[a11y] Slider should respect bold text setting (#149053)

Fix https://github.com/flutter/flutter/issues/147600

internal GAR issue: b/316933135

reopen from #148435

packages/flutter/lib/src/material/slider.dart

@@ -817,6 +817,11 @@ class _SliderState extends State<Slider> with TickerProviderStateMixin {
         ?? MaterialStateProperty.resolveAs<Color?>(defaults.overlayColor, states);
     }
 
+    TextStyle valueIndicatorTextStyle = sliderTheme.valueIndicatorTextStyle ?? defaults.valueIndicatorTextStyle!;
+    if (MediaQuery.boldTextOf(context)) {
+      valueIndicatorTextStyle = valueIndicatorTextStyle.merge(const TextStyle(fontWeight: FontWeight.bold));
+    }
+
     sliderTheme = sliderTheme.copyWith(
       trackHeight: sliderTheme.trackHeight ?? defaults.trackHeight,
       activeTrackColor: widget.activeColor ?? sliderTheme.activeTrackColor ?? defaults.activeTrackColor,
@@ -839,7 +844,7 @@ class _SliderState extends State<Slider> with TickerProviderStateMixin {
       overlayShape: sliderTheme.overlayShape ?? defaultOverlayShape,
       valueIndicatorShape: valueIndicatorShape,
       showValueIndicator: sliderTheme.showValueIndicator ?? defaultShowValueIndicator,
-      valueIndicatorTextStyle: sliderTheme.valueIndicatorTextStyle ?? defaults.valueIndicatorTextStyle,
+      valueIndicatorTextStyle: valueIndicatorTextStyle,
     );
     final MouseCursor effectiveMouseCursor = MaterialStateProperty.resolveAs<MouseCursor?>(widget.mouseCursor, states)
       ?? sliderTheme.mouseCursor?.resolve(states)

packages/flutter/test/material/slider_test.dart

@@ -49,6 +49,36 @@ class LoggingThumbShape extends SliderComponentShape {
   }
 }
 
+// A value indicator shape to log labelPainter text.
+class LoggingValueIndicatorShape extends SliderComponentShape {
+  LoggingValueIndicatorShape(this.logLabel);
+
+  final List<InlineSpan> logLabel;
+
+  @override
+  Size getPreferredSize(bool isEnabled, bool isDiscrete) {
+    return const Size(10.0, 10.0);
+  }
+
+  @override
+  void paint(
+    PaintingContext context,
+    Offset offset, {
+    required Animation<double> activationAnimation,
+    required Animation<double> enableAnimation,
+    required bool isDiscrete,
+    required TextPainter labelPainter,
+    required RenderBox parentBox,
+    required SliderThemeData sliderTheme,
+    required TextDirection textDirection,
+    required double value,
+    required double textScaleFactor,
+    required Size sizeWithOverflow,
+  }) {
+    logLabel.add(labelPainter.text!);
+  }
+}
+
 class TallSliderTickMarkShape extends SliderTickMarkShape {
   @override
   Size getPreferredSize({required SliderThemeData sliderTheme, required bool isEnabled}) {
@@ -975,6 +1005,79 @@ void main() {
     }
   });
 
+  testWidgets('Slider value indicator respects bold text', (WidgetTester tester) async {
+      final Key sliderKey = UniqueKey();
+      double value = 0.0;
+      final List<InlineSpan> log = <InlineSpan>[];
+      final LoggingValueIndicatorShape loggingValueIndicatorShape = LoggingValueIndicatorShape(log);
+
+      Widget buildSlider({ bool boldText = false }) {
+        return MaterialApp(
+          home: Directionality(
+            textDirection: TextDirection.ltr,
+            child: StatefulBuilder(
+              builder: (BuildContext context, StateSetter setState) {
+                return MediaQuery(
+                  data: MediaQueryData(boldText: boldText),
+                  child: Material(
+                    child: Theme(
+                      data: Theme.of(context).copyWith(
+                        sliderTheme: Theme.of(context).sliderTheme.copyWith(
+                          showValueIndicator: ShowValueIndicator.always,
+                          valueIndicatorShape: loggingValueIndicatorShape,
+                        ),
+                      ),
+                      child: Center(
+                        child: OverflowBox(
+                          maxWidth: double.infinity,
+                          maxHeight: double.infinity,
+                          child: Slider(
+                            key: sliderKey,
+                            max: 100.0,
+                            divisions: 4,
+                            label: '${value.round()}',
+                            value: value,
+                            onChanged: (double newValue) {
+                              setState(() {
+                                value = newValue;
+                              });
+                            },
+                          ),
+                        ),
+                      ),
+                    ),
+                  ),
+                );
+              },
+            ),
+          ),
+        );
+      }
+      // Normal text
+      await tester.pumpWidget(buildSlider());
+      Offset center = tester.getCenter(find.byType(Slider));
+      TestGesture gesture = await tester.startGesture(center);
+      await tester.pumpAndSettle();
+
+      expect(log.last.toPlainText(), '50');
+      expect(log.last.style!.fontWeight, FontWeight.w500);
+
+      await gesture.up();
+      await tester.pumpAndSettle();
+
+      // Bold text
+      await tester.pumpWidget(buildSlider(boldText: true));
+      center = tester.getCenter(find.byType(Slider));
+      gesture = await tester.startGesture(center);
+      await tester.pumpAndSettle();
+
+      expect(log.last.toPlainText(), '50');
+      expect(log.last.style!.fontWeight, FontWeight.w700);
+
+      await gesture.up();
+      await tester.pumpAndSettle();
+  });
+
   testWidgets('Tick marks are skipped when they are too dense', (WidgetTester tester) async {
     Widget buildSlider({
       required int divisions,