Add the ability to synthesize syntax for an operator

Author: DougGregor

Sources/SwiftOperators/SyntaxSynthesis.swift

@@ -0,0 +1,40 @@
+//===------------------ SyntaxSynthesis.swift -----------------------------===//
+//
+// 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 Operator {
+  /// Synthesize a syntactic representation of this operator based on its
+  /// semantic definition.
+  public func synthesizedSyntax() -> OperatorDeclSyntax {
+    let modifiers = ModifierListSyntax(
+      [DeclModifierSyntax(name: .identifier("\(kind)"), detail: nil)]
+    )
+    let operatorKeyword = TokenSyntax.operatorKeyword(leadingTrivia: .spaces(1))
+    let identifierSyntax =
+      TokenSyntax.identifier(name, leadingTrivia: .spaces(1))
+    let precedenceGroupSyntax = precedenceGroup.map { groupName in
+      OperatorPrecedenceAndTypesSyntax(
+        colon: .colonToken(),
+        precedenceGroupAndDesignatedTypes: IdentifierListSyntax(
+          [.identifier(groupName, leadingTrivia: .spaces(1))]
+        )
+      )
+    }
+
+    return OperatorDeclSyntax(
+      attributes: nil, modifiers: modifiers, operatorKeyword: operatorKeyword,
+      identifier: identifierSyntax,
+      operatorPrecedenceAndTypes: precedenceGroupSyntax
+    )
+  }
+}

Tests/SwiftOperatorsTest/SyntaxSynthesisTests.swift

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+//===------------------ SyntaxSynthesisTests.swift ------------------------===//
+//
+// 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 XCTest
+import SwiftSyntax
+import SwiftOperators
+
+public class SyntaxSynthesisTests: XCTestCase {
+  func testInfixOperator() {
+    let plus = Operator(
+      kind: .infix, name: "+", precedenceGroup: "AdditivePrecedence")
+    let plusSyntax = plus.synthesizedSyntax()
+    XCTAssertEqual(
+      plusSyntax.description, "infix operator +: AdditivePrecedence")
+  }
+}