Added ButtonStyle.fixedSize (#74773)

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

@@ -107,6 +107,7 @@ class ButtonStyle with Diagnosticable {
     this.elevation,
     this.padding,
     this.minimumSize,
+    this.fixedSize,
     this.side,
     this.shape,
     this.mouseCursor,
@@ -158,6 +159,16 @@ class ButtonStyle with Diagnosticable {
   /// per [tapTargetSize].
   final MaterialStateProperty<Size?>? minimumSize;
 
+  /// The button's size.
+  ///
+  /// This size is still constrained by the style's [minimumSize]. Fixed
+  /// size dimensions whose value is [double.infinity] are ignored.
+  ///
+  /// To specify buttons with a fixed width and the default height use
+  /// `fixedSize: Size.fromWidth(320)`. Similarly, to specify a fixed
+  /// height and the default width use `fixedSize: Size.fromHeight(100)`.
+  final MaterialStateProperty<Size?>? fixedSize;
+
   /// The color and weight of the button's outline.
   ///
   /// This value is combined with [shape] to create a shape decorated
@@ -230,6 +241,7 @@ class ButtonStyle with Diagnosticable {
     MaterialStateProperty<double?>? elevation,
     MaterialStateProperty<EdgeInsetsGeometry?>? padding,
     MaterialStateProperty<Size?>? minimumSize,
+    MaterialStateProperty<Size?>? fixedSize,
     MaterialStateProperty<BorderSide?>? side,
     MaterialStateProperty<OutlinedBorder?>? shape,
     MaterialStateProperty<MouseCursor?>? mouseCursor,
@@ -248,6 +260,7 @@ class ButtonStyle with Diagnosticable {
       elevation: elevation ?? this.elevation,
       padding: padding ?? this.padding,
       minimumSize: minimumSize ?? this.minimumSize,
+      fixedSize: fixedSize ?? this.fixedSize,
       side: side ?? this.side,
       shape: shape ?? this.shape,
       mouseCursor: mouseCursor ?? this.mouseCursor,
@@ -276,6 +289,7 @@ class ButtonStyle with Diagnosticable {
       elevation: elevation ?? style.elevation,
       padding: padding ?? style.padding,
       minimumSize: minimumSize ?? style.minimumSize,
+      fixedSize: fixedSize ?? style.fixedSize,
       side: side ?? style.side,
       shape: shape ?? style.shape,
       mouseCursor: mouseCursor ?? style.mouseCursor,
@@ -298,6 +312,7 @@ class ButtonStyle with Diagnosticable {
       elevation,
       padding,
       minimumSize,
+      fixedSize,
       side,
       shape,
       mouseCursor,
@@ -324,6 +339,7 @@ class ButtonStyle with Diagnosticable {
         && other.elevation == elevation
         && other.padding == padding
         && other.minimumSize == minimumSize
+        && other.fixedSize == fixedSize
         && other.side == side
         && other.shape == shape
         && other.mouseCursor == mouseCursor
@@ -345,6 +361,7 @@ class ButtonStyle with Diagnosticable {
     properties.add(DiagnosticsProperty<MaterialStateProperty<double?>>('elevation', elevation, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<EdgeInsetsGeometry?>>('padding', padding, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<Size?>>('minimumSize', minimumSize, defaultValue: null));
+    properties.add(DiagnosticsProperty<MaterialStateProperty<Size?>>('fixedSize', fixedSize, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<BorderSide?>>('side', side, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<OutlinedBorder?>>('shape', shape, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<MouseCursor?>>('mouseCursor', mouseCursor, defaultValue: null));
@@ -369,6 +386,7 @@ class ButtonStyle with Diagnosticable {
       elevation: _lerpProperties<double?>(a?.elevation, b?.elevation, t, lerpDouble),
       padding:  _lerpProperties<EdgeInsetsGeometry?>(a?.padding, b?.padding, t, EdgeInsetsGeometry.lerp),
       minimumSize: _lerpProperties<Size?>(a?.minimumSize, b?.minimumSize, t, Size.lerp),
+      fixedSize: _lerpProperties<Size?>(a?.fixedSize, b?.fixedSize, t, Size.lerp),
       side: _lerpSides(a?.side, b?.side, t),
       shape: _lerpShapes(a?.shape, b?.shape, t),
       mouseCursor: t < 0.5 ? a?.mouseCursor : b?.mouseCursor,

