Fix changelog processing when id attribute is missing.

Author: isoos

app/lib/shared/markdown.dart

@@ -371,9 +371,16 @@ Iterable<html.Node> _groupChangelogNodes(List<html.Node> nodes) sync* {
     final version = mayBeVersion ? _extractVersion(versionText) : null;
     if (version != null) {
       firstHeaderTag ??= nodeTag;
+      var id = node.attributes['id'];
+      if (id == null || id.isEmpty) {
+        // `package:markdown` generates ids without dots (`.`), using similar
+        // normalization here.
+        // TODO: consider replacing all uses with `<a>.<b>.<c>` id attributes
+        id = version.toString().replaceAll('.', '');
+      }
       final titleElem = html.Element.tag('h2')
         ..attributes['class'] = 'changelog-version'
-        ..attributes['id'] = node.attributes['id']!
+        ..attributes['id'] = id
         ..append(html.Text(versionText!));
 
       lastContentDiv = html.Element.tag('div')

app/test/shared/markdown_test.dart

@@ -405,6 +405,21 @@ void main() {
         '</h2>',
       );
     });
+
+    test('custom html', () {
+      final input = '''<h1>1.0.0</h1><hr><ul><li>a</li></ul>
+<h1>0.2.9</h1><hr><ul><li>b</li></ul>
+''';
+      final output = markdownToHtml(input, isChangelog: true);
+      expect(
+        output,
+        allOf([
+          contains('<h2 class="changelog-version hash-header" id="100">'
+              '1.0.0 <a href="#100" class="hash-link">#</a></h2>'),
+          contains('<div class="changelog-content"><hr><ul><li>a</li></ul>'),
+        ]),
+      );
+    });
   });
 
   group('alert blocks', () {