Directly generate a Mach-O dynamic library using gen_snapshot. [reland] (#181539)

Instead of generating assembly code that is then compiled to a Mach-O
dynamic library, use the new app-aot-macho-dylib output option for
gen_snapshot to generate the Mach-O dynamic library without the assembly
step.

This is a reland of https://github.com/flutter/flutter/pull/174870. No
changes from the previously landed PR are needed, as the fixes for the
App Store issue described in
https://github.com/flutter/flutter/issues/178602 are all on the Dart
side: https://github.com/dart-lang/sdk/commit/8cbf864.

Related issues:

* https://github.com/dart-lang/sdk/issues/43299
* https://github.com/dart-lang/sdk/issues/60307
* https://github.com/flutter/flutter/issues/178602
* https://github.com/dart-lang/sdk/issues/62414

## Pre-launch Checklist

- [X] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [X] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [X] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [X] I signed the [CLA].
- [X] I listed at least one issue that this PR fixes in the description
above.
- [X] I updated/added relevant documentation (doc comments with `///`).
- [X] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [X] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [X] All existing and new tests are passing.

packages/flutter_tools/lib/src/base/build.dart

@@ -161,11 +161,37 @@ class AOTSnapshotter {
       }
     }
 
-    final String assembly = _fileSystem.path.join(outputDir.path, 'snapshot_assembly.S');
+    String aotSharedLibrary = _fileSystem.path.join(outputDir.path, 'app.so');
+    String? frameworkPath;
     if (targetingApplePlatform) {
-      genSnapshotArgs.addAll(<String>['--snapshot_kind=app-aot-assembly', '--assembly=$assembly']);
+      // On iOS and macOS, we use Xcode to compile the snapshot into a dynamic
+      // library that the end-developer can link into their app.
+      const frameworkName = 'App.framework';
+      if (!quiet) {
+        final String targetArch = darwinArch!.name;
+        _logger.printStatus('Building $frameworkName for $targetArch...');
+      }
+      frameworkPath = _fileSystem.path.join(outputPath, frameworkName);
+      _fileSystem.directory(frameworkPath).createSync(recursive: true);
+
+      const frameworkSnapshotName = 'App';
+      aotSharedLibrary = _fileSystem.path.join(frameworkPath, frameworkSnapshotName);
+      final String relocatableObject = _fileSystem.path.join(outputPath, 'app.o');
+      // When the minimum version is updated, remember to update
+      // template MinimumOSVersion.
+      // https://github.com/flutter/flutter/pull/62902
+      final minOSVersion = platform == TargetPlatform.ios
+          ? FlutterDarwinPlatform.ios.deploymentTarget().toString()
+          : FlutterDarwinPlatform.macos.deploymentTarget().toString();
+      genSnapshotArgs.addAll(<String>[
+        '--snapshot_kind=app-aot-macho-dylib',
+        '--macho=$aotSharedLibrary',
+        '--macho-object=$relocatableObject',
+        '--macho-min-os-version=$minOSVersion',
+        '--macho-rpath=@executable_path/Frameworks,@loader_path/Frameworks',
+        '--macho-install-name=@rpath/$frameworkName/$frameworkSnapshotName',
+      ]);
     } else {
-      final String aotSharedLibrary = _fileSystem.path.join(outputDir.path, 'app.so');
       genSnapshotArgs.addAll(<String>['--snapshot_kind=app-aot-elf', '--elf=$aotSharedLibrary']);
     }
 
@@ -230,123 +256,38 @@ class AOTSnapshotter {
       return genSnapshotExitCode;
     }
 
