Extract shared library build from AOT snapshotting (#17166)

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

@@ -336,13 +336,35 @@ class AOTSnapshotter {
     // On iOS, we use Xcode to compile the snapshot into a dynamic library that the
     // end-developer can link into their app.
     if (platform == TargetPlatform.ios) {
+      final RunResult result = await _buildIosFramework(assemblyPath: assembly, outputPath: outputDir.path);
+      if (result.exitCode != 0)
+        return result.exitCode;
+    } else if (compileToSharedLibrary) {
+      final RunResult result = await _buildAndroidSharedLibrary(assemblyPath: assembly, outputPath: outputDir.path);
+      if (result.exitCode != 0)
+        return result.exitCode;
+    }
+
+    // Compute and record build fingerprint.
+    await _writeFingerprint(snapshotType, outputPaths, depfilePath, mainPath, fingerprintPath);
+    return 0;
+  }
+
+  /// Builds an iOS framework at [outputPath]/App.framework from the assembly
+  /// source at [assemblyPath].
+  Future<RunResult> _buildIosFramework({
+    @required String assemblyPath,
+    @required String outputPath,
+  }) async {
     printStatus('Building App.framework...');
     const List<String> commonBuildOptions = const <String>['-arch', 'arm64', '-miphoneos-version-min=8.0'];
 
-      final String assemblyO = fs.path.join(outputDir.path, 'snapshot_assembly.o');
-      await xcode.cc(commonBuildOptions.toList()..addAll(<String>['-c', assembly, '-o', assemblyO]));
+    final String assemblyO = fs.path.join(outputPath, 'snapshot_assembly.o');
+    final RunResult compileResult = await xcode.cc(commonBuildOptions.toList()..addAll(<String>['-c', assemblyPath, '-o', assemblyO]));
+    if (compileResult.exitCode != 0)
+      return compileResult;
 
-      final String frameworkDir = fs.path.join(outputDir.path, 'App.framework');
+    final String frameworkDir = fs.path.join(outputPath, 'App.framework');
     fs.directory(frameworkDir).createSync(recursive: true);
     final String appLib = fs.path.join(frameworkDir, 'App');
     final List<String> linkArgs = commonBuildOptions.toList()..addAll(<String>[
@@ -353,9 +375,16 @@ class AOTSnapshotter {
         '-o', appLib,
         assemblyO,
     ]);
-      await xcode.clang(linkArgs);
-    } else {
-      if (compileToSharedLibrary) {
+    final RunResult linkResult = await xcode.clang(linkArgs);
+    return linkResult;
+  }
+
+  /// Builds an Android shared library at [outputPath]/app.so from the assembly
+  /// source at [assemblyPath].
+  Future<RunResult> _buildAndroidSharedLibrary({
+    @required String assemblyPath,
+    @required String outputPath,
+  }) async {
     // A word of warning: Instead of compiling via two steps, to a .o file and
     // then to a .so file we use only one command. When using two commands
     // gcc will end up putting a .eh_frame and a .debug_frame into the shared
@@ -363,16 +392,10 @@ class AOTSnapshotter {
     // based upon libunwind use just one and ignore the contents of the other
     // (which causes it to not look into the other section and therefore not
     // find the correct unwinding information).
-        final String assemblySo = fs.path.join(outputDir.path, 'app.so');
-        await runCheckedAsync(<String>[androidSdk.ndkCompiler]
+    final String assemblySo = fs.path.join(outputPath, 'app.so');
+    return await runCheckedAsync(<String>[androidSdk.ndkCompiler]
         ..addAll(androidSdk.ndkCompilerArgs)
-            ..addAll(<String>[ '-shared', '-nostdlib', '-o', assemblySo, assembly ]));
-      }
-    }
-
-    // Compute and record build fingerprint.
-    await _writeFingerprint(snapshotType, outputPaths, depfilePath, mainPath, fingerprintPath);
-    return 0;
+        ..addAll(<String>[ '-shared', '-nostdlib', '-o', assemblySo, assemblyPath ]));
   }
 
   /// Compiles a Dart file to kernel.

packages/flutter_tools/test/base/build_test.dart

@@ -12,6 +12,8 @@ import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/base/build.dart';
 import 'package:flutter_tools/src/base/context.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/io.dart';
+import 'package:flutter_tools/src/base/process.dart';
 import 'package:flutter_tools/src/ios/mac.dart';
 import 'package:flutter_tools/src/version.dart';
 import 'package:mockito/mockito.dart';
@@ -646,6 +648,10 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '',
       };
 
+      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''));
+      when(xcode.cc(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
+      when(xcode.clang(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
+
       final int genSnapshotExitCode = await snapshotter.build(
         platform: TargetPlatform.ios,
         buildMode: BuildMode.profile,
@@ -688,6 +694,10 @@ void main() {
         fs.path.join(outputPath, 'snapshot.d'): '',
       };
 
+      final RunResult successResult = new RunResult(new ProcessResult(1, 0, '', ''));
+      when(xcode.cc(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
+      when(xcode.clang(any)).thenAnswer((_) => new Future<RunResult>.value(successResult));
+
       final int genSnapshotExitCode = await snapshotter.build(
         platform: TargetPlatform.ios,
         buildMode: BuildMode.release,