Reverts "Remove migration flag and unused header files" (#50229)

Reverts #50216
Initiated by: zanderso
This change reverts the following previous change:
Original Description:
The `applyRoundingHack` flag is no longer used by the framework. This also removes the [lib/ui/text/line_metrics.h](https://github.com/flutter/engine/pull/50216/files#diff-9175619f2b114dffef67eba38511b34afe6abefd4f697f4758647133895b34f5) file which doesn't seem to be referenced anywhere.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: auto-submit[bot]

ci/licenses_golden/licenses_flutter

@@ -5859,6 +5859,7 @@ ORIGIN: ../../../flutter/lib/ui/text/asset_manager_font_provider.cc + ../../../f
 ORIGIN: ../../../flutter/lib/ui/text/asset_manager_font_provider.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/text/font_collection.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/text/font_collection.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/lib/ui/text/line_metrics.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/text/paragraph.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/text/paragraph.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/text/paragraph_builder.cc + ../../../flutter/LICENSE
@@ -8721,6 +8722,7 @@ FILE: ../../../flutter/lib/ui/text/asset_manager_font_provider.cc
 FILE: ../../../flutter/lib/ui/text/asset_manager_font_provider.h
 FILE: ../../../flutter/lib/ui/text/font_collection.cc
 FILE: ../../../flutter/lib/ui/text/font_collection.h
+FILE: ../../../flutter/lib/ui/text/line_metrics.h
 FILE: ../../../flutter/lib/ui/text/paragraph.cc
 FILE: ../../../flutter/lib/ui/text/paragraph.h
 FILE: ../../../flutter/lib/ui/text/paragraph_builder.cc

lib/ui/BUILD.gn

@@ -123,6 +123,7 @@ source_set("ui") {
     "text/asset_manager_font_provider.h",
     "text/font_collection.cc",
     "text/font_collection.h",
+    "text/line_metrics.h",
     "text/paragraph.cc",
     "text/paragraph.h",
     "text/paragraph_builder.cc",

lib/ui/text.dart

@@ -3355,6 +3355,23 @@ abstract class ParagraphBuilder {
   /// [Paragraph].
   factory ParagraphBuilder(ParagraphStyle style) = _NativeParagraphBuilder;
 
+  /// Whether the rounding hack enabled by default in SkParagraph and TextPainter
+  /// is disabled.
+  ///
+  /// Do not rely on this getter as it exists for migration purposes only and
+  /// will soon be removed.
+  @Deprecated('''
+    The shouldDisableRoundingHack flag is for internal migration purposes only and should not be used.
+  ''')
+  static bool get shouldDisableRoundingHack => _shouldDisableRoundingHack;
+  static bool _shouldDisableRoundingHack = true;
+  /// Do not call this method as it is for migration purposes only and will soon
+  /// be removed.
+  // ignore: use_setters_to_change_properties
+  static void setDisableRoundingHack(bool disableRoundingHack) {
+    _shouldDisableRoundingHack = disableRoundingHack;
+  }
+
   /// The number of placeholders currently in the paragraph.
   int get placeholderCount;
 
@@ -3472,10 +3489,11 @@ base class _NativeParagraphBuilder extends NativeFieldWrapperClass1 implements P
         style._height ?? 0,
         style._ellipsis ?? '',
         _encodeLocale(style._locale),
+        !ParagraphBuilder.shouldDisableRoundingHack,
       );
   }
 
-  @Native<Void Function(Handle, Handle, Handle, Handle, Handle, Double, Double, Handle, Handle)>(symbol: 'ParagraphBuilder::Create')
+  @Native<Void Function(Handle, Handle, Handle, Handle, Handle, Double, Double, Handle, Handle, Bool)>(symbol: 'ParagraphBuilder::Create')
   external void _constructor(
       Int32List encoded,
       ByteData? strutData,
@@ -3485,7 +3503,7 @@ base class _NativeParagraphBuilder extends NativeFieldWrapperClass1 implements P
       double height,
       String ellipsis,
       String locale,
-  );
+      bool applyRoundingHack);
 
