Add += operator for Trivia

Author: fwcd

Sources/SwiftSyntax/Trivia.swift.gyb

@@ -210,9 +210,16 @@ extension Trivia: CustomStringConvertible {
   }
 }
 
-/// Concatenates two collections of `Trivia` into one collection.
-public func +(lhs: Trivia, rhs: Trivia) -> Trivia {
-  return Trivia(pieces: lhs.pieces + rhs.pieces)
+extension Trivia {
+  /// Concatenates two collections of `Trivia` into one collection.
+  public static func +(lhs: Trivia, rhs: Trivia) -> Trivia {
+    return Trivia(pieces: lhs.pieces + rhs.pieces)
+  }
+
+  /// Concatenates two collections of `Trivia` into the left-hand side.
+  public static func +=(lhs: inout Trivia, rhs: Trivia) {
+    lhs = lhs + rhs
+  }
 }
 
 extension TriviaPiece: Equatable {}

Sources/SwiftSyntax/gyb_generated/Trivia.swift

@@ -336,9 +336,16 @@ extension Trivia: CustomStringConvertible {
   }
 }
 
-/// Concatenates two collections of `Trivia` into one collection.
-public func +(lhs: Trivia, rhs: Trivia) -> Trivia {
-  return Trivia(pieces: lhs.pieces + rhs.pieces)
+extension Trivia {
+  /// Concatenates two collections of `Trivia` into one collection.
+  public static func +(lhs: Trivia, rhs: Trivia) -> Trivia {
+    return Trivia(pieces: lhs.pieces + rhs.pieces)
+  }
+
+  /// Concatenates two collections of `Trivia` into the left-hand side.
+  public static func +=(lhs: inout Trivia, rhs: Trivia) {
+    lhs = lhs + rhs
+  }
 }
 
 extension TriviaPiece: Equatable {}

Tests/SwiftSyntaxBuilderTest/TriviaTests.swift

@@ -24,4 +24,12 @@ final class TriviaTests: XCTestCase {
       /* An inline comment */ static var test: String
       """)
   }
+
+  func testTriviaConcatenation() {
+    let x = Trivia.newline
+    var y = x
+    y += .space
+    XCTAssertEqual(y, x + .space)
+    XCTAssertEqual(y, [.newlines(1), .spaces(1)])
+  }
 }