Tell user how to enable available but disabled features (#79977)

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

@@ -68,7 +68,7 @@ class BuildLinuxCommand extends BuildSubCommand {
             != getNameForTargetPlatformArch(targetPlatform);
 
     if (!featureFlags.isLinuxEnabled) {
-      throwToolExit('"build linux" is not currently supported.');
+      throwToolExit('"build linux" is not currently supported. To enable, run "flutter config --enable-linux-desktop".');
     }
     if (!globals.platform.isLinux) {
       throwToolExit('"build linux" only supported on Linux hosts.');

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

@@ -44,7 +44,7 @@ class BuildMacosCommand extends BuildSubCommand {
     final BuildInfo buildInfo = await getBuildInfo();
     final FlutterProject flutterProject = FlutterProject.current();
     if (!featureFlags.isMacOSEnabled) {
-      throwToolExit('"build macos" is not currently supported.');
+      throwToolExit('"build macos" is not currently supported. To enable, run "flutter config --enable-macos-desktop".');
     }
     if (!globals.platform.isMacOS) {
       throwToolExit('"build macos" only supported on macOS hosts.');

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

@@ -79,7 +79,7 @@ class BuildWebCommand extends BuildSubCommand {
   @override
   Future<FlutterCommandResult> runCommand() async {
     if (!featureFlags.isWebEnabled) {
-      throwToolExit('"build web" is not currently supported.');
+      throwToolExit('"build web" is not currently supported. To enable, run "flutter config --enable-web".');
     }
     final FlutterProject flutterProject = FlutterProject.current();
     final String target = stringArg('target');

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

@@ -46,7 +46,7 @@ class BuildWindowsCommand extends BuildSubCommand {
     final FlutterProject flutterProject = FlutterProject.current();
     final BuildInfo buildInfo = await getBuildInfo();
     if (!featureFlags.isWindowsEnabled) {
-      throwToolExit('"build windows" is not currently supported.');
+      throwToolExit('"build windows" is not currently supported. To enable, run "flutter config --enable-windows-desktop".');
     }
     if (!globals.platform.isWindows) {
       throwToolExit('"build windows" only supported on Windows hosts.');

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

@@ -46,10 +46,10 @@ class BuildWindowsUwpCommand extends BuildSubCommand {
     final FlutterProject flutterProject = FlutterProject.current();
     final BuildInfo buildInfo = await getBuildInfo();
     if (!featureFlags.isWindowsUwpEnabled) {
-      throwToolExit('"build windows" is not currently supported.');
+      throwToolExit('"build winuwp" is not currently supported.');
     }
     if (!globals.platform.isWindows) {
-      throwToolExit('"build windows" only supported on Windows hosts.');
+      throwToolExit('"build winuwp" only supported on Windows hosts.');
     }
     displayNullSafetyMode(buildInfo);
     await buildWindowsUwp(

packages/flutter_tools/test/commands.shard/hermetic/build_linux_test.dart

@@ -130,7 +130,7 @@ void main() {
 
     expect(createTestCommandRunner(command).run(
       const <String>['build', 'linux', '--no-pub']
-    ), throwsToolExit());
+    ), throwsToolExit(message: '"build linux" only supported on Linux hosts.'));
   }, overrides: <Type, Generator>{
     Platform: () => notLinuxPlatform,
     FileSystem: () => fileSystem,
@@ -138,6 +138,20 @@ void main() {
     FeatureFlags: () => TestFeatureFlags(isLinuxEnabled: true),
   });
 
+  testUsingContext('Linux build fails when feature is disabled', () async {
+    final BuildCommand command = BuildCommand();
+    setUpMockProjectFilesForBuild();
+
+    expect(createTestCommandRunner(command).run(
+        const <String>['build', 'linux', '--no-pub']
+    ), throwsToolExit(message: '"build linux" is not currently supported. To enable, run "flutter config --enable-linux-desktop".'));
+  }, overrides: <Type, Generator>{
+    Platform: () => linuxPlatform,
+    FileSystem: () => fileSystem,
+    ProcessManager: () => FakeProcessManager.any(),
+    FeatureFlags: () => TestFeatureFlags(isLinuxEnabled: false),
+  });
+
   testUsingContext('Linux build invokes CMake and ninja, and writes temporary files', () async {
     final BuildCommand command = BuildCommand();
     processManager = FakeProcessManager.list(<FakeCommand>[

packages/flutter_tools/test/commands.shard/hermetic/build_macos_test.dart

@@ -131,13 +131,12 @@ void main() {
   testUsingContext('macOS build fails on non-macOS platform', () async {
     final BuildCommand command = BuildCommand();
     fileSystem.file('pubspec.yaml').createSync();
-    fileSystem.file('.packages').createSync();
     fileSystem.file(fileSystem.path.join('lib', 'main.dart'))
       .createSync(recursive: true);
 
     expect(createTestCommandRunner(command).run(
       const <String>['build', 'macos', '--no-pub']
-    ), throwsToolExit());
+    ), throwsToolExit(message: '"build macos" only supported on macOS hosts.'));
   }, overrides: <Type, Generator>{
     Platform: () => notMacosPlatform,
     FileSystem: () => fileSystem,
@@ -145,6 +144,22 @@ void main() {
     FeatureFlags: () => TestFeatureFlags(isMacOSEnabled: true),
   });
 
