Add --config-only build option for Linux and Windows (flutter#172239)

Adds a `--config-only` option for Linux and Windows, which generates the
native build files (ninja and Visual Studio respectively) without
actually doing the build. This brings them into alignment with Android,
iOS, and macOS, which already have this flag, and will allow some
workflow improvements when running native plugin tests in environments
like the flutter/packages CI.

Fixes flutter#93407
Fixes flutter#172029

## 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.

<!-- Links -->
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[Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
[test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests
[Flutter Style Guide]:
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[Features we expect every widget to implement]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes
[Discord]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md
[Data Driven Fixes]:
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---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: stuartmorgan-g

packages/flutter_tools/lib/src/commands/build_linux.dart

@@ -40,6 +40,10 @@ class BuildLinuxCommand extends BuildSubCommand {
           'the app is compiled. This option is valid only '
           'if the current host and target architectures are different.',
     );
+    argParser.addFlag(
+      'config-only',
+      help: 'Update the project configuration without performing a build.',
+    );
   }
 
   final OperatingSystemUtils _operatingSystemUtils;
@@ -58,6 +62,8 @@ class BuildLinuxCommand extends BuildSubCommand {
   @override
   String get description => 'Build a Linux desktop application.';
 
+  bool get configOnly => boolArg('config-only');
+
   @override
   Future<FlutterCommandResult> runCommand() async {
     final BuildInfo buildInfo = await getBuildInfo();
@@ -95,6 +101,7 @@ class BuildLinuxCommand extends BuildSubCommand {
       targetPlatform: targetPlatform,
       targetSysroot: stringArg('target-sysroot')!,
       logger: logger,
+      configOnly: configOnly,
     );
     return FlutterCommandResult.success();
   }

packages/flutter_tools/lib/src/commands/build_windows.dart

@@ -25,6 +25,10 @@ class BuildWindowsCommand extends BuildSubCommand {
   }) : _operatingSystemUtils = operatingSystemUtils,
        super(verboseHelp: verboseHelp) {
     addCommonDesktopBuildOptions(verboseHelp: verboseHelp);
+    argParser.addFlag(
+      'config-only',
+      help: 'Update the project configuration without performing a build.',
+    );
   }
 
   final OperatingSystemUtils _operatingSystemUtils;
@@ -46,6 +50,8 @@ class BuildWindowsCommand extends BuildSubCommand {
   @visibleForTesting
   VisualStudio? visualStudioOverride;
 
+  bool get configOnly => boolArg('config-only');
+
   @override
   Future<FlutterCommandResult> runCommand() async {
     final BuildInfo buildInfo = await getBuildInfo();
@@ -75,6 +81,7 @@ class BuildWindowsCommand extends BuildSubCommand {
         appFilenamePattern: 'app.so',
         analytics: analytics,
       ),
+      configOnly: configOnly,
     );
     return FlutterCommandResult.success();
   }

packages/flutter_tools/lib/src/linux/build_linux.dart

@@ -42,6 +42,7 @@ Future<void> buildLinux(
   required TargetPlatform targetPlatform,
   String targetSysroot = '/',
   required Logger logger,
+  bool configOnly = false,
 }) async {
   target ??= 'lib/main.dart';
   if (!linuxProject.cmakeFile.existsSync()) {
@@ -93,6 +94,9 @@ Future<void> buildLinux(
       targetPlatform,
       targetSysroot,
     );
+    if (configOnly) {
+      return;
+    }
     await _runBuild(buildDirectory);
   } finally {
     status.cancel();

packages/flutter_tools/lib/src/windows/build_windows.dart

@@ -37,6 +37,7 @@ Future<void> buildWindows(
   String? target,
   VisualStudio? visualStudioOverride,
   SizeAnalyzer? sizeAnalyzer,
+  bool configOnly = false,
 }) async {
   // MSBuild files generated by CMake do not properly escape some characters
   // In the directories. This check produces more meaningful error messages
@@ -111,6 +112,9 @@ Future<void> buildWindows(
     if (visualStudio.displayVersion == '17.1.0') {
       _fixBrokenCmakeGeneration(buildDirectory);
     }
+    if (configOnly) {
+      return;
+    }
     await _runBuild(cmakePath, buildDirectory, buildModeName);
   } finally {
     status.stop();

