Honor parent_config / child_config in nested .swiftlint.yml files

CHANGELOG.md

@@ -42,6 +42,15 @@
 
 ### Bug Fixes
 
+* Honor `parent_config` and `child_config` keys in nested `.swiftlint.yml`
+  files. Previously these keys were silently dropped when the file was
+  discovered as a nested config during linting, causing per-directory
+  configs that pointed to a shared rule set (a common pattern for monorepos
+  and package fleets) to fall back to the parent's rules with no warning.
+  Nested configs are now resolved through the same `parent_config` /
+  `child_config` graph as the main config, with per-graph cycle detection.
+  [#3540](https://github.com/realm/SwiftLint/issues/3540)
+
 * Fix `literal_expression_end_indentation` autocorrection deleting source code
   when the closing bracket of a multiline literal shares a line with the end of
   a multiline last element (e.g. `...))]`). The corrector assumed everything

README.md

@@ -1060,8 +1060,12 @@ main configuration).
 `.swiftlint.yml` files are only considered as a nested configuration if they
 have not been used to build the main configuration already (e. g. by having
 been referenced via something like `child_config: Folder/.swiftlint.yml`).
-Also, `parent_config`/`child_config` specifications of nested configurations
-are getting ignored because there's no sense to that.
+
+Nested configurations may use `parent_config` and `child_config` references the
+same way as the main configuration — this is useful when several directories
+should share a delta on top of the same upstream rule set, for example a
+central `tests.yml` referenced from every `Tests/.swiftlint.yml` via
+`parent_config:`.
 
 If one (or more) SwiftLint file(s) are explicitly specified via the `--config`
 parameter, that configuration will be treated as an override, no matter whether

Source/SwiftLintFramework/Configuration/Configuration+Merging.swift

@@ -95,10 +95,13 @@ extension Configuration {
             // Use self merged with the nested config that was found
             // iff that nested config has not already been used to build the main config
 
-            // Ignore parent_config / child_config specifications of nested configs
+            // Resolve parent_config / child_config of nested configs the same way as for the main
+            // config. Cycle detection is scoped per nested file by FileGraph, and the
+            // `!fileGraph.includesFile(atPath:)` guard above prevents re-merging a file already in
+            // the main config chain.
             var childConfiguration = Configuration(
                 configurationFiles: [configurationSearchPath],
-                ignoreParentAndChildConfigs: true
+                ignoreParentAndChildConfigs: false
             )
             childConfiguration.fileGraph = FileGraph(rootDirectory: directory)
             config = merged(withChild: childConfiguration, rootDirectory: rootDirectory)

Tests/FileSystemAccessTests/ConfigurationTests+Mock.swift

@@ -25,6 +25,10 @@ enum Mock {
         static var childConfigCycle4: URL { level0.appending(path: "ChildConfig/Cycle4/") }
         static var parentConfigTest1: URL { level0.appending(path: "ParentConfig/Test1/") }
         static var parentConfigTest2: URL { level0.appending(path: "ParentConfig/Test2/") }
+        static var nestedParentConfig: URL { level0.appending(path: "NestedParentConfig/Test/") }
+        static var nestedParentConfigSub: URL { nestedParentConfig.appending(path: "Sub/") }
+        static var nestedParentConfigChild: URL { nestedParentConfig.appending(path: "Child/") }
+        static var nestedParentConfigChain: URL { nestedParentConfig.appending(path: "Chain/") }
         static var parentConfigCycle1: URL { level0.appending(path: "ParentConfig/Cycle1/") }
         static var parentConfigCycle2: URL { level0.appending(path: "ParentConfig/Cycle2/") }
         static var parentConfigCycle3: URL { level0.appending(path: "ParentConfig/Cycle3/") }
@@ -56,6 +60,9 @@ enum Mock {
         }
         static var _3: URL { Dir.level3.appending(path: Configuration.defaultFileName) }
         static var nested: URL { Dir.nested.appending(path: Configuration.defaultFileName) }
+        static var nestedParentConfig: URL {
+            Dir.nestedParentConfig.appending(path: Configuration.defaultFileName)
+        }
     }
 
