[gcc r14-11256] c++: friend vs inherited guide confusion [PR117855]

[Patrick Palka via Gcc-cvs]

https://gcc.gnu.org/g:c061ad5a36ba0c07d3d9d82a85aebb887def759d

commit r14-11256-gc061ad5a36ba0c07d3d9d82a85aebb887def759d
Author: Patrick Palka <ppa...@redhat.com>
Date:   Tue Jan 28 09:27:02 2025 -0500

    c++: friend vs inherited guide confusion [PR117855]
    
    We recently started using the lang_decl_fn::context field to track
    inheritedness of a deduction guide (for C++23 inherited CTAD).  This
    new overloading of the field accidentally made DECL_FRIEND_CONTEXT
    return non-NULL for inherited guides, which breaks the below testcase
    during overload resolution with an inherited guide.
    
    This patch fixes this by refining DECL_FRIEND_CONTEXT appropriately.
    
            PR c++/117855
    
    gcc/cp/ChangeLog:
    
            * cp-tree.h (DECL_FRIEND_CONTEXT): Exclude deduction guides.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp23/class-deduction-inherited7.C: New test.
    
    Reviewed-by: Jason Merrill <ja...@redhat.com>
    (cherry picked from commit ea578dd251eaf6304b0c95acc107f9a4d63bee8f)

Diff:
---
 gcc/cp/cp-tree.h                                        |  3 ++-
 gcc/testsuite/g++.dg/cpp23/class-deduction-inherited7.C | 12 ++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index ab2b0904ed60..a9a4a7abc40d 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -3575,7 +3575,8 @@ struct GTY(()) lang_decl {
    the DECL_FRIEND_CONTEXT for `f' will be `S'.  */
 #define DECL_FRIEND_CONTEXT(NODE)                              \
   ((DECL_DECLARES_FUNCTION_P (NODE) && !DECL_VIRTUAL_P (NODE)  \
-    && !DECL_CONSTRUCTOR_P (NODE))                             \
+    && !DECL_CONSTRUCTOR_P (NODE)                              \
+    && (cxx_dialect < cxx23 || !deduction_guide_p (NODE)))     \
    ? LANG_DECL_FN_CHECK (NODE)->context                                \
    : NULL_TREE)
 
diff --git a/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited7.C 
b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited7.C
new file mode 100644
index 000000000000..b1d5e89ad021
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/class-deduction-inherited7.C
@@ -0,0 +1,12 @@
+// PR c++/117855
+// { dg-do compile { target c++20 } }
+
+template <typename T, int _Extent = -1> struct span { span(T&&);};
+template <typename T> span(T &&) -> span<T>;
+template <typename et, int e = -1>
+struct this_span : span<et, e> {
+  using span<et, e>::span;
+};
+template <typename T> this_span(T &&) -> this_span<T>;
+int vec;
+this_span a = vec;