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

@@ -268,6 +268,7 @@ class _ButtonStyleState extends State<ButtonStyleButton> with TickerProviderStat
     final Color? resolvedShadowColor = resolve<Color?>((ButtonStyle? style) => style?.shadowColor);
     final EdgeInsetsGeometry? resolvedPadding = resolve<EdgeInsetsGeometry?>((ButtonStyle? style) => style?.padding);
     final Size? resolvedMinimumSize = resolve<Size?>((ButtonStyle? style) => style?.minimumSize);
+    final Size? resolvedFixedSize = resolve<Size?>((ButtonStyle? style) => style?.fixedSize);
     final BorderSide? resolvedSide = resolve<BorderSide?>((ButtonStyle? style) => style?.side);
     final OutlinedBorder? resolvedShape = resolve<OutlinedBorder?>((ButtonStyle? style) => style?.shape);
 
@@ -285,12 +286,29 @@ class _ButtonStyleState extends State<ButtonStyleButton> with TickerProviderStat
     final bool? resolvedEnableFeedback = effectiveValue((ButtonStyle? style) => style?.enableFeedback);
     final AlignmentGeometry? resolvedAlignment = effectiveValue((ButtonStyle? style) => style?.alignment);
     final Offset densityAdjustment = resolvedVisualDensity!.baseSizeAdjustment;
-    final BoxConstraints effectiveConstraints = resolvedVisualDensity.effectiveConstraints(
+
+    BoxConstraints effectiveConstraints = resolvedVisualDensity.effectiveConstraints(
       BoxConstraints(
         minWidth: resolvedMinimumSize!.width,
         minHeight: resolvedMinimumSize.height,
       ),
     );
+    if (resolvedFixedSize != null) {
+      final Size size = effectiveConstraints.constrain(resolvedFixedSize);
+      if (size.width.isFinite) {
+        effectiveConstraints = effectiveConstraints.copyWith(
+          minWidth: size.width,
+          maxWidth: size.width,
+        );
+      }
+      if (size.height.isFinite) {
+        effectiveConstraints = effectiveConstraints.copyWith(
+          minHeight: size.height,
+          maxHeight: size.height
+        );
+      }
+    }
+
     final EdgeInsetsGeometry padding = resolvedPadding!.add(
       EdgeInsets.only(
         left: densityAdjustment.dx,

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

@@ -139,6 +139,7 @@ class ElevatedButton extends ButtonStyleButton {
     TextStyle? textStyle,
     EdgeInsetsGeometry? padding,
     Size? minimumSize,
+    Size? fixedSize,
     BorderSide? side,
     OutlinedBorder? shape,
     MouseCursor? enabledMouseCursor,
@@ -174,6 +175,7 @@ class ElevatedButton extends ButtonStyleButton {
       elevation: elevationValue,
       padding: ButtonStyleButton.allOrNull<EdgeInsetsGeometry>(padding),
       minimumSize: ButtonStyleButton.allOrNull<Size>(minimumSize),
+      fixedSize: ButtonStyleButton.allOrNull<Size>(fixedSize),
       side: ButtonStyleButton.allOrNull<BorderSide>(side),
       shape: ButtonStyleButton.allOrNull<OutlinedBorder>(shape),
       mouseCursor: mouseCursor,
@@ -231,6 +233,7 @@ class ElevatedButton extends ButtonStyleButton {
   ///   * `2 < textScaleFactor <= 3` - lerp(horizontal(8), horizontal(4))
   ///   * `3 < textScaleFactor` - horizontal(4)
   /// * `minimumSize` - Size(64, 36)
+  /// * `fixedSize` - null
   /// * `side` - null
   /// * `shape` - RoundedRectangleBorder(borderRadius: BorderRadius.circular(4))
   /// * `mouseCursor`

