classical/track.mp3", 2),
+		Entry("shorter library", model.Libraries{{ID: 1, Path: "/music"}, {ID: 2, Path: "/music-classical"}}, "/music/track.mp3", 1),
+		Entry("exact library root", model.Libraries{{ID: 1, Path: "/music"}, {ID: 2, Path: "/music-classical"}}, "/music-classical", 2),
+		Entry("deeply nested libraries", model.Libraries{{ID: 1, Path: "/media"}, {ID: 2, Path: "/media/audio"}, {ID: 3, Path: "/media/audio/classical"}, {ID: 4, Path: "/media/audio/classical/baroque"}}, "/media/audio/classical/mozart/track.mp3", 3),
+		Entry("prefix that is not a path boundary", model.Libraries{{ID: 1, Path: "/a"}, {ID: 2, Path: "/ab"}, {ID: 3, Path: "/abc"}}, "/ab/file.mp3", 2),
+		Entry("special characters match literally", model.Libraries{{ID: 1, Path: "/music[test]"}, {ID: 2, Path: "/music(backup)"}}, "/music[test]/track.mp3", 1),
+		Entry("library path with a trailing slash", model.Libraries{{ID: 1, Path: "/music/"}}, "/music/track.mp3", 1),
+		Entry("library at the filesystem root", model.Libraries{{ID: 1, Path: "/"}}, "/music/track.mp3", 1),
+		Entry("nested library under a root library", model.Libraries{{ID: 1, Path: "/"}, {ID: 2, Path: "/music"}}, "/music/track.mp3", 2),
+	)
+
+	It("does not match a path outside every library", func() {
+		Expect(find(model.Libraries{{ID: 1, Path: "/music"}}, "/music-backup/track.mp3")).To(BeZero())
+	})
+
+	It("does not match anything without libraries", func() {
+		Expect(find(nil, "/music/track.mp3")).To(BeZero())
+	})
+
+	It("does not reorder the caller's libraries", func() {
+		libs := model.Libraries{{ID: 1, Path: "/a"}, {ID: 2, Path: "/abc"}}
+		model.NewLibraryMatcher(libs)
+		Expect(libs.IDs()).To(Equal([]int{1, 2}))
+	})
+})
+
+var _ = Describe("LibraryRelativePath", func() {
+	// Paths are built with filepath so the "absolute" cases stay absolute on every OS
+	// (a Unix-style "/foo" is not absolute on Windows).
+	libRoot, _ := filepath.Abs(filepath.Join("jukebox", "collection"))
+	outside, _ := filepath.Abs(filepath.Join("somewhere", "else"))
+
+	It("returns a relative path unchanged", func() {
+		Expect(model.LibraryRelativePath(libRoot, "_Collection")).To(Equal("_Collection"))
+	})
+
+	It("rebases an absolute target when the library root is relative", func() {
+		cwd, err := os.Getwd()
+		Expect(err).ToNot(HaveOccurred())
+		Expect(model.LibraryRelativePath(filepath.Join("music", "library"), filepath.Join(cwd, "music", "library", "rock"))).To(Equal("rock"))
+	})
+
+	It("rebases an absolute path that equals the library root to '.'", func() {
+		Expect(model.LibraryRelativePath(libRoot, libRoot)).To(Equal("."))
+	})
+
+	It("rebases an absolute path under the library root", func() {
+		Expect(model.LibraryRelativePath(libRoot, filepath.Join(libRoot, "_Collection"))).To(Equal("_Collection"))
+	})
+
+	It("handles a trailing slash on the library path", func() {
+		Expect(model.LibraryRelativePath(libRoot+string(filepath.Separator), filepath.Join(libRoot, "_Collection"))).To(Equal("_Collection"))
+	})
+
+	It("leaves an absolute path outside the library root unchanged", func() {
+		Expect(model.LibraryRelativePath(libRoot, outside)).To(Equal(outside))
+	})
+
+	It("returns an empty path unchanged", func() {
+		Expect(model.LibraryRelativePath(libRoot, "")).To(Equal(""))
+	})
+})

model/library_test.go

@@ -0,0 +1,73 @@
+package model_test
+
+import (
+	"encoding/json"
+	"time"
+
+	"github.com/navidrome/navidrome/conf"
+	"github.com/navidrome/navidrome/conf/configtest"
+	"github.com/navidrome/navidrome/model"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Library PID config", func() {
+	BeforeEach(func() {
+		DeferCleanup(configtest.SetupConfig())
+		conf.Server.PID.Album = "global_album"
+		conf.Server.PID.Track = "global_track"
+	})
+
+	Describe("EffectivePID", func() {
+		It("falls back to the global config", func() {
+			Expect(model.Library{}.EffectivePID()).To(Equal(model.PIDConfig{Track: "global_track", Album: "global_album"}))
+		})
+		It("uses the library overrides", func() {
+			lib := model.Library{PIDAlbum: "folder", PIDTrack: "title"}
+			Expect(lib.EffectivePID()).To(Equal(model.PIDConfig{Track: "title", Album: "folder"}))
+		})
+	})
+
+	Describe("PIDChanged", func() {
+		It("is false when the scanned specs match, ignoring case", func() {
+			lib := model.Library{ScannedPIDAlbum: "GLOBAL_ALBUM", ScannedPIDTrack: "global_track"}
+			Expect(lib.PIDChanged()).To(BeFalse())
+		})
+		It("is true when the album override differs from the scanned spec", func() {
+			lib := model.Library{PIDAlbum: "folder", ScannedPIDAlbum: "global_album", ScannedPIDTrack: "global_track"}
+			Expect(lib.PIDChanged()).To(BeTrue())
+		})
+		It("is true when only the track spec changed", func() {
+			lib := model.Library{PIDTrack: "title", ScannedPIDAlbum: "global_album", ScannedPIDTrack: "global_track"}
+			Expect(lib.PIDChanged()).To(BeTrue())
+		})
+		It("is true when the global config changed for a library without overrides", func() {
+			lib := model.Library{ScannedPIDAlbum: "old_album", ScannedPIDTrack: "global_track"}
+			Expect(lib.PIDChanged()).To(BeTrue())
+		})
+		It("is true for a library that was never scanned", func() {
+			Expect(model.Library{}.PIDChanged()).To(BeTrue())
+		})
+	})
+
+	Describe("NeedsPIDRescan", func() {
+		It("is false for a library that never finished a scan", func() {
+			Expect(model.Library{PIDAlbum: "folder"}.NeedsPIDRescan()).To(BeFalse())
+		})
+		It("is true for a scanned library whose PID config changed", func() {
+			lib := model.Library{PIDAlbum: "folder", ScannedPIDAlbum: "global_album", ScannedPIDTrack: "global_track", LastScanAt: time.Now()}
+			Expect(lib.NeedsPIDRescan()).To(BeTrue())
+		})
+		It("is false for a scanned library whose PID config did not change", func() {
+			lib := model.Library{ScannedPIDAlbum: "global_album", ScannedPIDTrack: "global_track", LastScanAt: time.Now()}
+			Expect(lib.NeedsPIDRescan()).To(BeFalse())
+		})
+	})
+
+	It("does not expose the scanned specs in JSON", func() {
+		data, err := json.Marshal(model.Library{PIDAlbum: "folder", ScannedPIDAlbum: "secret_album", ScannedPIDTrack: "secret_track"})
+		Expect(err).ToNot(HaveOccurred())
+		Expect(string(data)).To(ContainSubstring(`"pidAlbum":"folder"`))
+		Expect(string(data)).ToNot(ContainSubstring("secret_"))
+	})
+})

model/metadata/map_mediafile.go

@@ -8,15 +8,14 @@ import (
 	"math"
 	"strconv"
 
-	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/utils/str"
 )
 
-func (md Metadata) ToMediaFile(libID int, folderID string) model.MediaFile {
+func (md Metadata) ToMediaFile(lib model.Library, folderID string) model.MediaFile {
 	mf := model.MediaFile{
-		LibraryID: libID,
+		LibraryID: lib.ID,
 		FolderID:  folderID,
 		Tags:      maps.Clone(md.tags),
 	}
@@ -84,8 +83,9 @@ func (md Metadata) ToMediaFile(libID int, folderID string) model.MediaFile {
 	mf.AlbumArtist = md.mapDisplayAlbumArtist(mf)
 
 	// Persistent IDs
-	mf.PID = md.trackPID(mf)
-	mf.AlbumID = md.albumID(mf, conf.Server.PID.Album)
+	pid := lib.EffectivePID()
+	mf.PID = md.trackPID(mf, pid)
+	mf.AlbumID = md.albumID(mf, pid.Album)
 
 	// BFR These IDs will go away once the UI handle multiple participants.
 	// BFR For Legacy Subsonic compatibility, we will set them in the API handlers

model/metadata/map_mediafile_test.go

@@ -30,9 +30,23 @@ var _ = Describe("ToMediaFile", func() {
 	var toMediaFile = func(tags model.RawTags) model.MediaFile {
 		props.Tags = tags
 		md = metadata.New("filepath", props)
-		return md.ToMediaFile(1, "folderID")
+		return md.ToMediaFile(model.Library{ID: 1}, "folderID")
 	}
 
+	Describe("Persistent IDs", func() {
+		It("uses the library PID config for the album ID and for albumid in the track spec", func() {
+			props.Tags = model.RawTags{"ALBUM": {"Kind of Blue"}, "TITLE": {"So What"}}
+			md = metadata.New("Jazz/Loose/01.mp3", props)
+
+			byTags := md.ToMediaFile(model.Library{ID: 1, PIDAlbum: "album", PIDTrack: "albumid,title"}, "folderID")
+			byFolder := md.ToMediaFile(model.Library{ID: 1, PIDAlbum: "folder", PIDTrack: "albumid,title"}, "folderID")
+
+			Expect(byFolder.AlbumID).ToNot(Equal(byTags.AlbumID))
+			Expect(byFolder.AlbumID).To(Equal(md.AlbumID(byFolder, "folder")))
+			Expect(byFolder.PID).ToNot(Equal(byTags.PID))
+		})
+	})
+
 	Describe("Dates", func() {
 		It("should parse properly tagged dates ", func() {
 			mf = toMediaFile(model.RawTags{

model/metadata/map_participants_test.go

@@ -38,7 +38,7 @@ var _ = Describe("Participants", func() {
 	var toMediaFile = func(tags model.RawTags) model.MediaFile {
 		props.Tags = tags
 		md = metadata.New("filepath", props)
-		return md.ToMediaFile(1, "folderID")
+		return md.ToMediaFile(model.Library{ID: 1}, "folderID")
 	}
 
