[tool] Improve Swift lint error message (#8074)

If the Swift linter finds issues, log a message that communicates that rather than sounding like the linter failed to run.

Author: stuartmorgan-g

script/tool/lib/src/format_command.dart

@@ -35,6 +35,7 @@ const int _exitGitFailed = 6;
 const int _exitDependencyMissing = 7;
 const int _exitSwiftFormatFailed = 8;
 const int _exitKotlinFormatFailed = 9;
+const int _exitSwiftLintFoundIssues = 10;
 
 final Uri _javaFormatterUrl = Uri.https('github.com',
     '/google/google-java-format/releases/download/google-java-format-1.3/google-java-format-1.3-all-deps.jar');
@@ -239,7 +240,10 @@ class FormatCommand extends PackageLoopingCommand {
             '--strict',
           ],
           files: swiftFiles);
-      if (lintExitCode != 0) {
+      if (lintExitCode == 1) {
+        printError('Swift linter found issues. See above for linter output.');
+        throw ToolExit(_exitSwiftLintFoundIssues);
+      } else if (lintExitCode != 0) {
         printError('Failed to lint Swift files: exit code $lintExitCode.');
         throw ToolExit(_exitSwiftFormatFailed);
       }

script/tool/test/format_command_test.dart

@@ -643,7 +643,7 @@ void main() {
           ]));
     });
 
-    test('fails if swift-format lint fails', () async {
+    test('fails if swift-format lint finds issues', () async {
       const List<String> files = <String>[
         'macos/foo.swift',
       ];
@@ -675,7 +675,43 @@ void main() {
       expect(
           output,
           containsAllInOrder(<Matcher>[
-            contains('Failed to lint Swift files: exit code 1.'),
+            contains('Swift linter found issues. See above for linter output.'),
+          ]));
+    });
+
+    test('fails if swift-format lint fails', () async {
+      const List<String> files = <String>[
+        'macos/foo.swift',
+      ];
+      final RepositoryPackage plugin =
+          createFakePlugin('a_plugin', packagesDir, extraFiles: files);
+      fakePubGet(plugin);
+
+      processRunner.mockProcessesForExecutable['swift-format'] =
+          <FakeProcessInfo>[
+        FakeProcessInfo(MockProcess(),
+            <String>['--version']), // check for working swift-format
+        FakeProcessInfo(MockProcess(), <String>['-i']),
+        FakeProcessInfo(MockProcess(exitCode: 99), <String>[
+          'lint',
+          '--parallel',
+          '--strict',
+        ]),
+      ];
+      Error? commandError;
+      final List<String> output = await runCapturingPrint(runner, <String>[
+        'format',
+        '--swift',
+        '--swift-format-path=swift-format'
+      ], errorHandler: (Error e) {
+        commandError = e;
+      });
+
+      expect(commandError, isA<ToolExit>());
+      expect(
+          output,
+          containsAllInOrder(<Matcher>[
+            contains('Failed to lint Swift files: exit code 99.'),
           ]));
     });