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

@@ -131,6 +131,7 @@ class OutlinedButton extends ButtonStyleButton {
     TextStyle? textStyle,
     EdgeInsetsGeometry? padding,
     Size? minimumSize,
+    Size? fixedSize,
     BorderSide? side,
     OutlinedBorder? shape,
     MouseCursor? enabledMouseCursor,
@@ -160,6 +161,7 @@ class OutlinedButton extends ButtonStyleButton {
       elevation: ButtonStyleButton.allOrNull<double>(elevation),
       padding: ButtonStyleButton.allOrNull<EdgeInsetsGeometry>(padding),
       minimumSize: ButtonStyleButton.allOrNull<Size>(minimumSize),
+      fixedSize: ButtonStyleButton.allOrNull<Size>(fixedSize),
       side: ButtonStyleButton.allOrNull<BorderSide>(side),
       shape: ButtonStyleButton.allOrNull<OutlinedBorder>(shape),
       mouseCursor: mouseCursor,
@@ -210,6 +212,7 @@ class OutlinedButton extends ButtonStyleButton {
   ///   * `2 < textScaleFactor <= 3` - lerp(horizontal(8), horizontal(4))
   ///   * `3 < textScaleFactor` - horizontal(4)
   /// * `minimumSize` - Size(64, 36)
+  /// * `fixedSize` - null
   /// * `side` - BorderSide(width: 1, color: Theme.colorScheme.onSurface(0.12))
   /// * `shape` - RoundedRectangleBorder(borderRadius: BorderRadius.circular(4))
   /// * `mouseCursor`

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

@@ -137,6 +137,7 @@ class TextButton extends ButtonStyleButton {
     TextStyle? textStyle,
     EdgeInsetsGeometry? padding,
     Size? minimumSize,
+    Size? fixedSize,
     BorderSide? side,
     OutlinedBorder? shape,
     MouseCursor? enabledMouseCursor,
@@ -166,6 +167,7 @@ class TextButton extends ButtonStyleButton {
       elevation: ButtonStyleButton.allOrNull<double>(elevation),
       padding: ButtonStyleButton.allOrNull<EdgeInsetsGeometry>(padding),
       minimumSize: ButtonStyleButton.allOrNull<Size>(minimumSize),
+      fixedSize: ButtonStyleButton.allOrNull<Size>(fixedSize),
       side: ButtonStyleButton.allOrNull<BorderSide>(side),
       shape: ButtonStyleButton.allOrNull<OutlinedBorder>(shape),
       mouseCursor: mouseCursor,
@@ -219,6 +221,7 @@ class TextButton extends ButtonStyleButton {
   ///   * `2 < textScaleFactor <= 3` - lerp(horizontal(8), horizontal(4))
   ///   * `3 < textScaleFactor` - horizontal(4)
   /// * `minimumSize` - Size(64, 36)
+  /// * `fixedSize` - null
   /// * `side` - null
   /// * `shape` - RoundedRectangleBorder(borderRadius: BorderRadius.circular(4))
   /// * `mouseCursor`

packages/flutter/test/material/button_style_test.dart

@@ -24,6 +24,7 @@ void main() {
     expect(style.elevation, null);
     expect(style.padding, null);
     expect(style.minimumSize, null);
+    expect(style.fixedSize, null);
     expect(style.side, null);
     expect(style.shape, null);
     expect(style.mouseCursor, null);
@@ -93,6 +94,7 @@ void main() {
     final MaterialStateProperty<double> elevation =  MaterialStateProperty.all<double>(1);
     final MaterialStateProperty<EdgeInsets> padding = MaterialStateProperty.all<EdgeInsets>(const EdgeInsets.all(1));
     final MaterialStateProperty<Size> minimumSize = MaterialStateProperty.all<Size>(const Size(1, 2));
+    final MaterialStateProperty<Size> fixedSize = MaterialStateProperty.all<Size>(const Size(3, 4));
     final MaterialStateProperty<BorderSide> side = MaterialStateProperty.all<BorderSide>(const BorderSide());
     final MaterialStateProperty<OutlinedBorder> shape  = MaterialStateProperty.all<OutlinedBorder>(const StadiumBorder());
     final MaterialStateProperty<MouseCursor> mouseCursor = MaterialStateProperty.all<MouseCursor>(SystemMouseCursors.forbidden);
@@ -109,6 +111,7 @@ void main() {
       elevation: elevation,
       padding: padding,
       minimumSize: minimumSize,
+      fixedSize: fixedSize,
       side: side,
       shape: shape,
       mouseCursor: mouseCursor,
@@ -128,6 +131,7 @@ void main() {
         elevation: elevation,
         padding: padding,
         minimumSize: minimumSize,
+        fixedSize: fixedSize,
         side: side,
         shape: shape,
         mouseCursor: mouseCursor,