   @override
   int get placeholderCount => _placeholderCount;

lib/ui/text/line_metrics.h

@@ -0,0 +1,62 @@
+// 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.
+
+#ifndef FLUTTER_LIB_UI_TEXT_LINE_METRICS_H_
+#define FLUTTER_LIB_UI_TEXT_LINE_METRICS_H_
+
+#include "third_party/dart/runtime/include/dart_api.h"
+#include "third_party/tonic/converter/dart_converter.h"
+
+namespace flutter {
+
+struct LineMetrics {
+  const bool* hard_break;
+
+  // The final computed ascent and descent for the line. This can be impacted by
+  // the strut, height, scaling, as well as outlying runs that are very tall.
+  //
+  // The top edge is `baseline - ascent` and the bottom edge is `baseline +
+  // descent`. Ascent and descent are provided as positive numbers. Raw numbers
+  // for specific runs of text can be obtained in run_metrics_map. These values
+  // are the cumulative metrics for the entire line.
+  const double* ascent;
+  const double* descent;
+  const double* unscaled_ascent;
+  // Height of the line.
+  const double* height;
+  // Width of the line.
+  const double* width;
+  // The left edge of the line. The right edge can be obtained with `left +
+  // width`
+  const double* left;
+  // The y position of the baseline for this line from the top of the paragraph.
+  const double* baseline;
+  // Zero indexed line number.
+  const size_t* line_number;
+
+  LineMetrics();
+
+  LineMetrics(const bool* hard_break,
+              const double* ascent,
+              const double* descent,
+              const double* unscaled_ascent,
+              const double* height,
+              const double* width,
+              const double* left,
+              const double* baseline,
+              const size_t* line_number)
+      : hard_break(hard_break),
+        ascent(ascent),
+        descent(descent),
+        unscaled_ascent(unscaled_ascent),
+        height(height),
+        width(width),
+        left(left),
+        baseline(baseline),
+        line_number(line_number) {}
+};
+
+}  // namespace flutter
+
+#endif  // FLUTTER_LIB_UI_TEXT_LINE_METRICS_H_

lib/ui/text/paragraph.h

@@ -8,6 +8,7 @@
 #include "flutter/fml/message_loop.h"
 #include "flutter/lib/ui/dart_wrapper.h"
 #include "flutter/lib/ui/painting/canvas.h"
+#include "flutter/lib/ui/text/line_metrics.h"
 #include "flutter/third_party/txt/src/txt/paragraph.h"
 
 namespace flutter {

lib/ui/text/paragraph_builder.cc

@@ -151,11 +151,12 @@ void ParagraphBuilder::Create(Dart_Handle wrapper,
                               double fontSize,
                               double height,
                               const std::u16string& ellipsis,
-                              const std::string& locale) {
+                              const std::string& locale,
+                              bool applyRoundingHack) {
   UIDartState::ThrowIfUIOperationsProhibited();
   auto res = fml::MakeRefCounted<ParagraphBuilder>(
       encoded_handle, strutData, fontFamily, strutFontFamilies, fontSize,
-      height, ellipsis, locale);
+      height, ellipsis, locale, applyRoundingHack);
   res->AssociateWithDartWrapper(wrapper);
 }
 
@@ -230,7 +231,8 @@ ParagraphBuilder::ParagraphBuilder(
     double fontSize,
     double height,
     const std::u16string& ellipsis,
-    const std::string& locale) {
+    const std::string& locale,
+    bool applyRoundingHack) {
   int32_t mask = 0;
   txt::ParagraphStyle style;
   {
@@ -291,6 +293,7 @@ ParagraphBuilder::ParagraphBuilder(
   if (mask & kPSLocaleMask) {
     style.locale = locale;
   }
+  style.apply_rounding_hack = applyRoundingHack;
 
   FontCollection& font_collection = UIDartState::Current()
                                         ->platform_configuration()

lib/ui/text/paragraph_builder.h

@@ -30,7 +30,8 @@ class ParagraphBuilder : public RefCountedDartWrappable<ParagraphBuilder> {
                      double fontSize,
                      double height,
                      const std::u16string& ellipsis,
-                     const std::string& locale);
+                     const std::string& locale,
+                     bool applyRoundingHack);
 
   ~ParagraphBuilder() override;
 
@@ -76,7 +77,8 @@ class ParagraphBuilder : public RefCountedDartWrappable<ParagraphBuilder> {
                             double fontSize,
                             double height,
                             const std::u16string& ellipsis,
-                            const std::string& locale);
+                            const std::string& locale,
+                            bool applyRoundingHack);
 
   std::unique_ptr<txt::ParagraphBuilder> m_paragraph_builder_;
 };

lib/web_ui/lib/src/engine/canvaskit/renderer.dart

@@ -379,6 +379,7 @@ class CanvasKitRenderer implements Renderer {
     strutStyle: strutStyle,
     ellipsis: ellipsis,
     locale: locale,
+    applyRoundingHack: !ui.ParagraphBuilder.shouldDisableRoundingHack,
   );
 
