Merge pull request swiftlang#2977 from DougGregor/unsafe-for-in-disambig

[SE-0458] Improve disambiguation for "unsafe" effect on for..in loop

Author: DougGregor

Sources/SwiftParser/Statements.swift

@@ -574,8 +574,8 @@ extension Parser {
     if let modifierKeyword = ExpressionModifierKeyword(
       lexeme: self.currentToken,
       experimentalFeatures: self.experimentalFeatures
-    ), modifierKeyword == .unsafe, !self.peek(isAt: .keyword(.in)) {
-      unsafeKeyword = self.consumeAnyToken(remapping: .keyword)
+    ), modifierKeyword == .unsafe, !self.peek(isAt: .keyword(.in), .colon) {
+      unsafeKeyword = self.expectWithoutRecovery(.keyword(.unsafe))
     } else {
       unsafeKeyword = nil
     }

Tests/SwiftParserTest/StatementTests.swift

@@ -968,5 +968,15 @@ final class StatementTests: ParserTestCase {
       "for try await unsafe in e { }",
       experimentalFeatures: [.unsafeExpression]
     )
+
+    assertParse(
+      "for unsafe in e { }",
+      experimentalFeatures: [.unsafeExpression]
+    )
+
+    assertParse(
+      "for unsafe: Int in e { }",
+      experimentalFeatures: [.unsafeExpression]
+    )
   }
 }