On Tue, Jun 23, 2026 at 6:31 PM Jason Merrill <[email protected]> wrote:
>
> Tested x86_64-pc-linux-gnu, applying to trunk.
>
> -- 8< --
>
> Here A<S> is not instantiated in _a, so the exported a_s typedef is to an
> incomplete type. It's instantiated in _b, but when marking things reachable
> we get as far as the imported typedef and stop, so we don't write out the
> instantiation. Then in _c we read in the definition of Outer with an
> incomplete type for 'sub', and ICE when trying to initialize it in the
> constructor.
>
> Fixed by looking into the DECL_ORIGINAL_TYPE of an imported typedef when
> gathering dependencies.
>
> PR c++/125768
Nice, I think this also fixes PR125042.
>
> gcc/cp/ChangeLog:
>
> * module.cc (trees_out::decl_node): When not streaming,
> recurse into DECL_ORIGINAL_TYPE of an imported typedef.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/modules/alias-3_a.C: New test.
> * g++.dg/modules/alias-3_b.C: New test.
> * g++.dg/modules/alias-3_c.C: New test.
> ---
> gcc/cp/module.cc | 5 +++++
> gcc/testsuite/g++.dg/modules/alias-3_a.C | 7 +++++++
> gcc/testsuite/g++.dg/modules/alias-3_b.C | 9 +++++++++
> gcc/testsuite/g++.dg/modules/alias-3_c.C | 5 +++++
> 4 files changed, 26 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/modules/alias-3_a.C
> create mode 100644 gcc/testsuite/g++.dg/modules/alias-3_b.C
> create mode 100644 gcc/testsuite/g++.dg/modules/alias-3_c.C
>
> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> index d81db520bab..17390356b09 100644
> --- a/gcc/cp/module.cc
> +++ b/gcc/cp/module.cc
> @@ -9434,6 +9434,11 @@ trees_out::decl_node (tree decl, walk_kind ref)
> case TYPE_DECL:
> if (DECL_TINFO_P (decl))
> goto tinfo;
> + /* c++/125768: For an imported typedef, also mark the original type
> + reachable in case it was instantiated here. */
> + if (!streaming_p () && DECL_ORIGINAL_TYPE (decl)
> + && (DECL_LANG_SPECIFIC (decl) && DECL_MODULE_IMPORT_P (decl)))
> + tree_node (DECL_ORIGINAL_TYPE (decl));
> break;
> }
>
> diff --git a/gcc/testsuite/g++.dg/modules/alias-3_a.C
> b/gcc/testsuite/g++.dg/modules/alias-3_a.C
> new file mode 100644
> index 00000000000..5292a47c5c2
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/alias-3_a.C
> @@ -0,0 +1,7 @@
> +// PR c++/125768
> +// { dg-additional-options -fmodules }
> +
> +export module api;
> +export struct S { };
> +export template <class T> struct A { };
> +export using a_s = A<S>;
> diff --git a/gcc/testsuite/g++.dg/modules/alias-3_b.C
> b/gcc/testsuite/g++.dg/modules/alias-3_b.C
> new file mode 100644
> index 00000000000..441b090490c
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/alias-3_b.C
> @@ -0,0 +1,9 @@
> +// PR c++/125768
> +// { dg-additional-options -fmodules }
> +
> +export module outer;
> +import api;
> +struct Outer {
> + a_s sub;
> + Outer();
> +};
> diff --git a/gcc/testsuite/g++.dg/modules/alias-3_c.C
> b/gcc/testsuite/g++.dg/modules/alias-3_c.C
> new file mode 100644
> index 00000000000..708f2cdcfa2
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/alias-3_c.C
> @@ -0,0 +1,5 @@
> +// PR c++/125768
> +// { dg-additional-options -fmodules }
> +
> +module outer;
> +Outer::Outer() {}
>
> base-commit: 19bc99cb9c0f85da79bee41fabf40461b64d2cd1
> --
> 2.54.0
>