 	Describe("ARTIST(S) tags", func() {

model/metadata/metadata_test.go

@@ -323,7 +323,7 @@ var _ = Describe("Metadata", func() {
 					tag: {tagValue},
 				}
 				md = metadata.New(filePath, props)
-				return md.ToMediaFile(0, "0")
+				return md.ToMediaFile(model.Library{}, "0")
 			}
 
 			DescribeTable("Gain",

model/metadata/persistent_ids.go

@@ -2,11 +2,11 @@ package metadata
 
 import (
 	"cmp"
+	"errors"
 	"fmt"
 	"path/filepath"
 	"strings"
 
-	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/consts"
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
@@ -22,12 +22,13 @@ type hashFunc = func(...string) string
 // attributes. Attributes can be either tags or processed values like folder,
 // albumid, albumartistid, etc. For each field, it gets all its attribute values
 // and concatenates them, then hashes the result. If a field is empty, it is
-// skipped and the function looks for the next field.
+// skipped and the function looks for the next field. albumSpec is the album PID
+// spec used to resolve the `albumid` attribute.
 //
 // Taking hash as a parameter (instead of closing over it in a factory) keeps
 // mf on the stack: closing over mf would force the whole ~1KB MediaFile to the
 // heap on every call.
-func computePID(mf model.MediaFile, md Metadata, spec string, prependLibId bool, hash hashFunc) string {
+func computePID(mf model.MediaFile, md Metadata, spec, albumSpec string, prependLibId bool, hash hashFunc) string {
 	switch spec {
 	case "track_legacy":
 		return legacyTrackID(mf, prependLibId)
@@ -41,7 +42,7 @@ func computePID(mf model.MediaFile, md Metadata, spec string, prependLibId bool,
 		values := make([]string, len(attributes))
 		hasValue := false
 		for i, attr := range attributes {
-			v := getPIDAttr(mf, md, attr, prependLibId, spec, hash)
+			v := getPIDAttr(mf, md, attr, prependLibId, spec, albumSpec, hash)
 			if v != "" {
 				hasValue = true
 			}
@@ -58,15 +59,15 @@ func computePID(mf model.MediaFile, md Metadata, spec string, prependLibId bool,
 	return hash(pid)
 }
 
-func getPIDAttr(mf model.MediaFile, md Metadata, attr string, prependLibId bool, spec string, hash hashFunc) string {
+func getPIDAttr(mf model.MediaFile, md Metadata, attr string, prependLibId bool, spec, albumSpec string, hash hashFunc) string {
 	attr = strings.TrimSpace(strings.ToLower(attr))
 	switch attr {
 	case "albumid":
-		if spec == conf.Server.PID.Album {
+		if spec == albumSpec {
 			log.Error("Recursive PID definition detected, ignoring `albumid`", "spec", spec)
 			return ""
 		}
-		return computePID(mf, md, conf.Server.PID.Album, prependLibId, hash)
+		return computePID(mf, md, albumSpec, albumSpec, prependLibId, hash)
 	case "folder":
 		return filepath.Dir(mf.Path)
 	case "albumartistid":
@@ -79,18 +80,50 @@ func getPIDAttr(mf model.MediaFile, md Metadata, attr string, prependLibId bool,
 	return md.String(model.TagName(attr))
 }
 
-func (md Metadata) trackPID(mf model.MediaFile) string {
-	return computePID(mf, md, conf.Server.PID.Track, true, id.NewHash)
+// ValidatePIDSpec checks a PID override before it is stored; empty means "use the global config".
+// Aliases resolve to empty at scan time: accepted only in track specs, because the default one uses them.
+func ValidatePIDSpec(spec string, isAlbum bool) error {
+	switch {
+	case spec == "", isAlbum && spec == "album_legacy", !isAlbum && spec == "track_legacy":
+		return nil
+	}
+	for field := range strings.SplitSeq(spec, "|") {
+		for attr := range strings.SplitSeq(field, ",") {
+			attr = strings.TrimSpace(strings.ToLower(attr))
+			switch attr {
+			case "":
+				return fmt.Errorf("empty attribute in %q", spec)
+			case "albumid":
+				if isAlbum {
+					return errors.New("albumid cannot be used in an album PID")
+				}
+			case "folder", "albumartistid":
+			default:
+				name, ok := model.CanonicalTagName(attr)
+				if !ok {
+					return fmt.Errorf("unknown attribute %q", attr)
+				}
+				if isAlbum && string(name) != attr {
+					return fmt.Errorf("use the tag name %q instead of its alias %q", name, attr)
+				}
+			}
+		}
+	}
+	return nil
+}
+
+func (md Metadata) trackPID(mf model.MediaFile, pid model.PIDConfig) string {
+	return computePID(mf, md, pid.Track, pid.Album, true, id.NewHash)
 }
 
 func (md Metadata) albumID(mf model.MediaFile, pidConf string) string {
-	return computePID(mf, md, pidConf, true, id.NewHash)
+	return computePID(mf, md, pidConf, pidConf, true, id.NewHash)
 }
 
 // BFR Must be configurable?
 func (md Metadata) artistID(name string) string {
 	mf := model.MediaFile{AlbumArtist: name}
-	return computePID(mf, md, "albumartistid", false, id.NewHash)
+	return computePID(mf, md, "albumartistid", "", false, id.NewHash)
 }
 
 func (md Metadata) mapTrackTitle() string {

model/metadata/persistent_ids_test.go

@@ -3,8 +3,7 @@ package metadata
 import (
 	"strings"
 
-	"github.com/navidrome/navidrome/conf"
-	"github.com/navidrome/navidrome/conf/configtest"
+	"github.com/navidrome/navidrome/consts"
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/tests"
 	. "github.com/onsi/ginkgo/v2"
@@ -13,16 +12,18 @@ import (
 
 var _ = Describe("getPID", func() {
 	var (
-		md  Metadata
-		mf  model.MediaFile
-		sum hashFunc
+		md        Metadata
+		mf        model.MediaFile
+		sum       hashFunc
+		albumSpec string
 	)
 	getPID := func(mf model.MediaFile, md Metadata, spec string, prependLibId bool) string {
-		return computePID(mf, md, spec, prependLibId, sum)
+		return computePID(mf, md, spec, albumSpec, prependLibId, sum)
 	}
 
 	BeforeEach(func() {
 		sum = func(s ...string) string { return "(" + strings.Join(s, ",") + ")" }
+		albumSpec = consts.DefaultAlbumPID
 	})
 
 	Context("attributes are tags", func() {
@@ -66,8 +67,7 @@ var _ = Describe("getPID", func() {
 
 	Context("calculated attributes", func() {
 		BeforeEach(func() {
-			DeferCleanup(configtest.SetupConfig())
-			conf.Server.PID.Album = "musicbrainz_albumid|albumartistid,album,albumversion,releasedate"
+			albumSpec = "musicbrainz_albumid|albumartistid,album,albumversion,releasedate"
 		})
 		When("field is title", func() {
 			It("should return the pid", func() {
@@ -121,8 +121,8 @@ var _ = Describe("getPID", func() {
 		When("albumid configuration refers to albumid recursively", func() {
 			It("should avoid infinite recursion", func() {
 				// Reproduce the issue from #4920
-				conf.Server.PID.Album = "albumid,album,albumversion,releasedate"
-				spec := conf.Server.PID.Album
+				albumSpec = "albumid,album,albumversion,releasedate"
+				spec := albumSpec
 				md.tags = map[model.TagName][]string{
 					"album":        {"Album Name"},
 					"albumversion": {"Version"},
@@ -205,8 +205,7 @@ var _ = Describe("getPID", func() {
 		})
 		When("prependLibId is true with nested albumid", func() {
 			It("should handle nested albumid calls correctly", func() {
-				DeferCleanup(configtest.SetupConfig())
-				conf.Server.PID.Album = "album"
+				albumSpec = "album"
 				spec := "albumid"
 				md.tags = map[model.TagName][]string{"album": {"Test Album"}}
 				mf.AlbumArtist = "Test Artist"
@@ -306,3 +305,34 @@ var _ = Describe("getPID", func() {
 		})
 	})
 })
+
+var _ = Describe("ValidatePIDSpec", func() {
+	DescribeTable("accepts valid specs",
+		func(spec string, isAlbum bool) {
+			Expect(ValidatePIDSpec(spec, isAlbum)).To(Succeed())
+		},
+		Entry("empty, meaning the global config", "", true),
+		Entry("default album spec", consts.DefaultAlbumPID, true),
+		Entry("default track spec, which uses tag aliases", consts.DefaultTrackPID, false),
+		Entry("folder", "folder", true),
+		Entry("album legacy", "album_legacy", true),
+		Entry("track legacy", "track_legacy", false),
+		Entry("computed attributes", "albumartistid,album|title", true),
+		Entry("albumid in a track spec", "albumid,title", false),
+		Entry("spaces and mixed case", "MusicBrainz_AlbumID | Folder", true),
+	)
+
+	DescribeTable("rejects invalid specs",
+		func(spec string, isAlbum bool, msg string) {
+			Expect(ValidatePIDSpec(spec, isAlbum)).To(MatchError(ContainSubstring(msg)))
+		},
+		Entry("unknown tag", "albmversion", true, `unknown attribute "albmversion"`),
+		Entry("empty field", "album||title", true, "empty attribute"),
+		Entry("empty attribute", "album,,title", true, "empty attribute"),
+		Entry("trailing separator", "album|", true, "empty attribute"),
+		Entry("albumid in an album spec", "albumid,album", true, "albumid"),
+		Entry("tag alias in an album spec", "talb", true, `use the tag name "album" instead of its alias "talb"`),
+		Entry("track legacy in an album spec", "track_legacy", true, `unknown attribute "track_legacy"`),
+		Entry("album legacy in a track spec", "album_legacy", false, `unknown attribute "album_legacy"`),
+	)
+})

model/scanner.go

@@ -2,12 +2,15 @@ package model
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"strconv"
 	"strings"
 	"time"
 )
 