packages/flutter/test/material/elevated_button_test.dart

@@ -1039,6 +1039,39 @@ void main() {
 
     expect(find.byType(ElevatedButton), paints ..path(strokeWidth: 4) ..drrect(color: borderColor));
   });
+
+  testWidgets('Fixed size ElevatedButtons', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          body: Column(
+            mainAxisSize: MainAxisSize.min,
+            children: <Widget>[
+              ElevatedButton(
+                style: ElevatedButton.styleFrom(fixedSize: const Size(100, 100)),
+                onPressed: () {},
+                child: const Text('100x100'),
+              ),
+              ElevatedButton(
+                style: ElevatedButton.styleFrom(fixedSize: const Size.fromWidth(200)),
+                onPressed: () {},
+                child: const Text('200xh'),
+              ),
+              ElevatedButton(
+                style: ElevatedButton.styleFrom(fixedSize: const Size.fromHeight(200)),
+                onPressed: () {},
+                child: const Text('wx200'),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    expect(tester.getSize(find.widgetWithText(ElevatedButton, '100x100')), const Size(100, 100));
+    expect(tester.getSize(find.widgetWithText(ElevatedButton, '200xh')).width, 200);
+    expect(tester.getSize(find.widgetWithText(ElevatedButton, 'wx200')).height, 200);
+  });
 }
 
 TextStyle _iconStyle(WidgetTester tester, IconData icon) {

packages/flutter/test/material/outlined_button_test.dart

@@ -1215,6 +1215,39 @@ void main() {
     );
     expect(paddingWidget.padding, const EdgeInsets.all(22));
   });
+
+  testWidgets('Fixed size OutlinedButtons', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          body: Column(
+            mainAxisSize: MainAxisSize.min,
+            children: <Widget>[
+              OutlinedButton(
+                style: OutlinedButton.styleFrom(fixedSize: const Size(100, 100)),
+                onPressed: () {},
+                child: const Text('100x100'),
+              ),
+              OutlinedButton(
+                style: OutlinedButton.styleFrom(fixedSize: const Size.fromWidth(200)),
+                onPressed: () {},
+                child: const Text('200xh'),
+              ),
+              OutlinedButton(
+                style: OutlinedButton.styleFrom(fixedSize: const Size.fromHeight(200)),
+                onPressed: () {},
+                child: const Text('wx200'),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    expect(tester.getSize(find.widgetWithText(OutlinedButton, '100x100')), const Size(100, 100));
+    expect(tester.getSize(find.widgetWithText(OutlinedButton, '200xh')).width, 200);
+    expect(tester.getSize(find.widgetWithText(OutlinedButton, 'wx200')).height, 200);
+  });
 }
 
 PhysicalModelLayer _findPhysicalLayer(Element element) {

packages/flutter/test/material/text_button_test.dart

@@ -1012,8 +1012,39 @@ void main() {
     expect(paddingWidget.padding, const EdgeInsets.all(22));
   });
 
-}
+  testWidgets('Fixed size TextButtons', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          body: Column(
+            mainAxisSize: MainAxisSize.min,
+            children: <Widget>[
+              TextButton(
+                style: TextButton.styleFrom(fixedSize: const Size(100, 100)),
+                onPressed: () {},
+                child: const Text('100x100'),
+              ),
+              TextButton(
+                style: TextButton.styleFrom(fixedSize: const Size.fromWidth(200)),
+                onPressed: () {},
+                child: const Text('200xh'),
+              ),
+              TextButton(
+                style: TextButton.styleFrom(fixedSize: const Size.fromHeight(200)),
+                onPressed: () {},
+                child: const Text('wx200'),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
 
+    expect(tester.getSize(find.widgetWithText(TextButton, '100x100')), const Size(100, 100));
+    expect(tester.getSize(find.widgetWithText(TextButton, '200xh')).width, 200);
+    expect(tester.getSize(find.widgetWithText(TextButton, 'wx200')).height, 200);
+  });
+}
 
 TextStyle? _iconStyle(WidgetTester tester, IconData icon) {
   final RichText iconRichText = tester.widget<RichText>(