Added warning for multiple same anchors

[beilm]

• Changed url_map to dict[str, list[str]] to allow multiple entries per identifier
• Changed get_item_url to return always the first url found and add a warning because of multiple entries

[pawamoy]

Hi @beilm, thanks a lot for the PR!

LGTM! Just wanted to change a bit the warning and try/except flow, but GitHub rejected me 🤔

% git push
Enumerating objects: 9, done.
Counting objects: 100% (9/9), done.
Delta compression using up to 6 threads
Compressing objects: 100% (4/4), done.
Writing objects: 100% (5/5), 576 bytes | 288.00 KiB/s, done.
Total 5 (delta 3), reused 0 (delta 0), pack-reused 0 (from 0)
remote: Resolving deltas: 100% (3/3), completed with 3 local objects.
To github.com:beilm/autorefs.git
 ! [remote rejected] beilm/main -> beilm/main (permission denied)
error: failed to push some refs to 'github.com:beilm/autorefs.git'

Here's the diff if you'd like to apply it:

% git diff
diff --git a/src/mkdocs_autorefs/plugin.py b/src/mkdocs_autorefs/plugin.py
index c6c22a8..e7428ff 100644
--- a/src/mkdocs_autorefs/plugin.py
+++ b/src/mkdocs_autorefs/plugin.py
@@ -90,11 +90,7 @@ class AutorefsPlugin(BasePlugin):
         fallback: Callable[[str], Sequence[str]] | None = None,
     ) -> str:
         try:
-            if len(self._url_map[identifier]) > 1:
-                log.warning(
-                    f"Multiple urls found for '{identifier}': {self._url_map[identifier]}. Please specify a custom unique identifier.",
-                )
-            return self._url_map[identifier][0]
+            urls = self._url_map[identifier]
         except KeyError:
             if identifier in self._abs_url_map:
                 return self._abs_url_map[identifier]
@@ -106,6 +102,13 @@ class AutorefsPlugin(BasePlugin):
                         self._url_map[identifier] = [url]
                         return url
             raise
+        else:
+            if len(urls) > 1:
+                log.warning(
+                    f"Multiple URLs found for '{identifier}': {urls}. "
+                    "Please use unique identifiers, or unique Markdown anchors (see our docs).",
+                )
+            return urls[0]
 
     def get_item_url(
         self,

[pawamoy]

OK LGTM, thanks a lot! Will try to release soon.