Refactor ShaderTarget to not explicitly mention impeller or Skia (#141460)

Refactors `ShaderTarget` to make it opaque as to whether it's using Impeller or SkSL and instead has it focus on the target platform it's generating for.

ImpellerC includes SkSL right now whether you ask for it or not. 

The tester target also might need SkSL or Vulkan depending on whether `--enable-impeller` is passed.

Author: dnfield

packages/flutter_tools/lib/src/build_system/targets/android.dart

@@ -15,7 +15,6 @@ import '../exceptions.dart';
 import 'assets.dart';
 import 'common.dart';
 import 'icon_tree_shaker.dart';
-import 'shader_compiler.dart';
 
 /// Prepares the asset bundle in the format expected by flutter.gradle.
 ///
@@ -68,7 +67,6 @@ abstract class AndroidAssetBundle extends Target {
       outputDirectory,
       targetPlatform: TargetPlatform.android,
       buildMode: buildMode,
-      shaderTarget: ShaderTarget.impellerAndroid,
       flavor: environment.defines[kFlavor],
     );
     environment.depFileService.writeToFile(

packages/flutter_tools/lib/src/build_system/targets/assets.dart

@@ -32,7 +32,6 @@ Future<Depfile> copyAssets(
   Map<String, DevFSContent> additionalContent = const <String, DevFSContent>{},
   required TargetPlatform targetPlatform,
   BuildMode? buildMode,
-  required ShaderTarget shaderTarget,
   List<File> additionalInputs = const <File>[],
   String? flavor,
 }) async {
@@ -140,8 +139,7 @@ Future<Depfile> copyAssets(
               doCopy = !await shaderCompiler.compileShader(
                 input: content.file as File,
                 outputPath: file.path,
-                target: shaderTarget,
-                json: targetPlatform == TargetPlatform.web_javascript,
+                targetPlatform: targetPlatform,
               );
             case AssetKind.model:
               doCopy = !await sceneImporter.importScene(
@@ -328,7 +326,6 @@ class CopyAssets extends Target {
       environment,
       output,
       targetPlatform: TargetPlatform.android,
-      shaderTarget: ShaderTarget.sksl,
       flavor: environment.defines[kFlavor],
     );
     environment.depFileService.writeToFile(

packages/flutter_tools/lib/src/build_system/targets/common.dart

@@ -79,7 +79,6 @@ class CopyFlutterBundle extends Target {
       environment.outputDir,
       targetPlatform: TargetPlatform.android,
       buildMode: buildMode,
-      shaderTarget: ShaderTarget.sksl,
       flavor: flavor,
     );
     environment.depFileService.writeToFile(

packages/flutter_tools/lib/src/build_system/targets/ios.dart

@@ -503,9 +503,6 @@ abstract class IosAssetBundle extends Target {
       environment,
       assetDirectory,
       targetPlatform: TargetPlatform.ios,
-      // Always specify an impeller shader target so that we support runtime toggling and
-      // the --enable-impeller debug flag.
-      shaderTarget: ShaderTarget.impelleriOS,
       additionalInputs: <File>[
         flutterProject.ios.infoPlist,
         flutterProject.ios.appFrameworkInfoPlist,

packages/flutter_tools/lib/src/build_system/targets/linux.dart

@@ -15,7 +15,6 @@ import 'assets.dart';
 import 'common.dart';
 import 'desktop.dart';
 import 'icon_tree_shaker.dart';
-import 'shader_compiler.dart';
 
 /// The only files/subdirectories we care out.
 const List<String> _kLinuxArtifacts = <String>[
@@ -141,7 +140,6 @@ abstract class BundleLinuxAssets extends Target {
       additionalContent: <String, DevFSContent>{
         'version.json': DevFSStringContent(versionInfo),
       },
-      shaderTarget: ShaderTarget.sksl,
     );
     environment.depFileService.writeToFile(
       depfile,

packages/flutter_tools/lib/src/build_system/targets/macos.dart

@@ -18,7 +18,6 @@ import '../exceptions.dart';
 import 'assets.dart';
 import 'common.dart';
 import 'icon_tree_shaker.dart';
-import 'shader_compiler.dart';
 
