[cfe-dev] Local typedefs in templates

[David Blaikie via cfe-dev]

I'm not entirely clear on where the warnings are/aren't here, but some
general advice:

Warnings should usually only be issued from either template patterns of
template instantiations, not both. If the error can be detected in a
pattern (either because it's in a non-dependent expression, or the
dependence of the expression doesn't matter to the test) that's better
because you can warn exactly once no matter how many instantiations there
are.

Otherwise, defer to the instantiations.

On Wed, Apr 12, 2017 at 2:11 AM Alex L via cfe-dev <cfe-dev at lists.llvm.org>
wrote:

> Hi,
>
> I have observed something slightly different - both the dependent and
> non-dependent non-instantiated TypedefDecl are marked as referenced (ToT
> clang). It seems to me that you could try fixing the issue by marking the
> instantiated TypedefDecls as referenced if the non-instantiated is
> referenced (see TemplateDeclInstantiator::InstantiateTypedefNameDecl).
>
> Alex
>
> On 12 April 2017 at 08:29, Johannes Altmanninger via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
> Hi,
>
> I have been working on fixing [1]. To me it is not obvious what is the
> proper solution is. Maybe someone has an idea?
>
> Consider this small test program:
>
> template <class T>
> void Function(T) {
>   struct Struct {
>     typedef int Something;
>     Something x;
>   };
> }
> void test() { Function('c'); }
>
> Compiling it with -Wall -fsyntax-only generates the warning about the
> local typedef being unused.
>
> When adding -ast-dump one can see that there are two TypedefDecls, one
> for the FunctionTemplateDecl and another for the one instantiation of
> the template. The same thing applies when the typedef is dependent on a
> template parameter, say "typedef T Something" in this case.
>
> I observed this behaviour:
>
> When the typedef is independent, then neither of the TypedefDecls will
> be marked referenced as of now. Additionally, the type of ValueDecls
> like "Something x;" has the non-templated typedef as its declaration.
>
> When the typedef is dependent, then only the non-templated TypedefDecl
> will be marked referenced. The type of ValueDecls does naturally refer
> to the instantiated TypedefDecl.
>
> Is it supposed to be that way?
>
> If the types of declarations always referred to the instantiated
> typedefs, it would be straightforward to fix by traversing all
> declarations and marking the typedefs of their types referenced.
>
> Alternatively, it would be possible to only check non-instantiated
> types on being referenced. Actually, this might to be the simplest one..
>
>
> Johannes
>
>
> [1] https://bugs.llvm.org/show_bug.cgi?id=24883
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20170412/a2430d23/attachment.html>