Fix multiline_call_arguments with enum-case patterns.

CHANGELOG.md

@@ -95,6 +95,10 @@
   [SimplyDanny](https://github.com/SimplyDanny)
   [#6080](https://github.com/realm/SwiftLint/issues/6080)
 
+* `multiline_call_arguments` no longer reports violations for enum-case patterns in
+  pattern matching (e.g. if case, switch case, for case, catch).  
+  [GandaLF2006](https://github.com/GandaLF2006)
+
 ## 0.63.2: High-Speed Extraction
 
 ### Breaking

Source/SwiftLintBuiltInRules/Rules/Lint/MultilineCallArgumentsRule.swift

@@ -5,105 +5,188 @@ import SwiftSyntax
 struct MultilineCallArgumentsRule: Rule {
     var configuration = MultilineCallArgumentsConfiguration()
 
+    enum Reason {
+        static let singleLineMultipleArgumentsNotAllowed =
+            "Single-line calls with multiple arguments are not allowed"
+
+        static func tooManyArgumentsOnSingleLine(max: Int) -> String {
+            "Too many arguments on a single line (max: \(max))"
+        }
+
+        static let eachArgumentMustStartOnOwnLine =
+            "In multi-line calls, each argument must start on its own line"
+
+        static let newlineRequiredAfterCommaInMultilineCall =
+            "In multi-line calls, a newline is required after each comma"
+    }
+
     static let description = RuleDescription(
         identifier: "multiline_call_arguments",
         name: "Multiline Call Arguments",
-        description: "Call should have each parameter on a separate line",
+        description: """
+        Enforces one-argument-per-line for multi-line calls and requires a newline after commas \
+        when arguments are split across lines;
+        optionally limits or forbids multi-argument single-line calls via configuration.
+        """,
         kind: .style,
-        nonTriggeringExamples: [
-            Example("""
-                foo(
-                param1: "param1",
-                    param2: false,
-                    param3: []
-                )
-                """,
-                configuration: ["max_number_of_single_line_parameters": 2]),
-            Example("""
-                foo(param1: 1,
-                    param2: false,
-                    param3: [])
-                """,
-                configuration: ["max_number_of_single_line_parameters": 1]),
-            Example(
-                "foo(param1: 1, param2: false)",
-                configuration: ["max_number_of_single_line_parameters": 2]),
-            Example(
-                "Enum.foo(param1: 1, param2: false)",
-                configuration: ["max_number_of_single_line_parameters": 2]),
-            Example("foo(param1: 1)", configuration: ["allows_single_line": false]),
-            Example("Enum.foo(param1: 1)", configuration: ["allows_single_line": false]),
-            Example(
-                "Enum.foo(param1: 1, param2: 2, param3: 3)",
-                configuration: ["allows_single_line": true]),
-            Example("""
-                foo(
-                    param1: 1,
-                    param2: 2,
-                    param3: 3
-                )
-                """,
-                configuration: ["allows_single_line": false]),
-        ],
-        triggeringExamples: [
-            Example(
-                "↓foo(param1: 1, param2: false, param3: [])",
-                configuration: ["max_number_of_single_line_parameters": 2]),
-            Example(
-                "↓Enum.foo(param1: 1, param2: false, param3: [])",
-                configuration: ["max_number_of_single_line_parameters": 2]),
-            Example("""
-                ↓foo(param1: 1, param2: false,
-                        param3: [])
-                """,
-                configuration: ["max_number_of_single_line_parameters": 3]),
-            Example("""
-                ↓Enum.foo(param1: 1, param2: false,
-                        param3: [])
-                """,
-                configuration: ["max_number_of_single_line_parameters": 3]),
-            Example("↓foo(param1: 1, param2: false)", configuration: ["allows_single_line": false]),
-            Example("↓Enum.foo(param1: 1, param2: false)", configuration: ["allows_single_line": false]),
-        ]
+        nonTriggeringExamples: MultilineCallArgumentsRuleExamples.nonTriggeringExamples,
+        triggeringExamples: MultilineCallArgumentsRuleExamples.triggeringExamples
     )
 }
 
 private extension MultilineCallArgumentsRule {
     final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
+        /// Cache line lookups by utf8Offset (stable, cheap key)
+        private var lineCache: [Int: Int] = [:]
+
+        override init(configuration: ConfigurationType, file: SwiftLintFile) {
+            super.init(configuration: configuration, file: file)
+
+            // Most files trigger O(10–100) unique line lookups for this rule.
+            // Reserving a small initial capacity reduces rehashing; it is NOT a hard limit.
+            lineCache.reserveCapacity(64)
+        }
+
         override func visitPost(_ node: FunctionCallExprSyntax) {
-            if containsViolation(parameterPositions: node.arguments.map(\.positionAfterSkippingLeadingTrivia)) {
-                violations.append(node.calledExpression.positionAfterSkippingLeadingTrivia)
+            // Ignore calls that are part of pattern-matching syntax (patterns only, not bodies).
+            guard !node.isInPatternMatchingPatternPosition else { return }
+
+            let args = node.arguments
+            guard args.count > 1 else { return }
+
+            let argumentPositions = args.map(\.positionAfterSkippingLeadingTrivia)
+            guard let violation = reasonedViolation(argumentPositions: argumentPositions, arguments: args) else {
+                return
             }
+            violations.append(violation)
         }
 
