Strip #:~:text= directives when validating anchor links

With `file.md#:~:text=focus_on_text`, there should be nothing to validate.
With `file.md#anchor:~:text=focus_on_text`, 'anchor' is the part to validate.

Based on https://developer.mozilla.org/en-US/docs/Web/URI/Reference/Fragment/Text_fragments#syntax

Author: oprypin

properdocs/structure/pages.py

@@ -315,7 +315,10 @@ def validate_anchor_links(self, *, files: Files, log_level: int) -> None:
                     continue
                 context = ""
                 if to_file == self.file:
-                    problem = "there is no such anchor on this page"
+                    if original_link.endswith('#' + anchor):
+                        problem = "there is no such anchor on this page"
+                    else:
+                        problem = f"there is no anchor '#{anchor}' on this page"
                     if anchor.startswith('fnref:'):
                         context = " This seems to be a footnote that is never referenced."
                 else:
@@ -416,6 +419,16 @@ def _possible_target_uris(
                     yield guess
                     tried.add(guess)
 
+    def register_anchor(self, *, file: File, anchor: str, url: str) -> None:
+        if not anchor:
+            return
+        # Detect https://developer.mozilla.org/en-US/docs/Web/URI/Reference/Fragment/Text_fragments#syntax
+        if (index := anchor.find(':~:')) > -1:
+            if index == 0:
+                return  # This is entirely just a directive, no anchor.
+            anchor = anchor[:index]
+        self.links_to_anchors.setdefault(file, {}).setdefault(anchor, url)
+
     def path_to_url(self, url: str) -> str:
         scheme, netloc, path, query, anchor = urlsplit(url)
 
@@ -433,9 +446,8 @@ def path_to_url(self, url: str) -> str:
         elif AMP_SUBSTITUTE in url:  # AMP_SUBSTITUTE is used internally by Markdown only for email.
             return url
         elif not path:  # Self-link containing only query or anchor.
-            if anchor:
-                # Register that the page links to itself with an anchor.
-                self.links_to_anchors.setdefault(self.file, {}).setdefault(anchor, url)
+            # Register that the page links to itself with an anchor.
+            self.register_anchor(file=self.file, anchor=anchor, url=url)
             return url
 
         path = urlunquote(path)
@@ -498,9 +510,8 @@ def path_to_url(self, url: str) -> str:
         assert target_uri is not None
         assert target_file is not None
 
-        if anchor:
-            # Register that this page links to the target file with an anchor.
-            self.links_to_anchors.setdefault(target_file, {}).setdefault(anchor, url)
+        # Register that this page links to the target file with an anchor.
+        self.register_anchor(file=target_file, anchor=anchor, url=url)
 
         if target_file.inclusion.is_excluded():
             if self.file.inclusion.is_excluded():

properdocs/tests/build_tests.py

@@ -776,7 +776,7 @@ def test_anchor_no_warning_with_html(self, site_dir, docs_dir):
         }
     )
     @tempdir()
-    def test_anchor_warning_and_query(self, site_dir, docs_dir):
+    def test_anchor_and_query_warning(self, site_dir, docs_dir):
         cfg = load_config(docs_dir=docs_dir, site_dir=site_dir, validation={'anchors': 'info'})
 
         expected_logs = '''
@@ -806,6 +806,23 @@ def test_anchor_warning_for_footnote(self, site_dir, docs_dir):
         with self._assert_build_logs(expected_logs):
             build.build(cfg)
 
+    @tempdir(
+        files={
+            'test/foo.md': '# page1 heading\n\n[bar](bar.md#page1-heading:~:text=a)\n\n[just text](#:~:text=text)',
+            'test/bar.md': '# page2 heading\n\n[aaa](#a:~:text=a)\n\n[bbb](#page2-heading:~:text=a)',
+        }
+    )
+    @tempdir()
+    def test_anchor_with_directive_warnings(self, site_dir, docs_dir):
+        cfg = load_config(docs_dir=docs_dir, site_dir=site_dir, validation={'anchors': 'warn'})
+
+        expected_logs = '''
+            WARNING:Doc file 'test/bar.md' contains a link '#a:~:text=a', but there is no anchor '#a' on this page.
+            WARNING:Doc file 'test/foo.md' contains a link 'bar.md#page1-heading:~:text=a', but the doc 'test/bar.md' does not contain an anchor '#page1-heading'.
+        '''
+        with self._assert_build_logs(expected_logs):
+            build.build(cfg)
+
     @tempdir(
         files={
             'foo.md': 'page1 content',