Read previous msgids (#|) from PO files and keep them on update

babel/messages/catalog.py

@@ -1000,6 +1000,8 @@ def _merge(
             else:
                 oldmsg = remaining.pop(oldkey, None)
                 assert oldmsg is not None
+                if 'fuzzy' in oldmsg.flags:
+                    message.previous_id = list(oldmsg.previous_id)
             message.string = oldmsg.string
 
             if keep_user_comments and oldmsg.user_comments:

babel/messages/pofile.py

@@ -178,6 +178,7 @@ def _reset_message_state(self) -> None:
         self.flags = []
         self.user_comments = []
         self.auto_comments = []
+        self.previous = []
         self.context = None
         self.obsolete = False
         self.in_msgid = False
@@ -215,6 +216,7 @@ def _add_message(self) -> None:
             self.user_comments,
             lineno=self.offset + 1,
             context=msgctxt,
+            previous_id=[p.denormalize() for p in self.previous],
         )
         if self.obsolete:
             if not self.ignore_obsolete:
@@ -322,6 +324,17 @@ def _process_comment(self, line) -> None:
                 self.auto_comments.append(comment)
             return
 
+        if prefix == '#|':
+            # The previous msgid of a fuzzy message (msgmerge --previous). Message has
+            # no field for a previous msgctxt, so that line is dropped.
+            content = line[2:].strip()
+            keyword, _, arg = content.partition(' ')
+            if keyword in ('msgid', 'msgid_plural'):
+                self.previous.append(_NormalizedString(arg))
+            elif content.startswith('"') and self.previous:
+                self.previous[-1].append(content)
+            return
+
         # These are called user comments
         self.user_comments.append(line[1:].strip())
 
@@ -644,6 +657,14 @@ def _format_comment(comment, prefix=''):
         for line in comment_wrapper.wrap(comment):
             yield f"#{prefix} {line.strip()}\n"
 
+    def _format_previous(keyword, value):
+        # One "#| " line per line of the normalized string, as msgmerge writes it;
+        # wrapping it like a comment would split the quoted strings.
+        first, *rest = normalize(value, width=width).splitlines()
+        yield f"#| {keyword} {first}\n"
+        for line in rest:
+            yield f"#| {line}\n"
+
     def _format_conflict_comment(file, project, version, prefix=''):
         comment = f"#-#-#-#-#  {file} ({project} {version})  #-#-#-#-#"
         yield f"{normalize(comment, prefix=prefix, width=width)}\n"
@@ -737,13 +758,9 @@ def _format_message(message, prefix=''):
             yield f"#{', '.join(['', *sorted(message.flags)])}\n"
 
         if message.previous_id and include_previous:
-            yield from _format_comment(
-                f'msgid {normalize(message.previous_id[0], width=width)}',
-                prefix='|',
-            )
+            yield from _format_previous('msgid', message.previous_id[0])
             if len(message.previous_id) > 1:
-                norm_previous_id = normalize(message.previous_id[1], width=width)
-                yield from _format_comment(f'msgid_plural {norm_previous_id}', prefix='|')
+                yield from _format_previous('msgid_plural', message.previous_id[1])
 
         if len(conflicts := catalog.get_conflicts(message.id)) > 0:
             yield from _format_conflict(message.id, conflicts)

tests/messages/test_catalog.py

@@ -192,6 +192,15 @@ def test_catalog_update_fuzzy_matching_with_char_change():
     assert cat['foo'].fuzzy is True
 
 
+def test_catalog_update_keeps_previous_id_of_fuzzy_message():
+    cat = catalog.Catalog()
+    cat.add('foo', 'Voh', flags=['fuzzy'], previous_id='fo')
+    tmpl = catalog.Catalog()
+    tmpl.add('foo')
+    cat.update(tmpl)
+    assert cat['foo'].previous_id == ['fo']
+
+
 def test_catalog_update_fuzzy_matching_no_msgstr():
     cat = catalog.Catalog()
     cat.add('fo', '')

tests/messages/test_pofile.py

@@ -51,6 +51,30 @@ def test_wrapped_comments_roundtrip(attribute):
     assert second.getvalue() == first.getvalue()
 
 
+def test_previous_msgid_roundtrip():
+    catalog = Catalog()
+    catalog.add('Save this file', 'Datei speichern', flags=['fuzzy'], previous_id='Save the file')
+    first = BytesIO()
+    pofile.write_po(first, catalog, omit_header=True, include_previous=True)
+    first.seek(0)
+
+    restored = pofile.read_po(first)
+    assert restored['Save this file'].previous_id == ['Save the file']
+    assert restored['Save this file'].user_comments == []
+
+
+def test_long_previous_msgid_roundtrip():
+    previous = 'Save the file to the disk before closing the application window so nothing is lost'
+    catalog = Catalog()
+    catalog.add('Save this file', 'Datei speichern', flags=['fuzzy'], previous_id=previous)
+    first = BytesIO()
+    pofile.write_po(first, catalog, omit_header=True, include_previous=True)
+    first.seek(0)
+
+    restored = pofile.read_po(first)
+    assert restored['Save this file'].previous_id == [previous]
+
+
 def test_enclosed_filenames_in_location_comment():
     catalog = Catalog()
     catalog.add("foo", lineno=2, locations=[("main 1.py", 1)], string="")