Re: [PATCH] c++/modules: Propagate type of array with deduced size to its template [PR122422]

[Jason Merrill]

On 10/26/25 12:47 PM, Nathaniel Shead wrote:

Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?

OK.

-- >8 --

This is the same issue as solved in r16-1759-g98fd493db6216c for auto,
but this time for array with size deduced from their initializer.

        PR c++/122422

gcc/cp/ChangeLog:

        * decl.cc (maybe_deduce_size_from_array_init): Propagate type to
        corresponding TEMPLATE_DECL.

gcc/testsuite/ChangeLog:

        * g++.dg/modules/merge-20.h: New test.
        * g++.dg/modules/merge-20_a.H: New test.
        * g++.dg/modules/merge-20_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
---
  gcc/cp/decl.cc                            | 8 ++++++++
  gcc/testsuite/g++.dg/modules/merge-20.h   | 5 +++++
  gcc/testsuite/g++.dg/modules/merge-20_a.H | 5 +++++
  gcc/testsuite/g++.dg/modules/merge-20_b.C | 5 +++++
  4 files changed, 23 insertions(+)
  create mode 100644 gcc/testsuite/g++.dg/modules/merge-20.h
  create mode 100644 gcc/testsuite/g++.dg/modules/merge-20_a.H
  create mode 100644 gcc/testsuite/g++.dg/modules/merge-20_b.C

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 2089e4c21ac..e2c20a34e6f 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -7096,6 +7096,14 @@ maybe_deduce_size_from_array_init (tree decl, tree init)
        cp_apply_type_quals_to_decl (cp_type_quals (TREE_TYPE (decl)), decl);

relayout_decl (decl);

+
+      /* Update the type of the corresponding TEMPLATE_DECL to match.  */
+      if (DECL_LANG_SPECIFIC (decl) && DECL_TEMPLATE_INFO (decl))
+       {
+         tree tmpl = template_for_substitution (decl);
+         if (DECL_TEMPLATE_RESULT (tmpl) == decl)
+           TREE_TYPE (tmpl) = TREE_TYPE (decl);
+       }
      }
  }

diff --git a/gcc/testsuite/g++.dg/modules/merge-20.h b/gcc/testsuite/g++.dg/modules/merge-20.h

new file mode 100644
index 00000000000..c169d110fab
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/merge-20.h
@@ -0,0 +1,5 @@
+// PR c++/122422
+template <typename> struct Type {
+  constexpr static int arr[] = { 42, 43, 44 };
+};
+inline Type<int> tt;
diff --git a/gcc/testsuite/g++.dg/modules/merge-20_a.H 
b/gcc/testsuite/g++.dg/modules/merge-20_a.H
new file mode 100644
index 00000000000..2fca74b244d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/merge-20_a.H
@@ -0,0 +1,5 @@
+// PR c++/122422
+// { dg-additional-options "-fmodule-header" }
+// { dg-module-cmi {} }
+
+#include "merge-20.h"
diff --git a/gcc/testsuite/g++.dg/modules/merge-20_b.C 
b/gcc/testsuite/g++.dg/modules/merge-20_b.C
new file mode 100644
index 00000000000..fc69fa0478d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/merge-20_b.C
@@ -0,0 +1,5 @@
+// PR c++/122422
+// { dg-additional-options "-fmodules -fno-module-lazy" }
+
+#include "merge-20.h"
+import "merge-20_a.H";