+var ErrAlreadyScanning = errors.New("already scanning")
+
 // ScanTarget represents a specific folder within a library to be scanned.
 // NOTE: This struct is used as a map key, so it should only contain comparable types.
 type ScanTarget struct {

model/tag_mappings.go

@@ -195,6 +195,28 @@ func TagMappings() map[TagName]TagConf {
 	return mappings
 }
 
+// CanonicalTagName returns the mapped tag that name is, or is an alias of. Tags are stored under this name.
+func CanonicalTagName(name string) (TagName, bool) {
+	tagName, ok := tagNameIndex()[TagName(name).ToLower()]
+	return tagName, ok
+}
+
+// tagNameIndex maps every tag name and alias to its tag name. Names are added last, so they win over aliases
+// (musicbrainz_trackid is a tag and also an alias of musicbrainz_recordingid).
+var tagNameIndex = sync.OnceValue(func() map[TagName]TagName {
+	mappings := TagMappings()
+	index := make(map[TagName]TagName, len(mappings))
+	for name, tag := range mappings {
+		for _, alias := range tag.Aliases {
+			index[TagName(alias)] = name
+		}
+	}
+	for name := range mappings {
+		index[name] = name
+	}
+	return index
+})
+
 func TagRolesConf() TagConf {
 	_, cfg := parseMappings()
 	return cfg.Roles

model/tag_mappings_test.go

@@ -192,3 +192,22 @@ var _ = Describe("TagConf", func() {
 		})
 	})
 })
+
+var _ = Describe("CanonicalTagName", func() {
+	DescribeTable("resolves tag names and aliases",
+		func(name string, expected TagName) {
+			tagName, ok := CanonicalTagName(name)
+			Expect(ok).To(BeTrue())
+			Expect(tagName).To(Equal(expected))
+		},
+		Entry("tag name", "album", TagAlbum),
+		Entry("alias", "talb", TagAlbum),
+		Entry("mixed case alias", "TALB", TagAlbum),
+		Entry("tag name that is also an alias of another tag", "musicbrainz_trackid", TagMusicBrainzTrackID),
+	)
+
+	It("does not resolve an unknown name", func() {
+		_, ok := CanonicalTagName("nosuchtag")
+		Expect(ok).To(BeFalse())
+	})
+})

persistence/library_repository.go

@@ -93,6 +93,8 @@ func (r *libraryRepository) Put(ctx context.Context, l *model.Library, colsToUpd
 			"path":              l.Path,
 			"remote_path":       l.RemotePath,
 			"default_new_users": l.DefaultNewUsers,
+			"pid_album":         l.PIDAlbum,
+			"pid_track":         l.PIDTrack,
 		}, colsToUpdate...)
 		cols["updated_at"] = l.UpdatedAt
 		sq := Update(r.tableName).SetMap(cols).Where(Eq{"id": l.ID})
@@ -176,6 +178,15 @@ func (r *libraryRepository) ScanEnd(ctx context.Context, id int) error {
 	return err
 }
 
+func (r *libraryRepository) SetScannedPID(ctx context.Context, id int, pid model.PIDConfig) error {
+	sq := Update(r.tableName).
+		Set("scanned_pid_album", pid.Album).
+		Set("scanned_pid_track", pid.Track).
+		Where(Eq{"id": id})
+	_, err := r.executeSQL(ctx, sq)
+	return err
+}
+
 func (r *libraryRepository) ScanInProgress(ctx context.Context) (bool, error) {
 	query := r.newSelect(ctx).Where(NotEq{"last_scan_started_at": time.Time{}})
 	count, err := r.count(ctx, query)

persistence/library_repository_test.go

@@ -270,6 +270,38 @@ var _ = Describe("LibraryRepository", func() {
 		})
 	})
 
+	Describe("PID config", func() {
+		It("stores the overrides, and Put never touches the scanned specs", func() {
+			lib := &model.Library{Name: "PID Library", Path: "/music/pid", PIDAlbum: "folder", PIDTrack: "title"}
+			Expect(repo.Put(ctx, lib)).To(Succeed())
+			Expect(repo.SetScannedPID(ctx, lib.ID, model.PIDConfig{Album: "folder", Track: "title"})).To(Succeed())
+
+			// An update coming from the REST API has no scanned specs. It must not clear them
+			update := &model.Library{ID: lib.ID, Name: "PID Library", Path: "/music/pid", PIDTrack: "title"}
+			Expect(repo.Put(ctx, update)).To(Succeed())
+
+			saved, err := repo.Get(ctx, lib.ID)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(saved.PIDAlbum).To(BeEmpty())
+			Expect(saved.PIDTrack).To(Equal("title"))
+			Expect(saved.ScannedPIDAlbum).To(Equal("folder"))
+			Expect(saved.ScannedPIDTrack).To(Equal("title"))
+		})
+
+		It("keeps the overrides when a partial update does not send them", func() {
+			lib := &model.Library{Name: "Partial", Path: "/music/partial", PIDAlbum: "folder", PIDTrack: "title"}
+			Expect(repo.Put(ctx, lib)).To(Succeed())
+
+			Expect(repo.Put(ctx, &model.Library{ID: lib.ID, Name: "Renamed"}, "name")).To(Succeed())
+
+			saved, err := repo.Get(ctx, lib.ID)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(saved.Name).To(Equal("Renamed"))
+			Expect(saved.PIDAlbum).To(Equal("folder"))
+			Expect(saved.PIDTrack).To(Equal("title"))
+		})
+	})
+
 	Describe("Delete", func() {
 		var adminRepo model.LibraryRepository
 		var artistRepo model.ArtistRepository

resources/i18n/pt-br.json

@@ -328,11 +328,22 @@
         "totalDuration": "Duração",
         "defaultNewUsers": "Padrão para Novos Usuários",
         "createdAt": "Data de Criação",
-        "updatedAt": "Últ. Atualização"
+        "updatedAt": "Últ. Atualização",
+        "pidAlbum": "Agrupamento de álbuns",
+        "pidTrack": "Identificação das faixas"
       },
       "sections": {
         "basic": "Informações Básicas",
-        "statistics": "Estatísticas"
+        "statistics": "Estatísticas",
+        "pid": "IDs Persistentes"
+      },
+      "pid": {
+        "global": "Usar configuração global (%{value})",
+        "folder": "Pasta (um álbum por pasta)",
+        "custom": "Personalizado",
+        "spec": "Especificação do PID",
+        "help": "Tags e atributos que identificam um item. Consulte a sintaxe na documentação:",
+        "docs": "IDs Persistentes"
       },
       "actions": {
         "scan": "Scanear Biblioteca",
@@ -362,7 +373,9 @@
       "messages": {
         "deleteConfirm": "Tem certeza que deseja excluir esta biblioteca? Isso removerá todos os dados associados.",
         "scanInProgress": "Scan em progresso...",
-        "noLibrariesAssigned": "Nenhuma biblioteca atribuída a este usuário"
+        "noLibrariesAssigned": "Nenhuma biblioteca atribuída a este usuário",
+        "pidChangeTitle": "Alterar os IDs persistentes?",
+        "pidChangeConfirm": "Ao salvar, os álbuns desta biblioteca serão reagrupados e as faixas serão identificadas novamente. Um scan completo da biblioteca começará imediatamente. As marcações como favoritas, as classificações e as contagens de reprodução das faixas serão mantidas. Os favoritos e as classificações dos álbuns serão transferidos para os novos álbuns quando um álbum antigo corresponder a um novo."
       }
     },
     "plugin": {

scanner/controller.go

@@ -25,7 +25,7 @@ import (
 )
 
 var (
-	ErrAlreadyScanning = errors.New("already scanning")
+	ErrAlreadyScanning = model.ErrAlreadyScanning
 )
 
 func New(rootCtx context.Context, ds model.DataStore, broker events.Broker,
@@ -304,14 +304,14 @@ func LockForMaintenance() (func(), bool) {
 	return scanMaintenanceMux.Unlock, true
 }
 
-// EffectiveFullScan reports whether a scan was requested as full or will resume an interrupted
-// full scan in one of the included libraries.
+// EffectiveFullScan reports whether a scan was requested as full, will resume an interrupted full scan,
+// or will rescan a library in full because its PID config changed, in one of the included libraries.
 func EffectiveFullScan(ctx context.Context, ds model.DataStore, fullScan bool, targets []model.ScanTarget) bool {
 	if fullScan {
 		return true
 	}
 	return anyIncludedLibrary(ctx, ds, targets, func(library model.Library) bool {
-		return library.FullScanInProgress
+		return library.FullScanInProgress || library.NeedsPIDRescan()
 	})
 }
 

scanner/controller_test.go

@@ -2,6 +2,7 @@ package scanner_test
 
 import (
 	"context"
+	"time"
 
 	"github.com/navidrome/navidrome/conf/configtest"
 	"github.com/navidrome/navidrome/consts"
@@ -70,14 +71,21 @@ var _ = Describe("EffectiveFullScan", func() {
 	var ds *tests.MockDataStore
 
 	BeforeEach(func() {
+		pid := model.Library{}.EffectivePID()
 		libraries := &tests.MockLibraryRepo{}
 		libraries.SetData(model.Libraries{
-			{ID: 1, FullScanInProgress: true},
-			{ID: 2},
+			{ID: 1, FullScanInProgress: true, ScannedPIDAlbum: pid.Album, ScannedPIDTrack: pid.Track},
+			{ID: 2, ScannedPIDAlbum: pid.Album, ScannedPIDTrack: pid.Track},
+			{ID: 3, LastScanAt: time.Now(), PIDAlbum: "folder", ScannedPIDAlbum: pid.Album, ScannedPIDTrack: pid.Track},
 		})
 		ds = &tests.MockDataStore{MockedLibrary: libraries}
 	})
 
