[Bug c++/52953] New: g++-4.7.0 fails to detect function parameter name redeclarations.

[Bug c++/52953] New: g++-4.7.0 fails to detect function parameter name redeclarations.

[meng at g dot clemson.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

             Bug #: 52953
           Summary: g++-4.7.0 fails to detect function parameter name
                    redeclarations.
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: meng@g.clemson.edu


source code demonstrating the problem.
------------------------------- BEGIN ----------------------------
void f (int i) try
{
 void i (); // 1
}
catch (...)
{
 void i (); // 2
}

int main ()
{
 return 0;
}
-------------------------------  END  ----------------------------

compiled with :
$HOME/gcc/4.7.0/bin/c++ -std=c++0x -Wall -O3 tt.cc

compiler output : 
nothing

g++-4.7.0 accepts the code as it is, issuing no warnings and no errors. I think
this is wrong. According to c++11 3.3.3/2 
"A parameter name shall not be redeclared in the outermost block of the
function definition nor in the outermost block of any handler associated with a
function-try-block."

In the above example, i is the name of the parameter of function f. The name i,
therefore, cannot be redeclared in the outermost block of the function
definition (case 1) nor can it be redeclared in the outermost block of any
associated handler (case 2). But my g++ accepts both cases while they should be
rejected.

[Bug c++/52953] g++-4.7.0 fails to detect function parameter name redeclarations.

[meng at g dot clemson.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

--- Comment #1 from meng at g dot clemson.edu 2012-04-12 21:53:36 UTC ---
another example showing violation of c++11 3.3.3/4
---------------------------- BEGIN -------------------------------
int main ()
{
 if (int a = 1)
 {
  void a (); // 1
 }
 else
 {
  void a (); // 2
 }

 while (int a = 0)
 {
  void a (); // 3
 }

 for (int a = 0;;)
 {
  void a (); // 4
  break;
 }
 for (; int a = 0;)
 {
  void a (); // 5
 }

 return 0;
}
----------------------------  END  -------------------------------

According to my understanding, all numbered cases are illegal based on c++11
3.3.3/4.g++-4.7.0 correctly caught case 3 and 5 as compiler errors, the rest
are accepted.

[Bug c++/52953] g++-4.7.0 fails to detect function parameter name redeclarations.

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|meng at g dot clemson.edu   |

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-04-17 18:16:24 UTC ---
First blush, I'm not sure about 4, ICC doesn't error out either.

[Bug c++/52953] function parameter name redeclarations not detected

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jtcash at ucsd dot edu

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 89616 has been marked as a duplicate of this bug. ***

[Bug c++/52953] function parameter name redeclarations not detected

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |janschultke at googlemail dot com

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 111174 has been marked as a duplicate of this bug. ***

[Bug c++/52953] function parameter name redeclarations not detected

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 55819
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55819&action=edit
gcc14-pr52953-1.patch

Untested patch to diagnose invalid redeclaration of parameter in
function-try-block.

[Bug c++/52953] function parameter name redeclarations not detected

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 55820
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55820&action=edit
gcc14-pr52953-2.patch

Untested incremental patch to diagnose even extern redeclarations in the
https://eel.is/c++draft/basic.scope#block-2 case.
I'm not convinced this second part is correct though and there seems to be
high implementation variance (g++ vs. clang++ vs. ICC vs. MSVC).
Because https://eel.is/c++draft/basic.scope#block-2 talks about declarations
whose target scope is the block scope of S, while
https://eel.is/c++draft/basic.scope#scope-2.10 says that extern block-scope
declarations target larger scope but bind a name in the immediate scope.

[Bug c++/52953] function parameter name redeclarations not detected

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:c24982689b8af19da9a64f2283fb99764a1c5db0

commit r14-3713-gc24982689b8af19da9a64f2283fb99764a1c5db0
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Sep 5 17:26:59 2023 +0200

    c++: Diagnose [basic.scope.block]/2 violations even in compound-stmt of
function-try-block [PR52953]

    As the following testcase shows, while check_local_shadow diagnoses most of
    the [basic.scope.block]/2 violations, it doesn't diagnose when parameter's
    name is redeclared inside of the compound-stmt of a function-try-block.

    There is in that case an extra scope (sk_try with parent artificial
    sk_block with for FUNCTION_NEEDS_BODY_BLOCK another sk_block and only then
    sk_function_param).

    The in_function_try_handler case doesn't work correctly
    void
    foo (int x)
    try {
    }
    catch (int)
    {
      try {
      } catch (int x)
      {
      }
      try {
      } catch (int)
      {
        int x;
      }
    }
    (which is valid) is rejected, because
                    || (TREE_CODE (old) == PARM_DECL
                        && (current_binding_level->kind == sk_catch
                            || current_binding_level->level_chain->kind ==
sk_catch)
                        && in_function_try_handler))
    is true but nothing verified that for the first case
    current_binding_level->level_chain->kind == sk_function_params
    (with perhaps artificial scopes in between and in the latter case
    with one extra level in between).

