Disable SwiftPM for xcode-analyze

Until flutter/flutter#172427 is resolved,
`xcode-analyze` doesn't work as desired with SwiftPM enabled (it
analyzes only the test code, not the plugin code). To avoid losing
analysis coverage in the meantime, this disabled SwiftPM temporarily
while running analysis.

This PR also updates `build-examples` to use the newer pubspec-based
config option to set the SwiftPM flag state instead of setting global
state, to avoid future issues where we are unintentionally bleeding flag
changes across different tests, and to make local runs not impact
developer machine state.

To unit test this functionality, this adds a new feature to the existing
process mock system that allows running an arbitrary test callback at
the ponit where a process is being run, which in this case allows
reading the temporarily-modified pubspec contents at the right point in
the command execution.

Fixes flutter/flutter#171442

Author: stuartmorgan-g

script/tool/lib/src/build_examples_command.dart

@@ -118,20 +118,14 @@ class BuildExamplesCommand extends PackageLoopingCommand {
       'arguments.';
 
   /// Returns whether the Swift Package Manager feature should be enabled,
-  /// disabled, or left to the release channel's default value.
+  /// disabled, or left to the default value.
   bool? get _swiftPackageManagerFeatureConfig {
     final List<String> platformFlags = _platforms.keys.toList();
     if (!platformFlags.contains(platformIOS) &&
         !platformFlags.contains(platformMacOS)) {
       return null;
     }
 
-    // TODO(loic-sharma): Allow enabling on stable once Swift Package Manager
-    // feature is available on stable.
-    if (platform.environment['CHANNEL'] != 'master') {
-      return null;
-    }
-
     return getNullableBoolArg(_swiftPackageManagerFlag);
   }
 
@@ -150,23 +144,6 @@ class BuildExamplesCommand extends PackageLoopingCommand {
           'were specified. At least one platform must be provided.');
       throw ToolExit(_exitNoPlatformFlags);
     }
-
-    switch (_swiftPackageManagerFeatureConfig) {
-      case true:
-        await processRunner.runAndStream(
-          flutterCommand,
-          <String>['config', '--enable-swift-package-manager'],
-          exitOnError: true,
-        );
-      case false:
-        await processRunner.runAndStream(
-          flutterCommand,
-          <String>['config', '--no-enable-swift-package-manager'],
-          exitOnError: true,
-        );
-      case null:
-        break;
-    }
   }
 
   @override
@@ -212,8 +189,20 @@ class BuildExamplesCommand extends PackageLoopingCommand {
     }
     print('');
 
+    final bool? swiftPackageManagerOverride =
+        isPlugin ? _swiftPackageManagerFeatureConfig : null;
+
     bool builtSomething = false;
     for (final RepositoryPackage example in package.getExamples()) {
+      // Rather than changing global config state, enable SwiftPM via a
+      // temporary package-level override.
+      if (swiftPackageManagerOverride != null) {
+        print('Overriding enable-swift-package-manager to '
+            '$swiftPackageManagerOverride');
+        setSwiftPackageManagerState(example,
+            enabled: swiftPackageManagerOverride);
+      }
+
       final String packageName =
           getRelativePosixPath(example.directory, from: packagesDir);
 
@@ -240,6 +229,12 @@ class BuildExamplesCommand extends PackageLoopingCommand {
           errors.add('$packageName (${platform.label})');
         }
       }
+
+      // If an override was added, remove it.
+      if (swiftPackageManagerOverride != null) {
+        print('Removing enable-swift-package-manager override');
+        setSwiftPackageManagerState(example, enabled: null);
+      }
     }
 
     if (!builtSomething) {

script/tool/lib/src/common/plugin_utils.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:yaml/yaml.dart';
+import 'package:yaml_edit/yaml_edit.dart';
 
 import 'core.dart';
 import 'repository_package.dart';
@@ -83,6 +84,57 @@ bool pluginHasNativeCodeForPlatform(String platform, RepositoryPackage plugin) {
   return pluginClass != null && pluginClass != 'none';
 }
 
+/// Adds or removes a package-level Swift Package Manager override to the given
+/// package.
+///
+/// A null enabled state clears the package-local override, defaulting to whatever the
+/// global state is.
+void setSwiftPackageManagerState(RepositoryPackage package,
+    {required bool? enabled}) {
+  const String swiftPMFlag = 'enable-swift-package-manager';
+  const String flutterKey = 'flutter';
+  const List<String> flutterPath = <String>[flutterKey];
+  const List<String> configPath = <String>[flutterKey, 'config'];
+
+  final YamlEditor editablePubspec =
+      YamlEditor(package.pubspecFile.readAsStringSync());
+  final YamlMap configMap =
+      editablePubspec.parseAt(configPath, orElse: () => YamlMap()) as YamlMap;
+  if (enabled == null) {
+    if (!configMap.containsKey(swiftPMFlag)) {
+      // Nothing to do.
+      return;
+    } else if (configMap.length == 1) {
+      // The config section only exists for this override, so remove the whole
+      // section.
+      editablePubspec.remove(configPath);
+      // The entire flutter: section may also only have been added for the
+      // config, in which case it should be removed as well.
+      final YamlMap flutterMap = editablePubspec.parseAt(flutterPath,
+          orElse: () => YamlMap()) as YamlMap;
+      if (flutterMap.isEmpty) {
+        editablePubspec.remove(flutterPath);
+      }
+    } else {
+      // Remove the specific entry, leaving the rest of the config section.
+      editablePubspec.remove(<String>[...configPath, swiftPMFlag]);
+    }
+  } else {
+    // Ensure that the section exists.
+    if (configMap.isEmpty) {
+      final YamlMap root = editablePubspec.parseAt(<String>[]) as YamlMap;
+      if (!root.containsKey(flutterKey)) {
+        editablePubspec.update(flutterPath, YamlMap());
+      }
+      editablePubspec.update(configPath, YamlMap());
+    }
+    // Then add the flag.
+    editablePubspec.update(<String>[...configPath, swiftPMFlag], enabled);
+  }
+
+  package.pubspecFile.writeAsStringSync(editablePubspec.toString());
+}
+
 /// Returns the
 ///   flutter:
 ///     plugin:

script/tool/lib/src/xcode_analyze_command.dart

@@ -121,8 +121,14 @@ class XcodeAnalyzeCommand extends PackageLoopingCommand {
         targetPlatform == FlutterPlatform.ios ? 'iOS' : 'macOS';
     bool passing = true;
     for (final RepositoryPackage example in plugin.getExamples()) {
+      // See https://github.com/flutter/flutter/issues/172427 for discussion of
+      // why this is currently necessary.
+      print('Disabling Swift Package Manager...');
+      setSwiftPackageManagerState(example, enabled: false);
+
       // Unconditionally re-run build with --debug --config-only, to ensure that
-      // the project is in a debug state even if it was previously configured.
+      // the project is in a debug state even if it was previously configured,
+      // and that SwiftPM is disabled.
       print('Running flutter build --config-only...');
       final bool buildSuccess = await runConfigOnlyBuild(
         example,
@@ -162,6 +168,9 @@ class XcodeAnalyzeCommand extends PackageLoopingCommand {
         printError('$examplePath ($platformString) failed analysis.');
         passing = false;
       }
+
+      print('Removing Swift Package Manager override...');
+      setSwiftPackageManagerState(example, enabled: null);
     }
     return passing;
   }