From: Patrick Palka <ppalka@redhat.com>
Date: Thu, 30 Jul 2020 02:06:41 +0000 (-0400)
Subject: c++: alias_ctad_tweaks and constrained dguide [PR95486]
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=71141b1bd537cc516e485c834c2d36abba3f4544;p=gcc.git

c++: alias_ctad_tweaks and constrained dguide [PR95486]

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.
---

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 15be7b6d972..a7ab2bd2887 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -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
 	{
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias3.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias3.C
new file mode 100644
index 00000000000..318d4c942ce
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias3.C
@@ -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" }