Add convenience initializer for CustomAttribute

Author: fwcd

Sources/SwiftSyntaxBuilder/ConvenienceInitializers/CustomAttributeConvenienceInitializers.swift

@@ -0,0 +1,32 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2022 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 SwiftSyntax
+
+extension CustomAttribute {
+  /// A convenience initializer that allows passing in arguments using a result builder
+  /// and automatically adds parentheses as needed, similar to the convenience
+  /// initializer for `FunctionCallExpr`.
+  public init(
+    _ attributeName: ExpressibleAsTypeBuildable,
+    @TupleExprElementListBuilder argumentList: () -> ExpressibleAsTupleExprElementList? = { nil }
+  ) {
+    let argumentList = argumentList()
+    self.init(
+      attributeName: attributeName,
+      leftParen: argumentList.map { _ in .leftParen },
+      argumentList: argumentList,
+      rightParen: argumentList.map { _ in .rightParen }
+    )
+  }
+}
+

Tests/SwiftSyntaxBuilderTest/CustomAttributeTests.swift

@@ -0,0 +1,26 @@
+import XCTest
+import SwiftSyntax
+import SwiftSyntaxBuilder
+
+final class CustomAttributeTests: XCTestCase {
+  func testCustomAttributeConvenienceInitializer() {
+    let testCases: [UInt: (CustomAttribute, String)] = [
+      #line: (CustomAttribute("Test"), "@Test"),
+      #line: (CustomAttribute("WithParens") {}, "@WithParens()"),
+      #line: (CustomAttribute("WithArgs") {
+        TupleExprElement(expression: "value1")
+        TupleExprElement(label: "labelled", expression: "value2")
+      }, "@WithArgs(value1, labelled: value2)"),
+    ]
+
+    for (line, testCase) in testCases {
+      let (builder, expected) = testCase
+      let syntax = builder.buildSyntax(format: Format())
+
+      var text = ""
+      syntax.write(to: &text)
+
+      XCTAssertEqual(text, expected, line: line)
+    }
+  }
+}