MaterialButton must honor its minWidth and height parameters (#22919)

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

@@ -258,7 +258,10 @@ class MaterialButton extends StatelessWidget {
       elevation: buttonTheme.getElevation(this),
       highlightElevation: buttonTheme.getHighlightElevation(this),
       padding: buttonTheme.getPadding(this),
-      constraints: buttonTheme.constraints,
+      constraints: buttonTheme.getConstraints(this).copyWith(
+        minWidth: minWidth,
+        minHeight: height,
+      ),
       shape: buttonTheme.shape,
       clipBehavior: clipBehavior ?? Clip.none,
       animationDuration: buttonTheme.getAnimationDuration(this),

packages/flutter/test/material/buttons_test.dart

@@ -409,6 +409,73 @@ void main() {
     semantics.dispose();
   });
 
+  testWidgets('MaterialButton minWidth and height parameters', (WidgetTester tester) async {
+    Widget buildFrame({ double minWidth, double height, EdgeInsets padding = EdgeInsets.zero, Widget child }) {
+      return Directionality(
+        textDirection: TextDirection.ltr,
+        child: Center(
+          child: MaterialButton(
+            padding: padding,
+            minWidth: minWidth,
+            height: height,
+            onPressed: null,
+            materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
+            child: child,
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame(minWidth: 8.0, height: 24.0));
+    expect(tester.getSize(find.byType(MaterialButton)), const Size(8.0, 24.0));
+
+    await tester.pumpWidget(buildFrame(minWidth: 8.0));
+    // Default minHeight constraint is 36, see RawMaterialButton.
+    expect(tester.getSize(find.byType(MaterialButton)), const Size(8.0, 36.0));
+
+    await tester.pumpWidget(buildFrame(height: 8.0));
+    // Default minWidth constraint is 88, see RawMaterialButton.
+    expect(tester.getSize(find.byType(MaterialButton)), const Size(88.0, 8.0));
+
+    await tester.pumpWidget(buildFrame());
+    expect(tester.getSize(find.byType(MaterialButton)), const Size(88.0, 36.0));
+
+    await tester.pumpWidget(buildFrame(padding: const EdgeInsets.all(4.0)));
+    expect(tester.getSize(find.byType(MaterialButton)), const Size(88.0, 36.0));
+
+    // Size is defined by the padding.
+    await tester.pumpWidget(
+      buildFrame(
+        minWidth: 0.0,
+        height: 0.0,
+        padding: const EdgeInsets.all(4.0),
+      ),
+    );
+    expect(tester.getSize(find.byType(MaterialButton)), const Size(8.0, 8.0));
+
+    // Size is defined by the padded child.
+    await tester.pumpWidget(
+      buildFrame(
+        minWidth: 0.0,
+        height: 0.0,
+        padding: const EdgeInsets.all(4.0),
+        child: const SizedBox(width: 8.0, height: 8.0),
+      ),
+    );
+    expect(tester.getSize(find.byType(MaterialButton)), const Size(16.0, 16.0));
+
+    // Size is defined by the minWidth, height constraints.
+    await tester.pumpWidget(
+      buildFrame(
+        minWidth: 18.0,
+        height: 18.0,
+        padding: const EdgeInsets.all(4.0),
+        child: const SizedBox(width: 8.0, height: 8.0),
+      ),
+    );
+    expect(tester.getSize(find.byType(MaterialButton)), const Size(18.0, 18.0));
+  });
+
   testWidgets('MaterialButton size is configurable by ThemeData.materialTapTargetSize', (WidgetTester tester) async {
     final Key key1 = UniqueKey();
     await tester.pumpWidget(