From: Martin Uecker <uecker@tugraz.at>
Date: Sat, 28 Feb 2026 16:12:43 +0000 (+0100)
Subject: c: Fix recursive structure / union redeclaration with qualifiers [PR124303]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7c3e6df8ae01a473fba63e12efe2c82bd50ad502;p=thirdparty%2Fgcc.git

c: Fix recursive structure / union redeclaration with qualifiers [PR124303]

We reject correct recursive redeclarations when qualifiers are involved.
The reason is that the check is done before the variants are completed.

	PR c/124303

gcc/c/ChangeLog:
	* c-decl.cc (finish_struct): Check for consistency of
	declarations after completing variants.

gcc/testsuite/ChangeLog:
	* gcc.dg/pr124303.c: New test.
---

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 8a894de3a1b..37bd01ab7b0 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -9970,6 +9970,23 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
       warning_at (loc, 0, "union cannot be made transparent");
     }
 
+  tree incomplete_vars = C_TYPE_INCOMPLETE_VARS (TYPE_MAIN_VARIANT (t));
+  for (x = TYPE_MAIN_VARIANT (t); x; x = TYPE_NEXT_VARIANT (x))
+    {
+      TYPE_FIELDS (x) = TYPE_FIELDS (t);
+      TYPE_LANG_SPECIFIC (x) = TYPE_LANG_SPECIFIC (t);
+      TYPE_TRANSPARENT_AGGR (x) = TYPE_TRANSPARENT_AGGR (t);
+      TYPE_TYPELESS_STORAGE (x) = TYPE_TYPELESS_STORAGE (t);
+      C_TYPE_FIELDS_READONLY (x) = C_TYPE_FIELDS_READONLY (t);
+      C_TYPE_FIELDS_VOLATILE (x) = C_TYPE_FIELDS_VOLATILE (t);
+      C_TYPE_FIELDS_NON_CONSTEXPR (x) = C_TYPE_FIELDS_NON_CONSTEXPR (t);
+      C_TYPE_FIELDS_HAS_COUNTED_BY (x) = C_TYPE_FIELDS_HAS_COUNTED_BY (t);
+      C_TYPE_VARIABLE_SIZE (x) = C_TYPE_VARIABLE_SIZE (t);
+      C_TYPE_VARIABLY_MODIFIED (x) = C_TYPE_VARIABLY_MODIFIED (t);
+      C_TYPE_INCOMPLETE_VARS (x) = NULL_TREE;
+      TYPE_INCLUDES_FLEXARRAY (x) = TYPE_INCLUDES_FLEXARRAY (t);
+    }
+
   /* Check for consistency with previous definition.  */
   if (flag_isoc23 && NULL != enclosing_struct_parse_info)
     {
@@ -10024,23 +10041,6 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
       c_update_type_canonical (t);
     }
 
-  tree incomplete_vars = C_TYPE_INCOMPLETE_VARS (TYPE_MAIN_VARIANT (t));
-  for (x = TYPE_MAIN_VARIANT (t); x; x = TYPE_NEXT_VARIANT (x))
-    {
-      TYPE_FIELDS (x) = TYPE_FIELDS (t);
-      TYPE_LANG_SPECIFIC (x) = TYPE_LANG_SPECIFIC (t);
-      TYPE_TRANSPARENT_AGGR (x) = TYPE_TRANSPARENT_AGGR (t);
-      TYPE_TYPELESS_STORAGE (x) = TYPE_TYPELESS_STORAGE (t);
-      C_TYPE_FIELDS_READONLY (x) = C_TYPE_FIELDS_READONLY (t);
-      C_TYPE_FIELDS_VOLATILE (x) = C_TYPE_FIELDS_VOLATILE (t);
-      C_TYPE_FIELDS_NON_CONSTEXPR (x) = C_TYPE_FIELDS_NON_CONSTEXPR (t);
-      C_TYPE_FIELDS_HAS_COUNTED_BY (x) = C_TYPE_FIELDS_HAS_COUNTED_BY (t);
-      C_TYPE_VARIABLE_SIZE (x) = C_TYPE_VARIABLE_SIZE (t);
-      C_TYPE_VARIABLY_MODIFIED (x) = C_TYPE_VARIABLY_MODIFIED (t);
-      C_TYPE_INCOMPLETE_VARS (x) = NULL_TREE;
-      TYPE_INCLUDES_FLEXARRAY (x) = TYPE_INCLUDES_FLEXARRAY (t);
-    }
-
   /* Update type location to the one of the definition, instead of e.g.
      a forward declaration.  */
   if (TYPE_STUB_DECL (t))
diff --git a/gcc/testsuite/gcc.dg/pr124303.c b/gcc/testsuite/gcc.dg/pr124303.c
new file mode 100644
index 00000000000..e7075875108
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr124303.c
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c23" } */
+
+struct s { void (*p)(const struct s*); };
+struct s { void (*p)(const struct s*); };
+
+