Add support for fill, weight, grade, and optical size to `Icon` (#106896)

* wip

* update documentation

* x

* remove trailing spaces

* x

* remove useless CupertinoIconThemeData copyWith override

* add tests

* remove trailing spaces

* fix isConcrete

* x

* x

* x

* remove trailing spaces

* tweak docs

* mention that font filenames often indicate the supported axes

* add back cupertino IconThemeData copyWith

* update copyWith

packages/flutter/lib/src/cupertino/icon_theme_data.dart

@@ -10,13 +10,14 @@ import 'colors.dart';
 /// using [IconTheme.of].
 class CupertinoIconThemeData extends IconThemeData with Diagnosticable {
   /// Creates a [CupertinoIconThemeData].
-  ///
-  /// The opacity applies to both explicit and default icon colors. The value
-  /// is clamped between 0.0 and 1.0.
   const CupertinoIconThemeData({
+    super.size,
+    super.fill,
+    super.weight,
+    super.grade,
+    super.opticalSize,
     super.color,
     super.opacity,
-    super.size,
     super.shadows,
   });
 
@@ -30,11 +31,24 @@ class CupertinoIconThemeData extends IconThemeData with Diagnosticable {
   /// Creates a copy of this icon theme but with the given fields replaced with
   /// the new values.
   @override
-  CupertinoIconThemeData copyWith({ Color? color, double? opacity, double? size, List<Shadow>? shadows }) {
+  CupertinoIconThemeData copyWith({
+    double? size,
+    double? fill,
+    double? weight,
+    double? grade,
+    double? opticalSize,
+    Color? color,
+    double? opacity,
+    List<Shadow>? shadows,
+  }) {
     return CupertinoIconThemeData(
+      size: size ?? this.size,
+      fill: fill ?? this.fill,
+      weight: weight ?? this.weight,
+      grade: grade ?? this.grade,
+      opticalSize: opticalSize ?? this.opticalSize,
       color: color ?? this.color,
       opacity: opacity ?? this.opacity,
-      size: size ?? this.size,
       shadows: shadows ?? this.shadows,
     );
   }

packages/flutter/lib/src/widgets/icon.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui';
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 
@@ -61,22 +63,26 @@ import 'icon_theme_data.dart';
 /// See also:
 ///
 ///  * [IconButton], for interactive icons.
-///  * [Icons], the library of Material Icons available for use with this class.
+///  * [Icons], for the list of available Material Icons for use with this class.
 ///  * [IconTheme], which provides ambient configuration for icons.
 ///  * [ImageIcon], for showing icons from [AssetImage]s or other [ImageProvider]s.
 class Icon extends StatelessWidget {
   /// Creates an icon.
-  ///
-  /// The [size] and [color] default to the value given by the current [IconTheme].
   const Icon(
     this.icon, {
     super.key,
     this.size,
+    this.fill,
+    this.weight,
+    this.grade,
+    this.opticalSize,
     this.color,
+    this.shadows,
     this.semanticLabel,
     this.textDirection,
-    this.shadows,
-  });
+  }) : assert(fill == null || (0.0 <= fill && fill <= 1.0)),
+       assert(weight == null || (0.0 < weight)),
+       assert(opticalSize == null || (0.0 < opticalSize));
 
   /// The icon to display. The available icons are described in [Icons].
   ///
@@ -88,9 +94,7 @@ class Icon extends StatelessWidget {
   ///
   /// Icons occupy a square with width and height equal to size.
   ///
-  /// Defaults to the current [IconTheme] size, if any. If there is no
-  /// [IconTheme], or it does not specify an explicit size, then it defaults to
-  /// 24.0.
+  /// Defaults to the nearest [IconTheme]'s [IconThemeData.size].
   ///
   /// If this [Icon] is being placed inside an [IconButton], then use
   /// [IconButton.iconSize] instead, so that the [IconButton] can make the splash
@@ -98,23 +102,87 @@ class Icon extends StatelessWidget {
   /// pass down the size to the [Icon].
   final double? size;
 
