c++: normalization of non-templated return-type-req [PR100946]
Here the satisfaction cache is conflating the satisfaction value of the
two return-type-requirements because the corresponding constrained
'auto's have level 2, but they capture an empty current_template_parms.
This ultimately causes the satisfaction cache to think the type
constraint doesn't depend on the deduced type of the expression.
When normalizing the constraints on an 'auto', the assumption made by
normalize_placeholder_type_constraints is that the level of the 'auto'
is one greater than the depth of the captured current_template_parms, an
assumption which is not holding here. So this patch just makes n_p_t_c
adjust the normalization context appropriately in this situation.
PR c++/100946
gcc/cp/ChangeLog:
* constraint.cc (normalize_placeholder_type_constraints): When
normalizing a non-templated return-type-requirement, add a dummy
level to initial_parms.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-return-req3.C: New test.
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 03ce8eb..74b16d2 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3065,6 +3065,15 @@
scope for this placeholder type; use them as the initial template
parameters for normalization. */
tree initial_parms = TREE_PURPOSE (ci);
+
+ if (!initial_parms && TEMPLATE_TYPE_LEVEL (t) == 2)
+ /* This is a return-type-requirement of a non-templated requires-expression,
+ which are parsed under processing_template_decl == 1 and empty
+ current_template_parms; hence the 'auto' has level 2 and initial_parms
+ is empty. Fix up initial_parms to be consistent with the value of
+ processing_template_decl whence the 'auto' was created. */
+ initial_parms = build_tree_list (size_int (1), make_tree_vec (0));
+
/* The 'auto' itself is used as the first argument in its own constraints,
and its level is one greater than its template depth. So in order to
capture all used template parameters, we need to add an extra level of
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-return-req3.C b/gcc/testsuite/g++.dg/cpp2a/concepts-return-req3.C
new file mode 100644
index 0000000..a546c64
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-return-req3.C
@@ -0,0 +1,6 @@
+// PR c++/100946
+// { dg-do compile { target c++20 } }
+
+template<class T> concept C = __is_same(T, int);
+static_assert(requires { { 0 } -> C; });
+static_assert(requires { { true } -> C; }); // { dg-error "failed" }
