[clang] Call ActOnCaseExpr even if the 'case' is missing (#166326)

This otherwise happens in ParseCaseExpression.
If we don't call this, we don't perform the usual arithmetic
conversions, etc.

Author: tbaederr

clang/lib/Parse/ParseStmt.cpp

@@ -813,7 +813,7 @@ StmtResult Parser::ParseCaseStatement(ParsedStmtContext StmtCtx,
           return StmtError();
       }
     } else {
-      LHS = Expr;
+      LHS = Actions.ActOnCaseExpr(CaseLoc, Expr);
       MissingCase = false;
     }
 

clang/test/SemaCXX/constant-expression-cxx14.cpp

@@ -1450,3 +1450,9 @@ namespace GH149500 {
   unsigned int * p = &(*(unsigned int *)0x400);
   static const void *q = &(*(const struct sysrq_key_op *)0);
 }
+
+constexpr bool missingCase() {
+  switch (1) {
+    1u: return false; // expected-error {{expected 'case' keyword before expression}}
+  }
+}