[gcc r14-9066] c++: compound-requirement partial substitution [PR113966]

[Patrick Palka <ppalka@gcc.gnu.org>]

https://gcc.gnu.org/g:3a6f3354eaaf38b5e6be41e4ebf521d299593a6e

commit r14-9066-g3a6f3354eaaf38b5e6be41e4ebf521d299593a6e
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Feb 19 11:34:45 2024 -0500

    c++: compound-requirement partial substitution [PR113966]
    
    When partially substituting a requires-expr, we don't want to perform
    any additional checks beyond the substitution itself so as to minimize
    checking requirements out of order.  So don't check the return-type-req
    of a compound-requirement during partial substitution.  And don't check
    the noexcept condition either since we can't do that on templated trees.
    
            PR c++/113966
    
    gcc/cp/ChangeLog:
    
            * constraint.cc (tsubst_compound_requirement): Don't check
            the noexcept condition or the return-type-requirement when
            partially substituting.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/concepts-friend17.C: New test.
    
    Reviewed-by: Jason Merrill <jason@redhat.com>

Diff:
---
 gcc/cp/constraint.cc                           |  5 +++--
 gcc/testsuite/g++.dg/cpp2a/concepts-friend17.C | 15 +++++++++++++++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index d9569013bd34..49de3211d4c7 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -2134,7 +2134,8 @@ tsubst_compound_requirement (tree t, tree args, sat_info info)
 
   /* Check the noexcept condition.  */
   bool noexcept_p = COMPOUND_REQ_NOEXCEPT_P (t);
-  if (noexcept_p && !expr_noexcept_p (expr, quiet.complain))
+  if (noexcept_p && !processing_template_decl
+      && !expr_noexcept_p (expr, quiet.complain))
     {
       if (info.diagnose_unsatisfaction_p ())
 	inform (loc, "%qE is not %<noexcept%>", expr);
@@ -2148,7 +2149,7 @@ tsubst_compound_requirement (tree t, tree args, sat_info info)
     return error_mark_node;
 
   /* Check expression against the result type.  */
-  if (type)
+  if (type && !processing_template_decl)
     {
       if (tree placeholder = type_uses_auto (type))
 	{
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-friend17.C b/gcc/testsuite/g++.dg/cpp2a/concepts-friend17.C
new file mode 100644
index 000000000000..9b5091f14a81
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-friend17.C
@@ -0,0 +1,15 @@
+// PR c++/113966
+// { dg-do compile { target c++20 } }
+
+template<class T> concept C = T::value;
+
+template<class T>
+struct A {
+  template<class U> requires U::value || requires { { T() } -> C; }
+  friend void f(A, U) { }
+
+  template<class U> requires requires { { g(U()) } noexcept; }
+  friend void f(A, U, U) { }
+};
+
+template struct A<int>;