fix: Render linebreaks after blocks with fixed height

Consecutive line breaks following a block element get converted to vertical space with hte expected height. This avoids an issue where the RichText widget renders additional linebreaks after a block element with the same hight as the block element instead of returning to the default line height of the text.

Author: exomo

packages/core/lib/src/internal/ops/tag_br.dart

@@ -25,7 +25,44 @@ class TagBrBit extends BuildBit {
   BuildBit copyWith({BuildTree? parent}) => TagBrBit(parent ?? this.parent);
 
   @override
-  void flatten(Flattened f) => f.write(text: '\n');
+  void flatten(Flattened f) {
+    final next = _nextNonWhitespace;
+    if (next != null && next.isInline == false) {
+      // Keep behavior of skipping a single BR before a block, but convert
+      // additional BRs to vertical spacing outside RichText to avoid
+      // WidgetSpan line-metric artifacts.
+      final prev = _prevNonWhitespace;
+      if (prev is TagBrBit || prev?.isInline == false) {
+        const oneEm = CssLength(1, CssLengthUnit.em);
+        f.widget(
+          HeightPlaceholder(
+            oneEm,
+            parent.inheritanceResolvers,
+            debugLabel: '${parent.element.localName}--$oneEm',
+          ),
+        );
+      }
+      return;
+    }
+
+    f.write(text: '\n');
+  }
+
+  BuildBit? get _nextNonWhitespace {
+    var next = this.next;
+    while (next is WhitespaceBit) {
+      next = next.next;
+    }
+    return next;
+  }
+
+  BuildBit? get _prevNonWhitespace {
+    var prev = this.prev;
+    while (prev is WhitespaceBit) {
+      prev = prev.prev;
+    }
+    return prev;
+  }
 
   @override
   String toString() => '<BR />';

packages/core/test/tag_br_test.dart

@@ -0,0 +1,51 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter_widget_from_html_core/flutter_widget_from_html_core.dart';
+import 'package:html/dom.dart' as dom;
+
+import '_.dart' as helper;
+
+void main() {
+  // Some special test cases for BR handling, note that most of the tests for BR are in `core_test.dart`
+  group('BR', () {
+    testWidgets(
+      'avoids WidgetSpan newline artifact before block',
+      (WidgetTester tester) async {
+        Widget? customWidgetBuilder(dom.Element element) {
+          if (element.localName != 'x-inline') {
+            return null;
+          }
+
+          return const InlineCustomWidget(
+            child: SizedBox(width: 20, height: 20),
+          );
+        }
+
+        // Keep BR spacing outside RichText for inline widgets before a block:
+        // if a trailing newline remains in the same paragraph as WidgetSpan,
+        // paragraph line metrics may produce unexpectedly large vertical gaps.
+        const html = '<x-inline></x-inline><br><br><div>Next line!</div>';
+        final explained = await helper.explain(
+          tester,
+          null,
+          hw: HtmlWidget(
+            html,
+            customWidgetBuilder: customWidgetBuilder,
+            key: helper.hwKey,
+          ),
+        );
+
+        expect(
+          explained,
+          allOf(
+            startsWith('[Column:children=['),
+            contains('[SizedBox:20.0x20.0],'),
+            contains('[SizedBox:0.0x10.0],'),
+            contains('[CssBlock:child=[RichText:(:Next line!)]]'),
+            isNot(contains('[RichText:(:[SizedBox:20.0x20.0]')),
+          ),
+        );
+      },
+    );
+  });
+}

packages/core/test/tag_img_test.dart

@@ -13,8 +13,7 @@ void main() {
 
   group('image.png', () {
     const src = 'http://domain.com/image.png';
-    Future<String> explain(WidgetTester tester, String html) =>
-        mockNetworkImages(() => helper.explain(tester, html));
+    Future<String> explain(WidgetTester tester, String html) => mockNetworkImages(() => helper.explain(tester, html));
 
     testWidgets('renders src', (WidgetTester tester) async {
       const html = '<img src="$src" />';
@@ -424,8 +423,7 @@ class _LoadingBuilderFactory extends WidgetFactory {
   _LoadingBuilderFactory(this.streamCompleter);
 
   @override
-  ImageProvider<Object> imageProviderFromNetwork(String url) =>
-      _TestImageProvider(streamCompleter);
+  ImageProvider<Object> imageProviderFromNetwork(String url) => _TestImageProvider(streamCompleter);
 }
 
 class _TestImageProvider extends ImageProvider<Object> {
@@ -434,12 +432,10 @@ class _TestImageProvider extends ImageProvider<Object> {
   _TestImageProvider(this.streamCompleter);
 
   @override
-  Future<Object> obtainKey(ImageConfiguration configuration) =>
-      SynchronousFuture<_TestImageProvider>(this);
+  Future<Object> obtainKey(ImageConfiguration configuration) => SynchronousFuture<_TestImageProvider>(this);
 
   @override
-  ImageStreamCompleter loadImage(Object key, ImageDecoderCallback decode) =>
-      streamCompleter;
+  ImageStreamCompleter loadImage(Object key, ImageDecoderCallback decode) => streamCompleter;
 }
 
 class _TestImageStreamCompleter extends ImageStreamCompleter {