refactor(material/button): clean up fab tokens (#27994)

Reworks the tokens setup for the FAB by:
* Introducing a custom tokens map. It was necessary both for these changes and will come in handy later for the ripples.
* Using tokens specifically for the disabled state instead of passing in the non-disabled ones. This aligns the FAB with the rest of the library and allows us to reduce the specificity.
* Introducing a tokens specifically for the icon/text color. Currently we have an ad-hoc variable declared directly in the component styles.
* Using our own mixins for the elevation instead of MDC's. Our mixin calls into MDC eventually, but it has some safeguards as well.
* Generating the tokens that we pass into MDC's theme using our APIs, instead of creating the map directly.

(cherry picked from commit e9fc04d)

Author: crisbeto

src/material/button/_fab-theme.scss

@@ -9,6 +9,8 @@
 @use '../core/theming/inspection';
 @use '../core/tokens/m2/mdc/fab' as tokens-mdc-fab;
 @use '../core/tokens/m2/mdc/extended-fab' as tokens-mdc-extended-fab;
+@use '../core/tokens/m2/mat/fab' as tokens-mat-fab;
+@use '../core/tokens/token-utils';
 @use '../core/typography/typography';
 
 @mixin base($theme) {
@@ -21,37 +23,25 @@
   }
 }
 
-@mixin _fab-variant($foreground, $background) {
-  $color-tokens: (
-    container-color: $background,
-    icon-color: $foreground
+@mixin _fab-variant($theme, $palette) {
+  $mdc-tokens: if($palette,
+    tokens-mdc-fab.private-get-color-palette-color-tokens($theme, $palette),
+    tokens-mdc-fab.get-color-tokens($theme)
   );
-  @include mdc-fab-theme.theme($color-tokens);
 
-  --mat-mdc-fab-color: #{$foreground};
-}
+  $mat-tokens: if($palette,
+    tokens-mat-fab.private-get-color-palette-color-tokens($theme, $palette),
+    tokens-mat-fab.get-color-tokens($theme)
+  );
 
-@function white-or-black($color, $is-dark) {
-  @return if(mdc-helpers.variable-safe-contrast-tone($color, $is-dark) == 'dark', #000, #fff);
+  @include mdc-fab-theme.theme($mdc-tokens);
+  @include token-utils.create-token-values(tokens-mat-fab.$prefix, $mat-tokens);
 }
 
 @mixin color($theme) {
-  $is-dark: inspection.get-theme-type($theme) == dark;
-
-  $surface: inspection.get-theme-color($theme, background, card);
-  $primary: inspection.get-theme-color($theme, primary);
-  $accent: inspection.get-theme-color($theme, accent);
-  $warn: inspection.get-theme-color($theme, warn);
-
-  $on-surface: white-or-black($surface, $is-dark);
-  $on-primary: white-or-black($primary, $is-dark);
-  $on-accent: white-or-black($accent, $is-dark);
-  $on-warn: white-or-black($warn, $is-dark);
-
-  $disabled: rgba($on-surface, 0.12);
-  $on-disabled: rgba($on-surface, if($is-dark, 0.5, 0.38));
-
   @include sass-utils.current-selector-or-root() {
+    @include _fab-variant($theme, null);
+
     // TODO(wagnermaciel): The ripple-theme-styles mixin depends heavily on
     // being wrapped by using-mdc-theme. This workaround needs to be
     // revisited w/ a more holistic solution.
@@ -60,28 +50,18 @@
       @include mdc-helpers.using-mdc-theme($theme) {
         @include button-theme-private.ripple-theme-styles($theme, true);
       }
-    }
 
-    :disabled, a[disabled='true'] {
-      @include button-theme-private.apply-disabled-style() {
-        @include _fab-variant($on-disabled, $disabled);
+      &.mat-primary {
+        @include _fab-variant($theme, primary);
       }
-    }
-
-    .mat-unthemed {
-      @include _fab-variant($on-surface, $surface);
-    }
-
-    .mat-primary {
-      @include _fab-variant($on-primary, $primary);
-    }
 
