debian/control

@@ -112,4 +112,6 @@ Description: in-depth comparison of files, archives, and directories
  compare two tarballs, ISO images, or PDF just as easily. The differences can
  be shown in a text or HTML report.
  .
+ ${diffoscope:Description}
+ .
  diffoscope is developed as part of the “reproducible builds” project.

debian/rules

@@ -69,7 +69,7 @@ override_dh_auto_clean:
 	@echo "# EDIT debian/tests/control.in INSTEAD!" >> debian/tests/control.tmp
 	@echo "#" >> debian/tests/control.tmp
 	@cat debian/tests/control.in >> debian/tests/control.tmp
-	@sed -i "s#%RECOMMENDS%#$(shell bin/diffoscope --list-debian-substvars | cut -d= -f2)#" debian/tests/control.tmp
+	@sed -i "s#%RECOMMENDS%#$(shell bin/diffoscope --list-debian-substvars | awk -F= '/diffoscope:Recommends/ { print $$2 }')#" debian/tests/control.tmp
 	@sed -i "s#%PYRECOMMENDS%#$(shell python3 -c "import distutils.core; \
 		setup = distutils.core.run_setup('setup.py'); \
 		print(', '.join(sorted(['python3-{}'.format(x) for y in setup.extras_require.values() for x in y])))" \

diffoscope/comparators/__init__.py

@@ -152,9 +152,14 @@ class ComparatorManager:
 
         logger.debug("Loaded %d comparator classes", len(self.classes))
 
-    def get_descriptions(self):
-        for x in self.classes:
-            try:
-                yield x.DESCRIPTION
-            except AttributeError:
-                pass
+    def format_descriptions(self):
+        def gen_descriptions():
+            for x in self.classes:
+                try:
+                    yield x.DESCRIPTION
+                except AttributeError:
+                    pass
+
+        xs = list(sorted(set(gen_descriptions())))
+
+        return '{} and {}.\n'.format(', '.join(xs[:-1]), xs[-1])

diffoscope/main.py

@@ -474,12 +474,9 @@ class HelpFormatter(argparse.HelpFormatter):
                 title, textwrap.indent(wrapped, ' ' * indent)
             )
 
-        descriptions = list(sorted(ComparatorManager().get_descriptions()))
         append(
             'file formats supported',
-            '{} and {}.\n'.format(
-                ', '.join(descriptions[:-1]), descriptions[-1]
-            ),
+            ComparatorManager().format_descriptions(),
         )
 
         append('diffoscope homepage', '<https://diffoscope.org/>')
@@ -581,6 +578,13 @@ class ListDebianSubstvarsAction(argparse._StoreTrueAction):
         for x in ('gzip', 'tar', 'coreutils', 'diffutils', 'findutils'):
             packages.discard(x)
 
+        description = 'File formats supported include: {}'.format(
+            ComparatorManager().format_descriptions(),
+        )
+        wrapped = '${Newline}'.join(textwrap.wrap(description, 79))
+        wrapped = wrapped.replace('${Newline}.', '${Newline}')
+        print('diffoscope:Description={}'.format(wrapped))
+
         print('diffoscope:Recommends={}'.format(', '.join(sorted(packages))))
         sys.exit(0)