Added warning for multiple same anchors

src/mkdocs_autorefs/plugin.py

@@ -57,7 +57,7 @@ class AutorefsPlugin(BasePlugin):
     def __init__(self) -> None:
         """Initialize the object."""
         super().__init__()
-        self._url_map: dict[str, str] = {}
+        self._url_map: dict[str, list[str]] = {}
         self._abs_url_map: dict[str, str] = {}
         self.get_fallback_anchor: Callable[[str], tuple[str, ...]] | None = None
 
@@ -68,7 +68,12 @@ def register_anchor(self, page: str, identifier: str, anchor: str | None = None)
             page: The relative URL of the current page. Examples: `'foo/bar/'`, `'foo/index.html'`
             identifier: The HTML anchor (without '#') as a string.
         """
-        self._url_map[identifier] = f"{page}#{anchor or identifier}"
+        page_anchor = f"{page}#{anchor or identifier}"
+        if identifier in self._url_map:
+            if page_anchor not in self._url_map[identifier]:
+                self._url_map[identifier].append(page_anchor)
+        else:
+            self._url_map[identifier] = [page_anchor]
 
     def register_url(self, identifier: str, url: str) -> None:
         """Register that the identifier should be turned into a link to this URL.
@@ -85,7 +90,7 @@ def _get_item_url(
         fallback: Callable[[str], Sequence[str]] | None = None,
     ) -> str:
         try:
-            return self._url_map[identifier]
+            urls = self._url_map[identifier]
         except KeyError:
             if identifier in self._abs_url_map:
                 return self._abs_url_map[identifier]
@@ -94,9 +99,16 @@ def _get_item_url(
                 for new_identifier in new_identifiers:
                     with contextlib.suppress(KeyError):
                         url = self._get_item_url(new_identifier)
-                        self._url_map[identifier] = url
+                        self._url_map[identifier] = [url]
                         return url
             raise
+        else:
+            if len(urls) > 1:
+                log.warning(
+                    f"Multiple URLs found for '{identifier}': {urls}. "
+                    "Make sure to use unique headings, identifiers, or Markdown anchors (see our docs).",
+                )
+            return urls[0]
 
     def get_item_url(
         self,

tests/test_references.py

@@ -325,23 +325,29 @@ def test_register_markdown_anchors() -> None:
             [](){#alias9}
             ## Heading more2 {#heading-custom2}
 
+            [](){#aliasSame}
+            ## Same heading 1
+            [](){#aliasSame}
+            ## Same heading 2
+
             [](){#alias10}
             """,
         ),
     )
     assert plugin._url_map == {
-        "foo": "page#heading-foo",
-        "bar": "page#bar",
-        "alias1": "page#heading-bar",
-        "alias2": "page#heading-bar",
-        "alias3": "page#alias3",
-        "alias4": "page#heading-baz",
-        "alias5": "page#alias5",
-        "alias6": "page#alias6",
-        "alias7": "page#alias7",
-        "alias8": "page#alias8",
-        "alias9": "page#heading-custom2",
-        "alias10": "page#alias10",
+        "foo": ["page#heading-foo"],
+        "bar": ["page#bar"],
+        "alias1": ["page#heading-bar"],
+        "alias2": ["page#heading-bar"],
+        "alias3": ["page#alias3"],
+        "alias4": ["page#heading-baz"],
+        "alias5": ["page#alias5"],
+        "alias6": ["page#alias6"],
+        "alias7": ["page#alias7"],
+        "alias8": ["page#alias8"],
+        "alias9": ["page#heading-custom2"],
+        "alias10": ["page#alias10"],
+        "aliasSame": ["page#same-heading-1", "page#same-heading-2"],
     }
 
 
@@ -366,9 +372,9 @@ def test_register_markdown_anchors_with_admonition() -> None:
         ),
     )
     assert plugin._url_map == {
-        "alias1": "page#alias1",
-        "alias2": "page#heading-bar",
-        "alias3": "page#alias3",
+        "alias1": ["page#alias1"],
+        "alias2": ["page#heading-bar"],
+        "alias3": ["page#alias3"],
     }