-  /// The color to use when drawing the icon.
+  /// The fill for drawing the icon.
   ///
-  /// Defaults to the current [IconTheme] color, if any.
+  /// Requires the underlying icon font to support the `FILL` [FontVariation]
+  /// axis, otherwise has no effect. Variable font filenames often indicate
+  /// the supported axes. Must be between 0.0 (unfilled) and 1.0 (filled),
+  /// inclusive.
   ///
-  /// The color (whether specified explicitly here or obtained from the
-  /// [IconTheme]) will be further adjusted by the opacity of the current
-  /// [IconTheme], if any.
+  /// Can be used to convey a state transition for animation or interaction.
+  ///
+  /// Defaults to nearest [IconTheme]'s [IconThemeData.fill].
+  ///
+  /// See also:
+  ///  * [weight], for controlling stroke weight.
+  ///  * [grade], for controlling stroke weight in a more granular way.
+  ///  * [opticalSize], for controlling optical size.
+  final double? fill;
+
+  /// The stroke weight for drawing the icon.
+  ///
+  /// Requires the underlying icon font to support the `wght` [FontVariation]
+  /// axis, otherwise has no effect. Variable font filenames often indicate
+  /// the supported axes. Must be greater than 0.
+  ///
+  /// Defaults to nearest [IconTheme]'s [IconThemeData.weight].
+  ///
+  /// See also:
+  ///  * [fill], for controlling fill.
+  ///  * [grade], for controlling stroke weight in a more granular way.
+  ///  * [opticalSize], for controlling optical size.
+  ///  * https://fonts.google.com/knowledge/glossary/weight_axis
+  final double? weight;
+
+  /// The grade (granular stroke weight) for drawing the icon.
+  ///
+  /// Requires the underlying icon font to support the `GRAD` [FontVariation]
+  /// axis, otherwise has no effect. Variable font filenames often indicate
+  /// the supported axes. Can be negative.
+  ///
+  /// Grade and [weight] both affect a symbol's stroke weight (thickness), but
+  /// grade has a smaller impact on the size of the symbol.
+  ///
+  /// Grade is also available in some text fonts. One can match grade levels
+  /// between text and symbols for a harmonious visual effect. For example, if
+  /// the text font has a -25 grade value, the symbols can match it with a
+  /// suitable value, say -25.
+  ///
+  /// Defaults to nearest [IconTheme]'s [IconThemeData.grade].
+  ///
+  /// See also:
+  ///  * [fill], for controlling fill.
+  ///  * [weight], for controlling stroke weight in a less granular way.
+  ///  * [opticalSize], for controlling optical size.
+  ///  * https://fonts.google.com/knowledge/glossary/grade_axis
+  final double? grade;
+
+  /// The optical size for drawing the icon.
+  ///
+  /// Requires the underlying icon font to support the `opsz` [FontVariation]
+  /// axis, otherwise has no effect. Variable font filenames often indicate
+  /// the supported axes. Must be greater than 0.
+  ///
+  /// For an icon to look the same at different sizes, the stroke weight
+  /// (thickness) must change as the icon size scales. Optical size offers a way
+  /// to automatically adjust the stroke weight as icon size changes.
+  ///
+  /// Defaults to nearest [IconTheme]'s [IconThemeData.opticalSize].
   ///
-  /// In material apps, if there is a [Theme] without any [IconTheme]s
-  /// specified, icon colors default to white if the theme is dark
-  /// and black if the theme is light.
+  /// See also:
+  ///  * [fill], for controlling fill.
+  ///  * [weight], for controlling stroke weight.
+  ///  * [grade], for controlling stroke weight in a more granular way.
+  ///  * https://fonts.google.com/knowledge/glossary/optical_size_axis
+  final double? opticalSize;
+
+  /// The color to use when drawing the icon.
   ///
-  /// If no [IconTheme] and no [Theme] is specified, icons will default to
-  /// black.
+  /// Defaults to the nearest [IconTheme]'s [IconThemeData.color].
   ///
-  /// See [Theme] to set the current theme and [ThemeData.brightness]
-  /// for setting the current theme's brightness.
+  /// The color (whether specified explicitly here or obtained from the
+  /// [IconTheme]) will be further adjusted by the nearest [IconTheme]'s
+  /// [IconThemeData.opacity].
   ///
   /// {@tool snippet}
   /// Typically, a Material Design color will be used, as follows:
@@ -128,6 +196,17 @@ class Icon extends StatelessWidget {
   /// {@end-tool}
   final Color? color;
 
