[PATCH] D122249: [Clang] Add a compatibiliy warning for non-literals in constexpr.

[Corentin Jabot via Phabricator via cfe-commits]

cor3ntin added inline comments.


================
Comment at: clang/lib/Sema/SemaDeclCXX.cpp:1905
+        if (SemaRef.LangOpts.CPlusPlus2b) {
+          if (!VD->getType()->isLiteralType(SemaRef.Context))
+            SemaRef.Diag(VD->getLocation(),
----------------
hubert.reinterpretcast wrote:
> This seems to trigger even when the type is dependent:
> ```
> <stdin>:1:36: warning: definition of a variable of non-literal type in a constexpr function is incompatible with C++ standards before C++2b [-Wpre-c++2b-compat]
> auto qq = [](auto x) { decltype(x) n; };
>                                    ^
> 1 warning generated.
> ```
> 
> This also seems to emit even when `Kind` is not `Sema::CheckConstexprKind::Diagnose` (unlike the `static`/`thread_local` case above). Is the `CheckLiteralType` logic not reusable for this?
You are right, thanks for noticing that, it was rather bogus.
The reason I'm not using CheckLiteralType is to avoid duplicating a diagnostics message, as CheckLiteralType doesn't allow us to pass parameter to the diagnostic message.

It leaves us with an uncovered scenario though: We do not emit the warning on template instantiation, and I don't think there is an  easy way to do that.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D122249/new/

https://reviews.llvm.org/D122249