-    .mat-accent {
-      @include _fab-variant($on-accent, $accent);
-    }
+      &.mat-accent {
+        @include _fab-variant($theme, accent);
+      }
 
-    .mat-warn {
-      @include _fab-variant($on-warn, $warn);
+      &.mat-warn {
+        @include _fab-variant($theme, warn);
+      }
     }
   }
 }

src/material/button/fab.scss

@@ -1,19 +1,21 @@
 @use '@material/fab' as mdc-fab;
 @use '@material/fab/extended-fab-theme' as mdc-extended-fab-theme;
 @use '@material/fab/fab-theme' as mdc-fab-theme;
-@use '@material/elevation/elevation-theme' as mdc-elevation-theme;
 @use '@material/theme/custom-properties' as mdc-custom-properties;
 
 @use './button-base';
+@use '../core/style/elevation';
 @use '../core/mdc-helpers/mdc-helpers';
+@use '../core/tokens/token-utils';
 @use '../core/style/private' as style-private;
 @use '../core/focus-indicators/private' as focus-indicators-private;
-@use '../core/tokens/m2/mdc/extended-fab' as m2-mdc-extended-fab;
-@use '../core/tokens/m2/mdc/fab' as m2-mdc-fab;
+@use '../core/tokens/m2/mdc/extended-fab' as tokens-mdc-extended-fab;
+@use '../core/tokens/m2/mdc/fab' as tokens-mdc-fab;
+@use '../core/tokens/m2/mat/fab' as tokens-mat-fab;
 
 @include mdc-custom-properties.configure($emit-fallback-values: false, $emit-fallback-vars: false) {
-  $mdc-fab-token-slots: m2-mdc-fab.get-token-slots();
-  $mdc-extended-fab-token-slots: m2-mdc-extended-fab.get-token-slots();
+  $mdc-fab-token-slots: tokens-mdc-fab.get-token-slots();
+  $mdc-extended-fab-token-slots: tokens-mdc-extended-fab.get-token-slots();
 
   // Add the MDC fab static styles.
   @include mdc-fab.static-styles();
@@ -34,33 +36,31 @@
   @include button-base.mat-private-button-interactive();
   @include button-base.mat-private-button-touch-target(true);
   @include style-private.private-animation-noop();
+  @include elevation.elevation(6);
+  flex-shrink: 0; // Prevent the button from shrinking since it's always supposed to be a circle.
 
   @include mdc-helpers.disable-mdc-fallback-declarations {
-    // TODO(crisbeto): the elevation can be controlled using `container-elevation` in `theme-styles`
-    // however when it is passed in, MDC throws an error that `container-shadow-color` isn't
-    // passed in. When `container-shadow-color` is passed in, MDC throws another error, because
-    // the produced value isn't valid CSS. Eventually we should switch to it once it's fixed.
-    @include mdc-elevation-theme.elevation(6);
-
-    &:hover, &:focus {
-      @include mdc-elevation-theme.elevation(8);
+    @include token-utils.use-tokens(tokens-mat-fab.$prefix, tokens-mat-fab.get-token-slots()) {
+      @include token-utils.create-token-slot(color, foreground-color, inherit);
     }
+  }
 
-    &:active, &:focus:active {
-      @include mdc-elevation-theme.elevation(12);
-    }
+  &:hover, &:focus {
+    @include elevation.elevation(8);
+  }
 
-    @include button-base.mat-private-button-disabled {
-      @include mdc-elevation-theme.elevation(0);
-    }
+  &:active, &:focus:active {
+    @include elevation.elevation(12);
   }
 
-  // TODO(crisbeto): `theme-styles` doesn't allow for the color to be controlled. Define a custom
-  // variable for now so we have something to target.
-  color: var(--mat-mdc-fab-color, inherit);
+  @include button-base.mat-private-button-disabled {
+    @include elevation.elevation(0);
 
