Add option to add a newline between 2 adjacent attributes

Add an option that inserts hard line breaks between adjacent attributes.

Closes #773

Author: dduan

Sources/SwiftFormat/API/Configuration+Default.swift

@@ -30,6 +30,7 @@ extension Configuration {
     self.lineBreakBeforeControlFlowKeywords = false
     self.lineBreakBeforeEachArgument = false
     self.lineBreakBeforeEachGenericRequirement = false
+    self.lineBreakBetweenAttributes = false
     self.prioritizeKeepingFunctionOutputTogether = false
     self.indentConditionalCompilationBlocks = true
     self.lineBreakAroundMultilineExpressionChainComponents = false

Sources/SwiftFormat/API/Configuration.swift

@@ -34,6 +34,7 @@ public struct Configuration: Codable, Equatable {
     case lineBreakBeforeControlFlowKeywords
     case lineBreakBeforeEachArgument
     case lineBreakBeforeEachGenericRequirement
+    case lineBreakBetweenAttributes
     case prioritizeKeepingFunctionOutputTogether
     case indentConditionalCompilationBlocks
     case lineBreakAroundMultilineExpressionChainComponents
@@ -111,6 +112,9 @@ public struct Configuration: Codable, Equatable {
   /// horizontally first, with line breaks only being fired when the line length would be exceeded.
   public var lineBreakBeforeEachGenericRequirement: Bool
 
+  /// If true, a line break will be added between adjacent attributes.
+  public var lineBreakBetweenAttributes: Bool
+
   /// Determines if function-like declaration outputs should be prioritized to be together with the
   /// function signature right (closing) parenthesis.
   ///
@@ -243,6 +247,9 @@ public struct Configuration: Codable, Equatable {
     self.lineBreakBeforeEachGenericRequirement =
       try container.decodeIfPresent(Bool.self, forKey: .lineBreakBeforeEachGenericRequirement)
       ?? defaults.lineBreakBeforeEachGenericRequirement
+    self.lineBreakBetweenAttributes =
+      try container.decodeIfPresent(Bool.self, forKey: .lineBreakBetweenAttributes)
+      ?? defaults.lineBreakBetweenAttributes
     self.prioritizeKeepingFunctionOutputTogether =
       try container.decodeIfPresent(Bool.self, forKey: .prioritizeKeepingFunctionOutputTogether)
       ?? defaults.prioritizeKeepingFunctionOutputTogether
@@ -296,6 +303,7 @@ public struct Configuration: Codable, Equatable {
     try container.encode(lineBreakBeforeEachGenericRequirement, forKey: .lineBreakBeforeEachGenericRequirement)
     try container.encode(prioritizeKeepingFunctionOutputTogether, forKey: .prioritizeKeepingFunctionOutputTogether)
     try container.encode(indentConditionalCompilationBlocks, forKey: .indentConditionalCompilationBlocks)
+    try container.encode(lineBreakBetweenAttributes, forKey: .lineBreakBetweenAttributes)
     try container.encode(
       lineBreakAroundMultilineExpressionChainComponents,
       forKey: .lineBreakAroundMultilineExpressionChainComponents)

Sources/SwiftFormat/PrettyPrint/TokenStreamCreator.swift

@@ -2893,11 +2893,12 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
     suppressFinalBreak: Bool = false
   ) {
     if let attributes = attributes {
+      let behavior: NewlineBehavior = config.lineBreakBetweenAttributes ? .hard : .elective
       before(attributes.firstToken(viewMode: .sourceAccurate), tokens: .open)
-      insertTokens(.break(.same), betweenElementsOf: attributes)
+      insertTokens(.break(.same, newlines: behavior), betweenElementsOf: attributes)
       var afterAttributeTokens = [Token.close]
       if !suppressFinalBreak {
-        afterAttributeTokens.append(.break(.same))
+        afterAttributeTokens.append(.break(.same, newlines: behavior))
       }
       after(attributes.lastToken(viewMode: .sourceAccurate), tokens: afterAttributeTokens)
     }

Tests/SwiftFormatTests/PrettyPrint/AttributeTests.swift

@@ -468,4 +468,36 @@ final class AttributeTests: PrettyPrintTestCase {
 
     assertPrettyPrintEqual(input: input, expected: expected, linelength: 100)
   }
+
+  func testLineBreakBetweenAttributes() {
+    let input =
+      """
+      @available(iOS 16.0, *) @available(macOS 14.0, *)
+      @available(tvOS 16.0, *) @frozen
+      struct X {
+        @available(iOS 17.0, *) @available(macOS 15.0, *)
+        @MainActor @discardableResult
+        func f() -> Int { 0 }
+      }
+      """
+
+    let expected =
+      """
+      @available(iOS 16.0, *)
+      @available(macOS 14.0, *)
+      @available(tvOS 16.0, *)
+      @frozen
+      struct X {
+        @available(iOS 17.0, *)
+        @available(macOS 15.0, *)
+        @MainActor
+        @discardableResult
+        func f() -> Int { 0 }
+      }
+
+      """
+      var configuration = Configuration.forTesting
+      configuration.lineBreakBetweenAttributes = true
+      assertPrettyPrintEqual(input: input, expected: expected, linelength: 80, configuration: configuration)
+  }
 }