Add convert to trailing closure and editor placeholder refactorings

Adds three new refactorings:
  - `ConvertToTrailingClosures`
  - `ExpandEditorPlaceholder`
  - `ExpandEditorPlaceholders`

`ExpandEditorPlaceholders` is a combination of `ExpandEditorPlaceholder`
and `ConvertToTrailingClosures`, ie. it first expands any function-typed
closures at the end of a call using `ExpandEditorPlaceholder` and then
runs `ConvertToTrailingClosures` on that call.

Resolves rdar://107532856.

Author: bnbarham

Package.swift

@@ -247,12 +247,12 @@ let package = Package(
 
     .target(
       name: "SwiftRefactor",
-      dependencies: ["SwiftParser", "SwiftSyntax"]
+      dependencies: ["SwiftBasicFormat", "SwiftParser", "SwiftSyntax", "SwiftSyntaxBuilder"]
     ),
 
     .testTarget(
       name: "SwiftRefactorTest",
-      dependencies: ["_SwiftSyntaxTestSupport", "SwiftRefactor", "SwiftSyntaxBuilder"]
+      dependencies: ["_SwiftSyntaxTestSupport", "SwiftRefactor"]
     ),
 
     // MARK: - Executable targets

Sources/SwiftRefactor/CallToTrailingClosures.swift

@@ -0,0 +1,143 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftBasicFormat
+import SwiftSyntax
+
+/// Convert a call with inline closures to one that uses trailing closure
+/// syntax. Returns `nil` if there's already trailing closures or there are no
+/// closures within the call. Pass `startAtArgument` to specify the argument
+/// index to start the conversion from, ie. to skip converting closures before
+/// `startAtArgument`.
+///
+/// ## Before
+/// ```
+/// someCall(closure1: { arg in
+///   return 1
+/// }, closure2: { arg in
+///   return 2
+/// })
+/// ```
+///
+/// ## After
+/// ```
+/// someCall { arg in
+///   return 1
+/// } closure2: { arg in
+///   return 2
+/// }
+/// ```
+public struct CallToTrailingClosures: SyntaxRefactoringProvider {
+  public struct Context {
+    public let startAtArgument: Int
+
+    public init(startAtArgument: Int = 0) {
+      self.startAtArgument = startAtArgument
+    }
+  }
+
+  // TODO: Rather than returning nil, we should consider throwing errors with
+  // appropriate messages instead.
+  public static func refactor(syntax call: FunctionCallExprSyntax, in context: Context = Context()) -> FunctionCallExprSyntax? {
+    return call.convertToTrailingClosures(from: context.startAtArgument)?.formatted().as(FunctionCallExprSyntax.self)
+  }
+}
+
+extension FunctionCallExprSyntax {
+  fileprivate func convertToTrailingClosures(from startAtArgument: Int) -> FunctionCallExprSyntax? {
+    guard trailingClosure == nil, additionalTrailingClosures == nil, leftParen != nil, rightParen != nil else {
+      // Already have trailing closures
+      return nil
+    }
+
+    var closures = [(original: TupleExprElementSyntax, closure: ClosureExprSyntax)]()
+    for arg in argumentList.dropFirst(startAtArgument) {
+      guard var closure = arg.expression.as(ClosureExprSyntax.self) else {
+        closures.removeAll()
+        continue
+      }
+
+      // Trailing comma won't exist any more, move its trivia to the end of
+      // the closure instead
+      if let comma = arg.trailingComma {
+        closure = closure.with(\.trailingTrivia, closure.trailingTrivia.merging(triviaOf: comma))
+      }
+      closures.append((arg, closure))
+    }
+
+    guard !closures.isEmpty else {
+      return nil
+    }
+
+    // First trailing closure won't have label/colon. Transfer their trivia.
+    var trailingClosure = closures.first!.closure
+      .with(\.leadingTrivia, Trivia()
+        .merging(triviaOf: closures.first!.original.label)
+        .merging(triviaOf: closures.first!.original.colon)
+        .merging(closures.first!.closure.leadingTrivia))
+    let additionalTrailingClosures = closures.dropFirst().map {
+      MultipleTrailingClosureElementSyntax(
+        label: $0.original.label ?? .wildcardToken(),
+        colon: $0.original.colon ?? .colonToken(),
+        closure: $0.closure
+      )
+    }
+
+    var converted = self.detach()
+
+    // Remove parens if there's no non-closure arguments left and remove the
+    // last comma otherwise. Makes sure to keep the trivia of any removed node.
+    var argList = Array(argumentList.dropLast(closures.count))
+    if argList.isEmpty {
+      converted =
+        converted
+        .with(\.leftParen, nil)
+        .with(\.rightParen, nil)
+
+      // No left paren any more, right paren is handled below since it makes
+      // sense to keep its trivia of the end of the call, regardless of whether
+      // it was removed or not.
+      if let leftParen = leftParen {
+        trailingClosure = trailingClosure.with(\.leadingTrivia, Trivia()
+          .merging(triviaOf: leftParen)
+          .merging(trailingClosure.leadingTrivia))
+      }
+    } else {
+      let last = argList.last!
+      if let comma = last.trailingComma {
+        converted =
+          converted
+          .with(\.rightParen, TokenSyntax.rightParenToken(trailingTrivia: Trivia().merging(triviaOf: comma)))
+      }
+      argList[argList.count - 1] =
+        last
+        .with(\.trailingComma, nil)
+    }
+
+    // Update arguments and trailing closures
+    converted =
+      converted
+      .with(\.argumentList, TupleExprElementListSyntax(argList))
+      .with(\.trailingClosure, trailingClosure)
+    if !additionalTrailingClosures.isEmpty {
+      converted = converted.with(\.additionalTrailingClosures, MultipleTrailingClosureElementListSyntax(additionalTrailingClosures))
+    }
+
+    // The right paren either doesn't exist any more, or is before all the
+    // trailing closures. Moves its trivia to the end of the converted call.
+    if let rightParen = rightParen {
+      converted = converted.with(\.trailingTrivia, converted.trailingTrivia.merging(triviaOf: rightParen))
+    }
+
+    return converted
+  }
+}