-  // Prevent the button from shrinking since it's always supposed to be a circle.
-  flex-shrink: 0;
+    @include token-utils.use-tokens(tokens-mat-fab.$prefix, tokens-mat-fab.get-token-slots()) {
+      @include token-utils.create-token-slot(color, disabled-state-foreground-color);
+      @include token-utils.create-token-slot(background-color, disabled-state-container-color);
+    }
+  }
 
   // MDC adds some styles to fab and mini-fab that conflict with some of our focus indicator
   // styles and don't actually do anything. This undoes those conflicting styles.

src/material/core/tokens/m2/mat/_fab.scss

@@ -0,0 +1,57 @@
+@use '../../token-utils';
+@use '../../../theming/inspection';
+@use '../../../style/sass-utils';
+
+// The prefix used to generate the fully qualified name for tokens in this file.
+$prefix: (mat, fab);
+
+// Tokens that can't be configured through Angular Material's current theming API,
+// but may be in a future version of the theming API.
+@function get-unthemable-tokens() {
+  @return ();
+}
+
+// Tokens that can be configured through Angular Material's color theming API.
+@function get-color-tokens($theme) {
+  $is-dark: inspection.get-theme-type($theme) == dark;
+  $surface: if($is-dark, #fff, #000);
+
+  @return (
+    // Color of icons and text projected into a FAB.
+    foreground-color: inspection.get-theme-color($theme, foreground, base),
+
+    // MDC doesn't have tokens for disabled FABs so we need to implemented them ourselves.
+    // Background color of the container when the FAB is disabled.
+    disabled-state-container-color: rgba($surface, 0.12),
+    // Color of the icons and projected text when the FAB is disabled.
+    disabled-state-foreground-color: rgba($surface, if($is-dark, 0.5, 0.38)),
+  );
+}
+
+// Generates the mapping for the properties that change based on the FAB palette color.
+@function private-get-color-palette-color-tokens($theme, $palette-name) {
+  @return (
+    foreground-color: inspection.get-theme-color($theme, $palette-name, default-contrast),
+  );
+}
+
+// Tokens that can be configured through Angular Material's typography theming API.
+@function get-typography-tokens($theme) {
+  @return ();
+}
+
+// Tokens that can be configured through Angular Material's density theming API.
+@function get-density-tokens($theme) {
+  @return ();
+}
+
+// Combines the tokens generated by the above functions into a single map with placeholder values.
+// This is used to create token slots.
+@function get-token-slots() {
+  @return sass-utils.deep-merge-all(
+      get-unthemable-tokens(),
+      get-color-tokens(token-utils.$placeholder-color-config),
+      get-typography-tokens(token-utils.$placeholder-typography-config),
+      get-density-tokens(token-utils.$placeholder-density-config)
+  );
+}

src/material/core/tokens/m2/mdc/_fab.scss

@@ -22,6 +22,10 @@ $ripple-target: '.mdc-fab__ripple';
     container-shape: 50%,
     icon-size: 24px,
 
+    // We don't use this token, because it doesn't set the color of any text inside the FAB.
+    // We create a custom token for it instead.
+    icon-color: null,
+
     container-elevation: null,
     container-height: null,
     container-shadow-color: null,
@@ -56,10 +60,17 @@ $ripple-target: '.mdc-fab__ripple';
 
 // Tokens that can be configured through Angular Material's color theming API.
 @function get-color-tokens($theme) {
-  $surface: inspection.get-theme-color($theme, primary, default);
-  $on-surface: inspection.get-theme-color($theme, primary, default-contrast);
+  @return (
+    // Background color of the FAB.
+    container-color: inspection.get-theme-color($theme, background, card),
+  );
+}
 
-  @return (container-color: $surface, icon-color: $on-surface);
+// Generates the mapping for the properties that change based on the FAB palette color.
+@function private-get-color-palette-color-tokens($theme, $palette-name) {
+  @return (
+    container-color: inspection.get-theme-color($theme, $palette-name, default),
+  );
 }
 
 // Tokens that can be configured through Angular Material's typography theming API.