-    // On iOS and macOS, we use Xcode to compile the snapshot into a dynamic library that the
-    // end-developer can link into their app.
     if (targetingApplePlatform) {
-      return _buildFramework(
-        appleArch: darwinArch!,
-        isIOS: platform == TargetPlatform.ios,
-        sdkRoot: sdkRoot,
-        assemblyPath: assembly,
-        outputPath: outputDir.path,
-        quiet: quiet,
-        stripAfterBuild: stripAfterBuild,
-        extractAppleDebugSymbols: extractAppleDebugSymbols,
-      );
-    } else {
-      return 0;
-    }
-  }
-
-  /// Builds an iOS or macOS framework at [outputPath]/App.framework from the assembly
-  /// source at [assemblyPath].
-  Future<int> _buildFramework({
-    required DarwinArch appleArch,
-    required bool isIOS,
-    String? sdkRoot,
-    required String assemblyPath,
-    required String outputPath,
-    required bool quiet,
-    required bool stripAfterBuild,
-    required bool extractAppleDebugSymbols,
-  }) async {
-    final String targetArch = appleArch.name;
-    if (!quiet) {
-      _logger.printStatus('Building App.framework for $targetArch...');
-    }
-
-    final commonBuildOptions = <String>[
-      '-arch',
-      targetArch,
-      if (isIOS)
-        // When the minimum version is updated, remember to update
-        // template MinimumOSVersion.
-        // https://github.com/flutter/flutter/pull/62902
-        '-miphoneos-version-min=${FlutterDarwinPlatform.ios.deploymentTarget()}',
-      if (sdkRoot != null) ...<String>['-isysroot', sdkRoot],
-    ];
-
-    final String assemblyO = _fileSystem.path.join(outputPath, 'snapshot_assembly.o');
-
-    final RunResult compileResult = await _xcode.cc(<String>[
-      ...commonBuildOptions,
-      '-c',
-      assemblyPath,
-      '-o',
-      assemblyO,
-    ]);
-    if (compileResult.exitCode != 0) {
-      _logger.printError(
-        'Failed to compile AOT snapshot. Compiler terminated with exit code ${compileResult.exitCode}',
-      );
-      return compileResult.exitCode;
-    }
-
-    final String frameworkDir = _fileSystem.path.join(outputPath, 'App.framework');
-    _fileSystem.directory(frameworkDir).createSync(recursive: true);
-    final String appLib = _fileSystem.path.join(frameworkDir, 'App');
-    final linkArgs = <String>[
-      ...commonBuildOptions,
-      '-dynamiclib',
-      '-Xlinker',
-      '-rpath',
-      '-Xlinker',
-      '@executable_path/Frameworks',
-      '-Xlinker',
-      '-rpath',
-      '-Xlinker',
-      '@loader_path/Frameworks',
-      '-fapplication-extension',
-      '-install_name',
-      '@rpath/App.framework/App',
-      '-o',
-      appLib,
-      assemblyO,
-    ];
-
-    final RunResult linkResult = await _xcode.clang(linkArgs);
-    if (linkResult.exitCode != 0) {
-      _logger.printError(
-        'Failed to link AOT snapshot. Linker terminated with exit code ${linkResult.exitCode}',
-      );
-      return linkResult.exitCode;
-    }
-
-    if (extractAppleDebugSymbols) {
-      final RunResult dsymResult = await _xcode.dsymutil(<String>[
-        '-o',
-        '$frameworkDir.dSYM',
-        appLib,
-      ]);
-      if (dsymResult.exitCode != 0) {
-        _logger.printError(
-          'Failed to generate dSYM - dsymutil terminated with exit code ${dsymResult.exitCode}',
-        );
-        return dsymResult.exitCode;
-      }
-
-      if (stripAfterBuild) {
-        // See https://www.unix.com/man-page/osx/1/strip/ for arguments
-        final RunResult stripResult = await _xcode.strip(<String>['-x', appLib, '-o', appLib]);
-        if (stripResult.exitCode != 0) {
+      if (extractAppleDebugSymbols) {
+        final RunResult dsymResult = await _xcode.dsymutil(<String>[
+          '-o',
+          '$frameworkPath.dSYM',
+          aotSharedLibrary,
+        ]);
+        if (dsymResult.exitCode != 0) {
           _logger.printError(
-            'Failed to strip debugging symbols from the generated AOT snapshot - strip terminated with exit code ${stripResult.exitCode}',
+            'Failed to generate dSYM - dsymutil terminated with exit code ${dsymResult.exitCode}',
           );
-          return stripResult.exitCode;
+          return dsymResult.exitCode;
         }
+
+        if (stripAfterBuild) {
+          // See https://www.unix.com/man-page/osx/1/strip/ for arguments
+          final RunResult stripResult = await _xcode.strip(<String>[
+            '-x',
+            aotSharedLibrary,
+            '-o',
+            aotSharedLibrary,
+          ]);
+          if (stripResult.exitCode != 0) {
+            _logger.printError(
+              'Failed to strip debugging symbols from the generated AOT snapshot - strip terminated with exit code ${stripResult.exitCode}',
+            );
+            return stripResult.exitCode;
+          }
+        }
+      } else {
+        assert(!stripAfterBuild);
       }
-    } else {
-      assert(!stripAfterBuild);
     }
 
     return 0;

packages/flutter_tools/test/general.shard/base/build_test.dart

@@ -16,27 +16,6 @@ const kWhichSysctlCommand = FakeCommand(command: <String>['which', 'sysctl']);
 
 const kARMCheckCommand = FakeCommand(command: <String>['sysctl', 'hw.optional.arm64'], exitCode: 1);
 
