Properly parse the rethrows attribute.

Author: DougGregor

Sources/SwiftParser/Attributes.swift

@@ -183,7 +183,7 @@ extension Parser {
 
 
     let atSign = self.eat(.atSign)
-    let ident = self.consumeIdentifier()
+    let ident = self.consumeIdentifierOrRethrows()
     let leftParen: RawTokenSyntax?
     let arg: RawSyntax?
     let unexpectedBeforeRightParen: RawUnexpectedNodesSyntax?

Sources/SwiftParser/Lookahead.swift

@@ -146,7 +146,7 @@ extension Parser.Lookahead {
 
     repeat {
       self.eat(.atSign)
-      self.consumeIdentifier()
+      self.consumeIdentifierOrRethrows()
       if self.consume(if: .leftParen) != nil {
         while !self.at(.eof), !self.at(.rightParen), !self.at(.poundEndifKeyword) {
           self.skipSingle()

Sources/SwiftParser/Names.swift

@@ -330,6 +330,19 @@ extension TokenConsumer {
     }
   }
 
+  mutating func consumeIdentifierOrRethrows() -> Token {
+    switch self.currentToken.tokenKind {
+    case .selfKeyword,
+        .capitalSelfKeyword,
+        .anyKeyword,
+        .identifier,
+        .rethrowsKeyword:
+      return self.consumeAnyToken()
+    default:
+      return self.missingToken(.identifier)
+    }
+  }
+
   mutating func consumeInteger() -> Token {
     switch self.currentToken.tokenKind {
     case .integerLiteral:

Tests/SwiftParserTest/Attributes.swift

@@ -66,4 +66,13 @@ final class AttributeTests: XCTestCase {
       """
     )
   }
+
+  func testRethrowsAttribute() {
+    AssertParse(
+      """
+      @rethrows
+      protocol P { }
+      """
+    )
+  }
 }