ButtonStyle style side should default to shape.side (#69713)

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

@@ -229,7 +229,7 @@ class ElevatedButton extends ButtonStyleButton {
   ///   * `2 < textScaleFactor <= 3` - lerp(horizontal(8), horizontal(4))
   ///   * `3 < textScaleFactor` - horizontal(4)
   /// * `minimumSize` - Size(64, 36)
-  /// * `side` - BorderSide.none
+  /// * `side` - null
   /// * `shape` - RoundedRectangleBorder(borderRadius: BorderRadius.circular(4))
   /// * `mouseCursor`
   ///   * disabled - SystemMouseCursors.forbidden
@@ -246,6 +246,11 @@ class ElevatedButton extends ButtonStyleButton {
   ///   * `1 < textScaleFactor <= 2` - lerp(start(12) end(16), horizontal(8))
   ///   * `2 < textScaleFactor <= 3` - lerp(horizontal(8), horizontal(4))
   ///   * `3 < textScaleFactor` - horizontal(4)
+  ///
+  /// The default value for `side`, which defines the appearance of the button's
+  /// outline, is null. That means that the outline is defined by the button
+  /// shape's [OutlinedBorder.side]. Typically the default value of an
+  /// [OutlinedBorder]'s side is [BorderSide.none], so an outline is not drawn.
   @override
   ButtonStyle defaultStyleOf(BuildContext context) {
     final ThemeData theme = Theme.of(context);
@@ -267,7 +272,7 @@ class ElevatedButton extends ButtonStyleButton {
       textStyle: theme.textTheme.button,
       padding: scaledPadding,
       minimumSize: const Size(64, 36),
-      side: BorderSide.none,
+      side: null,
       shape: const RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(4))),
       enabledMouseCursor: SystemMouseCursors.click,
       disabledMouseCursor: SystemMouseCursors.forbidden,

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

@@ -217,7 +217,7 @@ class TextButton extends ButtonStyleButton {
   ///   * `2 < textScaleFactor <= 3` - lerp(horizontal(8), horizontal(4))
   ///   * `3 < textScaleFactor` - horizontal(4)
   /// * `minimumSize` - Size(64, 36)
-  /// * `side` - BorderSide.none
+  /// * `side` - null
   /// * `shape` - RoundedRectangleBorder(borderRadius: BorderRadius.circular(4))
   /// * `mouseCursor`
   ///   * disabled - SystemMouseCursors.forbidden
@@ -233,6 +233,11 @@ class TextButton extends ButtonStyleButton {
   ///   * `textScaleFactor <= 1` - all(8)
   ///   * `1 < textScaleFactor <= 2 `- lerp(all(8), horizontal(4))
   ///   * `2 < textScaleFactor` - horizontal(4)
+  ///
+  /// The default value for `side`, which defines the appearance of the button's
+  /// outline, is null. That means that the outline is defined by the button
+  /// shape's [OutlinedBorder.side]. Typically the default value of an
+  /// [OutlinedBorder]'s side is [BorderSide.none], so an outline is not drawn.
   @override
   ButtonStyle defaultStyleOf(BuildContext context) {
     final ThemeData theme = Theme.of(context);
@@ -254,7 +259,7 @@ class TextButton extends ButtonStyleButton {
       textStyle: theme.textTheme.button,
       padding: scaledPadding,
       minimumSize: const Size(64, 36),
-      side: BorderSide.none,
+      side: null,
       shape: const RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(4))),
       enabledMouseCursor: SystemMouseCursors.click,
       disabledMouseCursor: SystemMouseCursors.forbidden,

packages/flutter/test/material/elevated_button_test.dart

@@ -1011,6 +1011,31 @@ void main() {
     expect(physicalShape().elevation, 0);
     expect(physicalShape().color, disabledBackgroundColor);
   });
+
+  testWidgets('By default, ElevatedButton shape outline is defined by shape.side', (WidgetTester tester) async {
+    // This is a regression test for https://github.com/flutter/flutter/issues/69544
+
+    const Color borderColor = Color(0xff4caf50);
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData.from(colorScheme: const ColorScheme.light()),
+        home: Center(
+          child: ElevatedButton(
+            style: ElevatedButton.styleFrom(
+              shape: RoundedRectangleBorder(
+                borderRadius: BorderRadius.circular(16),
+                side: const BorderSide(width: 4, color: borderColor),
+              ),
+            ),
+            onPressed: () { },
+            child: const Text('button'),
+          ),
+        ),
+      ),
+    );
+
+    expect(find.byType(ElevatedButton), paints ..path(strokeWidth: 4) ..drrect(color: borderColor));
+  });
 }
 
 TextStyle _iconStyle(WidgetTester tester, IconData icon) {