mixin_markdown_widget: fix streaming block identity, highlight flicker, and selection details

packages/mixin_markdown_widget/README.md

@@ -94,4 +94,13 @@ controller.appendChunk('\n\nNew content arrived.');
 controller.commitStream();
 ```
 
+If you receive the full text so far instead of deltas, pass it to `updateData`. It appends only the new suffix when the text extends the current data, falls back to a full parse otherwise, and commits the stream unless `streaming` is true:
+
+```dart
+controller.updateData(fullTextSoFar, streaming: true);
+
+// When stream finishes:
+controller.updateData(finalText);
+```
+
 See the `/example` directory for a fully runnable desktop demo.

packages/mixin_markdown_widget/lib/src/parser/markdown_document_parser.dart

@@ -49,6 +49,10 @@ class MarkdownDocumentParser {
     );
   }
 
+  @Deprecated(
+    'This ignores previousDocument and parses the whole source. Use parse, '
+    'or MarkdownController.appendChunk / updateData for incremental parsing.',
+  )
   MarkdownDocument parseAppending(
     String source, {
     required MarkdownDocument previousDocument,
@@ -167,6 +171,9 @@ class MarkdownDocumentParser {
       version: version,
       sourceOffset: sourceOffset,
       initialKindCounts: initialKindCounts,
+      reusableIds: parseAppendedChunkAsNewBlocks
+          ? null
+          : _reusableIdsOf(previousDocument.blocks.last),
     );
 
     final document = MarkdownDocument(
@@ -237,6 +244,7 @@ class MarkdownDocumentParser {
     required int version,
     required int sourceOffset,
     required Map<MarkdownBlockKind, int> initialKindCounts,
+    Map<String, String>? reusableIds,
   }) {
     final timing = onTiming == null ? null : _MarkdownParserTimingBuilder();
     final totalStopwatch = timing == null ? null : (Stopwatch()..start());
@@ -254,6 +262,7 @@ class MarkdownDocumentParser {
     );
     final builder = _MarkdownAstBuilder(
       initialKindCounts: initialKindCounts,
+      reusableIds: reusableIds,
       timing: timing,
     );
     var blocks = _measure(
@@ -389,19 +398,43 @@ class MarkdownDocumentParser {
     BlockNode block,
     Map<MarkdownBlockKind, int> counts,
   ) {
-    counts[block.kind] = (counts[block.kind] ?? 0) + 1;
+    _visitBlockTree(block, (node) {
+      counts[node.kind] = (counts[node.kind] ?? 0) + 1;
+    });
+  }
+
+  /// The ids of [block] and its nested blocks by their `kind-count` part, so a
+  /// reparse of the same growing tail keeps its ids instead of churning the
+  /// content hash on every appended chunk. Images are left out: their error
+  /// state is keyed by id and must not follow a changed url.
+  Map<String, String> _reusableIdsOf(BlockNode block) {
+    final ids = <String, String>{};
+    _visitBlockTree(block, (node) {
+      if (node.kind == MarkdownBlockKind.image) {
+        return;
+      }
+      final hashStart = node.id.lastIndexOf('-');
+      if (hashStart > 0) {
+        ids[node.id.substring(0, hashStart)] = node.id;
+      }
+    });
+    return ids;
+  }
+
+  void _visitBlockTree(BlockNode block, void Function(BlockNode block) visit) {
+    visit(block);
 
     if (block is QuoteBlock) {
       for (final child in block.children) {
-        _countBlockKindsInBlock(child, counts);
+        _visitBlockTree(child, visit);
       }
       return;
     }
 
     if (block is ListBlock) {
       for (final item in block.items) {
         for (final child in item.children) {
-          _countBlockKindsInBlock(child, counts);
+          _visitBlockTree(child, visit);
         }
       }
       return;
@@ -410,15 +443,15 @@ class MarkdownDocumentParser {
     if (block is FootnoteListBlock) {
       for (final item in block.items) {
         for (final child in item.children) {
-          _countBlockKindsInBlock(child, counts);
