Implement InputDecorationTheme copyWith, ==, hashCode (#36411)

* Implement InputDecorationTheme copyWith, ==, hashCode 

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

@@ -3547,6 +3547,121 @@ class InputDecorationTheme extends Diagnosticable {
   /// behavior of aligning the label with the center of the [TextField].
   final bool alignLabelWithHint;
 
+  /// Creates a copy of this object but with the given fields replaced with the
+  /// new values.
+  InputDecorationTheme copyWith({
+    TextStyle labelStyle,
+    TextStyle helperStyle,
+    TextStyle hintStyle,
+    TextStyle errorStyle,
+    int errorMaxLines,
+    bool hasFloatingPlaceholder,
+    bool isDense,
+    EdgeInsetsGeometry contentPadding,
+    bool isCollapsed,
+    TextStyle prefixStyle,
+    TextStyle suffixStyle,
+    TextStyle counterStyle,
+    bool filled,
+    Color fillColor,
+    Color focusColor,
+    Color hoverColor,
+    InputBorder errorBorder,
+    InputBorder focusedBorder,
+    InputBorder focusedErrorBorder,
+    InputBorder disabledBorder,
+    InputBorder enabledBorder,
+    InputBorder border,
+    bool alignLabelWithHint,
+  }) {
+    return InputDecorationTheme(
+      labelStyle: labelStyle ?? this.labelStyle,
+      helperStyle: helperStyle ?? this.helperStyle,
+      hintStyle: hintStyle ?? this.hintStyle,
+      errorStyle: errorStyle ?? this.errorStyle,
+      errorMaxLines: errorMaxLines ?? this.errorMaxLines,
+      hasFloatingPlaceholder: hasFloatingPlaceholder ?? this.hasFloatingPlaceholder,
+      isDense: isDense ?? this.isDense,
+      contentPadding: contentPadding ?? this.contentPadding,
+      isCollapsed: isCollapsed ?? this.isCollapsed,
+      prefixStyle: prefixStyle ?? this.prefixStyle,
+      suffixStyle: suffixStyle ?? this.suffixStyle,
+      counterStyle: counterStyle ?? this.counterStyle,
+      filled: filled ?? this.filled,
+      fillColor: fillColor ?? this.fillColor,
+      focusColor: focusColor ?? this.focusColor,
+      hoverColor: hoverColor ?? this.hoverColor,
+      errorBorder: errorBorder ?? this.errorBorder,
+      focusedBorder: focusedBorder ?? this.focusedBorder,
+      focusedErrorBorder: focusedErrorBorder ?? this.focusedErrorBorder,
+      disabledBorder: disabledBorder ?? this.disabledBorder,
+      enabledBorder: enabledBorder ?? this.enabledBorder,
+      border: border ?? this.border,
+      alignLabelWithHint: alignLabelWithHint ?? this.alignLabelWithHint,
+    );
+  }
+
+  @override
+  int get hashCode {
+    return hashList(<dynamic>[
+      labelStyle,
+      helperStyle,
+      hintStyle,
+      errorStyle,
+      errorMaxLines,
+      hasFloatingPlaceholder,
+      isDense,
+      contentPadding,
+      isCollapsed,
+      prefixStyle,
+      suffixStyle,
+      counterStyle,
+      filled,
+      fillColor,
+      focusColor,
+      hoverColor,
+      errorBorder,
+      focusedBorder,
+      focusedErrorBorder,
+      disabledBorder,
+      enabledBorder,
+      border,
+      alignLabelWithHint,
+    ]);
+  }
+
+  @override
+  bool operator==(Object other) {
+    if (identical(this, other))
+      return true;
+    if (other.runtimeType != runtimeType)
+      return false;
+    final InputDecorationTheme typedOther = other;
+    return typedOther.labelStyle == labelStyle
+        && typedOther.helperStyle == helperStyle
+        && typedOther.hintStyle == hintStyle
+        && typedOther.errorStyle == errorStyle
+        && typedOther.errorMaxLines == errorMaxLines
+        && typedOther.isDense == isDense
+        && typedOther.contentPadding == contentPadding
+        && typedOther.isCollapsed == isCollapsed
+        && typedOther.prefixStyle == prefixStyle
+        && typedOther.suffixStyle == suffixStyle
+        && typedOther.counterStyle == counterStyle
+        && typedOther.filled == filled
+        && typedOther.fillColor == fillColor
+        && typedOther.focusColor == focusColor
+        && typedOther.hoverColor == hoverColor
+        && typedOther.errorBorder == errorBorder
+        && typedOther.focusedBorder == focusedBorder
+        && typedOther.focusedErrorBorder == focusedErrorBorder
+        && typedOther.disabledBorder == disabledBorder
+        && typedOther.enabledBorder == enabledBorder
+        && typedOther.border == border
+        && typedOther.alignLabelWithHint == alignLabelWithHint
+        && typedOther.disabledBorder == disabledBorder;
+  }
+
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
     super.debugFillProperties(properties);

packages/flutter/test/material/input_decorator_test.dart

@@ -2424,6 +2424,27 @@ void main() {
     expect(getOpacity(tester, 'label'), 0.0);
   }, skip: isBrowser);
 
+  test('InputDecorationTheme copyWith, ==, hashCode basics', () {
+    expect(const InputDecorationTheme(), const InputDecorationTheme().copyWith());
+    expect(const InputDecorationTheme().hashCode, const InputDecorationTheme().copyWith().hashCode);
+  });
+
+  test('InputDecorationTheme copyWith correctly copies and replaces values', () {
+    const InputDecorationTheme original = InputDecorationTheme(
+      focusColor: Colors.orange,
+      fillColor: Colors.green,
+    );
+    final InputDecorationTheme copy = original.copyWith(
+      focusColor: Colors.yellow,
+      fillColor: Colors.blue,
+    );
+
+    expect(original.focusColor, Colors.orange);
+    expect(original.fillColor, Colors.green);
+    expect(copy.focusColor, Colors.yellow);
+    expect(copy.fillColor, Colors.blue);
+  });
+
   testWidgets('InputDecorationTheme outline border', (WidgetTester tester) async {
     await tester.pumpWidget(
       buildInputDecorator(