Add ExprBuildable protocol for building ExprSyntax

Author: akkyie

Sources/SwiftSyntaxBuilder/Expression/ExprListBuildable.swift

@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2019 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
+
+public protocol ExprListBuildable: SyntaxListBuildable {
+  func buildExprList(format: Format, leadingTrivia: Trivia) -> [ExprSyntax]
+}
+
+public protocol ExprBuildable: SyntaxBuildable, ExprListBuildable {
+  func buildExpr(format: Format, leadingTrivia: Trivia) -> ExprSyntax
+}
+
+extension ExprBuildable {
+  public func buildSyntax(format: Format, leadingTrivia: Trivia) -> Syntax {
+    buildExpr(format: format, leadingTrivia: leadingTrivia)
+  }
+
+  public func buildExprList(format: Format, leadingTrivia: Trivia) -> [ExprSyntax] {
+    [buildExpr(format: format, leadingTrivia: leadingTrivia)]
+  }
+}