 /// Copy the macOS framework to the correct copy dir by invoking 'rsync'.
 ///
@@ -439,7 +438,6 @@ abstract class MacOSBundleFlutterAssets extends Target {
       environment,
       assetDirectory,
       targetPlatform: TargetPlatform.darwin,
-      shaderTarget: ShaderTarget.sksl,
       flavor: environment.defines[kFlavor],
     );
     environment.depFileService.writeToFile(

packages/flutter_tools/lib/src/build_system/targets/shader_compiler.dart

@@ -17,21 +17,8 @@ import '../../base/logger.dart';
 import '../../build_info.dart';
 import '../../convert.dart';
 import '../../devfs.dart';
-import '../../device.dart';
 import '../build_system.dart';
 
-/// The output shader format that should be used by the [ShaderCompiler].
-enum ShaderTarget {
-  impellerAndroid(<String>['--runtime-stage-gles', '--runtime-stage-vulkan']),
-  impelleriOS(<String>['--runtime-stage-metal']),
-  impellerSwiftShader(<String>['--runtime-stage-vulkan']),
-  sksl(<String>['--sksl']);
-
-  const ShaderTarget(this.stages);
-
-  final List<String> stages;
-}
-
 /// A wrapper around [ShaderCompiler] to support hot reload of shader sources.
 class DevelopmentShaderCompiler {
   DevelopmentShaderCompiler({
@@ -47,42 +34,16 @@ class DevelopmentShaderCompiler {
   final Pool _compilationPool = Pool(4);
   final math.Random _random;
 
-  late ShaderTarget _shaderTarget;
+  late TargetPlatform _targetPlatform;
   bool _debugConfigured = false;
-  bool _jsonMode = false;
 
   /// Configure the output format of the shader compiler for a particular
   /// flutter device.
-  void configureCompiler(TargetPlatform? platform, { required ImpellerStatus impellerStatus }) {
-    switch (platform) {
-      case TargetPlatform.ios:
-        _shaderTarget = ShaderTarget.impelleriOS;
-      case TargetPlatform.android_arm64:
-      case TargetPlatform.android_x64:
-      case TargetPlatform.android_x86:
-      case TargetPlatform.android_arm:
-      case TargetPlatform.android:
-        _shaderTarget = impellerStatus == ImpellerStatus.enabled
-          ? ShaderTarget.impellerAndroid
-          : ShaderTarget.sksl;
-      case TargetPlatform.darwin:
-      case TargetPlatform.linux_x64:
-      case TargetPlatform.linux_arm64:
-      case TargetPlatform.windows_x64:
-      case TargetPlatform.windows_arm64:
-      case TargetPlatform.fuchsia_arm64:
-      case TargetPlatform.fuchsia_x64:
-      case TargetPlatform.tester:
-        _shaderTarget =  impellerStatus == ImpellerStatus.enabled
-          ? ShaderTarget.impellerSwiftShader
-          : ShaderTarget.sksl;
-      case TargetPlatform.web_javascript:
-        assert(impellerStatus != ImpellerStatus.enabled);
-        _shaderTarget = ShaderTarget.sksl;
-        _jsonMode = true;
-      case null:
-        return;
+  void configureCompiler(TargetPlatform? platform) {
+    if (platform == null) {
+      return;
     }
+    _targetPlatform = platform;
     _debugConfigured = true;
   }
 
@@ -107,9 +68,8 @@ class DevelopmentShaderCompiler {
       final bool success = await _shaderCompiler.compileShader(
         input: inputFile,
         outputPath: output.path,
-        target: _shaderTarget,
+        targetPlatform: _targetPlatform,
         fatal: false,
-        json: _jsonMode,
       );
       if (!success) {
         return null;
@@ -144,6 +104,34 @@ class ShaderCompiler {
   final FileSystem _fs;
   final Artifacts _artifacts;
 