-const kDefaultClang = <String>[
-  '-miphoneos-version-min=13.0',
-  '-isysroot',
-  'path/to/sdk',
-  '-dynamiclib',
-  '-Xlinker',
-  '-rpath',
-  '-Xlinker',
-  '@executable_path/Frameworks',
-  '-Xlinker',
-  '-rpath',
-  '-Xlinker',
-  '@loader_path/Frameworks',
-  '-fapplication-extension',
-  '-install_name',
-  '@rpath/App.framework/App',
-  '-o',
-  'build/foo/App.framework/App',
-  'build/foo/snapshot_assembly.o',
-];
-
 void main() {
   group('GenSnapshot', () {
     late GenSnapshot genSnapshot;
@@ -191,7 +170,6 @@ void main() {
 
     testWithoutContext('builds iOS snapshot with dwarfStackTraces', () async {
       final String outputPath = fileSystem.path.join('build', 'foo');
-      final String assembly = fileSystem.path.join(outputPath, 'snapshot_assembly.S');
       final String debugPath = fileSystem.path.join('foo', 'app.ios-arm64.symbols');
       final String genSnapshotPath = artifacts.getArtifactPath(
         Artifact.genSnapshotArm64,
@@ -203,8 +181,12 @@ void main() {
           command: <String>[
             genSnapshotPath,
             '--deterministic',
-            '--snapshot_kind=app-aot-assembly',
-            '--assembly=$assembly',
+            '--snapshot_kind=app-aot-macho-dylib',
+            '--macho=$outputPath/App.framework/App',
+            '--macho-object=$outputPath/app.o',
+            '--macho-min-os-version=13.0',
+            '--macho-rpath=@executable_path/Frameworks,@loader_path/Frameworks',
+            '--macho-install-name=@rpath/App.framework/App',
             '--dwarf-stack-traces',
             '--resolve-dwarf-paths',
             '--save-debugging-info=$debugPath',
@@ -213,39 +195,23 @@ void main() {
         ),
         kWhichSysctlCommand,
         kARMCheckCommand,
-        const FakeCommand(
-          command: <String>[
-            'xcrun',
-            'cc',
-            '-arch',
-            'arm64',
-            '-miphoneos-version-min=13.0',
-            '-isysroot',
-            'path/to/sdk',
-            '-c',
-            'build/foo/snapshot_assembly.S',
-            '-o',
-            'build/foo/snapshot_assembly.o',
-          ],
-        ),
-        const FakeCommand(command: <String>['xcrun', 'clang', '-arch', 'arm64', ...kDefaultClang]),
-        const FakeCommand(
+        FakeCommand(
           command: <String>[
             'xcrun',
             'dsymutil',
             '-o',
-            'build/foo/App.framework.dSYM',
-            'build/foo/App.framework/App',
+            '$outputPath/App.framework.dSYM',
+            '$outputPath/App.framework/App',
           ],
         ),
-        const FakeCommand(
+        FakeCommand(
           command: <String>[
             'xcrun',
             'strip',
             '-x',
-            'build/foo/App.framework/App',
+            '$outputPath/App.framework/App',
             '-o',
-            'build/foo/App.framework/App',
+            '$outputPath/App.framework/App',
           ],
         ),
       ]);
@@ -267,7 +233,6 @@ void main() {
 