+  testUsingContext('macOS build fails when feature is disabled', () async {
+    final BuildCommand command = BuildCommand();
+    fileSystem.file('pubspec.yaml').createSync();
+    fileSystem.file(fileSystem.path.join('lib', 'main.dart'))
+        .createSync(recursive: true);
+
+    expect(createTestCommandRunner(command).run(
+        const <String>['build', 'macos', '--no-pub']
+    ), throwsToolExit(message: '"build macos" is not currently supported. To enable, run "flutter config --enable-macos-desktop".'));
+  }, overrides: <Type, Generator>{
+    Platform: () => macosPlatform,
+    FileSystem: () => fileSystem,
+    ProcessManager: () => FakeProcessManager.any(),
+    FeatureFlags: () => TestFeatureFlags(isMacOSEnabled: false),
+  });
+
   testUsingContext('macOS build forwards error stdout to status logger error', () async {
     final BuildCommand command = BuildCommand();
     createMinimalMockProjectFiles();

packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart

@@ -87,7 +87,7 @@ void main() {
 
     expect(
       () => runner.run(<String>['build', 'web']),
-      throwsToolExit(),
+      throwsToolExit(message: '"build web" is not currently supported. To enable, run "flutter config --enable-web".')
     );
   }, overrides: <Type, Generator>{
     Platform: () => fakePlatform,

packages/flutter_tools/test/commands.shard/hermetic/build_windows_test.dart

@@ -175,7 +175,7 @@ void main() {
 
     expect(createTestCommandRunner(command).run(
       const <String>['windows', '--no-pub']
-    ), throwsToolExit());
+    ), throwsToolExit(message: '"build windows" only supported on Windows hosts.'));
   }, overrides: <Type, Generator>{
     Platform: () => notWindowsPlatform,
     FileSystem: () => fileSystem,
@@ -183,6 +183,22 @@ void main() {
     FeatureFlags: () => TestFeatureFlags(isWindowsEnabled: true),
   });
 
+  testUsingContext('Windows build fails when feature is disabled', () async {
+    final FakeVisualStudio fakeVisualStudio = FakeVisualStudio(cmakePath);
+    final BuildWindowsCommand command = BuildWindowsCommand()
+      ..visualStudioOverride = fakeVisualStudio;
+    setUpMockProjectFilesForBuild();
+
+    expect(createTestCommandRunner(command).run(
+        const <String>['windows', '--no-pub']
+    ), throwsToolExit(message: '"build windows" is not currently supported. To enable, run "flutter config --enable-windows-desktop".'));
+  }, overrides: <Type, Generator>{
+    Platform: () => windowsPlatform,
+    FileSystem: () => fileSystem,
+    ProcessManager: () => FakeProcessManager.any(),
+    FeatureFlags: () => TestFeatureFlags(isWindowsEnabled: false),
+  });
+
   testUsingContext('Windows build does not spew stdout to status logger', () async {
     final FakeVisualStudio fakeVisualStudio = FakeVisualStudio(cmakePath);
     final BuildWindowsCommand command = BuildWindowsCommand()
@@ -474,6 +490,22 @@ C:\foo\windows\runner\main.cpp(17,1): error C2065: 'Baz': undeclared identifier
     FeatureFlags: () => TestFeatureFlags(isWindowsUwpEnabled: true),
   });
 
+  testUsingContext('Windows UWP uild fails on non windows platform', () async {
+    final FakeVisualStudio fakeVisualStudio = FakeVisualStudio(cmakePath);
+    final BuildWindowsUwpCommand command = BuildWindowsUwpCommand()
+      ..visualStudioOverride = fakeVisualStudio;
+    setUpMockProjectFilesForBuild();
+
+    expect(createTestCommandRunner(command).run(
+        const <String>['winuwp', '--no-pub']
+    ), throwsToolExit(message: '"build winuwp" only supported on Windows hosts.'));
+  }, overrides: <Type, Generator>{
+    Platform: () => notWindowsPlatform,
+    FileSystem: () => fileSystem,
+    ProcessManager: () => FakeProcessManager.any(),
+    FeatureFlags: () => TestFeatureFlags(isWindowsUwpEnabled: true),
+  });
+
   testUsingContext('Windows UWP build fails when the project version is out of date', () async {
     final FakeVisualStudio fakeVisualStudio = FakeVisualStudio(cmakePath);
     final BuildWindowsUwpCommand command = BuildWindowsUwpCommand()
@@ -491,6 +523,24 @@ C:\foo\windows\runner\main.cpp(17,1): error C2065: 'Baz': undeclared identifier
     FeatureFlags: () => TestFeatureFlags(isWindowsUwpEnabled: true),
   });
 
+  testUsingContext('Windows UWP build fails when feature is disabled', () async {
+    final FakeVisualStudio fakeVisualStudio = FakeVisualStudio(cmakePath);
+    final BuildWindowsUwpCommand command = BuildWindowsUwpCommand()
+      ..visualStudioOverride = fakeVisualStudio;
+    setUpMockProjectFilesForBuild();
+
+    // This message should include 'To enable, run "flutter config --enable-windows-uwp-desktop"."
+    // once the `windowsUwpEmbedding` feature is available on all platforms.
+    expect(createTestCommandRunner(command).run(
+        const <String>['winuwp', '--no-pub']
+    ), throwsToolExit(message: RegExp(r'"build winuwp" is not currently supported\.$')));
+  }, overrides: <Type, Generator>{
+    Platform: () => windowsPlatform,
+    FileSystem: () => fileSystem,
+    ProcessManager: () => FakeProcessManager.any(),
+    FeatureFlags: () => TestFeatureFlags(isWindowsUwpEnabled: false),
+  });
+
   testUsingContext('Windows UWP build fails after writing Cmake file', () async {
     final FakeVisualStudio fakeVisualStudio = FakeVisualStudio(cmakePath);
     final BuildWindowsUwpCommand command = BuildWindowsUwpCommand()