+          _visitBlockTree(child, visit);
         }
       }
       return;
     }
 
     if (block is DetailsBlock) {
       for (final child in block.children) {
-        _countBlockKindsInBlock(child, counts);
+        _visitBlockTree(child, visit);
       }
       return;
     }
@@ -427,7 +460,7 @@ class MarkdownDocumentParser {
       for (final item in block.items) {
         for (final definition in item.definitions) {
           for (final child in definition) {
-            _countBlockKindsInBlock(child, counts);
+            _visitBlockTree(child, visit);
           }
         }
       }
@@ -1135,15 +1168,22 @@ class _MarkdownParserTimingBuilder {
 class _MarkdownAstBuilder {
   _MarkdownAstBuilder({
     Map<MarkdownBlockKind, int>? initialKindCounts,
+    Map<String, String>? reusableIds,
     _MarkdownParserTimingBuilder? timing,
   })  : _timing = timing,
+        _reusableIds = reusableIds,
         _kindCounters = <MarkdownBlockKind, int>{
           ...?initialKindCounts,
         };
 
   final Map<MarkdownBlockKind, int> _kindCounters;
   final _MarkdownParserTimingBuilder? _timing;
 
+  /// Ids of the previous tail block, which the first top-level block of an
+  /// append reparse takes over. See [MarkdownDocumentParser._reusableIdsOf].
+  Map<String, String>? _reusableIds;
+  int _blockDepth = 0;
+
   Map<MarkdownBlockKind, int> get kindCounts =>
       Map<MarkdownBlockKind, int>.unmodifiable(_kindCounters);
 
@@ -1154,9 +1194,14 @@ class _MarkdownAstBuilder {
         blocks.addAll(buildBlocks(node.children ?? const <md.Node>[]));
         continue;
       }
+      _blockDepth += 1;
       final block = _buildBlock(node);
+      _blockDepth -= 1;
       if (block != null) {
         blocks.add(block);
+        if (_blockDepth == 0) {
+          _reusableIds = null;
+        }
       }
     }
     return blocks;
@@ -1973,7 +2018,8 @@ class _MarkdownAstBuilder {
       () {
         final nextCount = (_kindCounters[kind] ?? 0) + 1;
         _kindCounters[kind] = nextCount;
-        return '${kind.name}-$nextCount-${_stableHash(signature)}';
+        final prefix = '${kind.name}-$nextCount';
+        return _reusableIds?[prefix] ?? '$prefix-${_stableHash(signature)}';
       },
     );
   }

packages/mixin_markdown_widget/lib/src/render/builder/markdown_inline_builder.dart

@@ -7,6 +7,115 @@ import '../../widgets/markdown_theme.dart';
 import '../../widgets/markdown_types.dart';
 import '../pretext_text_block.dart';
 
+/// The tap recognizers of the links of a document.
+///
+/// A link keeps one recognizer while its [LinkInline] stays in the document,
+/// so block rows and descriptors cached across builds never hold a disposed
+/// recognizer.
+class MarkdownLinkRecognizers {
+  final Map<LinkInline, TapGestureRecognizer> _recognizers =
+      Map<LinkInline, TapGestureRecognizer>.identity();
+
+  int get length => _recognizers.length;
+
+  TapGestureRecognizer recognizerFor(LinkInline link, VoidCallback onTap) {
+    return _recognizers.putIfAbsent(
+      link,
+      () => TapGestureRecognizer()..onTap = onTap,
+    );
+  }
+
+  /// Disposes the recognizers of the links that the blocks of [previous] had
+  /// and the blocks of [current] no longer have.
+  void disposeRemovedLinks(List<BlockNode> previous, List<BlockNode> current) {
+    if (_recognizers.isEmpty || identical(previous, current)) {
+      return;
+    }
+    final currentBlocks = Set<BlockNode>.identity()..addAll(current);
+    final removed = Set<LinkInline>.identity();
+    for (final block in previous) {
+      if (!currentBlocks.contains(block)) {
+        _collectLinks(block, removed);
+      }
+    }
+    if (removed.isEmpty) {
+      return;
+    }
+    // A reparsed block can share link nodes with the block it replaces.
