[web] Add complex rich text test cases and fix them

lib/web_ui/lib/src/engine/text/layout_service.dart

@@ -188,6 +188,7 @@ class TextLayoutService {
       if (span is PlaceholderSpan) {
         // TODO(mdebbar): Do placeholders affect min/max intrinsic width?
       } else if (span is FlatTextSpan) {
+        spanometer.currentSpan = span;
         final LineBreakResult nextBreak = currentLine.findNextBreak(span.end);
 
         // For the purpose of max intrinsic width, we don't care if the line
@@ -251,6 +252,9 @@ class LineSegment {
 
   /// The width of the trailing white space in the segment.
   double get widthOfTrailingSpace => widthIncludingSpace - width;
+
+  /// Whether this segment is made of only white space.
+  bool get isSpaceOnly => start.index == end.indexWithoutTrailingSpaces;
 }
 
 /// Builds instances of [EngineLineMetrics] for the given [paragraph].
@@ -358,8 +362,12 @@ class LineBuilder {
   void _addSegment(LineSegment segment) {
     _segments.add(segment);
 
-    // Add the width of previous trailing space.
-    width += widthOfTrailingSpace + segment.width;
+    // Adding a space-only segment has no effect on `width` because it doesn't
+    // include trailing white space.
+    if (!segment.isSpaceOnly) {
+      // Add the width of previous trailing space.
+      width += widthOfTrailingSpace + segment.width;
+    }
     widthIncludingSpace += segment.widthIncludingSpace;
     end = segment.end;
   }
@@ -370,17 +378,39 @@ class LineBuilder {
   LineSegment _popSegment() {
     final LineSegment poppedSegment = _segments.removeLast();
 
-    double widthOfPrevTrailingSpace;
     if (_segments.isEmpty) {
-      widthOfPrevTrailingSpace = 0.0;
+      width = 0.0;
+      widthIncludingSpace = 0.0;
       end = start;
     } else {
-      widthOfPrevTrailingSpace = lastSegment.widthOfTrailingSpace;
+      widthIncludingSpace -= poppedSegment.widthIncludingSpace;
       end = lastSegment.end;
-    }
 
-    width = width - poppedSegment.width - widthOfPrevTrailingSpace;
-    widthIncludingSpace -= poppedSegment.widthIncludingSpace;
+      // Now, let's figure out what to do with `width`.
+
+      // Popping a space-only segment has no effect on `width`.
+      if (!poppedSegment.isSpaceOnly) {
+        // First, we subtract the width of the popped segment.
+        width -= poppedSegment.width;
+
+        // Second, we subtract all trailing spaces from `width`. There could be
+        // multiple trailing segments that are space-only.
+        double widthOfTrailingSpace = 0.0;
+        int i = _segments.length - 1;
+        while (i >= 0 && _segments[i].isSpaceOnly) {
+          // Since the segment is space-only, `widthIncludingSpace` contains
+          // the width of the space and nothing else.
+          widthOfTrailingSpace += _segments[i].widthIncludingSpace;
+          i--;
+        }
+        if (i >= 0) {
+          // Having `i >= 0` means in the above loop we stopped at a
+          // non-space-only segment. We should also subtract its trailing spaces.
+          widthOfTrailingSpace += _segments[i].widthOfTrailingSpace;
+        }
+        width -= widthOfTrailingSpace;
+      }
+    }
 