     // MARK: Swift File Paths
@@ -65,6 +72,9 @@ enum Mock {
         static var _2: URL { Dir.level2.appending(path: "Level2.swift") }
         static var _3: URL { Dir.level3.appending(path: "Level3.swift") }
         static var nestedSub: URL { Dir.nestedSub.appending(path: "Sub.swift") }
+        static var nestedParentConfigSub: URL { Dir.nestedParentConfigSub.appending(path: "Sub.swift") }
+        static var nestedParentConfigChild: URL { Dir.nestedParentConfigChild.appending(path: "Child.swift") }
+        static var nestedParentConfigChain: URL { Dir.nestedParentConfigChain.appending(path: "Chain.swift") }
     }
 
     // MARK: Configurations
@@ -84,5 +94,8 @@ enum Mock {
         }
         static var _3: Configuration { Configuration(configurationFiles: [Yml._3]) }
         static var nested: Configuration { Configuration(configurationFiles: [Yml.nested]) }
+        static var nestedParentConfig: Configuration {
+            Configuration(configurationFiles: [Yml.nestedParentConfig])
+        }
     }
 }

Tests/FileSystemAccessTests/ConfigurationTests.swift

@@ -354,6 +354,7 @@ final class ConfigurationTests: SwiftLintTestCase { // swiftlint:disable:this ty
                                                         excludeByPrefix: false)
         let filenames = paths.map(\.lastPathComponent).sorted()
         let expectedFilenames = [
+            "Chain.swift", "Child.swift",
             "DirectoryLevel1.swift",
             "Level0.swift", "Level1.swift", "Level2.swift", "Level3.swift",
             "Main.swift", "Sub.swift",
@@ -542,6 +543,7 @@ final class ConfigurationTests: SwiftLintTestCase { // swiftlint:disable:this ty
                 "ChildConfig".url(),
                 "ParentConfig".url(),
                 "NestedConfig".url(),
+                "NestedParentConfig".url(),
             ]
         )
         let paths = configuration.lintablePaths(inPath: URL.cwd,
@@ -560,6 +562,7 @@ final class ConfigurationTests: SwiftLintTestCase { // swiftlint:disable:this ty
                 "ChildConfig".url(),
                 "ParentConfig".url(),
                 "NestedConfig".url(),
+                "NestedParentConfig".url(),
             ]
         )
         let paths = configuration.lintablePaths(inPath: URL.cwd,

Tests/FileSystemAccessTests/GlobTests.swift

@@ -83,6 +83,9 @@ final class GlobTests: SwiftLintTestCase {
             "Level1/Level2/Level3/Level3.swift",
             "NestedConfig/Test/Main.swift",
             "NestedConfig/Test/Sub/Sub.swift",
+            "NestedParentConfig/Test/Chain/Chain.swift",
+            "NestedParentConfig/Test/Child/Child.swift",
+            "NestedParentConfig/Test/Sub/Sub.swift",
         ].map { mockPath.appending(path: $0) }
 
         let files = Glob.resolveGlob(mockPath.appending(path: "**/*.swift"))

Tests/FileSystemAccessTests/MultipleConfigurationsTests.swift

@@ -258,15 +258,54 @@ final class MultipleConfigurationsTests: SwiftLintTestCase {
         )
     }
 
-    func testParentConfigIsIgnoredAsNestedConfiguration() {
-        // If a configuration has already been used to build the main config,
-        // it should not again be regarded as a nested config
+    func testNestedConfigAlreadyInMainGraphIsSkipped() {
+        // If a configuration file has already been used to build the main config (e.g. as a
+        // parent_config), discovering the same file as a nested config during linting must not
+        // re-merge it; the per-file configuration must equal the main config unchanged.
         XCTAssertEqual(
             Mock.Config.nested.configuration(for: SwiftLintFile(path: Mock.Swift.nestedSub)!),
             Mock.Config.nested
         )
     }
 
