On 5/30/20 12:37 AM, Patrick Palka wrote:
On Wed, 13 May 2020, Jason Merrill wrote:
On 5/11/20 6:43 PM, Patrick Palka wrote:
In the testcase below we're prematurely folding away the
requires-expression to 'true' after substituting in the function's
template arguments, but before substituting in the lambda's deduced
template arguments.
This happens because during the first tsubst_requires_expr,
processing_template_decl is 1 but 'args' is just {void} and therefore
non-dependent, so we end up folding away the requires-expression to
boolean_true_node before we could substitute in the lambda's template
arguments and determine that '*v' is ill-formed.
This patch removes the uses_template_parms check when deciding in
tsubst_requires_expr whether to keep around a new requires-expression.
Regardless of whether the template arguments are dependent, there still
might be more template parameters to later substitute in -- as in the
testcase below -- and even if not, tsubst_expr doesn't perform full
semantic processing unless !processing_template_decl, so it seems we
should wait until then to fold away the requires-expression.
Passes 'make check-c++', does this look OK to commit after a full
bootstrap/regtest?
OK.
Would the same patch be OK to backport to the GCC 10 branch?
Yes.
gcc/cp/ChangeLog:
PR c++/95020
* constraint.c (tsubst_requires_expr): Produce a new
requires-expression when processing_template_decl, even if
template arguments are not dependent.
gcc/testsuite/ChangeLog:
PR c++/95020
* g++/cpp2a/concepts-lambda7.C: New test.
---
gcc/cp/constraint.cc | 4 +---
gcc/testsuite/g++.dg/cpp2a/concepts-lambda7.C | 14 ++++++++++++++
2 files changed, 15 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-lambda7.C
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 4ad17f3b7d8..8ee347cae60 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -2173,9 +2173,7 @@ tsubst_requires_expr (tree t, tree args,
if (reqs == error_mark_node)
return boolean_false_node;
- /* In certain cases, produce a new requires-expression.
- Otherwise the value of the expression is true. */
- if (processing_template_decl && uses_template_parms (args))
+ if (processing_template_decl)
return finish_requires_expr (cp_expr_location (t), parms, reqs);
return boolean_true_node;
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda7.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda7.C
new file mode 100644
index 00000000000..50746b777a3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda7.C
@@ -0,0 +1,14 @@
+// PR c++/95020
+// { dg-do compile { target c++2a } }
+
+template<typename>
+void foo() {
+ auto t = [](auto v) {
+ static_assert(requires { *v; }); // { dg-error "static assertion
failed" }
+ };
+ t(0);
+}
+
+void bar() {
+ foo<void>();
+}