+  /// A list of [Shadow]s that will be painted underneath the icon.
+  ///
+  /// Multiple shadows are supported to replicate lighting from multiple light
+  /// sources.
+  ///
+  /// Shadows must be in the same order for [Icon] to be considered as
+  /// equivalent as order produces differing transparency.
+  ///
+  /// Defaults to the nearest [IconTheme]'s [IconThemeData.shadows].
+  final List<Shadow>? shadows;
+
   /// Semantic label for the icon.
   ///
   /// Announced in accessibility modes (e.g TalkBack/VoiceOver).
@@ -152,15 +231,6 @@ class Icon extends StatelessWidget {
   /// specified, either directly using this property or using [Directionality].
   final TextDirection? textDirection;
 
-  /// A list of [Shadow]s that will be painted underneath the icon.
-  ///
-  /// Multiple shadows are supported to replicate lighting from multiple light
-  /// sources.
-  ///
-  /// Shadows must be in the same order for [Icon] to be considered as
-  /// equivalent as order produces differing transparency.
-  final List<Shadow>? shadows;
-
   @override
   Widget build(BuildContext context) {
     assert(this.textDirection != null || debugCheckHasDirectionality(context));
@@ -191,6 +261,12 @@ class Icon extends StatelessWidget {
       text: TextSpan(
         text: String.fromCharCode(icon!.codePoint),
         style: TextStyle(
+          fontVariations: <FontVariation>[
+            if (fill != null) FontVariation('FILL', fill!),
+            if (weight != null) FontVariation('wght', weight!),
+            if (grade != null) FontVariation('GRAD', grade!),
+            if (opticalSize != null) FontVariation('opsz', opticalSize!),
+          ],
           inherit: false,
           color: iconColor,
           fontSize: iconSize,
@@ -235,7 +311,13 @@ class Icon extends StatelessWidget {
     super.debugFillProperties(properties);
     properties.add(IconDataProperty('icon', icon, ifNull: '<empty>', showName: false));
     properties.add(DoubleProperty('size', size, defaultValue: null));
+    properties.add(DoubleProperty('fill', fill, defaultValue: null));
+    properties.add(DoubleProperty('weight', weight, defaultValue: null));
+    properties.add(DoubleProperty('grade', grade, defaultValue: null));
+    properties.add(DoubleProperty('opticalSize', opticalSize, defaultValue: null));
     properties.add(ColorProperty('color', color, defaultValue: null));
     properties.add(IterableProperty<Shadow>('shadows', shadows, defaultValue: null));
+    properties.add(StringProperty('semanticLabel', semanticLabel, defaultValue: null));
+    properties.add(EnumProperty<TextDirection>('textDirection', textDirection, defaultValue: null));
   }
 }

packages/flutter/lib/src/widgets/icon_theme.dart

@@ -9,12 +9,11 @@ import 'framework.dart';
 import 'icon_theme_data.dart';
 import 'inherited_theme.dart';
 
-/// Controls the default color, opacity, and size of icons in a widget subtree.
+/// Controls the default properties of icons in a widget subtree.
 ///
 /// The icon theme is honored by [Icon] and [ImageIcon] widgets.
 class IconTheme extends InheritedTheme {
-  /// Creates an icon theme that controls the color, opacity, and size of
-  /// descendant widgets.
+  /// Creates an icon theme that controls properties of descendant widgets.
   ///
   /// Both [data] and [child] arguments must not be null.
   const IconTheme({
@@ -24,7 +23,7 @@ class IconTheme extends InheritedTheme {
   }) : assert(data != null),
        assert(child != null);
 
-  /// Creates an icon theme that controls the color, opacity, and size of
+  /// Creates an icon theme that controls the properties of
   /// descendant widgets, and merges in the current icon theme, if any.
   ///
   /// The [data] and [child] arguments must not be null.
@@ -44,7 +43,7 @@ class IconTheme extends InheritedTheme {
     );
   }
 
-  /// The color, opacity, and size to use for icons in this subtree.
+  /// The set of properties to use for icons in this subtree.
   final IconThemeData data;
 
