c++: ICE in dependent_type_p with constrained auto [PR97052]

This patch fixes an "unguarded" call to coerce_template_parms in
build_standard_check: processing_template_decl could be zero if we
get here during processing of the first 'auto' parameter of an
abbreviated function template, or if we're processing the type
constraint of a non-templated variable.  In the testcase below, this
leads to an ICE when coerce_template_parms instantiates C's dependent
default template argument.

gcc/cp/ChangeLog:

	PR c++/97052
	* constraint.cc (build_type_constraint): Temporarily increment
	processing_template_decl before calling build_concept_check.
	* pt.c (make_constrained_placeholder_type): Likewise.

gcc/testsuite/ChangeLog:

	PR c++/97052
	* g++.dg/cpp2a/concepts-defarg2.C: New test.

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index d49957a6c4ab96d6eba2b1de25047cd08e45a575..050b55ce09298170c15108008b3d759493fa7bd0 100644 (file)
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -1427,7 +1427,9 @@ tree
 build_type_constraint (tree decl, tree args, tsubst_flags_t complain)
 {
   tree wildcard = build_nt (WILDCARD_DECL);
+  ++processing_template_decl;
   tree check = build_concept_check (decl, wildcard, args, complain);
+  --processing_template_decl;
   if (check == error_mark_node)
     return error_mark_node;
   return unpack_concept_check (check);

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index fc4b9bb7c7f9810f4daab5859a9ad9a20d1f98d5..9a83810b67c473a0c584463f09df1e23057ba5f1 100644 (file)
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -27928,7 +27928,9 @@ make_constrained_placeholder_type (tree type, tree con, tree args)
   tree expr = tmpl;
   if (TREE_CODE (con) == FUNCTION_DECL)
     expr = ovl_make (tmpl);
+  ++processing_template_decl;
   expr = build_concept_check (expr, type, args, tf_warning_or_error);
+  --processing_template_decl;
 
   PLACEHOLDER_TYPE_CONSTRAINTS (type) = expr;
 

diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C b/gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C
new file mode 100644 (file)
index 0000000..a63ca4e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C
@@ -0,0 +1,13 @@
+// PR c++/97052
+// { dg-do compile { target c++20 } }
+
+template<typename T, typename U = typename T::type>
+concept C = true;
+
+constexpr bool f(C auto) {
+  return true;
+}
+
+static_assert(f(0));
+
+C auto x = 0;