Support folding of function parameter clauses

Fixes #898
rdar://116877123

Author: ahoppen

Sources/SourceKitLSP/Swift/FoldingRange.swift

@@ -131,6 +131,12 @@ fileprivate final class FoldingRangeFinder: SyntaxAnyVisitor {
         end: braced.rightBrace.positionAfterSkippingLeadingTrivia
       )
     }
+    if let parenthesized = node.asProtocol(ParenthesizedSyntax.self) {
+      return self.addFoldingRange(
+        start: parenthesized.leftParen.endPositionBeforeTrailingTrivia,
+        end: parenthesized.rightParen.positionAfterSkippingLeadingTrivia
+      )
+    }
     return .visitChildren
   }
 
@@ -149,19 +155,13 @@ fileprivate final class FoldingRangeFinder: SyntaxAnyVisitor {
   }
 
   override func visit(_ node: FunctionCallExprSyntax) -> SyntaxVisitorContinueKind {
-    let start = node.leftParen?.endPositionBeforeTrailingTrivia ?? node.arguments.position
-    let end =
-      if !node.additionalTrailingClosures.isEmpty {
-        node.additionalTrailingClosures.endPositionBeforeTrailingTrivia
-      } else if let trailingClosure = node.trailingClosure {
-        trailingClosure.endPositionBeforeTrailingTrivia
-      } else if let rightParen = node.rightParen {
-        rightParen.positionAfterSkippingLeadingTrivia
-      } else {
-        // Should never happen because the call should have either a trailing closure or a closing ')'
-        node.arguments.endPositionBeforeTrailingTrivia
-      }
-    return self.addFoldingRange(start: start, end: end)
+    if let leftParen = node.leftParen, let rightParen = node.rightParen {
+      return self.addFoldingRange(
+        start: leftParen.endPositionBeforeTrailingTrivia,
+        end: rightParen.positionAfterSkippingLeadingTrivia
+      )
+    }
+    return .visitChildren
   }
 
   override func visit(_ node: SubscriptCallExprSyntax) -> SyntaxVisitorContinueKind {

Tests/SourceKitLSPTests/FoldingRangeTests.swift

@@ -317,32 +317,44 @@ final class FoldingRangeTests: XCTestCase {
   func testFoldCallWithTrailingClosure() async throws {
     try await assertFoldingRanges(
       markedSource: """
-        doSomething(1️⃣normalArg: 1) {2️⃣
+        doSomething(1️⃣normalArg: 12️⃣) {3️⃣
           _ = $0
-        3️⃣}4️⃣
+        4️⃣}
         """,
       expectedRanges: [
-        FoldingRangeSpec(from: "1️⃣", to: "4️⃣"),
-        FoldingRangeSpec(from: "2️⃣", to: "3️⃣"),
+        FoldingRangeSpec(from: "1️⃣", to: "2️⃣"),
+        FoldingRangeSpec(from: "3️⃣", to: "4️⃣"),
       ]
     )
   }
 
   func testFoldCallWithMultipleTrailingClosures() async throws {
     try await assertFoldingRanges(
       markedSource: """
-        doSomething(1️⃣normalArg: 1) {2️⃣
+        doSomething(1️⃣normalArg: 12️⃣) {3️⃣
           _ = $0
-        3️⃣}
-        additionalTrailing: {4️⃣
+        4️⃣}
+        additionalTrailing: {5️⃣
           _ = $0
-        5️⃣}6️⃣
+        6️⃣}
         """,
       expectedRanges: [
-        FoldingRangeSpec(from: "1️⃣", to: "6️⃣"),
-        FoldingRangeSpec(from: "2️⃣", to: "3️⃣"),
-        FoldingRangeSpec(from: "4️⃣", to: "5️⃣"),
+        FoldingRangeSpec(from: "1️⃣", to: "2️⃣"),
+        FoldingRangeSpec(from: "3️⃣", to: "4️⃣"),
+        FoldingRangeSpec(from: "5️⃣", to: "6️⃣"),
       ]
     )
   }
+
+  func testFoldArgumentsOfFunction() async throws {
+    try await assertFoldingRanges(
+      markedSource: """
+        func foo(1️⃣
+          arg1: Int,
+          arg2: Int
+        2️⃣)
+        """,
+      expectedRanges: [FoldingRangeSpec(from: "1️⃣", to: "2️⃣")]
+    )
+  }
 }