   /// The data from the closest instance of this class that encloses the given
@@ -72,6 +71,10 @@ class IconTheme extends InheritedTheme {
       ? iconThemeData
       : iconThemeData.copyWith(
         size: iconThemeData.size ?? const IconThemeData.fallback().size,
+        fill: iconThemeData.fill ?? const IconThemeData.fallback().fill,
+        weight: iconThemeData.weight ?? const IconThemeData.fallback().weight,
+        grade: iconThemeData.grade ?? const IconThemeData.fallback().grade,
+        opticalSize: iconThemeData.opticalSize ?? const IconThemeData.fallback().opticalSize,
         color: iconThemeData.color ?? const IconThemeData.fallback().color,
         opacity: iconThemeData.opacity ?? const IconThemeData.fallback().opacity,
         shadows: iconThemeData.shadows ?? const IconThemeData.fallback().shadows,

packages/flutter/lib/src/widgets/icon_theme_data.dart

@@ -9,38 +9,67 @@ import 'package:flutter/painting.dart';
 
 import 'framework.dart' show BuildContext;
 
-/// Defines the color, opacity, and size of icons.
+/// Defines the size, font variations, color, opacity, and shadows of icons.
 ///
-/// Used by [IconTheme] to control the color, opacity, and size of icons in a
-/// widget subtree.
+/// Used by [IconTheme] to control those properties in a widget subtree.
 ///
 /// To obtain the current icon theme, use [IconTheme.of]. To convert an icon
-/// theme to a version with all the fields filled in, use [
-/// IconThemeData.fallback].
+/// theme to a version with all the fields filled in, use
+/// [IconThemeData.fallback].
 @immutable
 class IconThemeData with Diagnosticable {
   /// Creates an icon theme data.
   ///
   /// The opacity applies to both explicit and default icon colors. The value
   /// is clamped between 0.0 and 1.0.
-  const IconThemeData({this.color, double? opacity, this.size, this.shadows}) : _opacity = opacity;
+  const IconThemeData({
+    this.size,
+    this.fill,
+    this.weight,
+    this.grade,
+    this.opticalSize,
+    this.color,
+    double? opacity,
+    this.shadows,
+  }) : _opacity = opacity,
+       assert(fill == null || (0.0 <= fill && fill <= 1.0)),
+       assert(weight == null || (0.0 < weight)),
+       assert(opticalSize == null || (0.0 < opticalSize));
 
   /// Creates an icon theme with some reasonable default values.
   ///
-  /// The [color] is black, the [opacity] is 1.0, and the [size] is 24.0.
+  /// The [size] is 24.0, [fill] is 0.0, [weight] is 400.0, [grade] is 0.0,
+  /// opticalSize is 48.0, [color] is black, and [opacity] is 1.0.
   const IconThemeData.fallback()
-      : color = const Color(0xFF000000),
+      : size = 24.0,
+        fill = 0.0,
+        weight = 400.0,
+        grade = 0.0,
+        opticalSize = 48.0,
+        color = const Color(0xFF000000),
         _opacity = 1.0,
-        size = 24.0,
         shadows = null;
 
   /// Creates a copy of this icon theme but with the given fields replaced with
   /// the new values.
-  IconThemeData copyWith({Color? color, double? opacity, double? size, List<Shadow>? shadows}) {
+  IconThemeData copyWith({
+    double? size,
+    double? fill,
+    double? weight,
+    double? grade,
+    double? opticalSize,
+    Color? color,
+    double? opacity,
+    List<Shadow>? shadows,
+  }) {
     return IconThemeData(
+      size: size ?? this.size,
+      fill: fill ?? this.fill,
+      weight: weight ?? this.weight,
+      grade: grade ?? this.grade,
+      opticalSize: opticalSize ?? this.opticalSize,
       color: color ?? this.color,
       opacity: opacity ?? this.opacity,
-      size: size ?? this.size,
       shadows: shadows ?? this.shadows,
     );
   }
@@ -53,9 +82,13 @@ class IconThemeData with Diagnosticable {
       return this;
     }
     return copyWith(
+      size: other.size,
+      fill: other.fill,
+      weight: other.weight,
+      grade: other.grade,
+      opticalSize: other.opticalSize,
       color: other.color,
       opacity: other.opacity,
-      size: other.size,
       shadows: other.shadows,
     );
   }
@@ -78,20 +111,56 @@ class IconThemeData with Diagnosticable {
   ///    the color of [CupertinoIconThemeData] before returning.
   IconThemeData resolve(BuildContext context) => this;
 