   @override

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

@@ -33,6 +33,7 @@ class CkParagraphStyle implements ui.ParagraphStyle {
     ui.StrutStyle? strutStyle,
     String? ellipsis,
     ui.Locale? locale,
+    bool applyRoundingHack = true,
   })  : skParagraphStyle = toSkParagraphStyle(
           textAlign,
           textDirection,
@@ -46,6 +47,7 @@ class CkParagraphStyle implements ui.ParagraphStyle {
           strutStyle,
           ellipsis,
           locale,
+          applyRoundingHack,
         ),
         _textAlign = textAlign,
         _textDirection = textDirection,
@@ -161,6 +163,7 @@ class CkParagraphStyle implements ui.ParagraphStyle {
     ui.StrutStyle? strutStyle,
     String? ellipsis,
     ui.Locale? locale,
+    bool applyRoundingHack,
   ) {
     final SkParagraphStyleProperties properties = SkParagraphStyleProperties();
 
@@ -197,7 +200,7 @@ class CkParagraphStyle implements ui.ParagraphStyle {
     properties.replaceTabCharacters = true;
     properties.textStyle = toSkTextStyleProperties(
         fontFamily, fontSize, height, fontWeight, fontStyle);
-    properties.applyRoundingHack = false;
+    properties.applyRoundingHack = applyRoundingHack;
 
     return canvasKit.ParagraphStyle(properties);
   }

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

@@ -87,6 +87,17 @@ class CanvasParagraph implements ui.Paragraph {
 
   @override
   void layout(ui.ParagraphConstraints constraints) {
+    // When constraint width has a decimal place, we floor it to avoid getting
+    // a layout width that's higher than the constraint width.
+    //
+    // For example, if constraint width is `30.8` and the text has a width of
+    // `30.5` then the TextPainter in the framework will ceil the `30.5` width
+    // which will result in a width of `40.0` that's higher than the constraint
+    // width.
+    if (!ui.ParagraphBuilder.shouldDisableRoundingHack) {
+      constraints = ui.ParagraphConstraints(width: constraints.width.floorToDouble());
+    }
+
     if (constraints == _lastUsedConstraints) {
       return;
     }

lib/web_ui/lib/text.dart

@@ -733,6 +733,13 @@ abstract class ParagraphBuilder {
   factory ParagraphBuilder(ParagraphStyle style) =>
     engine.renderer.createParagraphBuilder(style);
 
+  static bool get shouldDisableRoundingHack => _shouldDisableRoundingHack;
+  static bool _shouldDisableRoundingHack = true;
+  // ignore: use_setters_to_change_properties
+  static void setDisableRoundingHack(bool disableRoundingHack) {
+    _shouldDisableRoundingHack = disableRoundingHack;
+  }
+
   void pushStyle(TextStyle style);
   void pop();
   void addText(String text);

lib/web_ui/test/canvaskit/text_test.dart

@@ -204,7 +204,9 @@ void testMain() {
       expect(bottomRight?.writingDirection, ui.TextDirection.ltr);
     });
 
-    test('rounding hack disabled', () {
+    test('rounding hack disabled by default', () {
+      expect(ui.ParagraphBuilder.shouldDisableRoundingHack, isTrue);
+
       const double fontSize = 1.25;
       const String text = '12345';
       assert((fontSize * text.length).truncate() != fontSize * text.length);
@@ -224,6 +226,32 @@ void testMain() {
       }
     });
 
+    test('setDisableRoundinghHack to false works in tests', () {
+      bool assertsEnabled = false;
+      assert(() {
+        assertsEnabled = true;
+        return true;
+      }());
+      if (!assertsEnabled){
+        return;
+      }
+
+      if (ui.ParagraphBuilder.shouldDisableRoundingHack) {
+        ui.ParagraphBuilder.setDisableRoundingHack(false);
+        addTearDown(() => ui.ParagraphBuilder.setDisableRoundingHack(true));
+      }
+
+      assert(!ui.ParagraphBuilder.shouldDisableRoundingHack);
+      const double fontSize = 1.25;
+      const String text = '12345';
+      assert((fontSize * text.length).truncate() != fontSize * text.length);
+      final ui.ParagraphBuilder builder = ui.ParagraphBuilder(ui.ParagraphStyle(fontSize: fontSize, fontFamily: 'FlutterTest'));
+      builder.addText(text);
+      final ui.Paragraph paragraph = builder.build()
+        ..layout(const ui.ParagraphConstraints(width: text.length * fontSize));
+      expect(paragraph.computeLineMetrics().length, greaterThan(1));
+    });
+
     // TODO(hterkelsen): https://github.com/flutter/flutter/issues/71520
   }, skip: isSafari || isFirefox);
 }

lib/web_ui/test/html/text/canvas_paragraph_test.dart

@@ -777,6 +777,21 @@ Future<void> testMain() async {
     expect(paragraph.longestLine, 50.0);
   });
 
