Avoid indent for single-line argument lists in BasicFormat

Sources/SwiftBasicFormat/BasicFormat.swift

@@ -209,6 +209,9 @@ open class BasicFormat: SyntaxRewriter {
     case \EnumCaseParameterClauseSyntax.parameters:
       return true
     case \FunctionCallExprSyntax.arguments:
+      if let arguments = Syntax(node).as(LabeledExprListSyntax.self) {
+        return argumentListIsMultiLine(arguments)
+      }
       return true
     case \FunctionTypeSyntax.parameters:
       return true
@@ -219,6 +222,9 @@ open class BasicFormat: SyntaxRewriter {
     case \SwitchCaseSyntax.statements:
       return true
     case \TupleExprSyntax.elements:
+      if let elements = Syntax(node).as(LabeledExprListSyntax.self) {
+        return argumentListIsMultiLine(elements)
+      }
       return true
     case \TupleTypeSyntax.elements:
       return true
@@ -252,6 +258,25 @@ open class BasicFormat: SyntaxRewriter {
     }) != nil
   }
 
+  /// Returns `true` if the argument list (a `LabeledExprListSyntax` used by
+  /// `FunctionCallExprSyntax.arguments` or `TupleExprSyntax.elements`) is
+  /// laid out across multiple lines at the argument level (i.e. at least one
+  /// argument begins on its own line).
+  ///
+  /// When this is `false`, the argument list is single-line at the argument
+  /// level even if individual arguments contain multi-line expressions (such
+  /// as closures or collection literals). In that case, the argument-list
+  /// indentation scope shouldn't contribute, because any inner multi-line
+  /// expression brings its own indentation scope.
+  private func argumentListIsMultiLine(_ arguments: LabeledExprListSyntax) -> Bool {
+    for argument in arguments {
+      if argument.leadingTrivia.contains(where: \.isNewline) {
+        return true
+      }
+    }
+    return false
+  }
+
   open func requiresNewline(between first: TokenSyntax?, and second: TokenSyntax?) -> Bool {
     // We don't want to add newlines inside string interpolation.
     // When first or second ``TokenSyntax`` is a multiline quote we want special handling

Tests/SwiftBasicFormatTest/BasicFormatTests.swift

@@ -180,6 +180,36 @@ final class BasicFormatTest: XCTestCase {
     )
   }
 
+  func testSingleLineCallWithMultiLineClosureArgument() {
+    assertFormattingRoundTrips(
+      """
+      foo(someClosure: { _ in
+          return 1
+      })
+      """
+    )
+  }
+
+  func testSingleLineCallWithUnlabeledMultiLineClosureArgument() {
+    assertFormattingRoundTrips(
+      """
+      foo({ _ in
+          return 1
+      })
+      """
+    )
+  }
+
+  func testSingleLineTupleWithMultiLineClosureElement() {
+    assertFormattingRoundTrips(
+      """
+      _ = ({ _ in
+          return 1
+      })
+      """
+    )
+  }
+
   func testLineWrappingInsideIndentedBlock() {
     assertFormatted(
       source: """

Tests/SwiftRefactorTest/CallToTrailingClosureTests.swift

@@ -79,12 +79,10 @@ final class CallToTrailingClosuresTest: XCTestCase {
       })
       """
 
-    // TODO: The ident here is not great.
-    // https://github.com/swiftlang/swift-syntax/issues/1473
     let expected: ExprSyntax = """
       foo({ label in
           return 1
-          }, 1) { label2 in
+      }, 1) { label2 in
           return 2
       } _: { label3 in
           return 3
@@ -109,13 +107,12 @@ final class CallToTrailingClosuresTest: XCTestCase {
       })
       """
 
-    // TODO: BasicFormat is pretty messed up here
     let expected: ExprSyntax = """
       foo({ label in
           return 1
-          }, 1, { label2 in
+      }, 1, { label2 in
           return 2
-          }) { label3 in
+      }) { label3 in
           return 3
       } named: { label4 in
           return 4

Tests/SwiftSyntaxBuilderTest/VariableTests.swift

@@ -138,8 +138,8 @@ final class VariableTests: XCTestCase {
         """
         var bar: [String] {
             bar.map({
-                    $0.description
-                })
+                $0.description
+            })
         }
         """
       ),
@@ -148,8 +148,8 @@ final class VariableTests: XCTestCase {
         """
         inout bar: [String] {
             bar.map({
-                    $0.description
-                })
+                $0.description
+            })
         }
         """
       ),