-  /// Whether all the properties of this object are non-null.
-  bool get isConcrete => color != null && opacity != null && size != null;
+  /// Whether all the properties (except shadows) of this object are non-null.
+  bool get isConcrete => size != null
+    && fill != null
+    && weight != null
+    && grade != null
+    && opticalSize != null
+    && color != null
+    && opacity != null;
+
+  /// The default for [Icon.size].
+  ///
+  /// Falls back to 24.0.
+  final double? size;
+
+  /// The default for [Icon.fill].
+  ///
+  /// Falls back to 0.0.
+  final double? fill;
+
+  /// The default for [Icon.weight].
+  ///
+  /// Falls back to 400.0.
+  final double? weight;
+
+  /// The default for [Icon.grade].
+  ///
+  /// Falls back to 0.0.
+  final double? grade;
+
+  /// The default for [Icon.opticalSize].
+  ///
+  /// Falls back to 48.0.
+  final double? opticalSize;
 
-  /// The default color for icons.
+  /// The default for [Icon.color].
+  ///
+  /// In material apps, if there is a [Theme] without any [IconTheme]s
+  /// specified, icon colors default to white if [ThemeData.brightness] is dark
+  /// and black if [ThemeData.brightness] is light.
+  ///
+  /// Otherwise, falls back to black.
   final Color? color;
 
   /// An opacity to apply to both explicit and default icon colors.
+  ///
+  /// Falls back to 1.0.
   double? get opacity => _opacity == null ? null : clampDouble(_opacity!, 0.0, 1.0);
   final double? _opacity;
 
-  /// The default size for icons.
-  final double? size;
-
-  /// The default shadow for icons.
+  /// The default for [Icon.shadows].
   final List<Shadow>? shadows;
 
   /// Linearly interpolate between two icon theme data objects.
@@ -100,9 +169,13 @@ class IconThemeData with Diagnosticable {
   static IconThemeData lerp(IconThemeData? a, IconThemeData? b, double t) {
     assert(t != null);
     return IconThemeData(
+      size: ui.lerpDouble(a?.size, b?.size, t),
+      fill: ui.lerpDouble(a?.fill, b?.fill, t),
+      weight: ui.lerpDouble(a?.weight, b?.weight, t),
+      grade: ui.lerpDouble(a?.grade, b?.grade, t),
+      opticalSize: ui.lerpDouble(a?.opticalSize, b?.opticalSize, t),
       color: Color.lerp(a?.color, b?.color, t),
       opacity: ui.lerpDouble(a?.opacity, b?.opacity, t),
-      size: ui.lerpDouble(a?.size, b?.size, t),
       shadows: Shadow.lerpList(a?.shadows, b?.shadows, t),
     );
   }
@@ -113,26 +186,38 @@ class IconThemeData with Diagnosticable {
       return false;
     }
     return other is IconThemeData
+        && other.size == size
+        && other.fill == fill
+        && other.weight == weight
+        && other.grade == grade
+        && other.opticalSize == opticalSize
         && other.color == color
         && other.opacity == opacity
-        && other.size == size
         && listEquals(other.shadows, shadows);
   }
 
   @override
   int get hashCode => Object.hash(
+    size,
+    fill,
+    weight,
+    grade,
+    opticalSize,
     color,
     opacity,
-    size,
     shadows == null ? null : Object.hashAll(shadows!),
   );
 
   @override
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
     super.debugFillProperties(properties);
+    properties.add(DoubleProperty('size', size, defaultValue: null));
+    properties.add(DoubleProperty('fill', fill, defaultValue: null));
+    properties.add(DoubleProperty('weight', weight, defaultValue: null));
+    properties.add(DoubleProperty('grade', grade, defaultValue: null));
+    properties.add(DoubleProperty('opticalSize', opticalSize, defaultValue: null));
     properties.add(ColorProperty('color', color, defaultValue: null));
     properties.add(DoubleProperty('opacity', opacity, defaultValue: null));
-    properties.add(DoubleProperty('size', size, defaultValue: null));
     properties.add(IterableProperty<Shadow>('shadows', shadows, defaultValue: null));
   }
 }

packages/flutter/test/cupertino/icon_theme_data_test.dart

@@ -7,7 +7,15 @@ import 'package:flutter_test/flutter_test.dart';
 
