https://gcc.gnu.org/g:cc79849cc883146964f0001f33c8b7eb576825c4
commit r16-4028-gcc79849cc883146964f0001f33c8b7eb576825c4
Author: Nathaniel Shead <nathanielosh...@gmail.com>
Date: Tue Sep 23 00:18:43 2025 +1000
c++: Fix canonical type for lambda pack captures [PR122015]
comp_template_parms_position uses whether a TEMPLATE_TYPE_PARM is a pack
to determine equivalency. This in turn affects whether
canonical_type_parameter finds a pre-existing auto type as equivalent.
When generating the 'auto...' type for a lambda pack capture, we only
mark it as a pack after generating the node (and calculating its
canonical); this means that later when comparing a version streamed in
from a module we think that two equivalent types have different
TYPE_CANONICAL, because the latter already had
TEMPLATE_PARM_PARAMETER_PACK set before calculating its canonical.
This patch fixes this by using a new 'make_auto_pack' function to ensure
that packness is set before the canonical is looked up.
PR c++/122015
gcc/cp/ChangeLog:
* cp-tree.h (make_auto_pack): Declare.
* lambda.cc (lambda_capture_field_type): Use make_auto_pack to
ensure TYPE_CANONICAL is set correctly.
* pt.cc (make_auto_pack): New function.
gcc/testsuite/ChangeLog:
* g++.dg/modules/lambda-11.h: New test.
* g++.dg/modules/lambda-11_a.H: New test.
* g++.dg/modules/lambda-11_b.C: New test.
Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
Reviewed-by: Patrick Palka <ppa...@redhat.com>
Diff:
---
gcc/cp/cp-tree.h | 1 +
gcc/cp/lambda.cc | 25 +++++++++++++++----------
gcc/cp/pt.cc | 12 ++++++++++++
gcc/testsuite/g++.dg/modules/lambda-11.h | 6 ++++++
gcc/testsuite/g++.dg/modules/lambda-11_a.H | 6 ++++++
gcc/testsuite/g++.dg/modules/lambda-11_b.C | 6 ++++++
6 files changed, 46 insertions(+), 10 deletions(-)
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index d531bcd833b3..54156cb0d237 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7835,6 +7835,7 @@ extern tree make_constrained_auto (tree, tree);
extern tree make_constrained_decltype_auto (tree, tree);
extern tree make_template_placeholder (tree);
extern tree make_cast_auto (void);
+extern tree make_auto_pack (void);
extern bool template_placeholder_p (tree);
extern bool ctad_template_p (tree);
extern bool unparenthesized_id_or_class_member_access_p (tree);
diff --git a/gcc/cp/lambda.cc b/gcc/cp/lambda.cc
index bb0aa7d0a020..575daaa9d711 100644
--- a/gcc/cp/lambda.cc
+++ b/gcc/cp/lambda.cc
@@ -220,18 +220,23 @@ lambda_capture_field_type (tree expr, bool
explicit_init_p,
if (explicit_init_p)
{
- tree auto_node = make_auto ();
-
- type = auto_node;
- if (by_reference_p)
- /* Add the reference now, so deduction doesn't lose
- outermost CV qualifiers of EXPR. */
- type = build_reference_type (type);
if (uses_parameter_packs (expr))
- /* Stick with 'auto' even if the type could be deduced. */
- TEMPLATE_TYPE_PARAMETER_PACK (auto_node) = true;
+ {
+ /* Stick with 'auto...' even if the type could be deduced. */
+ type = make_auto_pack ();
+ if (by_reference_p)
+ type = build_reference_type (type);
+ }
else
- type = do_auto_deduction (type, expr, auto_node);
+ {
+ tree auto_node = make_auto ();
+ type = auto_node;
+ if (by_reference_p)
+ /* Add the reference now, so deduction doesn't lose
+ outermost CV qualifiers of EXPR. */
+ type = build_reference_type (type);
+ type = do_auto_deduction (type, expr, auto_node);
+ }
}
else if (!type_deducible_expression_p (expr))
{
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 494b6be7a240..06287f0b0452 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -30493,6 +30493,18 @@ make_constrained_decltype_auto (tree con, tree args)
return make_constrained_placeholder_type (type, con, args);
}
+/* Create an "auto..." type-specifier. */
+
+tree
+make_auto_pack ()
+{
+ tree type = make_auto_1 (auto_identifier, false);
+ TEMPLATE_TYPE_PARAMETER_PACK (type) = true;
+ /* Our canonical type depends on being a pack. */
+ TYPE_CANONICAL (type) = canonical_type_parameter (type);
+ return type;
+}
+
/* Returns true if the placeholder type constraint T has any dependent
(explicit) template arguments. */
diff --git a/gcc/testsuite/g++.dg/modules/lambda-11.h
b/gcc/testsuite/g++.dg/modules/lambda-11.h
new file mode 100644
index 000000000000..e4a07f22cf05
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/lambda-11.h
@@ -0,0 +1,6 @@
+// PR c++/122015
+
+template <typename> auto declval();
+template <typename... _BindArgs> void bind_front() {
+ [... __bound_args(_BindArgs{})] {};
+}
diff --git a/gcc/testsuite/g++.dg/modules/lambda-11_a.H
b/gcc/testsuite/g++.dg/modules/lambda-11_a.H
new file mode 100644
index 000000000000..03d024260c34
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/lambda-11_a.H
@@ -0,0 +1,6 @@
+// PR c++/122015
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fmodule-header" }
+// { dg-module-cmi {} }
+
+#include "lambda-11.h"
diff --git a/gcc/testsuite/g++.dg/modules/lambda-11_b.C
b/gcc/testsuite/g++.dg/modules/lambda-11_b.C
new file mode 100644
index 000000000000..c7a5f43ba42d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/lambda-11_b.C
@@ -0,0 +1,6 @@
+// PR c++/122015
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-fmodules -fno-module-lazy" }
+
+#include "lambda-11.h"
+import "lambda-11_a.H";
