Updated IconButton.iconSize to get value from theme (#87643)

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

@@ -116,7 +116,7 @@ class IconButton extends StatelessWidget {
   /// or an [ImageIcon].
   const IconButton({
     Key? key,
-    this.iconSize = 24.0,
+    this.iconSize,
     this.visualDensity,
     this.padding = const EdgeInsets.all(8.0),
     this.alignment = Alignment.center,
@@ -135,8 +135,7 @@ class IconButton extends StatelessWidget {
     this.enableFeedback = true,
     this.constraints,
     required this.icon,
-  }) : assert(iconSize != null),
-       assert(padding != null),
+  }) : assert(padding != null),
        assert(alignment != null),
        assert(splashRadius == null || splashRadius > 0),
        assert(autofocus != null),
@@ -145,7 +144,8 @@ class IconButton extends StatelessWidget {
 
   /// The size of the icon inside the button.
   ///
-  /// This property must not be null. It defaults to 24.0.
+  /// If null, uses [IconThemeData.size]. If it is also null, the default size
+  /// is 24.0.
   ///
   /// The size given here is passed down to the widget in the [icon] property
   /// via an [IconTheme]. Setting the size here instead of in, for example, the
@@ -153,7 +153,7 @@ class IconButton extends StatelessWidget {
   /// fit the [Icon]. If you were to set the size of the [Icon] using
   /// [Icon.size] instead, then the [IconButton] would default to 24.0 and then
   /// the [Icon] itself would likely get clipped.
-  final double iconSize;
+  final double? iconSize;
 
   /// Defines how compact the icon button's layout will be.
   ///
@@ -319,19 +319,20 @@ class IconButton extends StatelessWidget {
       minHeight: _kMinButtonSize,
     );
     final BoxConstraints adjustedConstraints = effectiveVisualDensity.effectiveConstraints(unadjustedConstraints);
+    final double effectiveIconSize = iconSize ?? IconTheme.of(context).size ?? 24.0;
 
     Widget result = ConstrainedBox(
       constraints: adjustedConstraints,
       child: Padding(
         padding: padding,
         child: SizedBox(
-          height: iconSize,
-          width: iconSize,
+          height: effectiveIconSize,
+          width: effectiveIconSize,
           child: Align(
             alignment: alignment,
             child: IconTheme.merge(
               data: IconThemeData(
-                size: iconSize,
+                size: effectiveIconSize,
                 color: currentColor,
               ),
               child: icon,
@@ -364,7 +365,7 @@ class IconButton extends StatelessWidget {
         splashColor: splashColor ?? theme.splashColor,
         radius: splashRadius ?? math.max(
           Material.defaultSplashRadius,
-          (iconSize + math.min(padding.horizontal, padding.vertical)) * 0.7,
+          (effectiveIconSize + math.min(padding.horizontal, padding.vertical)) * 0.7,
           // x 0.5 for diameter -> radius and + 40% overflow derived from other Material apps.
         ),
         child: result,

packages/flutter/test/material/icon_button_test.dart

@@ -75,6 +75,119 @@ void main() {
     expect(iconButton.size, const Size(70.0, 70.0));
   });
 
+  testWidgets('when both iconSize and IconTheme.of(context).size are null, size falls back to 24.0', (WidgetTester tester) async {
+    final FocusNode focusNode = FocusNode(debugLabel: 'Ink Focus');
+    await tester.pumpWidget(
+      wrap(
+          child: IconTheme(
+            data: const IconThemeData(size: null),
+            child: IconButton(
+              focusNode: focusNode,
+              onPressed: mockOnPressedFunction.handler,
+              icon: const Icon(Icons.link),
+            ),
+          )
+      ),
+    );
+
+    final RenderBox icon = tester.renderObject(find.byType(Icon));
+    expect(icon.size, const Size(24.0, 24.0));
+  });
+
+  testWidgets('when null, iconSize is overridden by closest IconTheme', (WidgetTester tester) async {
+    RenderBox icon;
+
+    await tester.pumpWidget(
+      wrap(
+        child: IconTheme(
+          data: const IconThemeData(size: 10),
+          child: IconButton(
+            onPressed: mockOnPressedFunction.handler,
+            icon: const Icon(Icons.link),
+          ),
+        )
+      ),
+    );
+
+    icon = tester.renderObject(find.byType(Icon));
+    expect(icon.size, const Size(10.0, 10.0));
+
+    await tester.pumpWidget(
+      wrap(
+          child: Theme(
+            data: ThemeData(
+              iconTheme: const IconThemeData(size: 10),
+            ),
+            child: IconButton(
+              onPressed: mockOnPressedFunction.handler,
+              icon: const Icon(Icons.link),
+            ),
+          )
+      ),
+    );
+
+    icon = tester.renderObject(find.byType(Icon));
+    expect(icon.size, const Size(10.0, 10.0));
+
+    await tester.pumpWidget(
+      wrap(
+          child: Theme(
+            data: ThemeData(
+              iconTheme: const IconThemeData(size: 20),
+            ),
+            child: IconTheme(
+              data: const IconThemeData(size: 10),
+              child: IconButton(
+                onPressed: mockOnPressedFunction.handler,
+                icon: const Icon(Icons.link),
+              ),
+            ),
+          )
+      ),
+    );
+
+    icon = tester.renderObject(find.byType(Icon));
+    expect(icon.size, const Size(10.0, 10.0));
+
+    await tester.pumpWidget(
+      wrap(
+          child: IconTheme(
+            data: const IconThemeData(size: 20),
+            child: Theme(
+              data: ThemeData(
+                iconTheme: const IconThemeData(size: 10),
+              ),
+              child: IconButton(
+                onPressed: mockOnPressedFunction.handler,
+                icon: const Icon(Icons.link),
+              ),
+            ),
+          )
+      ),
+    );
+
+    icon = tester.renderObject(find.byType(Icon));
+    expect(icon.size, const Size(10.0, 10.0));
+  });
+
+  testWidgets('when non-null, iconSize precedes IconTheme.of(context).size', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      wrap(
+          child: IconTheme(
+            data: const IconThemeData(size: 30.0),
+            child: IconButton(
+              iconSize: 10.0,
+              onPressed: mockOnPressedFunction.handler,
+              icon: const Icon(Icons.link),
+            ),
+          )
+      ),
+    );
+
+    final RenderBox icon = tester.renderObject(find.byType(Icon));
+    expect(icon.size, const Size(10.0, 10.0));
+  });
+
   testWidgets('Small icons with non-null constraints can be <48dp', (WidgetTester tester) async {
     await tester.pumpWidget(
       wrap(