Add --strict-baseline flag to fail lint when baselined violations are fixed

CHANGELOG.md

@@ -12,6 +12,13 @@
 
 ### Enhancements
 
+* Add `--strict-baseline` command-line flag (and `strict_baseline` configuration
+  key) that fails linting when violations recorded in the baseline are no longer
+  detected, encouraging users to regenerate the baseline once baselined
+  violations have been fixed.  
+  [swizzlr](https://github.com/swizzlr)
+  [#6511](https://github.com/realm/SwiftLint/issues/6511)
+
 * Print fixed code read from stdin to stdout.  
   [SimplyDanny](https://github.com/SimplyDanny)
   [#6501](https://github.com/realm/SwiftLint/issues/6501)

README.md

@@ -742,6 +742,10 @@ baseline: Baseline.json
 # The path to save detected violations to as a new baseline.
 write_baseline: Baseline.json
 
+# If true, SwiftLint will fail when violations recorded in the baseline are no
+# longer detected, encouraging the baseline to be regenerated after fixes.
+strict_baseline: false
+
 # If true, SwiftLint will check for updates after linting or analyzing.
 check_for_updates: true
 

Source/SwiftLintFramework/Configuration/Configuration+Merging.swift

@@ -29,6 +29,7 @@ extension Configuration {
             lenient: childConfiguration.lenient,
             baseline: childConfiguration.baseline,
             writeBaseline: childConfiguration.writeBaseline,
+            strictBaseline: childConfiguration.strictBaseline,
             checkForUpdates: childConfiguration.checkForUpdates
         )
     }

Source/SwiftLintFramework/Configuration/Configuration+Parsing.swift

@@ -18,6 +18,7 @@ extension Configuration {
         case lenient = "lenient"
         case baseline = "baseline"
         case writeBaseline = "write_baseline"
+        case strictBaseline = "strict_baseline"
         case checkForUpdates = "check_for_updates"
         case childConfig = "child_config"
         case parentConfig = "parent_config"
@@ -108,6 +109,7 @@ extension Configuration {
             lenient: dict[Key.lenient.rawValue] as? Bool ?? false,
             baseline: dict[Key.baseline.rawValue] as? String,
             writeBaseline: dict[Key.writeBaseline.rawValue] as? String,
+            strictBaseline: dict[Key.strictBaseline.rawValue] as? Bool ?? false,
             checkForUpdates: dict[Key.checkForUpdates.rawValue] as? Bool ?? false
         )
     }

Source/SwiftLintFramework/Configuration/Configuration.swift

@@ -47,6 +47,9 @@ public struct Configuration {
     /// The path to write a baseline to.
     public let writeBaseline: String?
 
+    /// Fail linting when violations recorded in the baseline are no longer detected.
+    public let strictBaseline: Bool
+
     /// Check for updates.
     public let checkForUpdates: Bool
 
@@ -89,6 +92,7 @@ public struct Configuration {
         lenient: Bool,
         baseline: String?,
         writeBaseline: String?,
+        strictBaseline: Bool,
         checkForUpdates: Bool
     ) {
         self.rulesWrapper = rulesWrapper
@@ -104,6 +108,7 @@ public struct Configuration {
         self.lenient = lenient
         self.baseline = baseline
         self.writeBaseline = writeBaseline
+        self.strictBaseline = strictBaseline
         self.checkForUpdates = checkForUpdates
     }
 
@@ -125,6 +130,7 @@ public struct Configuration {
         lenient = configuration.lenient
         baseline = configuration.baseline
         writeBaseline = configuration.writeBaseline
+        strictBaseline = configuration.strictBaseline
         checkForUpdates = configuration.checkForUpdates
     }
 