     testWithoutContext('builds iOS snapshot with obfuscate', () async {
       final String outputPath = fileSystem.path.join('build', 'foo');
-      final String assembly = fileSystem.path.join(outputPath, 'snapshot_assembly.S');
       final String genSnapshotPath = artifacts.getArtifactPath(
         Artifact.genSnapshotArm64,
         platform: TargetPlatform.ios,
@@ -278,47 +243,35 @@ void main() {
           command: <String>[
             genSnapshotPath,
             '--deterministic',
-            '--snapshot_kind=app-aot-assembly',
-            '--assembly=$assembly',
+            '--snapshot_kind=app-aot-macho-dylib',
+            '--macho=$outputPath/App.framework/App',
+            '--macho-object=$outputPath/app.o',
+            '--macho-min-os-version=13.0',
+            '--macho-rpath=@executable_path/Frameworks,@loader_path/Frameworks',
+            '--macho-install-name=@rpath/App.framework/App',
             '--obfuscate',
             'main.dill',
           ],
         ),
         kWhichSysctlCommand,
         kARMCheckCommand,
-        const FakeCommand(
-          command: <String>[
-            'xcrun',
-            'cc',
-            '-arch',
-            'arm64',
-            '-miphoneos-version-min=13.0',
-            '-isysroot',
-            'path/to/sdk',
-            '-c',
-            'build/foo/snapshot_assembly.S',
-            '-o',
-            'build/foo/snapshot_assembly.o',
-          ],
-        ),
-        const FakeCommand(command: <String>['xcrun', 'clang', '-arch', 'arm64', ...kDefaultClang]),
-        const FakeCommand(
+        FakeCommand(
           command: <String>[
             'xcrun',
             'dsymutil',
             '-o',
-            'build/foo/App.framework.dSYM',
-            'build/foo/App.framework/App',
+            '$outputPath/App.framework.dSYM',
+            '$outputPath/App.framework/App',
           ],
         ),
-        const FakeCommand(
+        FakeCommand(
           command: <String>[
             'xcrun',
             'strip',
             '-x',
-            'build/foo/App.framework/App',
+            '$outputPath/App.framework/App',
             '-o',
-            'build/foo/App.framework/App',
+            '$outputPath/App.framework/App',
           ],
         ),
       ]);
@@ -349,46 +302,34 @@ void main() {
           command: <String>[
             genSnapshotPath,
             '--deterministic',
-            '--snapshot_kind=app-aot-assembly',
-            '--assembly=${fileSystem.path.join(outputPath, 'snapshot_assembly.S')}',
+            '--snapshot_kind=app-aot-macho-dylib',
+            '--macho=$outputPath/App.framework/App',
+            '--macho-object=$outputPath/app.o',
+            '--macho-min-os-version=13.0',
+            '--macho-rpath=@executable_path/Frameworks,@loader_path/Frameworks',
+            '--macho-install-name=@rpath/App.framework/App',
             'main.dill',
           ],
         ),
         kWhichSysctlCommand,
         kARMCheckCommand,
-        const FakeCommand(
-          command: <String>[
-            'xcrun',
-            'cc',
-            '-arch',
-            'arm64',
-            '-miphoneos-version-min=13.0',
-            '-isysroot',
-            'path/to/sdk',
-            '-c',
-            'build/foo/snapshot_assembly.S',
-            '-o',
-            'build/foo/snapshot_assembly.o',
-          ],
-        ),
-        const FakeCommand(command: <String>['xcrun', 'clang', '-arch', 'arm64', ...kDefaultClang]),
-        const FakeCommand(
+        FakeCommand(
           command: <String>[
             'xcrun',
             'dsymutil',
             '-o',
-            'build/foo/App.framework.dSYM',
-            'build/foo/App.framework/App',
+            '$outputPath/App.framework.dSYM',
+            '$outputPath/App.framework/App',
           ],
         ),
-        const FakeCommand(
+        FakeCommand(
           command: <String>[
             'xcrun',
             'strip',
             '-x',
-            'build/foo/App.framework/App',
+            '$outputPath/App.framework/App',
             '-o',
-            'build/foo/App.framework/App',
+            '$outputPath/App.framework/App',
           ],
         ),
       ]);

packages/flutter_tools/test/general.shard/build_system/targets/common_test.dart

@@ -23,7 +23,7 @@ import '../../../src/fake_process_manager.dart';
 
 const kBoundaryKey = '4d2d9609-c662-4571-afde-31410f96caa6';
 const kElfAot = '--snapshot_kind=app-aot-elf';
-const kAssemblyAot = '--snapshot_kind=app-aot-assembly';
+const kMachoDylibAot = '--snapshot_kind=app-aot-macho-dylib';
 
 final Platform macPlatform = FakePlatform(
   operatingSystem: 'macos',
@@ -803,52 +803,15 @@ void main() {
             '--deterministic',
             '--write-v8-snapshot-profile-to=code_size_1/snapshot.arm64.json',
             '--trace-precompiler-to=code_size_1/trace.arm64.json',
-            kAssemblyAot,
-            '--assembly=$build/arm64/snapshot_assembly.S',
+            kMachoDylibAot,
+            '--macho=$build/arm64/App.framework/App',
+            '--macho-object=$build/arm64/app.o',
+            '--macho-min-os-version=13.0',
+            '--macho-rpath=@executable_path/Frameworks,@loader_path/Frameworks',
+            '--macho-install-name=@rpath/App.framework/App',
             '$build/app.dill',
           ],
         ),
-        FakeCommand(
-          command: <String>[
-            'xcrun',
-            'cc',
-            '-arch',
-            'arm64',
-            '-miphoneos-version-min=13.0',
-            '-isysroot',
-            'path/to/iPhoneOS.sdk',
-            '-c',
-            '$build/arm64/snapshot_assembly.S',
-            '-o',
-            '$build/arm64/snapshot_assembly.o',
-          ],
-        ),
-        FakeCommand(
-          command: <String>[
-            'xcrun',
-            'clang',
-            '-arch',
-            'arm64',
-            '-miphoneos-version-min=13.0',
-            '-isysroot',
-            'path/to/iPhoneOS.sdk',
-            '-dynamiclib',
-            '-Xlinker',
-            '-rpath',
-            '-Xlinker',
-            '@executable_path/Frameworks',
-            '-Xlinker',
-            '-rpath',
-            '-Xlinker',
-            '@loader_path/Frameworks',
-            '-fapplication-extension',
-            '-install_name',
-            '@rpath/App.framework/App',
-            '-o',
-            '$build/arm64/App.framework/App',
-            '$build/arm64/snapshot_assembly.o',
-          ],
-        ),
         FakeCommand(
           command: <String>[
             'xcrun',