packages/flutter_tools/test/integration.shard/build_linux_config_only_test.dart

@@ -0,0 +1,79 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:ffi';
+
+import 'package:file_testing/file_testing.dart';
+import 'package:flutter_tools/src/base/file_system.dart';
+
+import '../src/common.dart';
+import 'test_utils.dart';
+
+void main() {
+  test(
+    'flutter build linux --config-only updates generated build files without performing build',
+    () async {
+      final String workingDirectory = fileSystem.path.join(
+        getFlutterRoot(),
+        'dev',
+        'integration_tests',
+        'flutter_gallery',
+      );
+
+      await processManager.run(<String>[
+        flutterBin,
+        ...getLocalEngineArguments(),
+        'clean',
+      ], workingDirectory: workingDirectory);
+      final buildCommand = <String>[
+        flutterBin,
+        ...getLocalEngineArguments(),
+        'build',
+        'linux',
+        '--config-only',
+        '-v',
+      ];
+      await processManager.run(buildCommand, workingDirectory: workingDirectory);
+
+      final arch = Abi.current() == Abi.linuxArm64 ? 'arm64' : 'x64';
+
+      // Build file should be created.
+      final File generatedConfig = fileSystem.file(
+        fileSystem.path.join(workingDirectory, 'build', 'linux', arch, 'release', 'build.ninja'),
+      );
+      expect(generatedConfig, exists);
+
+      // No code should be compiled.
+      final File appLibrary = fileSystem.file(
+        fileSystem.path.join(workingDirectory, 'build', 'lib', 'libapp.so'),
+      );
+      final File exe = fileSystem.file(
+        fileSystem.path.join(
+          workingDirectory,
+          'build',
+          'linux',
+          arch,
+          'release',
+          'intermediates_do_not_run',
+          'flutter_gallery',
+        ),
+      );
+      final File bundleExe = fileSystem.file(
+        fileSystem.path.join(
+          workingDirectory,
+          'build',
+          'linux',
+          arch,
+          'release',
+          'bundle',
+          'flutter_gallery',
+        ),
+      );
+      expect(appLibrary, isNot(exists));
+      expect(exe, isNot(exists));
+      expect(bundleExe, isNot(exists));
+    },
+    skip: !platform.isLinux, // [intended] Linux builds only work on Linux.
+  );
+}

packages/flutter_tools/test/integration.shard/build_windows_config_only_test.dart

@@ -0,0 +1,67 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:ffi';
+
+import 'package:file_testing/file_testing.dart';
+import 'package:flutter_tools/src/base/file_system.dart';
+
+import '../src/common.dart';
+import 'test_utils.dart';
+
+void main() {
+  test(
+    'flutter build windows --config-only updates generated build files without performing build',
+    () async {
+      final String workingDirectory = fileSystem.path.join(
+        getFlutterRoot(),
+        'dev',
+        'integration_tests',
+        'flutter_gallery',
+      );
+
+      await processManager.run(<String>[
+        flutterBin,
+        ...getLocalEngineArguments(),
+        'clean',
+      ], workingDirectory: workingDirectory);
+      final buildCommand = <String>[
+        flutterBin,
+        ...getLocalEngineArguments(),
+        'build',
+        'windows',
+        '--config-only',
+        '-v',
+      ];
+      await processManager.run(buildCommand, workingDirectory: workingDirectory);
+
+      final arch = Abi.current() == Abi.windowsArm64 ? 'arm64' : 'x64';
+
+      // Solution file should be created.
+      final File generatedConfig = fileSystem.file(
+        fileSystem.path.join(workingDirectory, 'build', 'windows', arch, 'flutter_gallery.sln'),
+      );
+      expect(generatedConfig, exists);
+
+      // No code should be compiled.
+      final File appLibrary = fileSystem.file(
+        fileSystem.path.join(workingDirectory, 'build', 'windows', 'app.so'),
+      );
+      final File exe = fileSystem.file(
+        fileSystem.path.join(
+          workingDirectory,
+          'build',
+          'windows',
+          arch,
+          'runner',
+          'Release',
+          'flutter_gallery.exe',
+        ),
+      );
+      expect(appLibrary, isNot(exists));
+      expect(exe, isNot(exists));
+    },
+    skip: !platform.isWindows, // [intended] Windows builds only work on Windows.
+  );
+}