[pushed] c++: naming typedef and incomplete class [PR126031]

[Jason Merrill]

Tested x86_64-pc-linux-gnu, applying to trunk.

-- 8< --

We can't look at the bases and members of a forward-declared nested class,
and such a forward declaration can't contain problematic constructs, so
treat it as OK.

        PR c++/126031
        PR c++/121552

gcc/cp/ChangeLog:

        * decl.cc (maybe_diagnose_non_c_class_typedef_for_linkage): Handle
        incomplete type.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/typedef2.C: New test.
---
 gcc/cp/decl.cc                        | 2 ++
 gcc/testsuite/g++.dg/cpp2a/typedef2.C | 5 +++++
 2 files changed, 7 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/typedef2.C

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 79247302608..a2233107317 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -13775,6 +13775,8 @@ diagnose_non_c_class_typedef_for_linkage (tree type, 
tree orig)
 static bool
 maybe_diagnose_non_c_class_typedef_for_linkage (tree type, tree orig, tree t)
 {
+  if (!COMPLETE_TYPE_P (t))
+    return false;
   if (!BINFO_BASE_BINFOS (TYPE_BINFO (t))->is_empty ())
     {
       auto_diagnostic_group d;
diff --git a/gcc/testsuite/g++.dg/cpp2a/typedef2.C 
b/gcc/testsuite/g++.dg/cpp2a/typedef2.C
new file mode 100644
index 00000000000..e4a8195ce18
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/typedef2.C
@@ -0,0 +1,5 @@
+// PR c++/126031
+
+typedef struct {
+  struct S;
+} s;

base-commit: 17649698d6f1d1c626dcf245edd8e45f3f55a5eb
-- 
2.54.0