 void main() {
   testWidgets('IconTheme.of works', (WidgetTester tester) async {
-    const IconThemeData data = IconThemeData(color: Color(0xAAAAAAAA), opacity: 0.5, size: 16.0);
+    const IconThemeData data = IconThemeData(
+      size: 16.0,
+      fill: 0.0,
+      weight: 400.0,
+      grade: 0.0,
+      opticalSize: 48.0,
+      color: Color(0xAAAAAAAA),
+      opacity: 0.5
+    );
 
     late IconThemeData retrieved;
     await tester.pumpWidget(

packages/flutter/test/widgets/icon_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui';
+
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -207,4 +209,42 @@ void main() {
     expect(const IconData(123).hashCode, isNot(const IconData(123, fontPackage: 'p').hashCode));
     expect(const IconData(123).toString(), 'IconData(U+0007B)');
   });
+
+
+  testWidgets('Fill, weight, grade, and optical size variations are passed', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const Directionality(
+        textDirection: TextDirection.ltr,
+        child: Icon(Icons.abc),
+      ),
+    );
+
+    RichText text = tester.widget(find.byType(RichText));
+    expect(text.text.style!.fontVariations, <FontVariation>[]);
+
+    await tester.pumpWidget(
+      const Directionality(
+        textDirection: TextDirection.ltr,
+        child: Icon(Icons.abc, fill: 0.5, weight: 300, grade: 200, opticalSize: 48),
+      ),
+    );
+
+    text = tester.widget(find.byType(RichText));
+    expect(text.text.style!.fontVariations, isNotNull);
+    expect(text.text.style!.fontVariations, <FontVariation>[
+      const FontVariation('FILL', 0.5),
+      const FontVariation('wght', 300.0),
+      const FontVariation('GRAD', 200.0),
+      const FontVariation('opsz', 48.0)
+    ]);
+  });
+
+  test('Throws if given invalid values', () {
+    expect(() => Icon(Icons.abc, fill: -0.1), throwsAssertionError);
+    expect(() => Icon(Icons.abc, fill: 1.1), throwsAssertionError);
+    expect(() => Icon(Icons.abc, weight: -0.1), throwsAssertionError);
+    expect(() => Icon(Icons.abc, weight: 0.0), throwsAssertionError);
+    expect(() => Icon(Icons.abc, opticalSize: -0.1), throwsAssertionError);
+    expect(() => Icon(Icons.abc, opticalSize: 0), throwsAssertionError);
+  });
 }

packages/flutter/test/widgets/icon_theme_data_test.dart

@@ -7,44 +7,89 @@ import 'package:flutter_test/flutter_test.dart';
 
 void main() {
   test('IconThemeData control test', () {
-    const IconThemeData data = IconThemeData(color: Color(0xAAAAAAAA), opacity: 0.5, size: 16.0, shadows: <Shadow>[Shadow(color: Color(0xAAAAAAAA), blurRadius: 1.0, offset: Offset(1.0, 1.0))]);
-
+    const IconThemeData data = IconThemeData(
+      size: 16.0,
+      fill: 0.5,
+      weight: 600,
+      grade: 25,
+      opticalSize: 45,
+      color: Color(0xAAAAAAAA),
+      opacity: 0.5,
+      shadows: <Shadow>[Shadow(color: Color(0xAAAAAAAA), blurRadius: 1.0, offset: Offset(1.0, 1.0))],
+    );
     expect(data, hasOneLineDescription);
     expect(data, equals(data.copyWith()));
     expect(data.hashCode, equals(data.copyWith().hashCode));
 
     final IconThemeData lerped = IconThemeData.lerp(data, const IconThemeData.fallback(), 0.25);
+    expect(lerped.size, 18.0);
+    expect(lerped.fill, 0.375);
+    expect(lerped.weight, 550.0);
+    expect(lerped.grade, 18.75);
+    expect(lerped.opticalSize, 45.75);
     expect(lerped.color, const Color(0xBF7F7F7F));
     expect(lerped.opacity, 0.625);
-    expect(lerped.size, 18.0);
     expect(lerped.shadows, const <Shadow>[Shadow(color: Color(0xAAAAAAAA), blurRadius: 0.75, offset: Offset(0.75, 0.75))]);
   });
 
