[gcc r10-9415] c++: Normalization and deduction guide rewriting [PR96199]

[Jason Merrill]

https://gcc.gnu.org/g:a588c87ba309492b351c1a55b08d907b65913e2c

commit r10-9415-ga588c87ba309492b351c1a55b08d907b65913e2c
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Mar 3 17:38:55 2021 -0500

    c++: Normalization and deduction guide rewriting [PR96199]
    
    This is a subset of r11-2748; we don't want to rewrite all deduction guides
    in GCC 10, but we do need the push_nested_class in normalization to avoid
    breaking cmcstl2.
    
    gcc/cp/ChangeLog:
    
            PR c++/96199
            * cp-tree.h (struct push_nested_class_guard): New.
            * constraint.cc (get_normalized_constraints_from_decl): Use it.

Diff:
---
 gcc/cp/constraint.cc |  2 ++
 gcc/cp/cp-tree.h     | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index f54c220253f..89a2bb5223b 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -841,6 +841,8 @@ get_normalized_constraints_from_decl (tree d, bool diag = false)
     if (tree *p = hash_map_safe_get (normalized_map, tmpl))
       return *p;
 
+  push_nested_class_guard pncs (DECL_CONTEXT (d));
+
   tree args = generic_targs_for (tmpl);
   tree ci = get_constraints (decl);
   tree norm = get_normalized_constraints_from_info (ci, args, tmpl, diag);
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 82716d33c49..9a66fe5884f 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -8132,6 +8132,24 @@ is_constrained_auto (const_tree t)
   return is_auto (t) && PLACEHOLDER_TYPE_CONSTRAINTS (t);
 }
 
+/* RAII class to push/pop class scope T; if T is not a class, do nothing.  */
+
+struct push_nested_class_guard
+{
+  bool push;
+  push_nested_class_guard (tree t)
+    : push (t && CLASS_TYPE_P (t))
+  {
+    if (push)
+      push_nested_class (t);
+  }
+  ~push_nested_class_guard ()
+  {
+    if (push)
+      pop_nested_class ();
+  }
+};
+
 #if CHECKING_P
 namespace selftest {
   extern void run_cp_tests (void);