+  List<String> _shaderTargetsFromTargetPlatform(TargetPlatform targetPlatform) {
+    switch (targetPlatform) {
+      case TargetPlatform.android_x64:
+      case TargetPlatform.android_x86:
+      case TargetPlatform.android_arm:
+      case TargetPlatform.android_arm64:
+      case TargetPlatform.android:
+      case TargetPlatform.linux_x64:
+      case TargetPlatform.linux_arm64:
+      case TargetPlatform.windows_x64:
+      case TargetPlatform.windows_arm64:
+        return <String>['--sksl', '--runtime-stage-gles', '--runtime-stage-vulkan'];
+
+      case TargetPlatform.ios:
+      case TargetPlatform.darwin:
+        return <String>['--sksl', '--runtime-stage-metal'];
+
+      case TargetPlatform.fuchsia_arm64:
+      case TargetPlatform.fuchsia_x64:
+      case TargetPlatform.tester:
+        return <String>['--sksl', '--runtime-stage-vulkan'];
+
+      case TargetPlatform.web_javascript:
+        return <String>['--sksl'];
+
+    }
+  }
+
   /// The [Source] inputs that targets using this should depend on.
   ///
   /// See [Target.inputs].
@@ -163,9 +151,8 @@ class ShaderCompiler {
   Future<bool> compileShader({
     required File input,
     required String outputPath,
-    required ShaderTarget target,
+    required TargetPlatform targetPlatform,
     bool fatal = true,
-    required bool json,
   }) async {
     final File impellerc = _fs.file(
       _artifacts.getHostArtifact(HostArtifact.impellerc),
@@ -180,9 +167,9 @@ class ShaderCompiler {
     final String shaderLibPath = _fs.path.join(impellerc.parent.absolute.path, 'shader_lib');
     final List<String> cmd = <String>[
       impellerc.path,
-      ...target.stages,
+      ..._shaderTargetsFromTargetPlatform(targetPlatform),
       '--iplr',
-      if (json)
+      if (targetPlatform == TargetPlatform.web_javascript)
         '--json',
       '--sl=$outputPath',
       '--spirv=$outputPath.spirv',

packages/flutter_tools/lib/src/build_system/targets/web.dart

@@ -28,7 +28,6 @@ import '../depfile.dart';
 import '../exceptions.dart';
 import 'assets.dart';
 import 'localizations.dart';
-import 'shader_compiler.dart';
 
 /// Whether the application has web plugins.
 const String kHasWebPlugins = 'HasWebPlugins';
@@ -395,7 +394,6 @@ class WebReleaseBundle extends Target {
       environment,
       environment.outputDir.childDirectory('assets'),
       targetPlatform: TargetPlatform.web_javascript,
-      shaderTarget: ShaderTarget.sksl,
     );
     final DepfileService depfileService = environment.depFileService;
     depfileService.writeToFile(

packages/flutter_tools/lib/src/build_system/targets/windows.dart

@@ -12,7 +12,6 @@ import 'assets.dart';
 import 'common.dart';
 import 'desktop.dart';
 import 'icon_tree_shaker.dart';
-import 'shader_compiler.dart';
 
 /// The only files/subdirectories we care about.
 const List<String> _kWindowsArtifacts = <String>[
@@ -143,7 +142,6 @@ abstract class BundleWindowsAssets extends Target {
       environment,
       outputDirectory,
       targetPlatform: targetPlatform,
-      shaderTarget: ShaderTarget.sksl,
     );
     environment.depFileService.writeToFile(
       depfile,

packages/flutter_tools/lib/src/bundle_builder.dart

@@ -169,11 +169,6 @@ Future<void> writeBundle(
     artifacts: globals.artifacts!,
   );
 
-  ShaderTarget shaderTarget = ShaderTarget.sksl;
-  if (targetPlatform == TargetPlatform.tester && impellerStatus == ImpellerStatus.enabled) {
-    shaderTarget = ShaderTarget.impellerSwiftShader;
-  }
-
   // Limit number of open files to avoid running out of file descriptors.
   final Pool pool = Pool(64);
   await Future.wait<void>(
@@ -200,8 +195,7 @@ Future<void> writeBundle(
               doCopy = !await shaderCompiler.compileShader(
                 input: input,
                 outputPath: file.path,
-                target: shaderTarget,
-                json: targetPlatform == TargetPlatform.web_javascript,
+                targetPlatform: targetPlatform,
               );
             case AssetKind.model:
               doCopy = !await sceneImporter.importScene(