-        private func containsViolation(parameterPositions: [AbsolutePosition]) -> Bool {
-            var numberOfParameters = 0
-            var linesWithParameters: Set<Int> = []
-            var hasMultipleParametersOnSameLine = false
+        private func reasonedViolation(
+            argumentPositions: [AbsolutePosition],
+            arguments: LabeledExprListSyntax
+        ) -> ReasonedRuleViolation? {
+            guard let firstPos = argumentPositions.first else { return nil }
 
-            for position in parameterPositions {
-                let line = locationConverter.location(for: position).line
+            let firstLine = line(for: firstPos)
+            var allOnSameLine = true
+            for pos in argumentPositions.dropFirst() where line(for: pos) != firstLine {
+                allOnSameLine = false
+                break
+            }
+
+            if allOnSameLine {
+                if !configuration.allowsSingleLine {
+                    return ReasonedRuleViolation(
+                        position: argumentPositions[1],
+                        reason: Reason.singleLineMultipleArgumentsNotAllowed
+                    )
+                }
 
-                if !linesWithParameters.insert(line).inserted {
-                    hasMultipleParametersOnSameLine = true
+                if let max = configuration.maxNumberOfSingleLineParameters,
+                   argumentPositions.count > max {
+                    return ReasonedRuleViolation(
+                        position: argumentPositions[max],
+                        reason: Reason.tooManyArgumentsOnSingleLine(max: max)
+                    )
                 }
 
-                numberOfParameters += 1
+                return nil
+            }
+
+            if let startLineViolation = duplicateArgumentStartLineViolation(in: arguments) {
+                return startLineViolation
+            }
+
+            if let commaViolation = newlineAfterCommaViolation(in: arguments) {
+                return commaViolation
             }
 
-            if linesWithParameters.count == 1 {
-                guard configuration.allowsSingleLine else {
-                    return numberOfParameters > 1
+            return nil
+        }
+
+        private func duplicateArgumentStartLineViolation(
+            in arguments: LabeledExprListSyntax
+        ) -> ReasonedRuleViolation? {
+            let args = Array(arguments)
+            guard args.count > 1 else { return nil }
+
+            var seen: Set<Int> = []
+            for arg in args {
+                let startPos = startPosition(of: arg)
+                let line = line(for: startPos)
+                if !seen.insert(line).inserted {
+                    return ReasonedRuleViolation(
+                        position: startPos,
+                        reason: Reason.eachArgumentMustStartOnOwnLine
+                    )
                 }
+            }
+
+            return nil
+        }
+
+        private func newlineAfterCommaViolation(in arguments: LabeledExprListSyntax) -> ReasonedRuleViolation? {
+            let args = Array(arguments)
+            guard args.count > 1 else { return nil }
+
+            for index in args.indices.dropLast() {
+                let current = args[index]
+                let next = args[index + 1]
 
-                if let maxNumberOfSingleLineParameters = configuration.maxNumberOfSingleLineParameters {
-                    return numberOfParameters > maxNumberOfSingleLineParameters
+                guard let comma = current.trailingComma, comma.presence != .missing else { continue }
+
+                if let lastToken = current.expression.lastToken(viewMode: .sourceAccurate) {
+                    switch lastToken.tokenKind {
+                    case .rightBrace,
+                        .rightSquare:
+                        continue
+                    default:
+                        break
+                    }
                 }
 
-                return false
+                let commaLine = line(for: comma.positionAfterSkippingLeadingTrivia)
+                let currentStartLine = line(for: startPosition(of: current))
+                let nextStartPos = startPosition(of: next)
+                let nextStartLine = line(for: nextStartPos)
+
+                if commaLine == nextStartLine, currentStartLine != nextStartLine {
+                    return ReasonedRuleViolation(
+                        position: nextStartPos,
+                        reason: Reason.newlineRequiredAfterCommaInMultilineCall
+                    )
+                }
             }
 
-            return hasMultipleParametersOnSameLine
+            return nil
         }
+
+        private func startPosition(of argument: LabeledExprSyntax) -> AbsolutePosition {
+            if let label = argument.label, label.presence != .missing {
+                return label.positionAfterSkippingLeadingTrivia
+            }
+            return argument.expression.positionAfterSkippingLeadingTrivia
+        }
+
+        private func line(for position: AbsolutePosition) -> Int {
+            let key = position.utf8Offset
+            if let cached = lineCache[key] { return cached }
+            let line = locationConverter.location(for: position).line
+            lineCache[key] = line
+            return line
+        }
+    }
+}
+
+private extension FunctionCallExprSyntax {
+    /// Returns `true` if this call appears in a pattern position (e.g., `case .foo(a)`).
+    ///
+    /// Works because SwiftSyntax wraps pattern expressions in `ExpressionPatternSyntax`:
+    /// - `if case let .foo(a) = x` → parent is ExpressionPatternSyntax
+    /// - `switch x { case let .foo(a): }` → parent is ExpressionPatternSyntax
+    /// - `for case let .foo(a) in items` → parent is ExpressionPatternSyntax
+    /// - `catch .foo(1, 2)` → parent is ExpressionPatternSyntax
+    var isInPatternMatchingPatternPosition: Bool {
+        parent?.is(ExpressionPatternSyntax.self) == true
     }
 }