[clang] [C23] Fix typeof handling in enum declarations (PR #146394)

[Aaron Ballman via cfe-commits]

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@@ -4210,6 +4215,7 @@ class Parser : public CodeCompletionHandler {
   /// \endverbatim
   ExprResult ParseParenExpression(ParenParseOption &ExprType,
                                   bool stopIfCastExpr, bool isTypeCast,
+                                  bool ParenKnownToBeNonCast,
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AaronBallman wrote:

> Actually on that note, TypeCastState is a thing. Can we just merge this parameter with the isTypeCast one and make it a TypeCastState?

`TypeCastState` is cursed in that it doesn't mean what you might think it means: https://github.com/llvm/llvm-project/commit/77e21fca3cd1a9db882ac13ac5ddef3f278dfff2

So it doesn't mean "this is, is not, or maybe a cast expression", it means "if there's a typo, should we allow type names or not?" I verified this is not vestigial code after delayed typo correction was removed; it's still used for typo correction today. We probably should rename some stuff to make this far more clear though, because your suggestion is what I initially tried to implement and broke approximately every test in the suite.

> How about introducing a new enumeration here?

Given that there's three bools in a row, yeah, that's not a bad idea.

How about this for a solution:

1) Rename `TypeCastState` to `TypoCorrectionTypeBehavior`
2) Rename `NotTypeCast`, `IsTypeCast`, and `MaybeTypeCast` to `AllowNonTypes, `AllowTypes`, and `AllowBoth`
3) Add a new enumeration `TypeCastState` with members `IsTypeCast`, `IsNotTypeCast`, and `Unknown`
4) Change `ParseParenExpression` to take both a `TypoCorrectionTypeBehavior` and a `TypeCastState`.

WDYT?

https://github.com/llvm/llvm-project/pull/146394