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c++: find_template_parameters and TEMPLATE_DECLs [PR101247] 

r12-1989 fixed the testcase in the PR, but unfortunately the fix is
buggy: it breaks the case where the common template between the
TEMPLATE_DECL t and ctx_parms is the innermost template (as in
concepts-memtmpl5.C below).  This can be fixed by instead passing the
TREE_TYPE of ctmpl to common_enclosing_class when ctmpl is a class
template.

But even after that's fixed, the analogous case where the innermost
template is a partial specialization is still broken (as in
concepts-memtmpl5a.C below), because ctmpl is always a primary template.

So this patch instead takes a diferent approach that doesn't rely on
ctx_parms at all: when looking for the template parameters of a
TEMPLATE_DECL that are shared with the current template context, just
walk its DECL_CONTEXT.  As long as the template is not overly general
(e.g. we didn't pass it through most_general_template), this should give
us exactly what we want, since if a TEMPLATE_DECL can be referred to
from some template context then the template parameters it uses must all
be in-scope and contained in its DECL_CONTEXT.  This effectively makes
us treat TEMPLATE_DECLs more similarly to other _DECLs (whose DECL_CONTEXT
we also walk).

	PR c++/101247

gcc/cp/ChangeLog:

	* pt.c (any_template_parm_r) <case TEMPLATE_DECL>: Just walk the
	DECL_CONTEXT.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-memtmpl4.C: Uncomment the commented out
	example, which we now handle correctly.
	* g++.dg/cpp2a/concepts-memtmpl5.C: New test.
	* g++.dg/cpp2a/concepts-memtmpl5a.C: New test.
This commit is contained in:
Patrick Palka 2021-07-09 10:20:22 -04:00
parent 2e345e4ad6
commit f53e66019d
4 changed files with 32 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
gcc/cp/pt.c
View File

@ -10728,15 +10728,11 @@ any_template_parm_r (tree t, void *data)
break;
case TEMPLATE_DECL:
{
/* If T is a member template that shares template parameters with
ctx_parms, we need to mark all those parameters for mapping. */
if (tree ctmpl = TREE_TYPE (INNERMOST_TEMPLATE_PARMS (ftpi->ctx_parms)))
if (tree com = common_enclosing_class (DECL_CONTEXT (t),
DECL_CONTEXT (ctmpl)))
if (tree ti = CLASSTYPE_TEMPLATE_INFO (com))
WALK_SUBTREE (TI_ARGS (ti));
}
ctx_parms, we need to mark all those parameters for mapping.
To that end, it should suffice to just walk the DECL_CONTEXT of
the template (assuming the template is not overly general). */
WALK_SUBTREE (DECL_CONTEXT (t));
break;
case LAMBDA_EXPR:

2
gcc/testsuite/g++.dg/cpp2a/concepts-memtmpl4.C
View File

@ -24,5 +24,5 @@ int main()
{
A<void>::B::f(0);
A<void>::C<int>::f(0);
// A<void>::C<int>::g();
A<void>::C<int>::g();
}

11
gcc/testsuite/g++.dg/cpp2a/concepts-memtmpl5.C Normal file
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@ -0,0 +1,11 @@
// PR c++/101247
// { dg-do compile { target concepts } }
template<class T, class U> struct A {
template<class> static constexpr bool d = true;
static void g() requires d<U>;
};
int main() {
A<int, char>::g();
}

15
gcc/testsuite/g++.dg/cpp2a/concepts-memtmpl5a.C Normal file
View File

@ -0,0 +1,15 @@
// PR c++/101247
// { dg-do compile { target concepts } }
// A variant of concepts-memtmpl5.C that uses a partial specialization
// of A instead of the primary template.
template<class, class> struct A;
template<class T, class U> requires true struct A<T, U> {
template<class V> static constexpr bool d = true;
static void g() requires d<U>;
};
int main() {
A<int, char>::g();
}