[gcc r15-3489] c++: fn redecl in fn scope wrongly accepted [PR116239]

[Marek Polacek via Gcc-cvs]

https://gcc.gnu.org/g:d44cae2d9310660e3e47f15202e86e4f73f15b37

commit r15-3489-gd44cae2d9310660e3e47f15202e86e4f73f15b37
Author: Marek Polacek <pola...@redhat.com>
Date:   Fri Aug 30 14:12:22 2024 -0400

    c++: fn redecl in fn scope wrongly accepted [PR116239]
    
    Redeclaration such as
    
      void f(void);
      consteval void f(void);
    
    is invalid.  In a namespace scope, we detect the collision in
    validate_constexpr_redeclaration, but not when one declaration is
    at block scope.
    
    When we have
    
      void f(void);
      void g() { consteval void f(void); }
    
    we call pushdecl on the second f and call push_local_extern_decl_alias.
    It finds the namespace-scope f:
    
            for (ovl_iterator iter (binding); iter; ++iter)
              if (decls_match (decl, *iter, /*record_versions*/false))
                {
                  alias = *iter;
                  break;
                }
    
    but decls_match says they match so we just set DECL_LOCAL_DECL_ALIAS
    (and do not call another pushdecl leading to duplicate_decls which
    would detect mismatching return types, for example).  I don't think
    we want to change decls_match, so a simple fix is to detect the
    problem in push_local_extern_decl_alias.
    
            PR c++/116239
    
    gcc/cp/ChangeLog:
    
            * cp-tree.h (validate_constexpr_redeclaration): Declare.
            * decl.cc (validate_constexpr_redeclaration): No longer static.
            * name-lookup.cc (push_local_extern_decl_alias): Call
            validate_constexpr_redeclaration.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/diagnostic/redeclaration-6.C: New test.

Diff:
---
 gcc/cp/cp-tree.h                                  |  1 +
 gcc/cp/decl.cc                                    |  2 +-
 gcc/cp/name-lookup.cc                             |  2 ++
 gcc/testsuite/g++.dg/diagnostic/redeclaration-6.C | 34 +++++++++++++++++++++++
 4 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 2eeb5e3e8b1..1a763b683de 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -6992,6 +6992,7 @@ extern bool member_like_constrained_friend_p      (tree);
 extern bool fns_correspond                     (tree, tree);
 extern int decls_match                         (tree, tree, bool = true);
 extern bool maybe_version_functions            (tree, tree, bool);
+extern bool validate_constexpr_redeclaration   (tree, tree);
 extern bool merge_default_template_args                (tree, tree, bool);
 extern tree duplicate_decls                    (tree, tree,
                                                 bool hiding = false,
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 7bad3047ad9..f4128dbccdf 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -1412,7 +1412,7 @@ check_redeclaration_exception_specification (tree 
new_decl,
 /* Return true if OLD_DECL and NEW_DECL agree on constexprness.
    Otherwise issue diagnostics.  */
 
-static bool
+bool
 validate_constexpr_redeclaration (tree old_decl, tree new_decl)
 {
   old_decl = STRIP_TEMPLATE (old_decl);
diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc
index 7a6cc244c15..cd3947cbe4f 100644
--- a/gcc/cp/name-lookup.cc
+++ b/gcc/cp/name-lookup.cc
@@ -3637,6 +3637,8 @@ push_local_extern_decl_alias (tree decl)
          if (decls_match (decl, *iter, /*record_versions*/false))
            {
              alias = *iter;
+             if (!validate_constexpr_redeclaration (alias, decl))
+               return;
              break;
            }
 
diff --git a/gcc/testsuite/g++.dg/diagnostic/redeclaration-6.C 
b/gcc/testsuite/g++.dg/diagnostic/redeclaration-6.C
new file mode 100644
index 00000000000..ed8d4af7792
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/redeclaration-6.C
@@ -0,0 +1,34 @@
+// PR c++/116239
+// { dg-do compile { target c++20 } }
+
+consteval void f1();
+void f2();
+constexpr void f3();
+void f4();
+consteval void f5();
+constexpr void f6();
+
+void
+g ()
+{
+  void f1();           // { dg-error "differs in .consteval." }
+  consteval void f2(); // { dg-error "differs in .consteval." }
+
+  void f3();           // { dg-error "differs in .constexpr." }
+  constexpr void f4();  // { dg-error "differs in .constexpr." }
+
+  consteval void f5();
+  constexpr void f6();
+
+  void f7();
+  consteval void f7(); // { dg-error "differs in .consteval." }
+
+  consteval void f8();
+  void f8();           // { dg-error "differs in .consteval." }
+
+  void f9();
+  constexpr void f9(); // { dg-error "differs in .constexpr." }
+
+  constexpr void f10();
+  void f10();          // { dg-error "differs in .constexpr." }
+}