packages/flutter_tools/test/general.shard/build_system/targets/macos_test.dart

@@ -817,8 +817,12 @@ void main() {
           command: <String>[
             'Artifact.genSnapshotArm64.TargetPlatform.darwin.release',
             '--deterministic',
-            '--snapshot_kind=app-aot-assembly',
-            '--assembly=${environment.buildDir.childFile('arm64/snapshot_assembly.S').path}',
+            '--snapshot_kind=app-aot-macho-dylib',
+            '--macho=${environment.buildDir.childFile('arm64/App.framework/App').path}',
+            '--macho-object=${environment.buildDir.childFile('arm64/app.o').path}',
+            '--macho-min-os-version=10.15',
+            '--macho-rpath=@executable_path/Frameworks,@loader_path/Frameworks',
+            '--macho-install-name=@rpath/App.framework/App',
             environment.buildDir.childFile('app.dill').path,
           ],
         ),
@@ -826,81 +830,15 @@ void main() {
           command: <String>[
             'Artifact.genSnapshotX64.TargetPlatform.darwin.release',
             '--deterministic',
-            '--snapshot_kind=app-aot-assembly',
-            '--assembly=${environment.buildDir.childFile('x86_64/snapshot_assembly.S').path}',
+            '--snapshot_kind=app-aot-macho-dylib',
+            '--macho=${environment.buildDir.childFile('x86_64/App.framework/App').path}',
+            '--macho-object=${environment.buildDir.childFile('x86_64/app.o').path}',
+            '--macho-min-os-version=10.15',
+            '--macho-rpath=@executable_path/Frameworks,@loader_path/Frameworks',
+            '--macho-install-name=@rpath/App.framework/App',
             environment.buildDir.childFile('app.dill').path,
           ],
         ),
-        FakeCommand(
-          command: <String>[
-            'xcrun',
-            'cc',
-            '-arch',
-            'arm64',
-            '-c',
-            environment.buildDir.childFile('arm64/snapshot_assembly.S').path,
-            '-o',
-            environment.buildDir.childFile('arm64/snapshot_assembly.o').path,
-          ],
-        ),
-        FakeCommand(
-          command: <String>[
-            'xcrun',
-            'cc',
-            '-arch',
-            'x86_64',
-            '-c',
-            environment.buildDir.childFile('x86_64/snapshot_assembly.S').path,
-            '-o',
-            environment.buildDir.childFile('x86_64/snapshot_assembly.o').path,
-          ],
-        ),
-        FakeCommand(
-          command: <String>[
-            'xcrun',
-            'clang',
-            '-arch',
-            'arm64',
-            '-dynamiclib',
-            '-Xlinker',
-            '-rpath',
-            '-Xlinker',
-            '@executable_path/Frameworks',
-            '-Xlinker',
-            '-rpath',
-            '-Xlinker',
-            '@loader_path/Frameworks',
-            '-fapplication-extension',
-            '-install_name',
-            '@rpath/App.framework/App',
-            '-o',
-            environment.buildDir.childFile('arm64/App.framework/App').path,
-            environment.buildDir.childFile('arm64/snapshot_assembly.o').path,
-          ],
-        ),
-        FakeCommand(
-          command: <String>[
-            'xcrun',
-            'clang',
-            '-arch',
-            'x86_64',
-            '-dynamiclib',
-            '-Xlinker',
-            '-rpath',
-            '-Xlinker',
-            '@executable_path/Frameworks',
-            '-Xlinker',
-            '-rpath',
-            '-Xlinker',
-            '@loader_path/Frameworks',
-            '-fapplication-extension',
-            '-install_name',
-            '@rpath/App.framework/App',
-            '-o',
-            environment.buildDir.childFile('x86_64/App.framework/App').path,
-            environment.buildDir.childFile('x86_64/snapshot_assembly.o').path,
-          ],
-        ),
         FakeCommand(
           command: <String>[
             'xcrun',