-  test('IconThemeData lerp with first null', () {
-    const IconThemeData data = IconThemeData(color: Color(0xFFFFFFFF), opacity: 1.0, size: 16.0, shadows: <Shadow>[Shadow(color: Color(0xFFFFFFFF), blurRadius: 1.0, offset: Offset(1.0, 1.0))]);
+  group('IconThemeData lerp', () {
+    const IconThemeData data = IconThemeData(
+      size: 16.0,
+      fill: 0.5,
+      weight: 600,
+      grade: 25,
+      opticalSize: 45,
+      color: Color(0xFFFFFFFF),
+      opacity: 1.0,
+      shadows: <Shadow>[Shadow(color: Color(0xFFFFFFFF), blurRadius: 1.0, offset: Offset(1.0, 1.0))],
+    );
 
-    final IconThemeData lerped = IconThemeData.lerp(null, data, 0.25);
-    expect(lerped.color, const Color(0x40FFFFFF));
-    expect(lerped.opacity, 0.25);
-    expect(lerped.size, 4.0);
-    expect(lerped.shadows, const <Shadow>[Shadow(color: Color(0xFFFFFFFF), blurRadius: 0.25, offset: Offset(0.25, 0.25))]);
-  });
+    test('with first null', () {
+      final IconThemeData lerped = IconThemeData.lerp(null, data, 0.25);
+
+      expect(lerped.size, 4.0);
+      expect(lerped.fill, 0.125);
+      expect(lerped.weight, 150.0);
+      expect(lerped.grade, 6.25);
+      expect(lerped.opticalSize, 11.25);
+      expect(lerped.color, const Color(0x40FFFFFF));
+      expect(lerped.opacity, 0.25);
+      expect(lerped.shadows, const <Shadow>[Shadow(color: Color(0xFFFFFFFF), blurRadius: 0.25, offset: Offset(0.25, 0.25))]);
+    });
+
+    test('with second null', () {
+      final IconThemeData lerped = IconThemeData.lerp(data, null, 0.25);
+
+      expect(lerped.size, 12.0);
+      expect(lerped.fill, 0.375);
+      expect(lerped.weight, 450.0);
+      expect(lerped.grade, 18.75);
+      expect(lerped.opticalSize, 33.75);
+      expect(lerped.color, const Color(0xBFFFFFFF));
+      expect(lerped.opacity, 0.75);
+      expect(lerped.shadows, const <Shadow>[Shadow(color: Color(0xFFFFFFFF), blurRadius: 0.75, offset: Offset(0.75, 0.75))]);
+    });
 
-  test('IconThemeData lerp with second null', () {
-    const IconThemeData data = IconThemeData(color: Color(0xFFFFFFFF), opacity: 1.0, size: 16.0, shadows: <Shadow>[Shadow(color: Color(0xFFFFFFFF), blurRadius: 1.0, offset: Offset(1.0, 1.0))]);
+    test('with both null', () {
+      final IconThemeData lerped = IconThemeData.lerp(null, null, 0.25);
 
-    final IconThemeData lerped = IconThemeData.lerp(data, null, 0.25);
-    expect(lerped.color, const Color(0xBFFFFFFF));
-    expect(lerped.opacity, 0.75);
-    expect(lerped.size, 12.0);
-    expect(lerped.shadows, const <Shadow>[Shadow(color: Color(0xFFFFFFFF), blurRadius: 0.75, offset: Offset(0.75, 0.75))]);
+      expect(lerped.size, null);
+      expect(lerped.fill, null);
+      expect(lerped.weight, null);
+      expect(lerped.grade, null);
+      expect(lerped.opticalSize, null);
+      expect(lerped.color, null);
+      expect(lerped.opacity, null);
+      expect(lerped.shadows, null);
+    });
   });
 
-  test('IconThemeData lerp with both null', () {
-    final IconThemeData lerped = IconThemeData.lerp(null, null, 0.25);
-    expect(lerped.color, null);
-    expect(lerped.opacity, null);
-    expect(lerped.size, null);
-    expect(lerped.shadows, null);
+  test('Throws if given invalid values', () {
+    expect(() => IconThemeData(fill: -0.1), throwsAssertionError);
+    expect(() => IconThemeData(fill: 1.1), throwsAssertionError);
+    expect(() => IconThemeData(weight: -0.1), throwsAssertionError);
+    expect(() => IconThemeData(weight: 0.0), throwsAssertionError);
+    expect(() => IconThemeData(opticalSize: -0.1), throwsAssertionError);
+    expect(() => IconThemeData(opticalSize: 0), throwsAssertionError);
   });
 }