fix(config): fall back when nested YAML is invalid

CHANGELOG.md

@@ -693,7 +693,12 @@
   or other error.  
   [Martin Redington](https://github.com/mildm8nnered)
   [#6052](https://github.com/realm/SwiftLint/issues/6052)
-
+
+* Fall back to default configuration when a nested `.swiftlint.yml` cannot be parsed
+  instead of aborting (e.g. duplicate YAML keys in a subdirectory).  
+  [leno23](https://github.com/leno23)
+  [#6052](https://github.com/realm/SwiftLint/issues/6052)
+
 * Keep the default severity levels when neither `warning` nor `error` values are configured.
   Ensure especially that the `error` level is not set to `nil` when the `warning` level
   isn't set either.  

Source/SwiftLintCore/Models/Issue.swift

@@ -122,6 +122,8 @@ public enum Issue: LocalizedError, Equatable {
             return "error: \(message)"
         case .genericWarning:
             return "warning: \(message)"
+        case .yamlParsing:
+            return "warning: \(message)"
         default:
             return Self.genericWarning(message).errorDescription
         }

Source/SwiftLintFramework/Configuration/Configuration+Merging.swift

@@ -116,7 +116,8 @@ extension Configuration {
             // Ignore parent_config / child_config specifications of nested configs
             var childConfiguration = Configuration(
                 configurationFiles: [configurationSearchPath],
-                ignoreParentAndChildConfigs: true
+                ignoreParentAndChildConfigs: true,
+                useDefaultConfigOnFailure: true
             )
             childConfiguration.fileGraph = FileGraph(rootDirectory: directory)
             config = merged(withChild: childConfiguration, rootDirectory: rootDirectory)

Tests/FileSystemAccessTests/ConfigurationTests+Mock.swift

@@ -33,6 +33,7 @@ internal extension ConfigurationTests {
             static var remoteConfigLocalRef: String { level0.stringByAppendingPathComponent("RemoteConfig/LocalRef") }
             static var remoteConfigCycle: String { level0.stringByAppendingPathComponent("RemoteConfig/Cycle") }
             static var emptyFolder: String { level0.stringByAppendingPathComponent("EmptyFolder") }
+            static var duplicateYamlKeys: String { level0.stringByAppendingPathComponent("DuplicateYamlKeys") }
 
             static var exclusionTests: String { testResourcesPath.stringByAppendingPathComponent("ExclusionTests") }
             static var directory: String { exclusionTests.stringByAppendingPathComponent("directory") }
@@ -65,6 +66,9 @@ internal extension ConfigurationTests {
             static var _2: String { Dir.level2.stringByAppendingPathComponent("Level2.swift") }
             static var _3: String { Dir.level3.stringByAppendingPathComponent("Level3.swift") }
             static var nestedSub: String { Dir.nestedSub.stringByAppendingPathComponent("Sub.swift") }
+            static var duplicateYamlKeysSub: String {
+                Dir.duplicateYamlKeys.stringByAppendingPathComponent("subdir/a.swift")
+            }
         }
 
         // MARK: Configurations

Tests/FileSystemAccessTests/ConfigurationTests+MultipleConfigs.swift

@@ -234,6 +234,18 @@ extension ConfigurationTests {
         )
     }
 
+    func testNestedConfigurationWithInvalidYamlFallsBackToDefault() async throws {
+        XCTAssert(FileManager.default.changeCurrentDirectoryPath(Mock.Dir.duplicateYamlKeys))
+
+        let console = try await Issue.captureConsole {
+            let config = Configuration(configurationFiles: [])
+            _ = config.configuration(for: SwiftLintFile(path: Mock.Swift.duplicateYamlKeysSub)!)
+        }
+
+        XCTAssertTrue(console.contains("Cannot parse YAML file"))
+        XCTAssertTrue(console.contains("Falling back to default configuration"))
+    }
+
     func testNestedConfigurationForOnePathPassedIn() {
         // If a path to one or more configuration files is specified, nested configurations should be ignored
         let config = Configuration(configurationFiles: [Mock.Yml._0])

Tests/FileSystemAccessTests/Resources/ProjectMock/DuplicateYamlKeys/subdir/.swiftlint.yml

@@ -0,0 +1,5 @@
+opt_in_rules:
+  - closure_body_length
+
+opt_in_rules:
+  - closure_body_length

Tests/FileSystemAccessTests/Resources/ProjectMock/DuplicateYamlKeys/subdir/a.swift

@@ -0,0 +1 @@
+// Test file for nested configuration with invalid YAML.