text: Add bolderWghtTextStyle

Author: chrisbobbe

lib/widgets/text.dart

@@ -264,6 +264,44 @@ double bolderWght(double baseWght, {double by = 300}) {
   return clampDouble(baseWght + by, kWghtMin, kWghtMax);
 }
 
+/// A [TextStyle] whose [FontVariation] "wght" and [TextStyle.fontWeight]
+/// have been raised using [bolderWght].
+///
+/// [style] must have already been processed with [weightVariableTextStyle],
+/// and [by] must be positive.
+///
+/// The increase done here will commute with any increase that was done by
+/// [weightVariableTextStyle] to respond to the device bold-text setting,
+/// because both adjustments are done with [bolderWght] with positive `by`.
+///
+/// [by] defaults to 300.
+TextStyle bolderWghtTextStyle(TextStyle style, {double by = 300}) {
+  assert(
+    style.debugLabel!.contains('weightVariableTextStyle')
+    // ([ContentTheme.textStylePlainParagraph] applies [weightVariableTextStyle])
+    || style.debugLabel!.contains('ContentTheme.textStylePlainParagraph')
+    || style.debugLabel!.contains('bolderWghtTextStyle')
+  );
+  assert(by > 0);
+  assert(style.fontVariations!.where((v) => v.axis == 'wght').length == 1);
+
+  final newWght = bolderWght(wghtFromTextStyle(style)!, by: by);
+
+  TextStyle result = style.copyWith(
+    fontVariations: style.fontVariations!.map((v) => v.axis == 'wght'
+      ? FontVariation('wght', newWght)
+      : v).toList(),
+    fontWeight: clampVariableFontWeight(newWght),
+  );
+
+  assert(() {
+    result = result.copyWith(debugLabel: 'bolderWghtTextStyle(by: $by)');
+    return true;
+  }());
+
+  return result;
+}
+
 /// Find the nearest [FontWeight] constant for a variable-font "wght"-axis value.
 ///
 /// Use this for a reasonable [TextStyle.fontWeight] for glyphs that need to be

test/widgets/text_test.dart

@@ -1,4 +1,5 @@
 import 'package:checks/checks.dart';
+import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:zulip/widgets/text.dart';
@@ -169,6 +170,82 @@ void main() {
     check(bolderWght(900, by: 200)).equals(1000);
   });
 
+  group('bolderWghtTextStyle', () {
+    Future<void> testBolderWghtTextStyle(
+      String description, {
+      required TextStyle Function(BuildContext context) makeStyle,
+      bool platformRequestsBold = false,
+      required double expectedWght,
+      required FontWeight expectedFontWeight,
+    }) async {
+      testWidgets(description, (WidgetTester tester) async {
+        tester.platformDispatcher.accessibilityFeaturesTestValue =
+          FakeAccessibilityFeatures(boldText: platformRequestsBold);
+
+        await tester.pumpWidget(
+          MaterialApp(
+            home: Builder(builder: (context) =>
+              Text('', style: makeStyle(context)))));
+
+        final TextStyle? style = tester.widget<Text>(find.byType(Text)).style;
+
+        check(style).isNotNull().fontWeight.isNotNull().equals(expectedFontWeight);
+
+        final fontVariations = style!.fontVariations;
+        check(fontVariations).isNotNull();
+        final wghtVariation = fontVariations!.singleWhereOrNull((v) => v.axis == 'wght');
+        check(wghtVariation).isNotNull().value.equals(expectedWght);
+
+        tester.platformDispatcher.clearAccessibilityFeaturesTestValue();
+      });
+    }
+
+    testBolderWghtTextStyle('default + default',
+      makeStyle: (context) => bolderWghtTextStyle(weightVariableTextStyle(context)),
+      expectedWght: 700,
+      expectedFontWeight: FontWeight.w700);
+
+    testBolderWghtTextStyle('default + default (platform requests bold)',
+      platformRequestsBold: true,
+      makeStyle: (context) => bolderWghtTextStyle(weightVariableTextStyle(context)),
+      expectedWght: 1000,
+      expectedFontWeight: FontWeight.w900);
+
+    testBolderWghtTextStyle('320 + 200',
+      makeStyle: (context) => bolderWghtTextStyle(
+        weightVariableTextStyle(context, wght: 320),
+        by: 200,
+      ),
+      expectedWght: 520,
+      expectedFontWeight: FontWeight.w500);
+
+    testBolderWghtTextStyle('320 + 200 (platform requests bold)',
+      platformRequestsBold: true,
+      makeStyle: (context) => bolderWghtTextStyle(
+        weightVariableTextStyle(context, wght: 320),
+        by: 200,
+      ),
+      expectedWght: 820,
+      expectedFontWeight: FontWeight.w800);
+
+    testBolderWghtTextStyle('320 + 200 (platform requests bold; custom response to setting)',
+      platformRequestsBold: true,
+      makeStyle: (context) => bolderWghtTextStyle(
+        weightVariableTextStyle(context, wght: 320, wghtIfPlatformRequestsBold: 410),
+        by: 200,
+      ),
+      expectedWght: 610,
+      expectedFontWeight: FontWeight.w600);
+
+    testBolderWghtTextStyle('900 + 200',
+      makeStyle: (context) => bolderWghtTextStyle(
+        weightVariableTextStyle(context, wght: 900),
+        by: 200,
+      ),
+      expectedWght: 1000,
+      expectedFontWeight: FontWeight.w900);
+  });
+
   test('clampVariableFontWeight: FontWeight has the assumed list of values', () {
     // Implementation assumes specific FontWeight values; we should
     // adapt if these change in a new Flutter version.