Parse Opaque Return Type Attributes Correctly

Author: CodaFi

Sources/SwiftParser/Attributes.swift

@@ -773,6 +773,22 @@ extension Parser {
   }
 }
 
+extension Parser {
+  mutating func parseOpaqueReturnTypeOfAttributeArguments() -> RawOpaqueReturnTypeOfAttributeArgumentsSyntax {
+    let (unexpectedBeforeString, mangledName) = self.expect(.stringLiteral)
+    let (unexpectedBeforeComma, comma) = self.expect(.comma)
+    let (unexpectedBeforeOrdinal, ordinal) = self.expect(.integerLiteral)
+    return RawOpaqueReturnTypeOfAttributeArgumentsSyntax(
+      unexpectedBeforeString,
+      mangledName: mangledName,
+      unexpectedBeforeComma,
+      comma: comma,
+      unexpectedBeforeOrdinal,
+      ordinal: ordinal,
+      arena: self.arena)
+  }
+}
+
 // MARK: Lookahead
 
 extension Parser.Lookahead {

Sources/SwiftParser/Types.swift

@@ -820,6 +820,26 @@ extension Parser {
           arena: self.arena
         )
       )
+    case ._opaqueReturnTypeOf:
+      let (unexpectedBeforeAt, at) = self.expect(.atSign)
+      let ident = self.expectIdentifierWithoutRecovery()
+      let (unexpectedBeforeLeftParen, leftParen) = self.expect(.leftParen)
+      let argument = self.parseOpaqueReturnTypeOfAttributeArguments()
+      let (unexpectedBeforeRightParen, rightParen) = self.expect(.rightParen)
+      return RawSyntax(
+        RawAttributeSyntax(
+          unexpectedBeforeAt,
+          atSignToken: at,
+          attributeName: ident,
+          unexpectedBeforeLeftParen,
+          leftParen: leftParen,
+          argument: RawSyntax(argument),
+          unexpectedBeforeRightParen,
+          rightParen: rightParen,
+          tokenList: nil,
+          arena: self.arena
+        )
+      )
 
     default:
       let (unexpectedBeforeAt, at) = self.expect(.atSign)

Tests/SwiftParserTest/Types.swift

@@ -59,4 +59,11 @@ final class TypeTests: XCTestCase {
                   DiagnosticSpec(message: "Unexpected text '`' found in closure capture signature")
                 ])
   }
+
+  func testOpaqueReturnTypes() throws {
+    AssertParse("""
+                public typealias Body = @_opaqueReturnTypeOf("$s6CatKit10pspspspspsV5cmereV6lilguyQrvp", 0) __
+                """)
+  }
 }
+