fix(shorebird_cli): verify that validators can be run before running them (#1254)

packages/shorebird_cli/lib/src/shorebird_validator.dart

@@ -26,6 +26,13 @@ class ValidationFailedException implements PreconditionFailedException {
   ExitCode get exitCode => ExitCode.config;
 }
 
+class UnsupportedContextException implements PreconditionFailedException {
+  // coverage:ignore-start
+  @override
+  ExitCode get exitCode => ExitCode.unavailable;
+  // coverage:ignore-end
+}
+
 class UnsupportedOperatingSystemException
     implements PreconditionFailedException {
   @override
@@ -80,6 +87,13 @@ class ShorebirdValidator {
       throw ShorebirdNotInitializedException();
     }
 
+    for (final validator in validators) {
+      if (!validator.canRunInCurrentContext()) {
+        logger.err(validator.incorrectContextMessage);
+        throw UnsupportedContextException();
+      }
+    }
+
     final validationIssues = await runValidators(validators);
     if (validationIssuesContainsError(validationIssues)) {
       logValidationFailure(issues: validationIssues);

packages/shorebird_cli/lib/src/validators/android_internet_permission_validator.dart

@@ -24,6 +24,14 @@ class AndroidInternetPermissionValidator extends Validator {
   @override
   bool canRunInCurrentContext() => _androidSrcDirectory.existsSync();
 
+  // coverage:ignore-start
+  @override
+  String get incorrectContextMessage => '''
+The ${_androidSrcDirectory.path} directory does not exist.
+
+The command you are running must be run at the root of a Flutter app project that supports the Android platform. If you are releasing a Flutter module, use 'aar' in place of 'android' in your shorebird command.''';
+  // coverage:ignore-end
+
   @override
   Future<List<ValidationIssue>> validate() async {
     const manifestFileName = 'AndroidManifest.xml';

packages/shorebird_cli/lib/src/validators/shorebird_flutter_validator.dart

@@ -21,9 +21,6 @@ class ShorebirdFlutterValidator extends Validator {
   @override
   String get description => 'Flutter install is correct';
 
-  @override
-  bool canRunInCurrentContext() => true;
-
   @override
   Future<List<ValidationIssue>> validate() async {
     final issues = <ValidationIssue>[];

packages/shorebird_cli/lib/src/validators/shorebird_version_validator.dart

@@ -10,9 +10,6 @@ class ShorebirdVersionValidator extends Validator {
   @override
   String get description => 'Shorebird is up-to-date';
 
-  @override
-  bool canRunInCurrentContext() => true;
-
   @override
   Future<List<ValidationIssue>> validate() async {
     final bool isShorebirdUpToDate;

packages/shorebird_cli/lib/src/validators/validators.dart

@@ -85,5 +85,10 @@ abstract class Validator {
   /// Not all validators use [process].
   Future<List<ValidationIssue>> validate();
 
-  bool canRunInCurrentContext();
+  /// Whether it makes sense to run the validator in the current working
+  /// directory.
+  bool canRunInCurrentContext() => true;
+
+  /// User-facing message explaining why [canRunInCurrentContext] is false.
+  String? get incorrectContextMessage => null;
 }

packages/shorebird_cli/test/src/shorebird_validator_test.dart

@@ -153,6 +153,23 @@ void main() {
           ),
         ).called(1);
       });
+
+      test(
+          '''throws UnsupportedContextException if validator cannot be run in current context''',
+          () async {
+        const errorMessage = 'Cannot run in this context';
+        when(() => validator.canRunInCurrentContext()).thenReturn(false);
+        when(() => validator.incorrectContextMessage).thenReturn(errorMessage);
+        await expectLater(
+          runWithOverrides(
+            () => shorebirdValidator.validatePreconditions(
+              validators: [validator],
+            ),
+          ),
+          throwsA(isA<UnsupportedContextException>()),
+        );
+        verify(() => logger.err(errorMessage)).called(1);
+      });
     });
   });
 }

packages/shorebird_cli/test/src/validators/validator_test.dart

@@ -0,0 +1,24 @@
+import 'package:shorebird_cli/src/validators/validators.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group(Validator, () {
+    test('canRunInContext is true by default', () {
+      expect(FakeValidator().canRunInCurrentContext(), equals(true));
+    });
+
+    test('incorrectContextMessage is null by default', () {
+      expect(FakeValidator().incorrectContextMessage, isNull);
+    });
+  });
+}
+
+class FakeValidator extends Validator {
+  @override
+  String get description => 'A fake validator for testing';
+
+  @override
+  Future<List<ValidationIssue>> validate() async {
+    return [];
+  }
+}