@@ -170,6 +176,7 @@ public struct Configuration {
         lenient: Bool = false,
         baseline: String? = nil,
         writeBaseline: String? = nil,
+        strictBaseline: Bool = false,
         checkForUpdates: Bool = false
     ) {
         if let pinnedVersion, pinnedVersion != Version.current.value {
@@ -200,6 +207,7 @@ public struct Configuration {
             lenient: lenient,
             baseline: baseline,
             writeBaseline: writeBaseline,
+            strictBaseline: strictBaseline,
             checkForUpdates: checkForUpdates
         )
     }
@@ -316,6 +324,7 @@ extension Configuration: Hashable {
         hasher.combine(lenient)
         hasher.combine(baseline)
         hasher.combine(writeBaseline)
+        hasher.combine(strictBaseline)
         hasher.combine(checkForUpdates)
         hasher.combine(basedOnCustomConfigurationFiles)
         hasher.combine(cachePath)
@@ -338,6 +347,7 @@ extension Configuration: Hashable {
             lhs.lenient == rhs.lenient &&
             lhs.baseline == rhs.baseline &&
             lhs.writeBaseline == rhs.writeBaseline &&
+            lhs.strictBaseline == rhs.strictBaseline &&
             lhs.checkForUpdates == rhs.checkForUpdates &&
             lhs.rulesMode == rhs.rulesMode
     }

Source/SwiftLintFramework/LintOrAnalyzeCommand.swift

@@ -44,6 +44,7 @@ package struct LintOrAnalyzeOptions {
     let reporter: String?
     let baseline: String?
     let writeBaseline: String?
+    let strictBaseline: Bool
     let workingDirectory: String?
     let quiet: Bool
     let output: String?
@@ -73,6 +74,7 @@ package struct LintOrAnalyzeOptions {
                  reporter: String?,
                  baseline: String?,
                  writeBaseline: String?,
+                 strictBaseline: Bool,
                  workingDirectory: String?,
                  quiet: Bool,
                  output: String?,
@@ -101,6 +103,7 @@ package struct LintOrAnalyzeOptions {
         self.reporter = reporter
         self.baseline = baseline
         self.writeBaseline = writeBaseline
+        self.strictBaseline = strictBaseline
         self.workingDirectory = workingDirectory
         self.quiet = quiet
         self.output = output
@@ -150,6 +153,7 @@ package struct LintOrAnalyzeCommand {
         if let baselineOutputPath = options.writeBaseline ?? builder.configuration.writeBaseline {
             try Baseline(violations: builder.unfilteredViolations).write(toPath: baselineOutputPath)
         }
+        appendFixedBaselineViolations(builder: builder)
         let numberOfSeriousViolations = try Signposts.record(name: "LintOrAnalyzeCommand.PostProcessViolations") {
             try postProcessViolations(files: files, builder: builder)
         }
@@ -165,6 +169,7 @@ package struct LintOrAnalyzeCommand {
         let options = builder.options
         let visitorMutationQueue = DispatchQueue(label: "io.realm.swiftlint.lintVisitorMutation")
         let baseline = try baseline(options, builder.configuration)
+        builder.baseline = baseline
         return try await builder.configuration.visitLintableFiles(options: options, cache: builder.cache,
                                                                   storage: builder.storage) { linter in
             let currentViolations: [StyleViolation]
@@ -234,6 +239,22 @@ package struct LintOrAnalyzeCommand {
         return numberOfSeriousViolations
     }
 
+    private static func appendFixedBaselineViolations(builder: LintOrAnalyzeResultBuilder) {
+        let options = builder.options
+        let configuration = builder.configuration
+        guard options.strictBaseline || configuration.strictBaseline,
+              let baseline = builder.baseline else {
+            return
+        }
+        let currentBaseline = Baseline(violations: builder.unfilteredViolations)
+        let fixedViolations = currentBaseline.compare(baseline).map(createFixedBaselineViolation)
+        guard fixedViolations.isNotEmpty else {
+            return
+        }
+        builder.violations += fixedViolations
+        builder.report(violations: fixedViolations, realtimeCondition: true)
+    }
+
     private static func baseline(_ options: LintOrAnalyzeOptions, _ configuration: Configuration) throws -> Baseline? {
         if let baselinePath = options.baseline ?? configuration.baseline {
             do {
@@ -266,6 +287,24 @@ package struct LintOrAnalyzeCommand {
         return numberOfWarningViolations >= warningThreshold
     }
 
