[PATCH] c++: local_specializations and recursive constrained fn [PR103714]

[Patrick Palka via Gcc-patches]

Here during constraint checking for the recursive call to 'f',
substitution into the PARM_DECL 'd' in the atomic constraint gives us
the wrong local specialization because local_specializations at this
point contains entities associated with the _outer_ call to 'f'.

This patch fixes this by calling push_to_top_level during constraint
checking, which'll clear local_specializations for us.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/11?  Also tested on cmcstl2 and range-v3.

        PR c++/103714

gcc/cp/ChangeLog:

        * constraint.cc (satisfy_declaration_constraints): Do
        push_to_top_level and pop_from_top_level around the call to
        satisfy_normalized_constraints.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/concepts-uneval5.C: New test.
---
 gcc/cp/constraint.cc                          |  4 ++++
 gcc/testsuite/g++.dg/cpp2a/concepts-uneval5.C | 17 +++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-uneval5.C

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 566f4e38fac..9b0348dfdd6 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3186,9 +3186,11 @@ satisfy_declaration_constraints (tree t, sat_info info)
     {
       if (!push_tinst_level (t))
        return result;
+      push_to_top_level ();
       push_access_scope (t);
       result = satisfy_normalized_constraints (norm, args, info);
       pop_access_scope (t);
+      pop_from_top_level ();
       pop_tinst_level ();
     }
 
@@ -3244,9 +3246,11 @@ satisfy_declaration_constraints (tree t, tree args, 
sat_info info)
       if (!push_tinst_level (t, args))
        return result;
       tree pattern = DECL_TEMPLATE_RESULT (t);
+      push_to_top_level ();
       push_access_scope (pattern);
       result = satisfy_normalized_constraints (norm, args, info);
       pop_access_scope (pattern);
+      pop_from_top_level ();
       pop_tinst_level ();
     }
 
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-uneval5.C 
b/gcc/testsuite/g++.dg/cpp2a/concepts-uneval5.C
new file mode 100644
index 00000000000..a315a59b828
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-uneval5.C
@@ -0,0 +1,17 @@
+// PR c++/103714
+// { dg-do compile { target c++20 } }
+
+template<int I>
+struct A {
+  static const int i = I;
+
+  template<int J>
+  void f(A<J> d = {}) requires (d.i != i) {
+    f<I>(); // { dg-error "no match" }
+  }
+};
+
+int main() {
+  A<0> a;
+  a.f<1>();
+}
-- 
2.34.1.182.ge773545c7f