+	It("detects a library that needs a full rescan for a PID change", func() {
+		targets := []model.ScanTarget{{LibraryID: 3, FolderPath: "."}}
+		Expect(scanner.EffectiveFullScan(GinkgoT().Context(), ds, false, targets)).To(BeTrue())
+	})
+
 	It("detects an interrupted full scan in a targeted library", func() {
 		targets := []model.ScanTarget{{LibraryID: 1, FolderPath: "."}}
 		Expect(scanner.EffectiveFullScan(context.Background(), ds, false, targets)).To(BeTrue())

scanner/phase_1_folders.go

@@ -40,6 +40,7 @@ func createPhaseFolders(ctx context.Context, state *scanState, ds model.DataStor
 		if err != nil {
 			log.Error(ctx, "Scanner: Error creating scan context", "lib", lib.Name, err)
 			state.sendError(err)
+			state.markFailed(lib.ID)
 			continue
 		}
 		jobs = append(jobs, job)
@@ -51,12 +52,13 @@ func createPhaseFolders(ctx context.Context, state *scanState, ds model.DataStor
 }
 
 type scanJob struct {
-	lib           model.Library
-	fs            storage.MusicFS
-	lastUpdates   map[string]model.FolderUpdateInfo // Holds last update info for all (DB) folders in this library
-	targetFolders []string                          // Specific folders to scan (including all descendants)
-	lock          sync.Mutex
-	numFolders    atomic.Int64
+	lib              model.Library
+	fs               storage.MusicFS
+	lastUpdates      map[string]model.FolderUpdateInfo // Holds last update info for all (DB) folders in this library
+	targetFolders    []string                          // Specific folders to scan (including all descendants)
+	prevAlbumPIDConf string                            // Album PID spec of the last finished scan, only when it differs from the current one
+	lock             sync.Mutex
+	numFolders       atomic.Int64
 }
 
 func newScanJob(ctx context.Context, ds model.DataStore, lib model.Library, fullScan bool, targetFolders []string) (*scanJob, error) {
@@ -77,16 +79,32 @@ func newScanJob(ctx context.Context, ds model.DataStore, lib model.Library, full
 		return nil, fmt.Errorf("getting fs for library: %w", err)
 	}
 
+	pid := lib.EffectivePID()
+	if lib.NeedsPIDRescan() {
+		msg := "Scanner: PID config changed, rescanning library in full"
+		if len(targetFolders) > 0 {
+			msg = "Scanner: PID config changed, rescanning target folders in full"
+		}
+		log.Info(ctx, msg, "lib", lib.Name, "targetFolders", targetFolders,
+			"album", pid.Album, "track", pid.Track, "scannedAlbum", lib.ScannedPIDAlbum, "scannedTrack", lib.ScannedPIDTrack)
+		fullScan = true
+	}
+	var prevAlbumPIDConf string
+	if lib.ScannedPIDAlbum != pid.Album {
+		prevAlbumPIDConf = lib.ScannedPIDAlbum
+	}
+
 	// Ensure FullScanInProgress reflects the current scan request.
 	// This is important when resuming an interrupted quick scan as a full scan:
 	// the DB may have FullScanInProgress=false, but we need it true for isOutdated() to work correctly.
 	lib.FullScanInProgress = lib.FullScanInProgress || fullScan
 
 	return &scanJob{
-		lib:           lib,
-		fs:            fsys,
-		lastUpdates:   lastUpdates,
-		targetFolders: targetFolders,
+		lib:              lib,
+		fs:               fsys,
+		lastUpdates:      lastUpdates,
+		targetFolders:    targetFolders,
+		prevAlbumPIDConf: prevAlbumPIDConf,
 	}, nil
 }
 
@@ -122,14 +140,13 @@ func (j *scanJob) createFolderEntry(path string) *folderEntry {
 // The phaseFolders struct implements the phase interface, providing methods to produce
 // folder entries, process folders, persist changes to the database, and log the results.
 type phaseFolders struct {
-	jobs             []*scanJob
-	ds               model.DataStore
-	ctx              context.Context //nolint:containedctx // phase runs under a single scan ctx
-	walkCtx          context.Context //nolint:containedctx // cancelled when a folder fails to persist, so the walk stops early
-	stopWalk         context.CancelCauseFunc
-	state            *scanState
-	prevAlbumPIDConf string
-	imageChanges     *imageChangeCollector
+	jobs         []*scanJob
+	ds           model.DataStore
+	ctx          context.Context //nolint:containedctx // phase runs under a single scan ctx
+	walkCtx      context.Context //nolint:containedctx // cancelled when a folder fails to persist, so the walk stops early
+	stopWalk     context.CancelCauseFunc
+	state        *scanState
+	imageChanges *imageChangeCollector
 }
 
 func (p *phaseFolders) description() string {
@@ -138,12 +155,6 @@ func (p *phaseFolders) description() string {
 
 func (p *phaseFolders) producer() ppl.Producer[*folderEntry] {
 	return ppl.NewProducer(func(put func(entry *folderEntry)) error {
-		var err error
-		p.prevAlbumPIDConf, err = p.ds.Property().DefaultGet(p.ctx, consts.PIDAlbumKey, "")
-		if err != nil {
-			return fmt.Errorf("getting album PID conf: %w", err)
-		}
-
 		// TODO Parallelize multiple job when we have multiple libraries
 		var total int64
 		var totalChanged int64
@@ -173,7 +184,7 @@ func (p *phaseFolders) producer() ppl.Producer[*folderEntry] {
 
 				// Check if folder is outdated
 				if folder.isOutdated() {
-					if !p.state.fullScan {
+					if !folder.job.lib.FullScanInProgress {
 						// Ancestor folders need a row even with no files of their own: artwork
 						// resolution climbs them, and an image added later needs a state to diff.
 						if folder.isEmpty() && folder.isNew() {
@@ -239,7 +250,7 @@ func (p *phaseFolders) processFolder(entry *folderEntry) (*folderEntry, error) {
 	for afPath, af := range entry.audioFiles {
 		fullPath := path.Join(entry.path, afPath)
 		dbTrack, foundInDB := dbTracks[fullPath]
-		if !foundInDB || p.state.fullScan {
+		if !foundInDB || entry.job.lib.FullScanInProgress {
 			filesToImport[fullPath] = dbTrack
 		} else {
 			info, err := af.Info()
@@ -289,18 +300,18 @@ func (p *phaseFolders) loadTagsFromFiles(entry *folderEntry, toImport map[string
 		}
 		for filePath, info := range allInfo {
 			md := metadata.New(filePath, info)
-			track := md.ToMediaFile(entry.job.lib.ID, entry.id)
+			track := md.ToMediaFile(entry.job.lib, entry.id)
 			tracks = append(tracks, track)
 			for _, t := range track.Tags.FlattenAll() {
 				uniqueTags[t.ID] = t
 			}
 
 			// Keep track of any album ID changes, to reassign annotations later
-			prevAlbumID := ""
+			prevAlbumID := track.AlbumID
 			if prev := toImport[filePath]; prev != nil {
 				prevAlbumID = prev.AlbumID
-			} else {
-				prevAlbumID = md.AlbumID(track, p.prevAlbumPIDConf)
+			} else if entry.job.prevAlbumPIDConf != "" {
+				prevAlbumID = md.AlbumID(track, entry.job.prevAlbumPIDConf)
 			}
 			_, ok := entry.albumIDMap[track.AlbumID]
 			if prevAlbumID != track.AlbumID && !ok {
@@ -453,7 +464,7 @@ func (p *phaseFolders) persistFolder(ctx context.Context, tx model.DataStore, en
 	if len(queueItems) > 0 {
 		queue := tx.ArtworkQueue()
 		enqueue := queue.Enqueue
-		if p.state.fullScan {
+		if entry.job.lib.FullScanInProgress {
 			enqueue = queue.EnqueueIfMissing
 		}
 		if err := enqueue(ctx, queueItems...); err != nil {

scanner/scanner.go

@@ -4,13 +4,11 @@ import (
 	"context"
 	"fmt"
 	"maps"
-	"path/filepath"
 	"slices"
 	"sync/atomic"
 	"time"
 
 	ppl "github.com/google/go-pipeline/pkg/pipeline"
-	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/consts"
 	"github.com/navidrome/navidrome/core/playlists"
 	"github.com/navidrome/navidrome/log"
@@ -32,6 +30,7 @@ type scanState struct {
 	libraries         model.Libraries  // Store libraries list for consistency across phases
 	targets           map[int][]string // Optional: map[libraryID][]folderPaths for selective scans
 	totalLibraryCount int              // Total number of libraries (unfiltered), for cross-library move detection
+	failedLibs        map[int]bool     // Libraries that could not be scanned in this run
 }
 
 func (s *scanState) sendProgress(info *ProgressInfo) {
@@ -48,29 +47,15 @@ func (s *scanState) sendWarning(msg string) {
 	s.sendProgress(&ProgressInfo{Warning: msg})
 }
 
-func (s *scanState) sendError(err error) {
-	s.sendProgress(&ProgressInfo{Error: err.Error()})
+func (s *scanState) markFailed(libID int) {
+	if s.failedLibs == nil {
+		s.failedLibs = map[int]bool{}
+	}
+	s.failedLibs[libID] = true
 }
 
