--load-extension=spatialite shortcut, closes #1028

datasette/app.py

@@ -49,12 +49,14 @@ from .utils import (
     display_actor,
     escape_css_string,
     escape_sqlite,
+    find_spatialite,
     format_bytes,
     module_from_path,
     parse_metadata,
     resolve_env_secrets,
     sqlite3,
     to_css_class,
+    SpatialiteNotFound,
 )
 from .utils.asgi import (
     AsgiLifespan,
@@ -242,7 +244,14 @@ class Datasette:
                 metadata = parse_metadata(fp.read())
         self._metadata = metadata or {}
         self.sqlite_functions = []
-        self.sqlite_extensions = sqlite_extensions or []
+        self.sqlite_extensions = []
+        for extension in sqlite_extensions or []:
+            # Resolve spatialite, if requested
+            if extension == "spatialite":
+                # Could raise SpatialiteNotFound
+                self.sqlite_extensions.append(find_spatialite())
+            else:
+                self.sqlite_extensions.append(extension)
         if config_dir and (config_dir / "templates").is_dir() and not template_dir:
             template_dir = str((config_dir / "templates").resolve())
         self.template_dir = template_dir

datasette/cli.py

@@ -19,6 +19,7 @@ from .utils import (
     SpatialiteConnectionProblem,
     temporary_docker_directory,
     value_as_boolean,
+    SpatialiteNotFound,
     StaticMount,
     ValueAsBooleanError,
 )
@@ -78,7 +79,6 @@ def cli():
     "--load-extension",
     envvar="SQLITE_EXTENSIONS",
     multiple=True,
-    type=click.Path(exists=True, resolve_path=True),
     help="Path to a SQLite extension to load",
 )
 def inspect(files, inspect_file, sqlite_extensions):
@@ -299,7 +299,6 @@ def uninstall(packages, yes):
     "--load-extension",
     envvar="SQLITE_EXTENSIONS",
     multiple=True,
-    type=click.Path(exists=True, resolve_path=True),
     help="Path to a SQLite extension to load",
 )
 @click.option(
@@ -433,7 +432,10 @@ def serve(
         kwargs["config_dir"] = pathlib.Path(files[0])
         files = []
 
-    ds = Datasette(files, **kwargs)
+    try:
+        ds = Datasette(files, **kwargs)
+    except SpatialiteNotFound:
+        raise click.ClickException("Could not find SpatiaLite extension")
 
     if return_instance:
         # Private utility mechanism for writing unit tests

datasette/utils/__init__.py

@@ -54,6 +54,12 @@ RUN apt-get update && \
 ENV SQLITE_EXTENSIONS /usr/lib/x86_64-linux-gnu/mod_spatialite.so
 """
 
+# Can replace with sqlite-utils when I add that dependency
+SPATIALITE_PATHS = (
+    "/usr/lib/x86_64-linux-gnu/mod_spatialite.so",
+    "/usr/local/lib/mod_spatialite.dylib",
+)
+
 # Can replace this with Column from sqlite_utils when I add that dependency
 Column = namedtuple(
     "Column", ("cid", "name", "type", "notnull", "default_value", "is_pk")
@@ -971,3 +977,15 @@ def display_actor(actor):
         if actor.get(key):
             return actor[key]
     return str(actor)
+
+
+class SpatialiteNotFound(Exception):
+    pass
+
+
+# Can replace with sqlite-utils when I add that dependency
+def find_spatialite():
+    for path in SPATIALITE_PATHS:
+        if os.path.exists(path):
+            return path
+    raise SpatialiteNotFound

docs/installation.rst

@@ -170,7 +170,7 @@ module, use the following command::
     docker run -p 8001:8001 -v `pwd`:/mnt \
         datasetteproject/datasette \
         datasette -p 8001 -h 0.0.0.0 /mnt/fixtures.db \
-        --load-extension=/usr/local/lib/mod_spatialite.so
+        --load-extension=spatialite
 
 You can confirm that SpatiaLite is successfully loaded by visiting
 http://127.0.0.1:8001/-/versions

docs/spatialite.rst

@@ -8,6 +8,14 @@ The `SpatiaLite module <https://www.gaia-gis.it/fossil/libspatialite/index>`_ fo
 
 To use it with Datasette, you need to install the ``mod_spatialite`` dynamic library. This can then be loaded into Datasette using the ``--load-extension`` command-line option.
 
+Datasette can look for SpatiaLite in common installation locations if you run it like this::
+
+    datasette --load-extension=spatialite
+
+If SpatiaLite is in another location, use the full path to the extension instead::
+
+    datasette --load-extension=/usr/local/lib/mod_spatialite.dylib
+
 Installation
 ============
 
@@ -25,7 +33,7 @@ This will install the ``spatialite`` command-line tool and the ``mod_spatialite`
 
 You can now run Datasette like so::
 
-    datasette --load-extension=/usr/local/lib/mod_spatialite.dylib
+    datasette --load-extension=spatialite
 
 Installing SpatiaLite on Linux
 ------------------------------

tests/test_cli.py

@@ -59,6 +59,17 @@ def test_spatialite_error_if_attempt_to_open_spatialite():
     assert "trying to load a SpatiaLite database" in result.output
 
 
+@mock.patch("datasette.utils.SPATIALITE_PATHS", ["/does/not/exist"])
+def test_spatialite_error_if_cannot_find_load_extension_spatialite():
+    runner = CliRunner()
+    result = runner.invoke(
+        cli, ["serve", str(pathlib.Path(__file__).parent / "spatialite.db"),
+        "--load-extension", "spatialite"]
+    )
+    assert result.exit_code != 0
+    assert "Could not find SpatiaLite extension" in result.output
+
+
 def test_plugins_cli(app_client):
     runner = CliRunner()
     result1 = runner.invoke(cli, ["plugins"])