[tool/ci] Add iOS/macOS and Dart support to fetch-deps (flutter#4562)

Adds `fetch-deps` support for:
- iOS/macOS dependencies, using `pod install`
- Dart package dependencies, using `pub get`

To make avoid doing extra work in the Dart dependencies step when using this with `*_platform_tests` CI, also adds flags for all of the other platforms, and adds a flag that allows skipping Dart dependencies for any package that doesn't have an example supporting any requested platform. This means that we can pass, e.g., `--windows --supporting-target-platforms-only` to only fetch Dart packages for packages with examples that will be build during the build-and-drive Windows tests.

Adds this as a new step in every platform tests CI task, and in the standard analyze step, so that we will pre-fetch Dart packages (and for iOS/macOS, pods). This won't yet fully eliminate later network access (see flutter/flutter#131204), but will give us early warning on any major failures, such as pub being entirely unreachable from the bots.
- These are marked as an infrastructure step; we'll have to see if this ends up being confusing in practice. If `pub` resolution fails for legitimate reasons, such as a PR that tries to require a version of a package that doesn't exist or that has conflicts, this will cause a failure that is marked as infra. My assumption is that the much more common case is going to be that it is actually an infra failure.

Fixes flutter/flutter#130280

.ci/targets/analyze.yaml

@@ -4,6 +4,10 @@ tasks:
     infra_step: true # Note infra steps failing prevents "always" from running.
   - name: analyze repo tools
     script: .ci/scripts/analyze_repo_tools.sh
+  - name: download Dart deps
+    script: script/tool_runner.sh
+    args: ["fetch-deps"]
+    infra_step: true
   - name: analyze
     script: script/tool_runner.sh
     # DO NOT change the custom-analysis argument here without changing the Dart repo.

.ci/targets/android_platform_tests.yaml

@@ -2,10 +2,10 @@ tasks:
   - name: prepare tool
     script: .ci/scripts/prepare_tool.sh
     infra_step: true # Note infra steps failing prevents "always" from running.
-  - name: download android deps
+  - name: download Dart and Android deps
     script: script/tool_runner.sh
     infra_step: true
-    args: ["fetch-deps"]
+    args: ["fetch-deps", "--android", "--supporting-target-platforms-only"]
   - name: build examples
     script: script/tool_runner.sh
     args: ["build-examples", "--apk"]

.ci/targets/ios_platform_tests.yaml

@@ -5,6 +5,10 @@ tasks:
   - name: create simulator
     script: .ci/scripts/create_simulator.sh
     infra_step: true # Note infra steps failing prevents "always" from running.
+  - name: download Dart and iOS deps
+    script: script/tool_runner.sh
+    args: ["fetch-deps", "--ios", "--supporting-target-platforms-only"]
+    infra_step: true
   - name: build examples
     script: script/tool_runner.sh
     args: ["build-examples", "--ios"]

.ci/targets/linux_platform_tests.yaml

@@ -3,6 +3,11 @@ tasks:
     script: .ci/scripts/prepare_tool.sh
   - name: set default apps
     script: .ci/scripts/set_default_linux_apps.sh
+    infra_step: true
+  - name: download Dart deps
+    script: script/tool_runner.sh
+    args: ["fetch-deps", "--linux", "--supporting-target-platforms-only"]
+    infra_step: true
   - name: build examples
     script: script/tool_runner.sh
     args: ["build-examples", "--linux"]

.ci/targets/macos_platform_tests.yaml

@@ -2,6 +2,10 @@ tasks:
   - name: prepare tool
     script: .ci/scripts/prepare_tool.sh
     infra_step: true # Note infra steps failing prevents "always" from running.
+  - name: download Dart and macOS deps
+    script: script/tool_runner.sh
+    args: ["fetch-deps", "--macos", "--supporting-target-platforms-only"]
+    infra_step: true
   - name: build examples
     script: script/tool_runner.sh
     args: ["build-examples", "--macos"]

.ci/targets/web_platform_tests.yaml

@@ -2,6 +2,10 @@ tasks:
   - name: prepare tool
     script: .ci/scripts/prepare_tool.sh
     infra_step: true # Note infra steps failing prevents "always" from running.
+  - name: download Dart deps
+    script: script/tool_runner.sh
+    args: ["fetch-deps", "--web", "--supporting-target-platforms-only"]
+    infra_step: true
   - name: build examples
     script: script/tool_runner.sh
     args: ["build-examples", "--web"]

