Add support for locale-specific text styles (#16430)

See https://github.com/flutter/flutter/issues/12630 and
https://github.com/flutter/flutter/issues/16408

packages/flutter/lib/src/painting/text_painter.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui' as ui show Paragraph, ParagraphBuilder, ParagraphConstraints, ParagraphStyle;
+import 'dart:ui' as ui show Paragraph, ParagraphBuilder, ParagraphConstraints, ParagraphStyle, Locale;
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
@@ -48,6 +48,7 @@ class TextPainter {
     double textScaleFactor: 1.0,
     int maxLines,
     String ellipsis,
+    ui.Locale locale,
   }) : assert(text == null || text.debugAssertIsValid()),
        assert(textAlign != null),
        assert(textScaleFactor != null),
@@ -57,7 +58,8 @@ class TextPainter {
        _textDirection = textDirection,
        _textScaleFactor = textScaleFactor,
        _maxLines = maxLines,
-       _ellipsis = ellipsis;
+       _ellipsis = ellipsis,
+       _locale = locale;
 
   ui.Paragraph _paragraph;
   bool _needsLayout = true;
@@ -167,6 +169,17 @@ class TextPainter {
     _needsLayout = true;
   }
 
+  /// The locale used to select region-specific glyphs.
+  ui.Locale get locale => _locale;
+  ui.Locale _locale;
+  set locale(ui.Locale value) {
+    if (_locale == value)
+      return;
+    _locale = value;
+    _paragraph = null;
+    _needsLayout = true;
+  }
+
   /// An optional maximum number of lines for the text to span, wrapping if
   /// necessary.
   ///
@@ -199,11 +212,13 @@ class TextPainter {
       textScaleFactor: textScaleFactor,
       maxLines: _maxLines,
       ellipsis: _ellipsis,
+      locale: _locale,
     ) ?? new ui.ParagraphStyle(
       textAlign: textAlign,
       textDirection: textDirection ?? defaultTextDirection,
       maxLines: maxLines,
       ellipsis: ellipsis,
+      locale: locale,
     );
   }
 

packages/flutter/lib/src/painting/text_style.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui' as ui show ParagraphStyle, TextStyle, lerpDouble;
+import 'dart:ui' as ui show ParagraphStyle, TextStyle, lerpDouble, Locale;
 
 import 'package:flutter/foundation.dart';
 
@@ -229,6 +229,7 @@ class TextStyle extends Diagnosticable {
     this.wordSpacing,
     this.textBaseline,
     this.height,
+    this.locale,
     this.decoration,
     this.decorationColor,
     this.decorationStyle,
@@ -296,6 +297,9 @@ class TextStyle extends Diagnosticable {
   /// the font size.
   final double height;
 
+  /// The locale used to select region-specific glyphs.
+  final ui.Locale locale;
+
   /// The decorations to paint near the text (e.g., an underline).
   final TextDecoration decoration;
 
@@ -330,6 +334,7 @@ class TextStyle extends Diagnosticable {
     double wordSpacing,
     TextBaseline textBaseline,
     double height,
+    ui.Locale locale,
     TextDecoration decoration,
     Color decorationColor,
     TextDecorationStyle decorationStyle,
@@ -352,6 +357,7 @@ class TextStyle extends Diagnosticable {
       wordSpacing: wordSpacing ?? this.wordSpacing,
       textBaseline: textBaseline ?? this.textBaseline,
       height: height ?? this.height,
+      locale: locale ?? this.locale,
       decoration: decoration ?? this.decoration,
       decorationColor: decorationColor ?? this.decorationColor,
       decorationStyle: decorationStyle ?? this.decorationStyle,
@@ -429,6 +435,7 @@ class TextStyle extends Diagnosticable {
       wordSpacing: wordSpacing == null ? null : wordSpacing * wordSpacingFactor + wordSpacingDelta,
       textBaseline: textBaseline,
       height: height == null ? null : height * heightFactor + heightDelta,
+      locale: locale,
       decoration: decoration ?? this.decoration,
       decorationColor: decorationColor ?? this.decorationColor,
       decorationStyle: decorationStyle ?? this.decorationStyle,
@@ -473,6 +480,7 @@ class TextStyle extends Diagnosticable {
       wordSpacing: other.wordSpacing,
       textBaseline: other.textBaseline,
       height: other.height,
+      locale: other.locale,
       decoration: other.decoration,
       decorationColor: other.decorationColor,
       decorationStyle: other.decorationStyle,
@@ -518,6 +526,7 @@ class TextStyle extends Diagnosticable {
       wordSpacing: ui.lerpDouble(a.wordSpacing ?? b.wordSpacing, b.wordSpacing ?? a.wordSpacing, t),
       textBaseline: t < 0.5 ? a.textBaseline : b.textBaseline,
       height: ui.lerpDouble(a.height ?? b.height, b.height ?? a.height, t),
+      locale: t < 0.5 ? a.locale : b.locale,
       decoration: t < 0.5 ? a.decoration : b.decoration,
       decorationColor: Color.lerp(a.decorationColor, b.decorationColor, t),
       decorationStyle: t < 0.5 ? a.decorationStyle : b.decorationStyle,
@@ -539,7 +548,8 @@ class TextStyle extends Diagnosticable {
       fontSize: fontSize == null ? null : fontSize * textScaleFactor,
       letterSpacing: letterSpacing,
       wordSpacing: wordSpacing,
-      height: height
+      height: height,
+      locale: locale,
     );
   }
 
