r285856 - Don't require nullability on template parameters in typedefs.

[Jordan Rose via cfe-commits]

> On Nov 2, 2016, at 14:31, Richard Smith <richard at metafoo.co.uk> wrote:
> 
> On 2 Nov 2016 1:53 pm, "Jordan Rose via cfe-commits" <cfe-commits at lists.llvm.org <mailto:cfe-commits at lists.llvm.org>> wrote:
> Author: jrose
> Date: Wed Nov  2 15:44:07 2016
> New Revision: 285856
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=285856&view=rev <http://llvm.org/viewvc/llvm-project?rev=285856&view=rev>
> Log:
> Don't require nullability on template parameters in typedefs.
> 
> Previously the following code would warn on the use of "T":
> 
>   template <typename T>
>   struct X {
>     typedef T *type;
>   };
> 
> ...because nullability is /allowed/ on template parameters (because
> they could be pointers). (Actually putting nullability on this use of
> 'T' will of course break if the argument is a non-pointer type.)
> 
> This doesn't make any sense to me. Why would T need to be a pointer type for a nullability qualifier to be valid on a T*?

Sorry, this is referring to the following change to the example:

template <typename T>
struct X {
  typedef T _Nullable *type;
};

This is legal, but of course `X<int>` then produces an error. So we want to accept nullability in this position (in case T is implicitly required to be a pointer type by the definition of X) but not warn when it’s missing (in case it isn’t).

Jordan

> 
> This fix doesn't handle the case where a template parameter is used
> /outside/ of a typedef. That seems trickier, especially in parameter
> position.
> 
> Modified:
>     cfe/trunk/lib/Sema/SemaType.cpp
>     cfe/trunk/test/SemaObjCXX/Inputs/nullability-consistency-1.h
> 
> Modified: cfe/trunk/lib/Sema/SemaType.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaType.cpp?rev=285856&r1=285855&r2=285856&view=diff <http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaType.cpp?rev=285856&r1=285855&r2=285856&view=diff>
> ==============================================================================
> --- cfe/trunk/lib/Sema/SemaType.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaType.cpp Wed Nov  2 15:44:07 2016
> @@ -3600,7 +3600,17 @@ static TypeSourceInfo *GetFullTypeForDec
>      // inner pointers.
>      complainAboutMissingNullability = CAMN_InnerPointers;
> 
> -    if (T->canHaveNullability() && !T->getNullability(S.Context)) {
> +    auto isDependentNonPointerType = [](QualType T) -> bool {
> +      // Note: This is intended to be the same check as Type::canHaveNullability
> +      // except with all of the ambiguous cases being treated as 'false' rather
> +      // than 'true'.
> +      return T->isDependentType() && !T->isAnyPointerType() &&
> +        !T->isBlockPointerType() && !T->isMemberPointerType();
> +    };
> +
> +    if (T->canHaveNullability() && !T->getNullability(S.Context) &&
> +        !isDependentNonPointerType(T)) {
> +      // Note that we allow but don't require nullability on dependent types.
>        ++NumPointersRemaining;
>      }
> 
> 
> Modified: cfe/trunk/test/SemaObjCXX/Inputs/nullability-consistency-1.h
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaObjCXX/Inputs/nullability-consistency-1.h?rev=285856&r1=285855&r2=285856&view=diff <http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaObjCXX/Inputs/nullability-consistency-1.h?rev=285856&r1=285855&r2=285856&view=diff>
> ==============================================================================
> --- cfe/trunk/test/SemaObjCXX/Inputs/nullability-consistency-1.h (original)
> +++ cfe/trunk/test/SemaObjCXX/Inputs/nullability-consistency-1.h Wed Nov  2 15:44:07 2016
> @@ -13,5 +13,13 @@ class X {
>    int X:: *memptr; // expected-warning{{member pointer is missing a nullability type specifier}}
>  };
> 
> +template <typename T>
> +struct Typedefs {
> +  typedef T *Base; // no-warning
> +  typedef Base *type; // expected-warning{{pointer is missing a nullability type specifier}}
> +};
> +
> +Typedefs<int> xx;
> +Typedefs<void *> yy;
> 
> 
> 
> 
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