Fix false positives for 'multiple_closures_with_trailing_closure'

CHANGELOG.md

@@ -29,6 +29,11 @@
   [hank121314](https://github.com/hank121314)
   [#2367](https://github.com/realm/SwiftLint/issues/3267)
 
+* Rule `multiple_closures_with_trailing_closure` no longer triggers when Swift
+  5.3's 'multiple trailing closures' feature is used.
+  [Jumhyn](https://github.com/jumhyn)
+  [#3295](https://github.com/realm/SwiftLint/issues/3295)
+
 ## 0.40.2: Demo Unit
 
 #### Breaking

Source/SwiftLintFramework/Rules/Style/MultipleClosuresWithTrailingClosureRule.swift

@@ -20,7 +20,9 @@ public struct MultipleClosuresWithTrailingClosureRule: ASTRule, ConfigurationPro
             UIView.animate(withDuration: 1.0) {
                 someView.alpha = 0.0
             }
-            """)
+            """),
+            Example("foo.method { print(0) } arg2: { print(1) }"),
+            Example("foo.methodWithParenArgs((0, 1), arg2: (0, 1, 2)) { $0 } arg4: { $0 }")
         ],
         triggeringExamples: [
             Example("foo.something(param1: { $0 }) ↓{ $0 + 1 }"),
@@ -30,40 +32,98 @@ public struct MultipleClosuresWithTrailingClosureRule: ASTRule, ConfigurationPro
             }) ↓{ _ in
                 someView.removeFromSuperview()
             }
-            """)
+            """),
+            Example("foo.multipleTrailing(arg1: { $0 }) { $0 } arg3: { $0 }"),
+            Example("foo.methodWithParenArgs(param1: { $0 }, param2: (0, 1), (0, 1)) { $0 }")
         ]
     )
 
     public func validate(file: SwiftLintFile, kind: SwiftExpressionKind,
                          dictionary: SourceKittenDictionary) -> [StyleViolation] {
         guard kind == .call,
             case let arguments = dictionary.enclosedArguments,
-            arguments.count > 1,
-            let lastArgument = arguments.last,
-            isTrailingClosure(argument: lastArgument, call: dictionary),
             case let closureArguments = arguments.filterClosures(file: file),
-            closureArguments.count > 1,
-            let trailingClosureOffset = lastArgument.offset else {
+            // Any violations must have at least one closure argument.
+            closureArguments.isEmpty == false,
+            // If there is no closing paren (e.g. `foo { ... }`), there is no violation.
+            let closingParenOffset = dictionary.closingParenLocation(file: file),
+            // Find all trailing closures.
+            case let trailingClosureArguments = closureArguments.filter({
+                isTrailingClosure(argument: $0, closingParenOffset: closingParenOffset)
+            }),
+            // If there are no trailing closures, there is no violation.
+            trailingClosureArguments.isEmpty == false,
+            // If all closure arguments are trailing closures, there is no violation
+            trailingClosureArguments.count != closureArguments.count,
+            let firstTrailingClosureOffset = trailingClosureArguments.first?.offset else {
                 return []
         }
 
         return [
             StyleViolation(ruleDescription: Self.description,
                            severity: configuration.severity,
-                           location: Location(file: file, byteOffset: trailingClosureOffset))
+                           location: Location(file: file, byteOffset: firstTrailingClosureOffset))
         ]
     }
 
+    // A closure is 'trailing' if it appears outside the closing paren.
     private func isTrailingClosure(argument: SourceKittenDictionary,
-                                   call: SourceKittenDictionary) -> Bool {
-        guard let callOffset = call.offset,
-            let callLength = call.length,
-            let argumentOffset = argument.offset,
-            let argumentLength = argument.length else {
+                                   closingParenOffset: ByteCount) -> Bool {
+        guard let argOffset = argument.offset else {
             return false
         }
 
-        return callOffset + callLength == argumentOffset + argumentLength
+        return argOffset > closingParenOffset
+    }
+}
+
+private extension SourceKittenDictionary {
+    func closingParenLocation(file: SwiftLintFile) -> ByteCount? {
+        guard self.expressionKind == .call,
+              case let arguments = self.enclosedArguments,
+              arguments.isEmpty == false else {
+            return nil
+        }
+
+        func rangeBetween(_ expr1: SourceKittenDictionary, and expr2: SourceKittenDictionary) -> ByteRange? {
+            guard let offset1 = expr1.offset,
+                  let length1 = expr1.length,
+                  let offset2 = expr2.offset,
+                  case let end1 = offset1 + length1,
+                  end1 <= offset2 else {
+                return nil
+            }
+
+            return ByteRange(location: end1, length: offset2 - end1)
+        }
+
+        var searchRanges: [ByteRange] = []
+        for index in arguments.indices.dropLast() {
+            let currentArg = arguments[index]
+            let nextArg = arguments[index + 1]
+            if let range = rangeBetween(currentArg, and: nextArg) {
+                searchRanges.append(range)
+            }
+        }
+
+        if let lastOffset = arguments.last?.offset,
+           let lastLength = arguments.last?.length,
+           let callOffset = self.offset,
+           let callLength = self.length,
+           case let lastEnd = lastOffset + lastLength,
+           case let callEnd = callOffset + callLength,
+           lastEnd <= callEnd {
+            searchRanges.append(ByteRange(location: lastEnd, length: callEnd - lastEnd))
+        }
+
+        for byteRange in searchRanges {
+            if let range = file.stringView.byteRangeToNSRange(byteRange),
+               let match = regex("^\\s*\\)").firstMatch(in: file.contents, options: [], range: range)?.range {
+                return file.stringView.byteOffset(fromLocation: match.location)
+            }
+        }
+
+        return nil
     }
 }