[SR-510] Make closure as enum raw value parses as normal

enum raw value is parsed as a normal expression using `parseExpr()`. However,
for a closure, the parser expects a local context that doesn't exist for raw
values.

We create a temporary context to ensure the closure gets parsed as normal.
As a consequence, `parseExpr()` returns normally for closure and correct
diagnosis for raw value gets issued.

Author: dduan

lib/Parse/ParseDecl.cpp

@@ -4405,7 +4405,16 @@ ParserStatus Parser::parseDeclEnumCase(ParseDeclOptions Flags,
       {
         CodeCompletionCallbacks::InEnumElementRawValueRAII
             InEnumElementRawValue(CodeCompletion);
-        RawValueExpr = parseExpr(diag::expected_expr_enum_case_raw_value);
+        if (!CurLocalContext) {
+          // A local context is needed for parsing closures. We want to parse
+          // them anyways for proper diagnosis.
+          LocalContext tempContext{};
+          CurLocalContext = &tempContext;
+          RawValueExpr = parseExpr(diag::expected_expr_enum_case_raw_value);
+          CurLocalContext = nullptr;
+        } else {
+          RawValueExpr = parseExpr(diag::expected_expr_enum_case_raw_value);
+        }
       }
       if (RawValueExpr.hasCodeCompletion()) {
         Status.setHasCodeCompletion();

test/decl/enum/enumtest.swift

@@ -290,4 +290,9 @@ func testSimpleEnum() {
   let _ : SimpleEnum=.X    // expected-error {{'=' must have consistent whitespace on both sides}}
 }
 
+enum SR510: String {
+    case Thing = "thing"
+    case Bob = {"test"} // expected-error {{raw value for enum case must be a literal}}
+}
+