+  test('$CanvasParagraph.width should be a whole integer when shouldDisableRoundingHack is false', () {
+    if (ui.ParagraphBuilder.shouldDisableRoundingHack) {
+      ui.ParagraphBuilder.setDisableRoundingHack(false);
+      addTearDown(() => ui.ParagraphBuilder.setDisableRoundingHack(true));
+    }
+    // The paragraph width is only rounded to a whole integer if
+    // shouldDisableRoundingHack is false.
+    assert(!ui.ParagraphBuilder.shouldDisableRoundingHack);
+    final ui.Paragraph paragraph = plain(ahemStyle, 'abc');
+    paragraph.layout(const ui.ParagraphConstraints(width: 30.8));
+
+    expect(paragraph.width, 30);
+    expect(paragraph.height, 10);
+  });
+
   test('Render after dispose', () async {
     final ui.Paragraph paragraph = plain(ahemStyle, 'abc');
     paragraph.layout(const ui.ParagraphConstraints(width: 30.8));

lib/web_ui/test/html/text_test.dart

@@ -200,7 +200,12 @@ Future<void> testMain() async {
     expect(bottomRight?.graphemeClusterLayoutBounds, const Rect.fromLTWH(0.0, 0.0, 10.0, 10.0));
   }, skip: domIntl.v8BreakIterator == null); // Intended: Intl.v8breakiterator is needed for correctly breaking grapheme clusters.
 
-  test('disable rounding hack', () {
+  test('Can disable rounding hack', () {
+    if (!ParagraphBuilder.shouldDisableRoundingHack) {
+      ParagraphBuilder.setDisableRoundingHack(true);
+      addTearDown(() => ParagraphBuilder.setDisableRoundingHack(false));
+    }
+    assert(ParagraphBuilder.shouldDisableRoundingHack);
     const double fontSize = 1;
     const String text = '12345';
     const double letterSpacing = 0.25;

testing/dart/paragraph_test.dart

@@ -333,10 +333,42 @@ void main() {
     }
   });
 
-  test('rounding hack disabled', () {
+  test('can set disableRoundingHack to false in tests', () {
+    bool assertsEnabled = false;
+    assert(() {
+      assertsEnabled = true;
+      return true;
+    }());
+    if (!assertsEnabled){
+      return;
+    }
+    const double fontSize = 1.25;
+    const String text = '12345';
+    assert((fontSize * text.length).truncate() != fontSize * text.length);
+    // ignore: deprecated_member_use
+    final bool roundingHackWasDisabled = ParagraphBuilder.shouldDisableRoundingHack;
+    if (roundingHackWasDisabled) {
+      ParagraphBuilder.setDisableRoundingHack(false);
+    }
+    // ignore: deprecated_member_use
+    assert(!ParagraphBuilder.shouldDisableRoundingHack);
+    final ParagraphBuilder builder = ParagraphBuilder(ParagraphStyle(fontSize: fontSize));
+    builder.addText(text);
+    final Paragraph paragraph = builder.build()
+      ..layout(const ParagraphConstraints(width: text.length * fontSize));
+    expect(paragraph.computeLineMetrics().length, greaterThan(1));
+
+    if (roundingHackWasDisabled) {
+      ParagraphBuilder.setDisableRoundingHack(true);
+    }
+  });
+
+  test('rounding hack disabled by default', () {
     const double fontSize = 1.25;
     const String text = '12345';
     assert((fontSize * text.length).truncate() != fontSize * text.length);
+    // ignore: deprecated_member_use
+    expect(ParagraphBuilder.shouldDisableRoundingHack, isTrue);
     final ParagraphBuilder builder = ParagraphBuilder(ParagraphStyle(fontSize: fontSize));
     builder.addText(text);
     final Paragraph paragraph = builder.build()

third_party/txt/src/skia/paragraph_builder_skia.cc

@@ -139,7 +139,7 @@ skt::ParagraphStyle ParagraphBuilderSkia::TxtToSkia(const ParagraphStyle& txt) {
 
   skia.turnHintingOff();
   skia.setReplaceTabCharacters(true);
-  skia.setApplyRoundingHack(false);
+  skia.setApplyRoundingHack(txt.apply_rounding_hack);
 
   return skia;
 }