     return poppedSegment;
   }

lib/web_ui/test/text/layout_service_rich_test.dart

@@ -0,0 +1,152 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// @dart = 2.12
+
+import 'package:test/bootstrap/browser.dart';
+import 'package:test/test.dart';
+import 'package:ui/src/engine.dart';
+import 'package:ui/ui.dart' as ui;
+
+import 'layout_service_helper.dart';
+
+const ui.Color white = ui.Color(0xFFFFFFFF);
+const ui.Color black = ui.Color(0xFF000000);
+const ui.Color red = ui.Color(0xFFFF0000);
+const ui.Color green = ui.Color(0xFF00FF00);
+const ui.Color blue = ui.Color(0xFF0000FF);
+
+final EngineParagraphStyle ahemStyle = EngineParagraphStyle(
+  fontFamily: 'ahem',
+  fontSize: 10,
+);
+
+ui.ParagraphConstraints constrain(double width) {
+  return ui.ParagraphConstraints(width: width);
+}
+
+CanvasParagraph rich(
+  EngineParagraphStyle style,
+  void Function(CanvasParagraphBuilder) callback,
+) {
+  final CanvasParagraphBuilder builder = CanvasParagraphBuilder(style);
+  callback(builder);
+  return builder.build();
+}
+
+void main() {
+  internalBootstrapBrowserTest(() => testMain);
+}
+
+void testMain() async {
+  await ui.webOnlyInitializeTestDomRenderer();
+
+  test('measures spans in the same line correctly', () {
+    final CanvasParagraph paragraph = rich(ahemStyle, (builder) {
+      builder.pushStyle(EngineTextStyle.only(fontSize: 12.0));
+      // 12.0 * 6 = 72.0 (with spaces)
+      // 12.0 * 5 = 60.0 (without spaces)
+      builder.addText('Lorem ');
+
+      builder.pushStyle(EngineTextStyle.only(fontSize: 13.0));
+      // 13.0 * 6 = 78.0 (with spaces)
+      // 13.0 * 5 = 65.0 (without spaces)
+      builder.addText('ipsum ');
+
+      builder.pushStyle(EngineTextStyle.only(fontSize: 11.0));
+      // 11.0 * 5 = 55.0
+      builder.addText('dolor');
+    })..layout(constrain(double.infinity));
+
+    expect(paragraph.maxIntrinsicWidth, 205.0);
+    expect(paragraph.minIntrinsicWidth, 65.0); // "ipsum"
+    expect(paragraph.width, double.infinity);
+    expectLines(paragraph, [
+      l('Lorem ipsum dolor', 0, 17, hardBreak: true, width: 205.0, left: 0.0),
+    ]);
+  });
+
+  test('breaks lines correctly at the end of spans', () {
+    final CanvasParagraph paragraph = rich(ahemStyle, (builder) {
+      builder.addText('Lorem ');
+      builder.pushStyle(EngineTextStyle.only(fontSize: 15.0));
+      builder.addText('sit ');
+      builder.pop();
+      builder.addText('.');
+    })..layout(constrain(60.0));
+
+    expect(paragraph.maxIntrinsicWidth, 130.0);
+    expect(paragraph.minIntrinsicWidth, 50.0); // "Lorem"
+    expect(paragraph.width, 60.0);
+    expectLines(paragraph, [
+      l('Lorem ', 0, 6, hardBreak: false, width: 50.0, left: 0.0),
+      l('sit ', 6, 10, hardBreak: false, width: 45.0, left: 0.0),
+      l('.', 10, 11, hardBreak: true, width: 10.0, left: 0.0),
+    ]);
+  });
+
+  test('breaks lines correctly in the middle of spans', () {
+    final CanvasParagraph paragraph = rich(ahemStyle, (builder) {
+      builder.addText('Lorem ipsum ');
+      builder.pushStyle(EngineTextStyle.only(fontSize: 11.0));
+      builder.addText('sit dolor');
+    })..layout(constrain(100.0));
+
+    expect(paragraph.maxIntrinsicWidth, 219.0);
+    expect(paragraph.minIntrinsicWidth, 55.0); // "dolor"
+    expect(paragraph.width, 100.0);
+    expectLines(paragraph, [
+      l('Lorem ', 0, 6, hardBreak: false, width: 50.0, left: 0.0),
+      l('ipsum sit ', 6, 16, hardBreak: false, width: 93.0, left: 0.0),
+      l('dolor', 16, 21, hardBreak: true, width: 55.0, left: 0.0),
+    ]);
+  });
+
+  test('handles space-only spans', () {
+    final CanvasParagraph paragraph = rich(ahemStyle, (builder) {
+      builder.pushStyle(EngineTextStyle.only(color: red));
+      builder.addText('Lorem ');
+      builder.pop();
+      builder.pushStyle(EngineTextStyle.only(color: blue));
+      builder.addText('   ');
+      builder.pushStyle(EngineTextStyle.only(color: green));
+      builder.addText('  ');
+      builder.pushStyle(EngineTextStyle.only(color: black));
+      builder.addText('ipsum');
+    });
+    paragraph.layout(constrain(80.0));
+
+    expect(paragraph.maxIntrinsicWidth, 160.0);
+    expect(paragraph.minIntrinsicWidth, 50.0); // "Lorem" or "ipsum"
+    expect(paragraph.width, 80.0);
+    expectLines(paragraph, [
+      l('Lorem      ', 0, 11, hardBreak: false, width: 50.0, widthWithTrailingSpaces: 110.0, left: 0.0),
+      l('ipsum', 11, 16, hardBreak: true, width: 50.0, left: 0.0),
+    ]);
+  });
+
+  test('should not break at span end if it is not a line break', () {
+    final CanvasParagraph paragraph = rich(ahemStyle, (builder) {
+      builder.pushStyle(EngineTextStyle.only(color: red));
+      builder.addText('Lorem');
+      builder.pop();
+      builder.pushStyle(EngineTextStyle.only(color: blue));
+      builder.addText(' ');
+      builder.pushStyle(EngineTextStyle.only(color: black));
+      builder.addText('ip');
+      builder.pushStyle(EngineTextStyle.only(color: green));
+      builder.addText('su');
+      builder.pushStyle(EngineTextStyle.only(color: white));
+      builder.addText('m');
+    })..layout(constrain(50.0));
+
+    expect(paragraph.maxIntrinsicWidth, 110.0);
+    expect(paragraph.minIntrinsicWidth, 50.0); // "Lorem" or "ipsum"
+    expect(paragraph.width, 50.0);
+    expectLines(paragraph, [
+      l('Lorem ', 0, 6, hardBreak: false, width: 50.0, left: 0.0),
+      l('ipsum', 6, 11, hardBreak: true, width: 50.0, left: 0.0),
+    ]);
+  });
+}