[PATCH] c++: matching deduced template template parameters [PR67829]

Patrick Palka ppalka@redhat.com
Wed Jun 9 19:56:57 GMT 2021


On Wed, 9 Jun 2021, Patrick Palka wrote:

> During deduction, when the template of a BOUND_TEMPLATE_TEMPLATE_PARM is

Ah sorry, this should instead say "when the template of _the argument for_
a BOUND_TEMPLATE_TEMPLATE_PARM is ..."

> a template template parameter, we need to consider the
> TEMPLATE_TEMPLATE_PARAMETER rather than the TEMPLATE_DECL thereof,
> because the canonical form of a template template parameter in a
> template argument list is the TEMPLATE_TEMPLATE_PARAMETER tree.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
> 
> 	PR c++/67829
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.c (unify) <case BOUND_TEMPLATE_TEMPLATE_PARM>: When
> 	the TEMPLATE_DECL of a BOUND_TEMPLATE_TEMPLATE_PARM argument is
> 	a template template parameter, adjust to the
> 	TEMPLATE_TEMPLATE_PARAMETER before falling through.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/template/ttp34.C: New test.
> 	* g++.dg/template/ttp34a.C: New test.
> 	* g++.dg/template/ttp34b.C: New test.
> ---
>  gcc/cp/pt.c                            |  4 ++++
>  gcc/testsuite/g++.dg/template/ttp34.C  | 14 ++++++++++++++
>  gcc/testsuite/g++.dg/template/ttp34a.C | 14 ++++++++++++++
>  gcc/testsuite/g++.dg/template/ttp34b.C | 14 ++++++++++++++
>  4 files changed, 46 insertions(+)
>  create mode 100644 gcc/testsuite/g++.dg/template/ttp34.C
>  create mode 100644 gcc/testsuite/g++.dg/template/ttp34a.C
>  create mode 100644 gcc/testsuite/g++.dg/template/ttp34b.C
> 
> diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> index 05679b12973..963a182b9e5 100644
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -23555,6 +23555,10 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
>  	    return 1;
>  
>  	  arg = TYPE_TI_TEMPLATE (arg);
> +	  if (TREE_CODE (TREE_TYPE (arg)) == TEMPLATE_TEMPLATE_PARM)
> +	    /* If the template is a template template parameter, use the
> +	       TEMPLATE_TEMPLATE_PARM for matching.  */
> +	    arg = TREE_TYPE (arg);
>  
>  	  /* Fall through to deduce template name.  */
>  	}
> diff --git a/gcc/testsuite/g++.dg/template/ttp34.C b/gcc/testsuite/g++.dg/template/ttp34.C
> new file mode 100644
> index 00000000000..67094063ba5
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/ttp34.C
> @@ -0,0 +1,14 @@
> +// PR c++/67829
> +
> +template<class> class Purr;
> +
> +template<template<class> class, class, class>
> +class Meow;
> +
> +template<template<class> class P>
> +class Meow<P, P<int>, int> { }; // 1
> +
> +template<template<class> class P, class T>
> +class Meow<P, P<int>, T>; // 2
> +
> +Meow<Purr, Purr<int>, int> kitty;
> diff --git a/gcc/testsuite/g++.dg/template/ttp34a.C b/gcc/testsuite/g++.dg/template/ttp34a.C
> new file mode 100644
> index 00000000000..e3303dcf212
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/ttp34a.C
> @@ -0,0 +1,14 @@
> +// PR c++/67829
> +
> +template<class> class Purr;
> +
> +template<template<class> class, class>
> +class Meow;
> +
> +template<template<class> class P>
> +class Meow<P, P<int> > { }; // 1
> +
> +template<template<class> class P, class T>
> +class Meow<P, P<T> >; // 2
> +
> +Meow<Purr, Purr<int> > kitty;
> diff --git a/gcc/testsuite/g++.dg/template/ttp34b.C b/gcc/testsuite/g++.dg/template/ttp34b.C
> new file mode 100644
> index 00000000000..ed3b3e8ab05
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/ttp34b.C
> @@ -0,0 +1,14 @@
> +// PR c++/67829
> +
> +template<class> class Purr;
> +
> +template<class, template<class> class>
> +class Meow;
> +
> +template<template<class> class P>
> +class Meow<P<int>, P> { }; // 1
> +
> +template<template<class> class P, class T>
> +class Meow<P<T>, P>; // 2
> +
> +Meow<Purr<int>, Purr> kitty;
> -- 
> 2.32.0.rc2
> 
> 



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