-// libraryRelativePath rebases an absolute scan target path onto the library root, since the
-// scanner's fs.FS only accepts paths relative to it. Relative paths, and absolute paths outside
-// the library root, are returned unchanged.
-func libraryRelativePath(libPath, folderPath string) string {
-	if !filepath.IsAbs(folderPath) {
-		return folderPath
-	}
-	// The library root may be relative (e.g. the default "./music"); it must be made absolute
-	// to match against an absolute target, and it resolves against the same cwd as the scanner's fs.
-	absLib, err := filepath.Abs(libPath)
-	if err != nil {
-		return folderPath
-	}
-	rel, err := filepath.Rel(absLib, folderPath)
-	if err != nil || !filepath.IsLocal(rel) {
-		return folderPath
-	}
-	// The scanner's fs.FS is an io/fs, which always uses forward slashes.
-	return filepath.ToSlash(rel)
+func (s *scanState) sendError(err error) {
+	s.sendProgress(&ProgressInfo{Error: err.Error()})
 }
 
 func (s *scannerImpl) scanFolders(ctx context.Context, fullScan bool, targets []model.ScanTarget, progress chan<- *ProgressInfo) {
@@ -104,7 +89,7 @@ func (s *scannerImpl) scanFolders(ctx context.Context, fullScan bool, targets []
 		})
 
 		for _, target := range targets {
-			folderPath := libraryRelativePath(libPaths[target.LibraryID], target.FolderPath)
+			folderPath := model.LibraryRelativePath(libPaths[target.LibraryID], target.FolderPath)
 			if folderPath == "" {
 				folderPath = "."
 			}
@@ -137,6 +122,10 @@ func (s *scannerImpl) scanFolders(ctx context.Context, fullScan bool, targets []
 	// if there was a full scan in progress, force a full scan
 	if !state.fullScan {
 		for _, lib := range state.libraries {
+			// A pending PID rescan already restarts in full through its own job
+			if lib.NeedsPIDRescan() {
+				continue
+			}
 			if lib.FullScanInProgress {
 				log.Info(ctx, "Scanner: Interrupted full scan detected", "lib", lib.Name)
 				state.fullScan = true
@@ -215,10 +204,13 @@ func (s *scannerImpl) prepareLibrariesForScan(ctx context.Context, state *scanSt
 	var successfulLibs []model.Library
 
 	for _, lib := range state.libraries {
-		if lib.LastScanStartedAt.IsZero() {
+		// A library with a changed PID config restarts its scan: resuming would skip the folders that
+		// the interrupted scan already processed with the old config
+		pidRescan := lib.NeedsPIDRescan()
+		if lib.LastScanStartedAt.IsZero() || pidRescan {
 			// This is a new scan - mark it as started
 			err := s.ds.WithTxRetry(ctx, func(ctx context.Context, tx model.DataStore) error {
-				return tx.Library().ScanBegin(ctx, lib.ID, state.fullScan)
+				return tx.Library().ScanBegin(ctx, lib.ID, state.fullScan || pidRescan)
 			}, "scanner: begin library scan")
 			if err != nil {
 				log.Error(ctx, "Scanner: Error marking scan start", "lib", lib.Name, err)
@@ -340,11 +332,12 @@ func (s *scannerImpl) runUpdateLibraries(ctx context.Context, state *scanState)
 				if err := tx.Library().ScanEnd(ctx, lib.ID); err != nil {
 					return fmt.Errorf("updating last scan completed for %s: %w", lib.Name, err)
 				}
-				if err := tx.Property().Put(ctx, consts.PIDTrackKey, conf.Server.PID.Track); err != nil {
-					return fmt.Errorf("updating track PID conf: %w", err)
-				}
-				if err := tx.Property().Put(ctx, consts.PIDAlbumKey, conf.Server.PID.Album); err != nil {
-					return fmt.Errorf("updating album PID conf: %w", err)
+				// A selective scan covers only part of the library, so the rest may still use the old PID
+				// config. A library that could not be scanned did not apply it either.
+				if !state.isSelectiveScan() && !state.failedLibs[lib.ID] {
+					if err := tx.Library().SetScannedPID(ctx, lib.ID, lib.EffectivePID()); err != nil {
+						return fmt.Errorf("updating PID conf for %s: %w", lib.Name, err)
+					}
 				}
 				if state.changesDetected.Load() {
 					log.Debug(ctx, "Scanner: Refreshing library stats", "lib", lib.Name)

scanner/scanner_internal_test.go

@@ -4,8 +4,6 @@ package scanner
 import (
 	"context"
 	"errors"
-	"os"
-	"path/filepath"
 	"sync/atomic"
 
 	ppl "github.com/google/go-pipeline/pkg/pipeline"
@@ -13,43 +11,6 @@ import (
 	. "github.com/onsi/gomega"
 )
 
-var _ = Describe("libraryRelativePath", func() {
-	// Paths are built with filepath so the "absolute" cases stay absolute on every OS
-	// (a Unix-style "/foo" is not absolute on Windows).
-	libRoot, _ := filepath.Abs(filepath.Join("jukebox", "collection"))
-	outside, _ := filepath.Abs(filepath.Join("somewhere", "else"))
-
-	It("returns a relative path unchanged", func() {
-		Expect(libraryRelativePath(libRoot, "_Collection")).To(Equal("_Collection"))
-	})
-
-	It("rebases an absolute target when the library root is relative", func() {
-		cwd, err := os.Getwd()
-		Expect(err).ToNot(HaveOccurred())
-		Expect(libraryRelativePath(filepath.Join("music", "library"), filepath.Join(cwd, "music", "library", "rock"))).To(Equal("rock"))
-	})
-
-	It("rebases an absolute path that equals the library root to '.'", func() {
-		Expect(libraryRelativePath(libRoot, libRoot)).To(Equal("."))
-	})
-
-	It("rebases an absolute path under the library root", func() {
-		Expect(libraryRelativePath(libRoot, filepath.Join(libRoot, "_Collection"))).To(Equal("_Collection"))
-	})
-
-	It("handles a trailing slash on the library path", func() {
-		Expect(libraryRelativePath(libRoot+string(filepath.Separator), filepath.Join(libRoot, "_Collection"))).To(Equal("_Collection"))
-	})
-
-	It("leaves an absolute path outside the library root unchanged", func() {
-		Expect(libraryRelativePath(libRoot, outside)).To(Equal(outside))
-	})
-
-	It("returns an empty path unchanged", func() {
-		Expect(libraryRelativePath(libRoot, "")).To(Equal(""))
-	})
-})
-
 type mockPhase struct {
 	num           int
 	produceFunc   func() ppl.Producer[int]

scanner/scanner_multilibrary_test.go

@@ -835,4 +835,170 @@ var _ = Describe("Scanner - Multi-Library", Ordered, func() {
 			Expect(lastError).To(BeEmpty())
 		})
 	})
+
+	Context("Per-library PID config", func() {
+		albumsOf := func(libID int) model.Albums {
+			// The mock datastore's GC is a no-op, so run the real one to purge the albums left
+			// empty by a regroup, as the scanner does in production
+			Expect(ds.RealDS.GC(ctx)).To(Succeed())
+			albums, err := ds.Album().GetAll(ctx, model.QueryOptions{
+				Filters: squirrel.Eq{"library_id": libID, "missing": false},
+				Sort:    "name",
+			})
+			Expect(err).ToNot(HaveOccurred())
+			return albums
+		}
+		trackByTitle := func(libID int, title string) model.MediaFile {
+			mfs, err := ds.MediaFile().GetAll(ctx, model.QueryOptions{
+				Filters: squirrel.Eq{"library_id": libID, "title": title},
+			})
+			Expect(err).ToNot(HaveOccurred())
+			Expect(mfs).To(HaveLen(1))
+			return mfs[0]
+		}
+		rockTitles := func() []string {
+			mfs, err := ds.MediaFile().GetAll(ctx, model.QueryOptions{Filters: squirrel.Eq{"library_id": lib1.ID}})
+			Expect(err).ToNot(HaveOccurred())
+			return slice.Map(mfs, func(mf model.MediaFile) string { return mf.Title })
+		}
+		// changeRockInDB edits the rock track in the DB only. A full rescan of the rock library would
+		// restore the title from the file tags, a quick scan leaves it alone.
+		changeRockInDB := func() {
+			_, err := db.Db().ExecContext(ctx, "update media_file set title = 'Changed In DB' where library_id = ?", lib1.ID)
+			Expect(err).ToNot(HaveOccurred())
+		}
+		// changeBlueTrainInDB does the same for one jazz track
+		changeBlueTrainInDB := func() {
+			_, err := db.Db().ExecContext(ctx, "update media_file set title = 'Blue Train In DB' where library_id = ? and title = 'Blue Train'", lib2.ID)
+			Expect(err).ToNot(HaveOccurred())
+		}
+
+		BeforeEach(func() {
+			beatles := template(_t{"albumartist": "The Beatles", "album": "Abbey Road", "year": 1969})
+			_ = createFS("rock", fstest.MapFS{
+				"The Beatles/Abbey Road/01 - Come Together.mp3": beatles(track(1, "Come Together")),
+			})
+
+			miles := template(_t{"albumartist": "Miles Davis", "album": "Kind of Blue", "year": 1959})
+			coltrane := template(_t{"albumartist": "John Coltrane", "album": "Giant Steps", "year": 1960})
+			blueTrain := template(_t{"albumartist": "John Coltrane", "album": "Blue Train", "year": 1957})
+			_ = createFS("jazz", fstest.MapFS{
+				"Loose/01 - So What.mp3":                  miles(track(1, "So What")),
+				"Loose/02 - Giant Steps.mp3":              coltrane(track(1, "Giant Steps")),
+				"Coltrane/Blue Train/01 - Blue Train.mp3": blueTrain(track(1, "Blue Train")),
+			})
+		})
+
+		It("regroups only the library whose PID config changed, keeping annotations", func() {
+			Expect(runScanner(ctx, true)).To(Succeed())
+			Expect(albumsOf(lib2.ID)).To(HaveLen(3))
+
+			// Star Blue Train, to check the star follows the album to its new ID
+			oldBlueTrain := trackByTitle(lib2.ID, "Blue Train")
+			Expect(ds.Album().SetStar(ctx, true, oldBlueTrain.AlbumID)).To(Succeed())
+			changeRockInDB()
+
+			lib2.PIDAlbum = "folder"
+			Expect(ds.Library().Put(ctx, &lib2)).To(Succeed())
+			Expect(runScanner(ctx, false)).To(Succeed())
+
+			// Jazz is grouped by folder now: "Loose" is one album
+			Expect(albumsOf(lib2.ID)).To(HaveLen(2))
+			Expect(trackByTitle(lib2.ID, "So What").AlbumID).To(Equal(trackByTitle(lib2.ID, "Giant Steps").AlbumID))
+
+			newBlueTrain := trackByTitle(lib2.ID, "Blue Train")
+			Expect(newBlueTrain.AlbumID).ToNot(Equal(oldBlueTrain.AlbumID))
+			album, err := ds.Album().Get(ctx, newBlueTrain.AlbumID)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(album.Starred).To(BeTrue())
+
+			// Rock only got a quick scan
+			Expect(rockTitles()).To(ConsistOf("Changed In DB"))
+
+			jazz, err := ds.Library().Get(ctx, lib2.ID)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(jazz.ScannedPIDAlbum).To(Equal("folder"))
+			Expect(jazz.PIDChanged()).To(BeFalse())
+			rock, err := ds.Library().Get(ctx, lib1.ID)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(rock.PIDChanged()).To(BeFalse())
+		})
+
+		It("rescans only libraries that follow the global config", func() {
+			lib2.PIDAlbum = "folder"
+			Expect(ds.Library().Put(ctx, &lib2)).To(Succeed())
+			Expect(runScanner(ctx, true)).To(Succeed())
+			changeRockInDB()
+			changeBlueTrainInDB()
+
+			conf.Server.PID.Album = "album"
+			Expect(runScanner(ctx, false)).To(Succeed())
+
+			// Rock follows the global config, so it was rescanned in full and its title restored
+			Expect(rockTitles()).To(ConsistOf("Come Together"))
+			// Jazz has its own override, so it only got a quick scan
+			trackByTitle(lib2.ID, "Blue Train In DB")
+			jazz, err := ds.Library().Get(ctx, lib2.ID)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(jazz.ScannedPIDAlbum).To(Equal("folder"))
+		})
+
+		It("restarts an interrupted scan when the PID config changed meanwhile", func() {
+			Expect(runScanner(ctx, true)).To(Succeed())
+
+			// Simulate a quick scan of jazz that was interrupted after it had processed every folder:
+			// the folders were updated after the (old) scan start time
+			_, err := db.Db().ExecContext(ctx, "update library set last_scan_started_at = ?, full_scan_in_progress = false where id = ?",
+				time.Now().Add(-time.Hour), lib2.ID)
+			Expect(err).ToNot(HaveOccurred())
+
+			lib2.PIDAlbum = "folder"
+			Expect(ds.Library().Put(ctx, &lib2)).To(Succeed())
+			Expect(runScanner(ctx, false)).To(Succeed())
+
+			// Every folder was revisited with the new config
+			Expect(albumsOf(lib2.ID)).To(HaveLen(2))
+		})
+
+		It("does not turn an interrupted PID rescan into a full scan of every library", func() {
+			Expect(runScanner(ctx, true)).To(Succeed())
+			changeRockInDB()
+			lib2.PIDAlbum = "folder"
+			Expect(ds.Library().Put(ctx, &lib2)).To(Succeed())
+
+			// Simulate a PID full scan of jazz that was interrupted
+			Expect(ds.Library().ScanBegin(ctx, lib2.ID, true)).To(Succeed())
+			Expect(runScanner(ctx, false)).To(Succeed())
+
+			// Rock only got a quick scan, jazz was rescanned with the new config
+			Expect(rockTitles()).To(ConsistOf("Changed In DB"))
+			Expect(albumsOf(lib2.ID)).To(HaveLen(2))
+		})
+
+		It("does not record the PID config for a library that could not be scanned", func() {
+			Expect(runScanner(ctx, true)).To(Succeed())
+			broken := model.Library{Name: "Broken", Path: "unregistered:///music", PIDAlbum: "folder"}
+			Expect(ds.Library().Put(ctx, &broken)).To(Succeed())
+
+			// The scan reports an error for the broken library, and still finishes the others
+			_ = runScanner(ctx, false)
+
+			reloaded, err := ds.Library().Get(ctx, broken.ID)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(reloaded.PIDChanged()).To(BeTrue())
+		})
+
+		It("does not record the PID config after a selective scan", func() {
+			Expect(runScanner(ctx, true)).To(Succeed())
+			lib2.PIDAlbum = "folder"
+			Expect(ds.Library().Put(ctx, &lib2)).To(Succeed())
+
+			_, err := s.ScanFolders(ctx, false, []model.ScanTarget{{LibraryID: lib2.ID, FolderPath: "Loose"}})
+			Expect(err).ToNot(HaveOccurred())
+
+			jazz, err := ds.Library().Get(ctx, lib2.ID)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(jazz.PIDChanged()).To(BeTrue())
+		})
+	})
 })