+    private static func createFixedBaselineViolation(fromBaseline violation: StyleViolation) -> StyleViolation {
+        let description = RuleDescription(
+            identifier: "fixed_baseline_violation",
+            name: "Fixed Baseline",
+            description: "A violation recorded in the baseline has been fixed or is no longer detected",
+            kind: .lint
+        )
+        return StyleViolation(
+            ruleDescription: description,
+            severity: .error,
+            location: violation.location,
+            reason: """
+                Violation previously recorded in the baseline for '\(violation.ruleIdentifier)' is no longer \
+                detected. Regenerate the baseline to acknowledge this fix
+                """
+        )
+    }
+
     private static func createThresholdViolation(threshold: Int) -> StyleViolation {
         let description = RuleDescription(
             identifier: "warning_threshold",
@@ -374,6 +413,7 @@ private class LintOrAnalyzeResultBuilder {
     var unfilteredViolations = [StyleViolation]()
     /// The violations to be reported, possibly filtered by a baseline, plus any threshold violations.
     var violations = [StyleViolation]()
+    var baseline: Baseline?
     let storage = RuleStorage()
     let configuration: Configuration
     let reporter: any Reporter.Type

Source/swiftlint/Commands/Analyze.swift

@@ -34,6 +34,7 @@ extension SwiftLint {
                 reporter: common.reporter,
                 baseline: common.baseline,
                 writeBaseline: common.writeBaseline,
+                strictBaseline: common.strictBaseline,
                 workingDirectory: common.workingDirectory,
                 quiet: quiet,
                 output: common.output,

Source/swiftlint/Commands/Lint.swift

@@ -51,6 +51,7 @@ extension SwiftLint {
                 reporter: common.reporter,
                 baseline: common.baseline,
                 writeBaseline: common.writeBaseline,
+                strictBaseline: common.strictBaseline,
                 workingDirectory: common.workingDirectory,
                 quiet: quiet,
                 output: common.output,

Source/swiftlint/Common/LintOrAnalyzeArguments.swift

@@ -46,6 +46,12 @@ struct LintOrAnalyzeArguments: ParsableArguments {
     var baseline: String?
     @Option(help: "The path to save detected violations to as a new baseline.")
     var writeBaseline: String?
+    @Flag(help: """
+        Fail linting if violations previously recorded in the baseline are no longer \
+        detected. Encourages keeping the baseline up-to-date by regenerating it \
+        once baselined violations have been fixed.
+        """)
+    var strictBaseline = false
     @Option(help: "The working directory to use when running SwiftLint.")
     var workingDirectory: String?
     @Option(help: "The file where violations should be saved. Prints to stdout by default.")

Tests/FileSystemAccessTests/BaselineTests.swift

@@ -137,6 +137,20 @@ final class BaselineTests: XCTestCase {
         }
     }
 
+    func testCompareDetectsFixedViolations() throws {
+        try withExampleFileCreated { sourceFilePath in
+            let originalViolations = Self.violations(for: sourceFilePath)
+            let oldBaseline = Baseline(violations: originalViolations)
+            // Simulate some baselined violations being fixed.
+            let remainingViolations = Array(originalViolations.dropFirst(2))
+            let newBaseline = Baseline(violations: remainingViolations)
+            // `newBaseline.compare(oldBaseline)` yields violations in the old
+            // baseline that are no longer detected — i.e., fixed violations.
+            let fixed = newBaseline.compare(oldBaseline)
+            XCTAssertEqual(fixed.count, 2)
+        }
+    }
+
     func testCompare() throws {
         try withExampleFileCreated { sourceFilePath in
             let ruleDescriptions = Self.ruleDescriptions + Self.ruleDescriptions

Tests/FrameworkTests/LintOrAnalyzeOptionsTests.swift

@@ -54,6 +54,7 @@ private extension LintOrAnalyzeOptions {
                   reporter: nil,
                   baseline: nil,
                   writeBaseline: nil,
+                  strictBaseline: false,
                   workingDirectory: nil,
                   quiet: false,
                   output: nil,