[gcc r16-319] c++/modules: Ensure deduction guides for imported types are reachable [PR120023]

[Nathaniel Shead via Gcc-cvs]

https://gcc.gnu.org/g:fb4583566afdee50aad12e1219610813b44bdff4

commit r16-319-gfb4583566afdee50aad12e1219610813b44bdff4
Author: Nathaniel Shead <nathanielosh...@gmail.com>
Date:   Wed Apr 30 23:35:51 2025 +1000

    c++/modules: Ensure deduction guides for imported types are reachable 
[PR120023]
    
    In the linked PR, because the deduction guides depend on an imported
    type, we never walk the type and so never call add_deduction_guides.
    This patch ensures that we make bindings for deduction guides if we saw
    any deduction guide at all.
    
            PR c++/120023
    
    gcc/cp/ChangeLog:
    
            * module.cc (depset::hash::find_dependencies): Also call
            add_deduction_guides when walking one.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/modules/dguide-7_a.C: New test.
            * g++.dg/modules/dguide-7_b.C: New test.
            * g++.dg/modules/dguide-7_c.C: New test.
    
    Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
    Reviewed-by: Jason Merrill <ja...@redhat.com>

Diff:
---
 gcc/cp/module.cc                          |  7 +++++++
 gcc/testsuite/g++.dg/modules/dguide-7_a.C |  9 +++++++++
 gcc/testsuite/g++.dg/modules/dguide-7_b.C | 10 ++++++++++
 gcc/testsuite/g++.dg/modules/dguide-7_c.C | 12 ++++++++++++
 4 files changed, 38 insertions(+)

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 7e3b24e2e42e..f562bf8cd915 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -14823,9 +14823,16 @@ depset::hash::find_dependencies (module_state *module)
                }
              walker.end ();
 
+             /* If we see either a class template or a deduction guide, make
+                sure to add all visible deduction guides.  We need to check
+                both in case they have been added in separate modules, or
+                one is in the GMF and would have otherwise been discarded.  */
              if (!is_key_order ()
                  && DECL_CLASS_TEMPLATE_P (decl))
                add_deduction_guides (decl);
+             if (!is_key_order ()
+                 && deduction_guide_p (decl))
+               add_deduction_guides (TYPE_NAME (TREE_TYPE (TREE_TYPE (decl))));
 
              if (!is_key_order ()
                  && TREE_CODE (decl) == TEMPLATE_DECL
diff --git a/gcc/testsuite/g++.dg/modules/dguide-7_a.C 
b/gcc/testsuite/g++.dg/modules/dguide-7_a.C
new file mode 100644
index 000000000000..8d0eb8088596
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/dguide-7_a.C
@@ -0,0 +1,9 @@
+// PR c++/120023
+// { dg-additional-options "-fmodules" }
+// { dg-module-cmi M.S }
+
+export module M.S;
+
+namespace ns {
+  export template <typename T> struct S;
+}
diff --git a/gcc/testsuite/g++.dg/modules/dguide-7_b.C 
b/gcc/testsuite/g++.dg/modules/dguide-7_b.C
new file mode 100644
index 000000000000..85246b22dc34
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/dguide-7_b.C
@@ -0,0 +1,10 @@
+// PR c++/120023
+// { dg-additional-options "-fmodules" }
+// { dg-module-cmi M.D }
+
+export module M.D;
+import M.S;
+
+namespace ns {
+  S(int) -> S<int>;
+}
diff --git a/gcc/testsuite/g++.dg/modules/dguide-7_c.C 
b/gcc/testsuite/g++.dg/modules/dguide-7_c.C
new file mode 100644
index 000000000000..9579d9d32b31
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/dguide-7_c.C
@@ -0,0 +1,12 @@
+// PR c++/120023
+// { dg-additional-options "-fmodules" }
+
+import M.S;
+import M.D;
+
+template <> struct ns::S<int> { S(int) {} };
+
+int main() {
+  ns::S s(123);
+  ns::S<int> s2 = s;
+}