+    // MARK: - Nested Configs with parent_config / child_config (issue #3540)
+    func testNestedConfigHonorsParentConfig() {
+        // A nested .swiftlint.yml may reference a parent_config. The resolved per-file
+        // configuration must equal "main merged with the parent's contents on top".
+        XCTAssert(FileManager.default.changeCurrentDirectoryPath(Mock.Dir.nestedParentConfig.filepath))
+        let mainConfig = Configuration(configurationFiles: [])
+        let actual = mainConfig.configuration(for: SwiftLintFile(path: Mock.Swift.nestedParentConfigSub)!)
+        let expected = Configuration(
+            configurationFiles: [".swiftlint.yml".url(), "refinements.yml".url()]
+        )
+        assertEqualExceptForFileGraph(actual, expected)
+    }
+
+    func testNestedConfigHonorsChildConfig() {
+        // A nested .swiftlint.yml may reference a child_config. The child wins over the
+        // nested file itself, then the combined result is merged on top of the main config.
+        XCTAssert(FileManager.default.changeCurrentDirectoryPath(Mock.Dir.nestedParentConfig.filepath))
+        let mainConfig = Configuration(configurationFiles: [])
+        let actual = mainConfig.configuration(for: SwiftLintFile(path: Mock.Swift.nestedParentConfigChild)!)
+        let expected = Configuration(
+            configurationFiles: [".swiftlint.yml".url(), "child_refinements.yml".url()]
+        )
+        assertEqualExceptForFileGraph(actual, expected)
+    }
+
+    func testNestedConfigParentChain() {
+        // A nested .swiftlint.yml whose parent_config itself has a parent_config: the full
+        // chain must be merged in order (deepest ancestor first) before being applied on top
+        // of the main config.
+        XCTAssert(FileManager.default.changeCurrentDirectoryPath(Mock.Dir.nestedParentConfig.filepath))
+        let mainConfig = Configuration(configurationFiles: [])
+        let actual = mainConfig.configuration(for: SwiftLintFile(path: Mock.Swift.nestedParentConfigChain)!)
+        let expected = Configuration(
+            configurationFiles: [".swiftlint.yml".url(), "chain_base.yml".url(), "chain_refinements.yml".url()]
+        )
+        assertEqualExceptForFileGraph(actual, expected)
+    }
+
     // MARK: - Child & Parent Configs
     func testValidChildConfig() {
         guard !isRunningWithBazel else {

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/.swiftlint.yml

@@ -0,0 +1,3 @@
+line_length: 80
+disabled_rules:
+  - todo

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/Chain/.swiftlint.yml

@@ -0,0 +1 @@
+parent_config: ../chain_refinements.yml

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/Chain/Chain.swift

@@ -0,0 +1 @@
+// Empty placeholder for nested-config lookup tests.

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/Child/.swiftlint.yml

@@ -0,0 +1 @@
+child_config: ../child_refinements.yml

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/Child/Child.swift

@@ -0,0 +1 @@
+// Empty placeholder for nested-config lookup tests.

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/Sub/.swiftlint.yml

@@ -0,0 +1 @@
+parent_config: ../refinements.yml

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/Sub/Sub.swift

@@ -0,0 +1 @@
+// Empty placeholder for nested-config lookup tests.

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/chain_base.yml

@@ -0,0 +1 @@
+line_length: 500

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/chain_refinements.yml

@@ -0,0 +1,2 @@
+parent_config: chain_base.yml
+line_length: 300

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/child_refinements.yml

@@ -0,0 +1 @@
+line_length: 250

Tests/FileSystemAccessTests/Resources/ProjectMock/NestedParentConfig/Test/refinements.yml

@@ -0,0 +1 @@
+line_length: 200