Fixed the issue sphinx-doc#10104 after the code reviews from Adam Tur…

…ner and Takeshi Komiya:

- Added the class variable 'builder' to Catalog class, so any instances of Catalog can access the information within the builder, including things such as app, config, srcdir, outdir etc.. see MessageCatalogBuilder for details.
- Initialise this Catalog.builder as the instance of MessageCatalogBuilder is created, ie. in the init()
- As Message class is created, list of locations passing to it will be made singular, using set(), sorted alphabetically for easier searching and identifying origins where the message can be found.
- source dir is used within the __iter__ of the Catalog, using sphinx.util.osutil.relpath, for safer functionality, to work out the relative path for each location entry.

sphinx/builders/gettext.py

@@ -32,13 +32,14 @@ class Message:
     """An entry of translatable message."""
     def __init__(self, text: str, locations: List[Tuple[str, int]], uuids: List[str]):
         self.text = text
-        self.locations = list(set(locations))
+        self.locations = list(sorted(list(set(locations))))     #make list unique and sorted alphabetically
         self.uuids = uuids
 
 
 class Catalog:
     """Catalog of translatable messages."""
-
+    # make a class var so any instance can share this parent class, where all building info can be found, such as srcdir etc..
+    builder = None
     def __init__(self) -> None:
         self.messages: List[str] = []  # retain insertion order, a la OrderedDict
 
@@ -56,8 +57,9 @@ def add(self, msg: str, origin: Union[Element, "MsgOrigin"]) -> None:
         self.metadata[msg].append((origin.source, origin.line, origin.uid))  # type: ignore
 
     def __iter__(self) -> Generator[Message, None, None]:
+        src_dir = Catalog.builder.srcdir
         for message in self.messages:
-            positions = [(os.path.relpath(source, start=os.getcwd()), line) for source, line, uuid in self.metadata[message]]
+            positions = [(relpath(source, start=src_dir), line) for source, line, uuid in self.metadata[message]]
             uuids = [uuid for source, line, uuid in self.metadata[message]]
             yield Message(message, positions, uuids)
 
@@ -213,7 +215,8 @@ class MessageCatalogBuilder(I18nBuilder):
     def init(self) -> None:
         super().init()
         self.create_template_bridge()
-        self.templates.init(self)
+        self.templates.init(self)        
+        Catalog.builder = self  # make the builder visible to instances of catalog
 
     def _collect_templates(self) -> Set[str]:
         template_files = set()