[PATCH] D152003: [clang] Fix `static_cast` to array of unknown bound

[Mariya Podchishchaeva via Phabricator via cfe-commits]

Fznamznon added inline comments.


================
Comment at: clang/lib/Sema/SemaType.cpp:8824
+  if (auto *Cast = dyn_cast<CXXStaticCastExpr>(E)) {
+    if (auto *SubInit = dyn_cast<CXXParenListInitExpr>(Cast->getSubExpr())) {
+      const Type *InnerType = SubInit->getType().getTypePtr();
----------------
erichkeane wrote:
> Fznamznon wrote:
> > erichkeane wrote:
> > > I am not really sure this is the right way about this.  You're supposed to be testing `T`, but this looks like it is checking the type of `E`, isn't it?  I think you just need to check `Cast->getType()`.
> > For the case I'm trying to fix, `T` is array of unknown bound, it is already checked before calling `completeExprArrayBound`. Right now when you write something like
> > ```
> > int (&&arr1)[1] = static_cast<int[]>(42);
> > ```
> > Clang actually is able to realize that parenthesized initialization is made, so it actually generates `CXXParenListInitExpr` that has type int[1]. Here I'm just paranoidally double-checking that is the case before switching the type. Maybe I don't need this double-check at all then?
> > 
> That makes me wonder if this is the correct place for this?  Should when we generate this type when we do the `CXXParenListInitExpr` fixup?
> 
> Either way, I think making this depend on that behavior (which would possibly be fragile), we should just do it based on the type passed ot the `static_cast`.
> 
> Another question: is this something that needs to be done for other cast types?  Does similar behavior exist for the other casts?  Should it also happen with 'clobber' casts (C-style) that are effectively static?
> That makes me wonder if this is the correct place for this? Should when we generate this type when we do the CXXParenListInitExpr fixup?

The function called `completeExprArrayBound` seemed like an appropriate place for me.
Could you please elaborate what you mean under `CXXParenListInitExpr fixup`? 

> is this something that needs to be done for other cast types?

I'm not sure. https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1975r0.html seems to be extending only static_casts. And this was the original purpose of this bugfix.
gcc and msvc don't agree on that matter https://godbolt.org/z/1M3ahhsYr.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D152003/new/

https://reviews.llvm.org/D152003