c++: unexpanded pack in requires-expr parm list [PR107417]
Commit Message
Here find_parameter_packs_r isn't recognizing the unexpanded pack T
inside the requires-expr's parameter list ultimately because
cp_walk_trees avoids walking the parameters, for good reason: in
requires (Ts... ts) { }
walking 'ts' would trigger a false positive in the unexpanded pack
checker since it's, well, an unexpanded pack. But we might as well walk
the TREE_TYPE of each parameter still, which for_each_template_parm_r
already does.
Bootstrapped and regtested on x86_64-pc-linux-gne, does this look OK for
trunk/12?
PR c++/107417
gcc/cp/ChangeLog:
* pt.cc (for_each_template_parm_r) <case REQUIRES_EXPR>: Move
walking of the TREE_TYPE of each parameter to ...
* tree.cc (cp_walk_subtrees) <case REQUIRES_EXPR>: ... here.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-requires33.C: New test.
---
gcc/cp/pt.cc | 15 --------------
gcc/cp/tree.cc | 20 ++++++++++---------
.../g++.dg/cpp2a/concepts-requires33.C | 11 ++++++++++
3 files changed, 22 insertions(+), 24 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires33.C
Comments
On 12/2/22 14:42, Patrick Palka wrote:
> Here find_parameter_packs_r isn't recognizing the unexpanded pack T
> inside the requires-expr's parameter list ultimately because
> cp_walk_trees avoids walking the parameters, for good reason: in
>
> requires (Ts... ts) { }
>
> walking 'ts' would trigger a false positive in the unexpanded pack
> checker since it's, well, an unexpanded pack. But we might as well walk
> the TREE_TYPE of each parameter still, which for_each_template_parm_r
> already does.
>
> Bootstrapped and regtested on x86_64-pc-linux-gne, does this look OK for
> trunk/12?
OK.
> PR c++/107417
>
> gcc/cp/ChangeLog:
>
> * pt.cc (for_each_template_parm_r) <case REQUIRES_EXPR>: Move
> walking of the TREE_TYPE of each parameter to ...
> * tree.cc (cp_walk_subtrees) <case REQUIRES_EXPR>: ... here.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp2a/concepts-requires33.C: New test.
> ---
> gcc/cp/pt.cc | 15 --------------
> gcc/cp/tree.cc | 20 ++++++++++---------
> .../g++.dg/cpp2a/concepts-requires33.C | 11 ++++++++++
> 3 files changed, 22 insertions(+), 24 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires33.C
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index bc8ea06ceae..80110da2d8a 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -10573,21 +10573,6 @@ for_each_template_parm_r (tree *tp, int *walk_subtrees, void *d)
> return error_mark_node;
> break;
>
> - case REQUIRES_EXPR:
> - {
> - if (!fn)
> - return error_mark_node;
> -
> - /* Recursively walk the type of each constraint variable. */
> - tree p = TREE_OPERAND (t, 0);
> - while (p)
> - {
> - WALK_SUBTREE (TREE_TYPE (p));
> - p = TREE_CHAIN (p);
> - }
> - }
> - break;
> -
> default:
> break;
> }
> diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
> index 04a055d9d77..e9b6921df6a 100644
> --- a/gcc/cp/tree.cc
> +++ b/gcc/cp/tree.cc
> @@ -5603,15 +5603,17 @@ cp_walk_subtrees (tree *tp, int *walk_subtrees_p, walk_tree_fn func,
> break;
>
> case REQUIRES_EXPR:
> - // Only recurse through the nested expression. Do not
> - // walk the parameter list. Doing so causes false
> - // positives in the pack expansion checker since the
> - // requires parameters are introduced as pack expansions.
> - ++cp_unevaluated_operand;
> - result = cp_walk_tree (&REQUIRES_EXPR_REQS (*tp), func, data, pset);
> - --cp_unevaluated_operand;
> - *walk_subtrees_p = 0;
> - break;
> + {
> + cp_unevaluated u;
> + for (tree parm = REQUIRES_EXPR_PARMS (*tp); parm; parm = DECL_CHAIN (parm))
> + /* Walk the types of each parameter, but not the parameter itself.
> + Doing so would cause false positives in the unexpanded parameter
> + pack checker since a introduced parameter pack is bare. */
> + WALK_SUBTREE (TREE_TYPE (parm));
> + WALK_SUBTREE (REQUIRES_EXPR_REQS (*tp));
> + *walk_subtrees_p = 0;
> + break;
> + }
>
> case DECL_EXPR:
> /* User variables should be mentioned in BIND_EXPR_VARS
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires33.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires33.C
> new file mode 100644
> index 00000000000..d07ae6dee7b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires33.C
> @@ -0,0 +1,11 @@
> +// PR c++/107417
> +// { dg-do compile { target c++20 } }
> +
> +template<typename... T>
> +requires (requires (T x) { true; } && ...)
> +void f();
> +
> +int main() {
> + f<int>();
> + f<int, void>(); // { dg-error "no match" }
> +}
@@ -10573,21 +10573,6 @@ for_each_template_parm_r (tree *tp, int *walk_subtrees, void *d)
return error_mark_node;
break;
- case REQUIRES_EXPR:
- {
- if (!fn)
- return error_mark_node;
-
- /* Recursively walk the type of each constraint variable. */
- tree p = TREE_OPERAND (t, 0);
- while (p)
- {
- WALK_SUBTREE (TREE_TYPE (p));
- p = TREE_CHAIN (p);
- }
- }
- break;
-
default:
break;
}
@@ -5603,15 +5603,17 @@ cp_walk_subtrees (tree *tp, int *walk_subtrees_p, walk_tree_fn func,
break;
case REQUIRES_EXPR:
- // Only recurse through the nested expression. Do not
- // walk the parameter list. Doing so causes false
- // positives in the pack expansion checker since the
- // requires parameters are introduced as pack expansions.
- ++cp_unevaluated_operand;
- result = cp_walk_tree (&REQUIRES_EXPR_REQS (*tp), func, data, pset);
- --cp_unevaluated_operand;
- *walk_subtrees_p = 0;
- break;
+ {
+ cp_unevaluated u;
+ for (tree parm = REQUIRES_EXPR_PARMS (*tp); parm; parm = DECL_CHAIN (parm))
+ /* Walk the types of each parameter, but not the parameter itself.
+ Doing so would cause false positives in the unexpanded parameter
+ pack checker since a introduced parameter pack is bare. */
+ WALK_SUBTREE (TREE_TYPE (parm));
+ WALK_SUBTREE (REQUIRES_EXPR_REQS (*tp));
+ *walk_subtrees_p = 0;
+ break;
+ }
case DECL_EXPR:
/* User variables should be mentioned in BIND_EXPR_VARS
new file mode 100644
@@ -0,0 +1,11 @@
+// PR c++/107417
+// { dg-do compile { target c++20 } }
+
+template<typename... T>
+requires (requires (T x) { true; } && ...)
+void f();
+
+int main() {
+ f<int>();
+ f<int, void>(); // { dg-error "no match" }
+}