server/nativeapi/inspect.go

@@ -22,7 +22,12 @@ func doInspect(ctx context.Context, ds model.DataStore, id string) (*core.Inspec
 		return nil, model.ErrNotFound
 	}
 
-	return core.Inspect(file.AbsolutePath(), file.LibraryID, file.FolderID)
+	lib, err := ds.Library().Get(ctx, file.LibraryID)
+	if err != nil {
+		return nil, err
+	}
+
+	return core.Inspect(file.AbsolutePath(), *lib, file.FolderID)
 }
 
 func inspect(ds model.DataStore) http.HandlerFunc {

server/serve_index.go

@@ -58,6 +58,8 @@ func serveIndex(ds model.DataStore, fs fs.FS, shareInfo *model.Share) http.Handl
 			"uiSearchDebounceMs":        conf.Server.UISearchDebounceMs,
 			"uiCoverArtSize":            conf.Server.UICoverArtSize,
 			"enableCoverAnimation":      conf.Server.EnableCoverAnimation,
+			"pidAlbum":                  conf.Server.PID.Album,
+			"pidTrack":                  conf.Server.PID.Track,
 			"enableNowPlaying":          conf.Server.EnableNowPlaying,
 			"playbackReportIntervalMs":  conf.Server.UIPlaybackReportInterval.Milliseconds(),
 			"gaTrackingId":              conf.Server.GATrackingID,

server/serve_index_test.go

@@ -89,6 +89,8 @@ var _ = Describe("serveIndex", func() {
 		Entry("uiSearchDebounceMs", func() { conf.Server.UISearchDebounceMs = 500 }, "uiSearchDebounceMs", float64(500)),
 		Entry("uiCoverArtSize", func() { conf.Server.UICoverArtSize = 300 }, "uiCoverArtSize", float64(300)),
 		Entry("enableCoverAnimation", func() { conf.Server.EnableCoverAnimation = true }, "enableCoverAnimation", true),
+		Entry("pidAlbum", func() { conf.Server.PID.Album = "folder" }, "pidAlbum", "folder"),
+		Entry("pidTrack", func() { conf.Server.PID.Track = "title" }, "pidTrack", "title"),
 		Entry("enableNowPlaying", func() { conf.Server.EnableNowPlaying = true }, "enableNowPlaying", true),
 		Entry("gaTrackingId", func() { conf.Server.GATrackingID = "UA-12345" }, "gaTrackingId", "UA-12345"),
 		Entry("defaultDownloadableShare", func() { conf.Server.DefaultDownloadableShare = true }, "defaultDownloadableShare", true),

tests/mock_library_repo.go

@@ -145,6 +145,17 @@ func (m *MockLibraryRepo) ScanEnd(_ context.Context, id int) error {
 	return nil
 }
 
+func (m *MockLibraryRepo) SetScannedPID(_ context.Context, id int, pid model.PIDConfig) error {
+	if m.Err != nil {
+		return m.Err
+	}
+	if lib, ok := m.Data[id]; ok {
+		lib.ScannedPIDAlbum, lib.ScannedPIDTrack = pid.Album, pid.Track
+		m.Data[id] = lib
+	}
+	return nil
+}
+
 func (m *MockLibraryRepo) ScanInProgress(_ context.Context) (bool, error) {
 	if m.Err != nil {
 		return false, m.Err

ui/src/config.js

@@ -32,6 +32,8 @@ const defaultConfig = {
   listenBrainzEnabled: true,
   enableExternalServices: true,
   enableCoverAnimation: true,
+  pidAlbum: 'musicbrainz_albumid|albumartistid,album,albumversion,releasedate', // See consts.DefaultAlbumPID
+  pidTrack: 'musicbrainz_trackid|albumid,discnumber,tracknumber,title', // See consts.DefaultTrackPID
   enableNowPlaying: true,
   playbackReportIntervalMs: 60000,
   devShowArtistPage: true,

ui/src/i18n/en.json

@@ -331,11 +331,22 @@
         "totalDuration": "Duration",
         "defaultNewUsers": "Default for New Users",
         "createdAt": "Created",
-        "updatedAt": "Updated"
+        "updatedAt": "Updated",
+        "pidAlbum": "Album grouping",
+        "pidTrack": "Track identity"
       },
       "sections": {
         "basic": "Basic Information",
-        "statistics": "Statistics"
+        "statistics": "Statistics",
+        "pid": "Persistent IDs"
+      },
+      "pid": {
+        "global": "Use global setting (%{value})",
+        "folder": "Folder (one album per folder)",
+        "custom": "Custom",
+        "spec": "PID spec",
+        "help": "Tags and attributes that identify an item. See the documentation for the syntax:",
+        "docs": "Persistent IDs"
       },
       "actions": {
         "scan": "Scan Library",
@@ -365,7 +376,9 @@
       "messages": {
         "deleteConfirm": "Are you sure you want to delete this library? This will remove all associated data and user access.",
         "scanInProgress": "Scan in progress...",
-        "noLibrariesAssigned": "No libraries assigned to this user"
+        "noLibrariesAssigned": "No libraries assigned to this user",
+        "pidChangeTitle": "Change persistent IDs?",
+        "pidChangeConfirm": "This regroups albums and tracks in this library. A full rescan of this library starts now. Track stars, ratings and play counts are kept. Album stars and ratings move to the new albums where an old album maps to a new one."
       }
     },
     "plugin": {

ui/src/library/LibraryCreate.jsx

@@ -1,4 +1,5 @@
 import React, { useCallback } from 'react'
+import PropTypes from 'prop-types'
 import {
   Create,
   SimpleForm,
@@ -10,7 +11,34 @@ import {
   useNotify,
   useRedirect,
 } from 'react-admin'
+import { Typography } from '@material-ui/core'
+import { makeStyles } from '@material-ui/core/styles'
 import { Title } from '../common'
+import { PIDInputs } from './PIDInput'
+
+const useStyles = makeStyles((theme) => ({
+  spaced: { marginTop: theme.spacing(3) },
+}))
+
+// SimpleForm passes form props (variant, record, ...) to its children, so Typography can't be used directly
+const SectionTitle = ({ label, spaced }) => {
+  const translate = useTranslate()
+  const classes = useStyles()
+  return (
+    <Typography
+      variant="h6"
+      gutterBottom
+      className={spaced ? classes.spaced : undefined}
+    >
+      {translate(label)}
+    </Typography>
+  )
+}
+
+SectionTitle.propTypes = {
+  label: PropTypes.string.isRequired,
+  spaced: PropTypes.bool,
+}
 
 const LibraryCreate = (props) => {
   const translate = useTranslate()
@@ -73,9 +101,12 @@ const LibraryCreate = (props) => {
   return (
     <Create title={<Title subTitle={title} />} {...props}>
       <SimpleForm save={save} variant={'outlined'}>
+        <SectionTitle label="resources.library.sections.basic" />
         <TextInput source="name" validate={[required()]} />
         <TextInput source="path" validate={[required()]} fullWidth />
         <BooleanInput source="defaultNewUsers" />
+        <SectionTitle label="resources.library.sections.pid" spaced />
+        <PIDInputs />
       </SimpleForm>
     </Create>
   )

ui/src/library/LibraryEdit.jsx

@@ -1,9 +1,11 @@
-import React, { useCallback } from 'react'
+import React, { useCallback, useState } from 'react'
+import PropTypes from 'prop-types'
 import {
   Edit,
   FormWithRedirect,
   TextInput,
   BooleanInput,
+  Confirm,
   required,
   SaveButton,
   useTranslate,
@@ -22,6 +24,9 @@ import {
   ReadOnlySizeField,
   Title,
 } from '../common'
+import config from '../config'
+import { PIDInputs } from './PIDInput'
+import { pidConfigChanged } from './pidPresets'
 
 const useStyles = makeStyles({
   toolbar: {
@@ -53,8 +58,131 @@ const CustomToolbar = ({ showDelete, ...props }) => (
   </Toolbar>
 )
 
