Fix finding the nested config when a single file path is passed (#3342)

Fixes #3341

When SwiftLint searches for nested configurations and only one file has been passed in via the `paths` argument, SwiftLint returns early after inadvertently comparing the containing directory of the file-to-be-linted to itself. This happens because `rootDirectory` is calculated from `rootPath`, which is set to the file being linted in this scenario.

CHANGELOG.md

@@ -29,6 +29,9 @@
   [hank121314](https://github.com/hank121314)
   [#2367](https://github.com/realm/SwiftLint/issues/3267)
 
+* Fix finding a nested config when a single file path is passed.  
+  [Seth Friedman](https://github.com/sethfri)
+
 ## 0.40.2: Demo Unit
 
 #### Breaking

Source/SwiftLintFramework/Extensions/Configuration+Merging.swift

@@ -16,7 +16,9 @@ extension Configuration {
     }
 
     private func configuration(forPath path: String) -> Configuration {
-        if path == rootDirectory {
+        let rootConfigurationDirectory = configurationPath?.bridge().deletingLastPathComponent
+        // We're linting a file in the same directory as the root configuration we've already loaded
+        if path == rootConfigurationDirectory {
             return self
         }
 
@@ -49,23 +51,6 @@ extension Configuration {
         return self
     }
 
-    private var rootDirectory: String? {
-        guard let rootPath = rootPath else {
-            return nil
-        }
-
-        var isDirectoryObjC: ObjCBool = false
-        guard FileManager.default.fileExists(atPath: rootPath, isDirectory: &isDirectoryObjC) else {
-            return nil
-        }
-
-        if isDirectoryObjC.boolValue {
-            return rootPath
-        } else {
-            return rootPath.bridge().deletingLastPathComponent
-        }
-    }
-
     private struct HashableRule: Hashable {
         fileprivate let rule: Rule
 

Tests/LinuxMain.swift

@@ -1,4 +1,4 @@
-// Generated using Sourcery 0.18.0 — https://github.com/krzysztofzablocki/Sourcery
+// Generated using Sourcery 1.0.0 — https://github.com/krzysztofzablocki/Sourcery
 // DO NOT EDIT
 
 @testable import SwiftLintFrameworkTests
@@ -208,6 +208,7 @@ extension ConfigurationTests {
         ("testLevel2", testLevel2),
         ("testLevel3", testLevel3),
         ("testNestedConfigurationWithCustomRootPath", testNestedConfigurationWithCustomRootPath),
+        ("testNestedConfigurationForOnePathPassedIn", testNestedConfigurationForOnePathPassedIn),
         ("testMergedWarningThreshold", testMergedWarningThreshold),
         ("testNestedWhitelistedRules", testNestedWhitelistedRules),
         ("testNestedConfigurationsWithCustomRulesMerge", testNestedConfigurationsWithCustomRulesMerge),

Tests/SwiftLintFrameworkTests/ConfigurationTests+Nested.swift

@@ -45,6 +45,14 @@ extension ConfigurationTests {
         XCTAssertEqual(projectMockConfig0.merge(with: projectMockConfig3).rootPath, projectMockConfig3.rootPath)
     }
 
+    func testNestedConfigurationForOnePathPassedIn() {
+        let config = Configuration(path: projectMockYAML0, rootPath: projectMockSwift3)
+        XCTAssertEqual(
+            config.configuration(for: SwiftLintFile(path: projectMockSwift3)!),
+            config.merge(with: projectMockConfig3)
+        )
+    }
+
     func testMergedWarningThreshold() {
         func configuration(forWarningThreshold warningThreshold: Int?) -> Configuration {
             return Configuration(warningThreshold: warningThreshold,