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c++: alias_ctad_tweaks and constrained dguide [PR95486]

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In the below testcase, we're ICEing from alias_ctad_tweaks ultimately
because the implied deduction guide for X's user-defined constructor
already has constraints associated with it.  We then carry over these
constraints to 'fprime', the overlying deduction guide for the alias
template Y, via tsubst_decl from alias_ctad_tweaks.  Later in
alias_ctad_tweaks we call get_constraints followed by set_constraints
without doing remove_constraints in between, which triggers the !found
assert in set_constraints.

This patch fixes this issue by adding an intervening call to
remove_constraints.

gcc/cp/ChangeLog:

	PR c++/95486
	* pt.c (alias_ctad_tweaks): Call remove_constraints before
	calling set_constraints.

gcc/testsuite/ChangeLog:

	PR c++/95486
	* g++.dg/cpp2a/class-deduction-alias3.C: New test.
This commit is contained in:
Patrick Palka 2020-07-29 22:06:41 -04:00
parent f31dd9beb9
commit 71141b1bd5
2 changed files with 15 additions and 1 deletions
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5
gcc/cp/pt.c
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@ -28620,7 +28620,10 @@ alias_ctad_tweaks (tree tmpl, tree uguides)
}
if (ci)
set_constraints (fprime, ci);
{
remove_constraints (fprime);
set_constraints (fprime, ci);
}
}
else
{

11
gcc/testsuite/g++.dg/cpp2a/class-deduction-alias3.C Normal file
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@ -0,0 +1,11 @@
// PR c++/95486
// { dg-do compile { target c++20 } }
template<class T, class U>
struct X { X(U) requires __is_same(U, int) {} };
template<class U>
using Y = X<void, U>;
Y y{1};
Y z{'a'}; // { dg-error "failed|no match" }