@@ -557,6 +567,7 @@ class TextStyle extends Diagnosticable {
       double textScaleFactor: 1.0,
       String ellipsis,
       int maxLines,
+      ui.Locale locale,
   }) {
     assert(textScaleFactor != null);
     assert(maxLines == null || maxLines > 0);
@@ -570,6 +581,7 @@ class TextStyle extends Diagnosticable {
       lineHeight: height,
       maxLines: maxLines,
       ellipsis: ellipsis,
+      locale: locale,
     );
   }
 
@@ -590,7 +602,8 @@ class TextStyle extends Diagnosticable {
         letterSpacing != other.letterSpacing ||
         wordSpacing != other.wordSpacing ||
         textBaseline != other.textBaseline ||
-        height != other.height)
+        height != other.height ||
+        locale != other.locale)
       return RenderComparison.layout;
     if (color != other.color ||
         decoration != other.decoration ||
@@ -617,6 +630,7 @@ class TextStyle extends Diagnosticable {
            wordSpacing == typedOther.wordSpacing &&
            textBaseline == typedOther.textBaseline &&
            height == typedOther.height &&
+           locale == typedOther.locale &&
            decoration == typedOther.decoration &&
            decorationColor == typedOther.decorationColor &&
            decorationStyle == typedOther.decorationStyle;
@@ -635,6 +649,7 @@ class TextStyle extends Diagnosticable {
       wordSpacing,
       textBaseline,
       height,
+      locale,
       decoration,
       decorationColor,
       decorationStyle
@@ -700,6 +715,7 @@ class TextStyle extends Diagnosticable {
     styles.add(new DoubleProperty('${prefix}wordSpacing', wordSpacing, defaultValue: null));
     styles.add(new EnumProperty<TextBaseline>('${prefix}baseline', textBaseline, defaultValue: null));
     styles.add(new DoubleProperty('${prefix}height', height, unit: 'x', defaultValue: null));
+    styles.add(new StringProperty('${prefix}locale', locale?.toString(), defaultValue: null, quoted: false));
     if (decoration != null || decorationColor != null || decorationStyle != null) {
       final List<String> decorationDescription = <String>[];
       if (decorationStyle != null)

packages/flutter/test/material/theme_test.dart

@@ -462,6 +462,7 @@ class _TextStyleProxy implements TextStyle {
   @override FontStyle get fontStyle => _delegate.fontStyle;
   @override FontWeight get fontWeight => _delegate.fontWeight;
   @override double get height => _delegate.height;
+  @override ui.Locale get locale => _delegate.locale;
   @override bool get inherit => _delegate.inherit;
   @override double get letterSpacing => _delegate.letterSpacing;
   @override TextBaseline get textBaseline => _delegate.textBaseline;
@@ -488,7 +489,7 @@ class _TextStyleProxy implements TextStyle {
   }
 
   @override
-  TextStyle copyWith({Color color, String fontFamily, double fontSize, FontWeight fontWeight, FontStyle fontStyle, double letterSpacing, double wordSpacing, TextBaseline textBaseline, double height, TextDecoration decoration, Color decorationColor, TextDecorationStyle decorationStyle, String debugLabel}) {
+  TextStyle copyWith({Color color, String fontFamily, double fontSize, FontWeight fontWeight, FontStyle fontStyle, double letterSpacing, double wordSpacing, TextBaseline textBaseline, double height, ui.Locale locale, TextDecoration decoration, Color decorationColor, TextDecorationStyle decorationStyle, String debugLabel}) {
     throw new UnimplementedError();
   }
 
@@ -498,7 +499,7 @@ class _TextStyleProxy implements TextStyle {
   }
 
   @override
-  ui.ParagraphStyle getParagraphStyle({TextAlign textAlign, TextDirection textDirection, double textScaleFactor: 1.0, String ellipsis, int maxLines}) {
+  ui.ParagraphStyle getParagraphStyle({TextAlign textAlign, TextDirection textDirection, double textScaleFactor: 1.0, String ellipsis, int maxLines, ui.Locale locale}) {
     throw new UnimplementedError();
   }