Tests/SwiftSyntaxMacroExpansionTest/ExpressionMacroTests.swift

@@ -193,7 +193,7 @@ final class ExpressionMacroTests: XCTestCase {
         _ = ({ () -> Bool in
           print("hello")
           return true
-          }, #"{ () -> Bool in\\#n  print("hello")\\#n  return true\\#n}"#)
+        }, #"{ () -> Bool in\\#n  print("hello")\\#n  return true\\#n}"#)
         """,
       macros: ["stringify": StringifyMacro.self],
       indentationWidth: indentationWidth

Tests/SwiftSyntaxTest/DebugDescriptionTests.swift

@@ -181,47 +181,47 @@ class DebugDescriptionTests: XCTestCase {
       sourceFile.debugInitCall(includeTrivia: true).trimmingTrailingWhitespace(),
       """
       SourceFileSyntax(
-          statements: CodeBlockItemListSyntax([
-                CodeBlockItemSyntax(item: CodeBlockItemSyntax.Item(FunctionCallExprSyntax(
-                        calledExpression: ExprSyntax(DeclReferenceExprSyntax(baseName: .identifier("test"))),
-                        leftParen: .leftParenToken(),
-                        arguments: LabeledExprListSyntax([
-                              LabeledExprSyntax(
-                                  expression: ExprSyntax(IntegerLiteralExprSyntax(literal: .integerLiteral("1"))),
-                                  trailingComma: .commaToken(trailingTrivia: .space)
-                                ),
-                              LabeledExprSyntax(expression: ExprSyntax(IntegerLiteralExprSyntax(literal: .integerLiteral("2"))))
-                            ]),
-                        rightParen: .rightParenToken(),
-                        additionalTrailingClosures: MultipleTrailingClosureElementListSyntax([])
-                      )))
-              ]),
-          endOfFileToken: .endOfFileToken()
-        )
+        statements: CodeBlockItemListSyntax([
+            CodeBlockItemSyntax(item: CodeBlockItemSyntax.Item(FunctionCallExprSyntax(
+              calledExpression: ExprSyntax(DeclReferenceExprSyntax(baseName: .identifier("test"))),
+              leftParen: .leftParenToken(),
+              arguments: LabeledExprListSyntax([
+                  LabeledExprSyntax(
+                    expression: ExprSyntax(IntegerLiteralExprSyntax(literal: .integerLiteral("1"))),
+                    trailingComma: .commaToken(trailingTrivia: .space)
+                  ),
+                  LabeledExprSyntax(expression: ExprSyntax(IntegerLiteralExprSyntax(literal: .integerLiteral("2"))))
+                ]),
+              rightParen: .rightParenToken(),
+              additionalTrailingClosures: MultipleTrailingClosureElementListSyntax([])
+            )))
+          ]),
+        endOfFileToken: .endOfFileToken()
+      )
       """
     )
 
     assertStringsEqualWithDiff(
       sourceFile.debugInitCall(includeTrivia: false).trimmingTrailingWhitespace(),
       """
       SourceFileSyntax(
-          statements: CodeBlockItemListSyntax([
-                CodeBlockItemSyntax(item: CodeBlockItemSyntax.Item(FunctionCallExprSyntax(
-                        calledExpression: ExprSyntax(DeclReferenceExprSyntax(baseName: .identifier("test"))),
-                        leftParen: .leftParenToken(),
-                        arguments: LabeledExprListSyntax([
-                              LabeledExprSyntax(
-                                  expression: ExprSyntax(IntegerLiteralExprSyntax(literal: .integerLiteral("1"))),
-                                  trailingComma: .commaToken()
-                                ),
-                              LabeledExprSyntax(expression: ExprSyntax(IntegerLiteralExprSyntax(literal: .integerLiteral("2"))))
-                            ]),
-                        rightParen: .rightParenToken(),
-                        additionalTrailingClosures: MultipleTrailingClosureElementListSyntax([])
-                      )))
-              ]),
-          endOfFileToken: .endOfFileToken()
-        )
+        statements: CodeBlockItemListSyntax([
+            CodeBlockItemSyntax(item: CodeBlockItemSyntax.Item(FunctionCallExprSyntax(
+              calledExpression: ExprSyntax(DeclReferenceExprSyntax(baseName: .identifier("test"))),
+              leftParen: .leftParenToken(),
+              arguments: LabeledExprListSyntax([
+                  LabeledExprSyntax(
+                    expression: ExprSyntax(IntegerLiteralExprSyntax(literal: .integerLiteral("1"))),
+                    trailingComma: .commaToken()
+                  ),
+                  LabeledExprSyntax(expression: ExprSyntax(IntegerLiteralExprSyntax(literal: .integerLiteral("2"))))
+                ]),
+              rightParen: .rightParenToken(),
+              additionalTrailingClosures: MultipleTrailingClosureElementListSyntax([])
+            )))
+          ]),
+        endOfFileToken: .endOfFileToken()
+      )
       """
     )
   }