Delib. overriding and overwrite detect. Fixes #938

Make deliberate overriding (*) works with overwrites detection.

(*) first introduced by d0e9c52410

The following are decided to be deliberate override:
 - articles using the `save_as` metadata
 - pages using the `save_as` metadata
 - template pages (always)

Pelican now exits in the following 2 cases:
 - at least 2 not deliberate writes to the same file name (behaviour introduced
   by the overwrite detection feature ff7410ce2a)
 - at least 2 deliberate writes to the same file name (new behaviour)

Also added info logging when deliberate overrides are performed.

Switched to StandardError instead of IOError, thanks to @ametaireau and
@russkel.

pelican/generators.py

@@ -168,7 +168,8 @@ class TemplatePagesGenerator(Generator):
             try:
                 template = self.env.get_template(source)
                 rurls = self.settings['RELATIVE_URLS']
-                writer.write_file(dest, template, self.context, rurls)
+                writer.write_file(dest, template, self.context, rurls,
+                                  override_output=True)
             finally:
                 del self.env.loader.loaders[0]
 
@@ -262,7 +263,8 @@ class ArticlesGenerator(Generator):
         """Generate the articles."""
         for article in chain(self.translations, self.articles):
             write(article.save_as, self.get_template(article.template),
-                self.context, article=article, category=article.category)
+                self.context, article=article, category=article.category,
+                override_output=hasattr(article, 'override_save_as'))
 
     def generate_period_archives(self, write):
         """Generate per-year, per-month, and per-day archives."""
@@ -533,7 +535,8 @@ class PagesGenerator(Generator):
                             self.hidden_translations, self.hidden_pages):
             writer.write_file(page.save_as, self.get_template(page.template),
                     self.context, page=page,
-                    relative_urls=self.settings['RELATIVE_URLS'])
+                    relative_urls=self.settings['RELATIVE_URLS'],
+                    override_output=hasattr(page, 'override_save_as'))
 
 
 class StaticGenerator(Generator):

pelican/writers.py

@@ -24,6 +24,7 @@ class Writer(object):
         self.reminder = dict()
         self.settings = settings or {}
         self._written_files = set()
+        self._overridden_files = set()
 
     def _create_new_feed(self, feed_type, context):
         feed_class = Rss201rev2Feed if feed_type == 'rss' else Atom1Feed
@@ -49,13 +50,26 @@ class Writer(object):
             pubdate=set_date_tzinfo(item.date,
                 self.settings.get('TIMEZONE', None)))
 
-    def _open_w(self, filename, encoding):
+    def _open_w(self, filename, encoding, override=False):
         """Open a file to write some content to it.
 
-        Exit if we have already written to that file.
+        Exit if we have already written to that file, unless one (and no more
+        than one) of the writes has the override parameter set to True.
         """
-        if filename in self._written_files:
-            raise IOError('File %s is to be overwritten' % filename)
+        if filename in self._overridden_files:
+            if override:
+                raise StandardError('File %s is set to be overridden twice'
+                                    % filename)
+            else:
+                logger.info('skipping %s' % filename)
+                filename = os.devnull
+        elif filename in self._written_files:
+            if override:
+                logger.info('overwriting %s' % filename)
+            else:
+                raise StandardError('File %s is to be overwritten' % filename)
+        if override:
+            self._overridden_files.add(filename)
         self._written_files.add(filename)
         return open(filename, 'w', encoding=encoding)
 
@@ -103,7 +117,7 @@ class Writer(object):
             locale.setlocale(locale.LC_ALL, old_locale)
 
     def write_file(self, name, template, context, relative_urls=False,
-        paginated=None, **kwargs):
+        paginated=None, override_output=False, **kwargs):
         """Render the template and write the file.
 
         :param name: name of the file to output
@@ -112,6 +126,9 @@ class Writer(object):
         :param relative_urls: use relative urls or absolutes ones
         :param paginated: dict of article list to paginate - must have the
             same length (same list in different orders)
+        :param override_output: boolean telling if we can override previous
+            output with the same name (and if next files written with the same
+            name should be skipped to keep that one)
         :param **kwargs: additional variables to pass to the templates
         """
 
@@ -121,7 +138,7 @@ class Writer(object):
             # other stuff, just return for now
             return
 
-        def _write_file(template, localcontext, output_path, name):
+        def _write_file(template, localcontext, output_path, name, override):
             """Render the template write the file."""
             old_locale = locale.setlocale(locale.LC_ALL)
             locale.setlocale(locale.LC_ALL, str('C'))
@@ -134,7 +151,7 @@ class Writer(object):
                 os.makedirs(os.path.dirname(path))
             except Exception:
                 pass
-            with self._open_w(path, 'utf-8') as f:
+            with self._open_w(path, 'utf-8', override=override) as f:
                 f.write(output)
             logger.info('writing {}'.format(path))
 
@@ -180,7 +197,8 @@ class Writer(object):
                              '%s_next_page' % key: next_page})
 
                 _write_file(template, paginated_localcontext, self.output_path,
-                            page.save_as)
+                            page.save_as, override_output)
         else:
             # no pagination
-            _write_file(template, localcontext, self.output_path, name)
+            _write_file(template, localcontext, self.output_path, name,
+                        override_output)