-const LibraryEdit = (props) => {
+export const LibraryEditForm = ({ formProps, canEditPath, canDelete }) => {
   const translate = useTranslate()
+  const [confirmOpen, setConfirmOpen] = useState(false)
+
+  // Every submit path (Save button and Enter key) goes through here, so a PID change always asks first
+  const submit = () => {
+    if (
+      pidConfigChanged(
+        formProps.form.getState().values,
+        formProps.record,
+        config,
+      )
+    ) {
+      setConfirmOpen(true)
+      return
+    }
+    formProps.handleSubmit()
+  }
+
+  const handleConfirm = () => {
+    setConfirmOpen(false)
+    formProps.handleSubmit()
+  }
+
+  return (
+    <form
+      onSubmit={(event) => {
+        event.preventDefault()
+        submit()
+      }}
+    >
+      <Box p="1em" maxWidth="800px">
+        <Box display="flex">
+          <Box flex={1} mr="1em">
+            {/* Basic Information */}
+            <Typography variant="h6" gutterBottom>
+              {translate('resources.library.sections.basic')}
+            </Typography>
+
+            <TextInput
+              source="name"
+              label={translate('resources.library.fields.name')}
+              validate={[required()]}
+              variant="outlined"
+            />
+            <TextInput
+              source="path"
+              label={translate('resources.library.fields.path')}
+              validate={[required()]}
+              fullWidth
+              variant="outlined"
+              InputProps={{ readOnly: !canEditPath }} // Disable editing path for library 1
+            />
+            <BooleanInput
+              source="defaultNewUsers"
+              label={translate('resources.library.fields.defaultNewUsers')}
+              variant="outlined"
+            />
+
+            <Box mt="2em" />
+            <Typography variant="h6" gutterBottom>
+              {translate('resources.library.sections.pid')}
+            </Typography>
+            <PIDInputs />
+
+            <Box mt="2em" />
+
+            {/* Statistics - Two Column Layout */}
+            <Typography variant="h6" gutterBottom>
+              {translate('resources.library.sections.statistics')}
+            </Typography>
+
+            <Box
+              display="grid"
+              gridTemplateColumns="1fr 1fr"
+              gridColumnGap="1em"
+            >
+              <ReadOnlyNumberField source="totalSongs" {...readOnlyProps} />
+              <ReadOnlyNumberField source="totalAlbums" {...readOnlyProps} />
+              <ReadOnlyNumberField source="totalArtists" {...readOnlyProps} />
+              <ReadOnlySizeField source="totalSize" {...readOnlyProps} />
+              <ReadOnlyDurationField
+                source="totalDuration"
+                {...readOnlyProps}
+              />
+              <ReadOnlyNumberField
+                source="totalMissingFiles"
+                {...readOnlyProps}
+              />
+              <Box gridColumn="1 / -1">
+                <ReadOnlyDateField source="lastScanAt" {...readOnlyProps} />
+              </Box>
+              <ReadOnlyDateField source="updatedAt" {...readOnlyProps} />
+              <ReadOnlyDateField source="createdAt" {...readOnlyProps} />
+            </Box>
+          </Box>
+        </Box>
+      </Box>
+
+      <CustomToolbar
+        handleSubmitWithRedirect={submit}
+        pristine={formProps.pristine}
+        saving={formProps.saving}
+        record={formProps.record}
+        showDelete={canDelete}
+      />
+      <Confirm
+        isOpen={confirmOpen}
+        loading={formProps.saving}
+        title="resources.library.messages.pidChangeTitle"
+        content="resources.library.messages.pidChangeConfirm"
+        onConfirm={handleConfirm}
+        onClose={() => setConfirmOpen(false)}
+      />
+    </form>
+  )
+}
+
+LibraryEditForm.propTypes = {
+  formProps: PropTypes.object.isRequired,
+  canEditPath: PropTypes.bool,
+  canDelete: PropTypes.bool,
+}
+
+const LibraryEdit = (props) => {
   const [mutate] = useMutation()
   const notify = useNotify()
   const redirect = useRedirect()
@@ -93,91 +221,11 @@ const LibraryEdit = (props) => {
         {...props}
         save={save}
         render={(formProps) => (
-          <form onSubmit={formProps.handleSubmit}>
-            <Box p="1em" maxWidth="800px">
-              <Box display="flex">
-                <Box flex={1} mr="1em">
-                  {/* Basic Information */}
-                  <Typography variant="h6" gutterBottom>
-                    {translate('resources.library.sections.basic')}
-                  </Typography>
-
-                  <TextInput
-                    source="name"
-                    label={translate('resources.library.fields.name')}
-                    validate={[required()]}
-                    variant="outlined"
-                  />
-                  <TextInput
-                    source="path"
-                    label={translate('resources.library.fields.path')}
-                    validate={[required()]}
-                    fullWidth
-                    variant="outlined"
-                    InputProps={{ readOnly: !canEditPath }} // Disable editing path for library 1
-                  />
-                  <BooleanInput
-                    source="defaultNewUsers"
-                    label={translate(
-                      'resources.library.fields.defaultNewUsers',
-                    )}
-                    variant="outlined"
-                  />
-
-                  <Box mt="2em" />
-
-                  {/* Statistics - Two Column Layout */}
-                  <Typography variant="h6" gutterBottom>
-                    {translate('resources.library.sections.statistics')}
-                  </Typography>
-
-                  <Box
-                    display="grid"
-                    gridTemplateColumns="1fr 1fr"
-                    gridColumnGap="1em"
-                  >
-                    <ReadOnlyNumberField
-                      source="totalSongs"
-                      {...readOnlyProps}
-                    />
-                    <ReadOnlyNumberField
-                      source="totalAlbums"
-                      {...readOnlyProps}
-                    />
-                    <ReadOnlyNumberField
-                      source="totalArtists"
-                      {...readOnlyProps}
-                    />
-                    <ReadOnlySizeField source="totalSize" {...readOnlyProps} />
-                    <ReadOnlyDurationField
-                      source="totalDuration"
-                      {...readOnlyProps}
-                    />
-                    <ReadOnlyNumberField
-                      source="totalMissingFiles"
-                      {...readOnlyProps}
-                    />
-                    <Box gridColumn="1 / -1">
-                      <ReadOnlyDateField
-                        source="lastScanAt"
-                        {...readOnlyProps}
-                      />
-                    </Box>
-                    <ReadOnlyDateField source="updatedAt" {...readOnlyProps} />
-                    <ReadOnlyDateField source="createdAt" {...readOnlyProps} />
-                  </Box>
-                </Box>
-              </Box>
-            </Box>
-
-            <CustomToolbar
-              handleSubmitWithRedirect={formProps.handleSubmitWithRedirect}
-              pristine={formProps.pristine}
-              saving={formProps.saving}
-              record={formProps.record}
-              showDelete={canDelete}
-            />
-          </form>
+          <LibraryEditForm
+            formProps={formProps}
+            canEditPath={canEditPath}
+            canDelete={canDelete}
+          />
         )}
       />
     </Edit>

