[gcc r14-5504] c++: partially inst requires-expr in noexcept-spec [PR101043]

[gcc r14-5504] c++: partially inst requires-expr in noexcept-spec [PR101043]

[Patrick Palka]

https://gcc.gnu.org/g:40a7707a7ea3568cee2cd80cd7e83b7eda678410

commit r14-5504-g40a7707a7ea3568cee2cd80cd7e83b7eda678410
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Nov 15 12:17:55 2023 -0500

    c++: partially inst requires-expr in noexcept-spec [PR101043]
    
    Here we're ICEing from strip_typedefs for the partially instantiated
    requires-expression when walking its REQUIRES_EXPR_EXTRA_ARGS which
    in this case is a TREE_LIST with non-empty TREE_PURPOSE (to hold the
    captured local specialization 't' as per build_extra_args) which
    strip_typedefs doesn't expect.
    
    We can probably skip walking REQUIRES_EXPR_EXTRA_ARGS at all since it
    shouldn't contain any typedefs in the first place, but it seems safer
    and more generally useful to just teach strip_typedefs to handle non-empty
    TREE_PURPOSE the obvious way.  (The code asserts TREE_PURPOSE was empty
    even since since its inception i.e. r189298.)
    
            PR c++/101043
    
    gcc/cp/ChangeLog:
    
            * tree.cc (strip_typedefs_expr) <case TREE_LIST>: Handle
            non-empty TREE_PURPOSE.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/concepts-requires37.C: New test.

Diff:
---
 gcc/cp/tree.cc                                   | 19 ++++++++++++-------
 gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C | 11 +++++++++++
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index dc4126f935c..0736e8d8f48 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -1911,19 +1911,24 @@ strip_typedefs_expr (tree t, bool *remove_attributes, unsigned int flags)
     case TREE_LIST:
       {
 	bool changed = false;
-	releasing_vec vec;
+	auto_vec<tree_pair, 4> vec;
 	r = t;
 	for (; t; t = TREE_CHAIN (t))
 	  {
-	    gcc_assert (!TREE_PURPOSE (t));
-	    tree elt = strip_typedefs (TREE_VALUE (t),
-				       remove_attributes, flags);
-	    if (elt != TREE_VALUE (t))
+	    tree purpose = strip_typedefs (TREE_PURPOSE (t),
+					   remove_attributes, flags);
+	    tree value = strip_typedefs (TREE_VALUE (t),
+					 remove_attributes, flags);
+	    if (purpose != TREE_PURPOSE (t) || value != TREE_VALUE (t))
 	      changed = true;
-	    vec_safe_push (vec, elt);
+	    vec.safe_push ({purpose, value});
 	  }
 	if (changed)
-	  r = build_tree_list_vec (vec);
+	  {
+	    r = NULL_TREE;
+	    for (int i = vec.length () - 1; i >= 0; i--)
+	      r = tree_cons (vec[i].first, vec[i].second, r);
+	  }
 	return r;
       }
 
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C
new file mode 100644
index 00000000000..fa4095ed494
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C
@@ -0,0 +1,11 @@
+// PR c++/101043
+// { dg-do compile { target c++20 } }
+
+template<class T>
+void f(T t) {
+  [&](auto) noexcept(requires { t.g(); }) { }(0);
+}
+
+int main() {
+  f(0);
+}