Add convenience initializer for TernaryExpr

Author: fwcd

Sources/SwiftSyntaxBuilder/TernaryExprConvenienceInitializers.swift

@@ -0,0 +1,30 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 TernaryExpr {
+  public init(
+    if condition: ExpressibleAsExprBuildable,
+    then firstChoice: ExpressibleAsExprBuildable,
+    else secondChoice: ExpressibleAsExprBuildable
+  ) {
+    self.init(
+      conditionExpression: condition,
+      questionMark: .infixQuestionMarkToken(leadingTrivia: .space, trailingTrivia: .space),
+      firstChoice: firstChoice,
+      colonMark: .colonToken(leadingTrivia: .space),
+      secondChoice: secondChoice
+    )
+  }
+}
+

Tests/SwiftSyntaxBuilderTest/TernaryExprTests.swift

@@ -0,0 +1,14 @@
+import XCTest
+import SwiftSyntax
+import SwiftSyntaxBuilder
+
+final class TernaryExprTests: XCTestCase {
+  func testTernaryExpr() {
+    let buildable = TernaryExpr(if: BooleanLiteralExpr(true), then: "a", else: "b")
+    let syntax = buildable.buildSyntax(format: Format())
+    XCTAssertEqual(syntax.description, """
+      true ? a : b
+      """)
+  }
+}
+