.ci/targets/windows_build_and_platform_tests.yaml

@@ -2,6 +2,10 @@ tasks:
   - name: prepare tool
     script: .ci/scripts/prepare_tool.sh
     infra_step: true # Note infra steps failing prevents "always" from running.
+  - name: download Dart deps
+    script: script/tool_runner.sh
+    args: ["fetch-deps", "--windows", "--supporting-target-platforms-only"]
+    infra_step: true
   - name: build examples (Win32)
     script: .ci/scripts/build_examples_win32.sh
   - name: native unit tests (Win32)

script/tool/lib/src/build_examples_command.dart

@@ -176,9 +176,8 @@ class BuildExamplesCommand extends PackageLoopingCommand {
         // supported platforms. For packages, just log and skip any requested
         // platform that a package doesn't have set up.
         if (!isPlugin &&
-            !example.directory
-                .childDirectory(platform.flutterPlatformDirectory)
-                .existsSync()) {
+            !example.appSupportsPlatform(
+                getPlatformByName(platform.pluginPlatform))) {
           print('Skipping ${platform.label} for $packageName; not supported.');
           continue;
         }
@@ -304,11 +303,6 @@ class _PlatformDetails {
   /// The `flutter build` build type.
   final String flutterBuildType;
 
-  /// The Flutter platform directory name.
-  // In practice, this is the same as the plugin platform key for all platforms.
-  // If that changes, this can be adjusted.
-  String get flutterPlatformDirectory => pluginPlatform;
-
   /// Any extra flags to pass to `flutter build`.
   final List<String> extraBuildFlags;
 }

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

@@ -37,6 +37,25 @@ const String kEnableExperiment = 'enable-experiment';
 // ignore: public_member_api_docs
 enum FlutterPlatform { android, ios, linux, macos, web, windows }
 
+const Map<String, FlutterPlatform> _platformByName = <String, FlutterPlatform>{
+  platformAndroid: FlutterPlatform.android,
+  platformIOS: FlutterPlatform.ios,
+  platformLinux: FlutterPlatform.linux,
+  platformMacOS: FlutterPlatform.macos,
+  platformWeb: FlutterPlatform.web,
+  platformWindows: FlutterPlatform.windows,
+};
+
+/// Maps from a platform name (e.g., flag or platform directory) to the
+/// corresponding platform enum.
+FlutterPlatform getPlatformByName(String name) {
+  final FlutterPlatform? platform = _platformByName[name];
+  if (platform == null) {
+    throw ArgumentError('Invalid platform: $name');
+  }
+  return platform;
+}
+
 // Flutter->Dart SDK version mapping. Any time a command fails to look up a
 // corresponding version, this map should be updated.
 final Map<Version, Version> _dartSdkForFlutterSdk = <Version, Version>{

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

@@ -30,12 +30,13 @@ class ProcessRunner {
     String executable,
     List<String> args, {
     Directory? workingDir,
+    Map<String, String>? environment,
     bool exitOnError = false,
   }) async {
     print(
         'Running command: "$executable ${args.join(' ')}" in ${workingDir?.path ?? io.Directory.current.path}');
     final io.Process process = await io.Process.start(executable, args,
-        workingDirectory: workingDir?.path);
+        workingDirectory: workingDir?.path, environment: environment);
     await Future.wait(<Future<dynamic>>[
       io.stdout.addStream(process.stdout),
       io.stderr.addStream(process.stderr),
@@ -62,14 +63,19 @@ class ProcessRunner {
   /// Defaults to `false`
   ///
   /// Returns the [io.ProcessResult] of the [executable].
-  Future<io.ProcessResult> run(String executable, List<String> args,
-      {Directory? workingDir,
-      bool exitOnError = false,
-      bool logOnError = false,
-      Encoding stdoutEncoding = io.systemEncoding,
-      Encoding stderrEncoding = io.systemEncoding}) async {
+  Future<io.ProcessResult> run(
+    String executable,
+    List<String> args, {
+    Directory? workingDir,
+    Map<String, String>? environment,
+    bool exitOnError = false,
+    bool logOnError = false,
+    Encoding stdoutEncoding = io.systemEncoding,
+    Encoding stderrEncoding = io.systemEncoding,
+  }) async {
     final io.ProcessResult result = await io.Process.run(executable, args,
         workingDirectory: workingDir?.path,
+        environment: environment,
         stdoutEncoding: stdoutEncoding,
         stderrEncoding: stderrEncoding);
     if (result.exitCode != 0) {

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

@@ -92,6 +92,16 @@ class RepositoryPackage {
     return directory.childDirectory(directoryName);
   }
 
+  /// Returns true if the package is an app that supports [platform].
+  ///
+  /// The "app" prefix on this method is because this currently only works
+  /// for app packages (e.g., examples).
+  // TODO(stuartmorgan): Add support for non-app packages, by parsing the
+  // pubspec for `flutter:platform:` or `platform:` sections.
+  bool appSupportsPlatform(FlutterPlatform platform) {
+    return platformDirectory(platform).existsSync();
+  }
+
   late final Pubspec _parsedPubspec =
       Pubspec.parse(pubspecFile.readAsStringSync());
 

script/tool/lib/src/drive_examples_command.dart

@@ -254,7 +254,7 @@ class DriveExamplesCommand extends PackageLoopingCommand {
     for (final MapEntry<String, List<String>> entry
         in _targetDeviceFlags.entries) {
       final String platform = entry.key;
-      if (example.directory.childDirectory(platform).existsSync()) {
+      if (example.appSupportsPlatform(getPlatformByName(platform))) {
         deviceFlags.addAll(entry.value);
       } else {
         final String exampleName =