+    final previousBlocks = Set<BlockNode>.identity()..addAll(previous);
+    final kept = Set<LinkInline>.identity();
+    for (final block in current) {
+      if (!previousBlocks.contains(block)) {
+        _collectLinks(block, kept);
+      }
+    }
+    for (final link in removed) {
+      if (!kept.contains(link)) {
+        _recognizers.remove(link)?.dispose();
+      }
+    }
+  }
+
+  void dispose() {
+    for (final recognizer in _recognizers.values) {
+      recognizer.dispose();
+    }
+    _recognizers.clear();
+  }
+
+  static void _collectLinks(BlockNode block, Set<LinkInline> links) {
+    void visitInlines(List<InlineNode> inlines) {
+      for (final inline in inlines) {
+        switch (inline) {
+          case LinkInline(:final children):
+            links.add(inline);
+            visitInlines(children);
+          case EmphasisInline(:final children) ||
+                StrongInline(:final children) ||
+                StrikethroughInline(:final children) ||
+                HighlightInline(:final children) ||
+                SubscriptInline(:final children) ||
+                SuperscriptInline(:final children):
+            visitInlines(children);
+          default:
+        }
+      }
+    }
+
+    void visitBlock(BlockNode block) {
+      switch (block) {
+        case HeadingBlock(:final inlines) || ParagraphBlock(:final inlines):
+          visitInlines(inlines);
+        case QuoteBlock(:final children):
+          children.forEach(visitBlock);
+        case DetailsBlock(:final summary, :final children):
+          visitInlines(summary);
+          children.forEach(visitBlock);
+        case ListBlock(:final items) || FootnoteListBlock(:final items):
+          for (final item in items) {
+            item.children.forEach(visitBlock);
+          }
+        case DefinitionListBlock(:final items):
+          for (final item in items) {
+            visitInlines(item.term);
+            for (final definition in item.definitions) {
+              definition.forEach(visitBlock);
+            }
+          }
+        case TableBlock(:final rows):
+          for (final row in rows) {
+            for (final cell in row.cells) {
+              visitInlines(cell.inlines);
+            }
+          }
+        default:
+      }
+    }
+
+    visitBlock(block);
+  }
+}
+
 class MarkdownInlineBuilder {
   MarkdownInlineBuilder({
     required this.theme,
@@ -15,7 +124,7 @@ class MarkdownInlineBuilder {
   });
 
   final MarkdownThemeData theme;
-  final List<TapGestureRecognizer> recognizers;
+  final MarkdownLinkRecognizers recognizers;
   final MarkdownTapLinkCallback? onTapLink;
 
   List<MarkdownPretextInlineRun> buildPretextRuns(
@@ -110,7 +219,7 @@ class MarkdownInlineBuilder {
         final label = flattenInlineText(link.children);
         final recognizer = onTapLink == null
             ? null
-            : _registerLink(() {
+            : recognizers.recognizerFor(link, () {
                 onTapLink!(link.destination, link.title, label);
               });
         final style = _linkTextStyle(baseStyle, linkStyle);
@@ -298,7 +407,7 @@ class MarkdownInlineBuilder {
         final label = flattenInlineText(link.children);
         final recognizer = onTapLink == null
             ? null
-            : _registerLink(() {
+            : recognizers.recognizerFor(link, () {
                 onTapLink!(link.destination, link.title, label);
               });
         final style = _linkTextStyle(baseStyle, linkStyle);
@@ -400,12 +509,6 @@ class MarkdownInlineBuilder {
     return inlineFontSize * baseFontSize / bodyFontSize;
   }
 
-  TapGestureRecognizer _registerLink(VoidCallback onTap) {
-    final recognizer = TapGestureRecognizer()..onTap = onTap;
-    recognizers.add(recognizer);
-    return recognizer;
-  }
-
   TextStyle highlightStyle(TextStyle baseStyle) {
     final accent = theme.linkStyle.color ?? theme.dividerColor;
     return baseStyle.copyWith(