ui/src/library/LibraryEdit.test.jsx

@@ -0,0 +1,125 @@
+import * as React from 'react'
+import { TestContext } from 'ra-test'
+import {
+  FormWithRedirect,
+  RecordContextProvider,
+  SaveContextProvider,
+} from 'react-admin'
+import {
+  cleanup,
+  fireEvent,
+  render,
+  screen,
+  waitFor,
+  within,
+} from '@testing-library/react'
+import { describe, it, expect, vi, afterEach } from 'vitest'
+import { LibraryEditForm } from './LibraryEdit'
+import config from '../config'
+
+const record = {
+  id: '2',
+  name: 'Jazz',
+  path: '/music/jazz',
+  pidAlbum: '',
+  pidTrack: '',
+}
+
+// Edit provides a save context in the app. SaveButton only reads these setters from it
+const saveContext = {
+  save: vi.fn(),
+  setOnSuccess: vi.fn(),
+  setOnFailure: vi.fn(),
+  setTransform: vi.fn(),
+}
+
+const renderForm = (save) =>
+  render(
+    <TestContext>
+      <SaveContextProvider value={saveContext}>
+        <RecordContextProvider value={record}>
+          <FormWithRedirect
+            record={record}
+            save={save}
+            render={(formProps) => (
+              <LibraryEditForm
+                formProps={formProps}
+                canEditPath
+                canDelete={false}
+              />
+            )}
+          />
+        </RecordContextProvider>
+      </SaveContextProvider>
+    </TestContext>,
+  )
+
+const chooseAlbumGrouping = (optionText) => {
+  fireEvent.mouseDown(
+    screen.getByLabelText('resources.library.fields.pidAlbum'),
+  )
+  fireEvent.click(within(screen.getByRole('listbox')).getByText(optionText))
+}
+
+const dialogTitle = 'resources.library.messages.pidChangeTitle'
+
+describe('LibraryEditForm', () => {
+  afterEach(cleanup)
+
+  it('saves directly when the PID config did not change', async () => {
+    const save = vi.fn()
+    renderForm(save)
+    fireEvent.change(screen.getByLabelText(/resources.library.fields.name/), {
+      target: { value: 'Jazz Renamed' },
+    })
+    fireEvent.click(screen.getByText('ra.action.save'))
+    await waitFor(() => expect(save).toHaveBeenCalled())
+    expect(screen.queryByText(dialogTitle)).not.toBeInTheDocument()
+  })
+
+  it('asks before saving a PID change, and Cancel keeps the edits', async () => {
+    const save = vi.fn()
+    renderForm(save)
+    chooseAlbumGrouping('resources.library.pid.folder')
+    fireEvent.click(screen.getByText('ra.action.save'))
+
+    expect(await screen.findByText(dialogTitle)).toBeInTheDocument()
+    expect(save).not.toHaveBeenCalled()
+
+    fireEvent.click(screen.getByText('ra.action.cancel'))
+    await waitFor(() =>
+      expect(screen.queryByText(dialogTitle)).not.toBeInTheDocument(),
+    )
+    expect(save).not.toHaveBeenCalled()
+    expect(screen.getByText('resources.library.pid.folder')).toBeInTheDocument()
+  })
+
+  it('saves the PID change after Confirm', async () => {
+    const save = vi.fn()
+    renderForm(save)
+    chooseAlbumGrouping('resources.library.pid.folder')
+    fireEvent.click(screen.getByText('ra.action.save'))
+    fireEvent.click(await screen.findByText('ra.action.confirm'))
+
+    await waitFor(() => expect(save).toHaveBeenCalled())
+    expect(save.mock.calls[0][0]).toMatchObject({ pidAlbum: 'folder' })
+  })
+
+  it('pre-fills a Custom spec with the global spec', () => {
+    renderForm(vi.fn())
+    chooseAlbumGrouping('resources.library.pid.custom')
+    expect(screen.getByLabelText(/resources.library.pid.spec/)).toHaveValue(
+      config.pidAlbum,
+    )
+  })
+
+  it('asks before saving when the form is submitted with Enter', async () => {
+    const save = vi.fn()
+    const { container } = renderForm(save)
+    chooseAlbumGrouping('resources.library.pid.folder')
+    fireEvent.submit(container.querySelector('form'))
+
+    expect(await screen.findByText(dialogTitle)).toBeInTheDocument()
+    expect(save).not.toHaveBeenCalled()
+  })
+})

ui/src/library/PIDInput.jsx

@@ -0,0 +1,114 @@
+import React, { useState } from 'react'
+import PropTypes from 'prop-types'
+import { TextInput, required, useTranslate } from 'react-admin'
+import { useField } from 'react-final-form'
+import { FormHelperText, Link, MenuItem, TextField } from '@material-ui/core'
+import { makeStyles } from '@material-ui/core/styles'
+import {
+  PID_CUSTOM,
+  PID_FOLDER,
+  PID_GLOBAL,
+  pidModeFromValue,
+  pidValueForMode,
+} from './pidPresets'
+import config from '../config'
+import { docsUrl } from '../utils'
+
+const PID_DOCS_URL = docsUrl('/docs/usage/pids/')
+
+const useStyles = makeStyles((theme) => ({
+  help: { marginBottom: theme.spacing(1) },
+}))
+
+// PIDInput edits a library PID override: use the global setting, a preset, or a custom spec
+export const PIDInput = ({ source, label, globalValue, allowFolder }) => {
+  const translate = useTranslate()
+  const classes = useStyles()
+  const { input } = useField(source)
+  // Local state, so choosing Custom shows the text box before anything is typed
+  const [mode, setMode] = useState(() =>
+    pidModeFromValue(input.value, allowFolder),
+  )
+
+  const choices = [
+    {
+      id: PID_GLOBAL,
+      name: translate('resources.library.pid.global', { value: globalValue }),
+    },
+    ...(allowFolder
+      ? [{ id: PID_FOLDER, name: translate('resources.library.pid.folder') }]
+      : []),
+    { id: PID_CUSTOM, name: translate('resources.library.pid.custom') },
+  ]
+
+  const handleModeChange = (event) => {
+    const newMode = event.target.value
+    setMode(newMode)
+    input.onChange(pidValueForMode(newMode, globalValue))
+  }
+
+  return (
+    <>
+      <TextField
+        id={`${source}-mode`}
+        select
+        fullWidth
+        variant="outlined"
+        margin="dense"
+        label={label}
+        value={mode}
+        onChange={handleModeChange}
+      >
+        {choices.map((choice) => (
+          <MenuItem key={choice.id} value={choice.id}>
+            {choice.name}
+          </MenuItem>
+        ))}
+      </TextField>
+      {mode === PID_CUSTOM && (
+        <>
+          <TextInput
+            source={source}
+            label={translate('resources.library.pid.spec')}
+            validate={[required()]}
+            fullWidth
+            variant="outlined"
+            helperText={false}
+          />
+          <FormHelperText className={classes.help}>
+            {translate('resources.library.pid.help')}{' '}
+            <Link href={PID_DOCS_URL} target="_blank" rel="noopener noreferrer">
+              {translate('resources.library.pid.docs')}
+            </Link>
+          </FormHelperText>
+        </>
+      )}
+    </>
+  )
+}
+
+PIDInput.propTypes = {
+  source: PropTypes.string.isRequired,
+  label: PropTypes.string.isRequired,
+  globalValue: PropTypes.string,
+  allowFolder: PropTypes.bool,
+}
+
+export const PIDInputs = () => {
+  const translate = useTranslate()
+  return (
+    <>
+      <PIDInput
+        source="pidAlbum"
+        label={translate('resources.library.fields.pidAlbum')}
+        globalValue={config.pidAlbum}
+        allowFolder
+      />
+      <PIDInput
+        source="pidTrack"
+        label={translate('resources.library.fields.pidTrack')}
+        globalValue={config.pidTrack}
+      />
+    </>
+  )
+}

ui/src/library/pidPresets.js

@@ -0,0 +1,33 @@
+export const PID_GLOBAL = 'global'
+export const PID_FOLDER = 'folder'
+export const PID_CUSTOM = 'custom'
+
+export const pidModeFromValue = (value, allowFolder) => {
+  const v = (value || '').trim()
+  if (v === '') return PID_GLOBAL
+  if (allowFolder && v === PID_FOLDER) return PID_FOLDER
+  return PID_CUSTOM
+}
+
+// Returns the value to store for a dropdown choice. Custom starts from the global spec
+export const pidValueForMode = (mode, globalValue) => {
+  switch (mode) {
+    case PID_GLOBAL:
+      return ''
+    case PID_FOLDER:
+      return PID_FOLDER
+    default:
+      return globalValue || ''
+  }
+}
+
+// Reports whether the form values change the effective PID spec of the saved record. Like the
+// server, it trims, treats empty as the global value and compares case-insensitively
+export const pidConfigChanged = (values, record, globals) => {
+  const effective = (value, field) =>
+    ((value || '').trim() || globals[field] || '').toLowerCase()
+  return ['pidAlbum', 'pidTrack'].some(
+    (field) =>
+      effective(values[field], field) !== effective(record[field], field),
+  )
+}

ui/src/library/pidPresets.test.js

@@ -0,0 +1,65 @@
+import { describe, it, expect } from 'vitest'
+import {
+  PID_CUSTOM,
+  PID_FOLDER,
+  PID_GLOBAL,
+  pidConfigChanged,
+  pidModeFromValue,
+  pidValueForMode,
+} from './pidPresets'
+
+describe('pidModeFromValue', () => {
+  it('maps an empty value to the global setting', () => {
+    expect(pidModeFromValue('', true)).toBe(PID_GLOBAL)
+    expect(pidModeFromValue(undefined, true)).toBe(PID_GLOBAL)
+  })
+  it('maps folder to the Folder preset when allowed', () => {
+    expect(pidModeFromValue('folder', true)).toBe(PID_FOLDER)
+  })
+  it('maps folder to Custom when the Folder preset is not offered', () => {
+    expect(pidModeFromValue('folder', false)).toBe(PID_CUSTOM)
+  })
+  it('maps any other value to Custom', () => {
+    expect(pidModeFromValue('album|title', true)).toBe(PID_CUSTOM)
+  })
+})
+
+describe('pidValueForMode', () => {
+  it('stores an empty value for the global setting', () => {
+    expect(pidValueForMode(PID_GLOBAL, 'album')).toBe('')
+  })
+  it('stores folder for the Folder preset', () => {
+    expect(pidValueForMode(PID_FOLDER, '')).toBe('folder')
+  })
+  it('starts Custom from the global spec', () => {
+    expect(pidValueForMode(PID_CUSTOM, 'album|title')).toBe('album|title')
+    expect(pidValueForMode(PID_CUSTOM, undefined)).toBe('')
+  })
+})
+
+describe('pidConfigChanged', () => {
+  const record = { pidAlbum: 'folder', pidTrack: '' }
+  const globals = {
+    pidAlbum: 'musicbrainz_albumid|albumartistid,album',
+    pidTrack: 'musicbrainz_trackid|albumid,discnumber,tracknumber,title',
+  }
+  it.each([
+    ['nothing changed', { pidAlbum: 'folder', pidTrack: '' }, false],
+    ['a missing value equals an empty one', { pidAlbum: 'folder' }, false],
+    [
+      'Custom set to the global value',
+      { pidAlbum: 'folder', pidTrack: globals.pidTrack },
+      false,
+    ],
+    ['a case-only change', { pidAlbum: 'FOLDER', pidTrack: '' }, false],
+    [
+      'a whitespace-only change',
+      { pidAlbum: ' folder ', pidTrack: '  ' },
+      false,
+    ],
+    ['the album PID changed', { pidAlbum: '', pidTrack: '' }, true],
+    ['the track PID changed', { pidAlbum: 'folder', pidTrack: 'title' }, true],
+  ])('%s', (_, values, expected) => {
+    expect(pidConfigChanged(values, record, globals)).toBe(expected)
+  })
+})