    The patch also changes behavior where for catch handlers of
function-try-block
    the diagnostics will have the shadows function parameter wording as pedwarn
    rather than the old redeclaration permerror.

    2023-09-05  Jakub Jelinek  <jakub@redhat.com>

            PR c++/52953
            * name-lookup.h (struct cp_binding_level): Add artificial
bit-field.
            Formatting fixes.
            * name-lookup.cc (check_local_shadow): Skip artificial bindings
when
            checking if parameter scope is parent scope.  Don't special case
            FUNCTION_NEEDS_BODY_BLOCK.  Diagnose the in_function_try_handler
            cases in the b->kind == sk_function_parms test and verify no
            non-artificial intervening scopes.  Add missing
auto_diagnostic_group.
            * decl.cc (begin_function_body): Set
            current_binding_level->artificial.
            * semantics.cc (begin_function_try_block): Likewise.

            * g++.dg/diagnostic/redeclaration-1.C: Expect different diagnostic
            wording.
            * g++.dg/diagnostic/redeclaration-3.C: New test.
            * g++.dg/parse/pr31952-1.C: Expect different diagnostic wording.
            * g++.dg/parse/pr31952-3.C: Likewise.

[Bug c++/52953] function parameter name redeclarations not detected

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:efafa66c294d261a4d964383674ab9ee51feaf88

commit r14-3714-gefafa66c294d261a4d964383674ab9ee51feaf88
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Sep 5 17:31:12 2023 +0200

    c++: Diagnose [basic.scope.block]/2 violations even for block externs
[PR52953]

    C++17 had in [basic.block.scope]/2
    "A parameter name shall not be redeclared in the outermost block of the
function
    definition nor in the outermost block of any handler associated with a
    function-try-block."
    and in [basic.block.scope]/4 similar rule for selection/iteration
    statements.  My reading of that is that it applied even for block local
    externs in all those spots, while they declare something at namespace
scope,
    the redeclaration happens in that outermost block etc. and introduces names
    into that.
    Those wordings seemed to have been moved somewhere else in C++20, but
what's
    worse, they were moved back and completely rewritten in
    P1787R6: Declarations and where to find them
    which has been applied as a DR (but admittedly, we don't claim yet to
    implement that).
    The current wording at https://eel.is/c++draft/basic.scope#block-2
    and https://eel.is/c++draft/basic.scope#scope-2.10 seem to imply at least
    to me that it doesn't apply to extern block local decls because their
    target scope is the namespace scope and [basic.scope.block]/2 says
    "and whose target scope is the block scope"...
    Now, it is unclear if that is actually the intent or not.

    There seems to be quite large implementation divergence on this as well.

    Unpatched g++ e.g. on the redeclaration-5.C testcase diagnoses just
    lines 55,58,67,70 (i.e. where the previous declaration is in for's
    condition).

    clang++ trunk diagnoses just lines 8 and 27, i.e. redeclaration in the
    function body vs. parameter both in normal fn and lambda (but not e.g.
    function-try-block and others, including ctors, but it diagnoses those
    for non-extern decls).

    ICC 19 diagnoses lines 8,32,38,41,45,52,55,58,61,64,67,70,76.

    And MSCV trunk diagnoses 8,27,32,38,41,45,48,52,55,58,67,70,76,87,100,137
    although the last 4 are just warnings.

    g++ with the patch diagnoses
    8,15,27,32,38,41,45,48,52,55,58,61,64,67,70,76,87,100,121,137
    as the dg-error directives test.

    Jason said:
    > Yes, I suspect that should be
    >
    > If a declaration that is not a name-independent declaration and
<del>whose
    > target scope is</del><ins>that binds a name in</ins> the block scope S of
a
    >
    > which seems to also be needed to prohibit the already-diagnosed
    >
    > void f(int i) { union { int i; }; }
    > void g(int i) { enum { i }; }

    The following patch diagnoses DECL_EXTERNAL in check_local_shadow like
    !DECL_EXTERNAL, except that
    1) it uses pedwarn instead of errors for those cases
    2) it doesn't diagnose shadowing of namespace scope identifiers by block
       local externs, as they could be not actually shadowing but just
redeclaring
       the same objects

    2023-09-05  Jakub Jelinek  <jakub@redhat.com>

            PR c++/52953
            * name-lookup.cc (check_local_shadow): Don't punt early for
            DECL_EXTERNAL decls, instead just disable the shadowing of
namespace
            decls check for those and emit a pedwarn rather than error_at or
            permerror for those.  Formatting fix.

            * g++.dg/diagnostic/redeclaration-4.C: New test.
            * g++.dg/diagnostic/redeclaration-5.C: New test.
            * g++.dg/warn/Wshadow-19.C: New test.

[Bug c++/52953] function parameter name redeclarations not detected

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Should be fixed now for GCC 14.

[Bug c++/52953] function parameter name redeclarations not detected

[gayathri.gottumukkala.27 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

Gayathri Gottumukkala <gayathri.gottumukkala.27 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gayathri.gottumukkala.27@gm
                   |                            |ail.com

--- Comment #12 from Gayathri Gottumukkala <gayathri.gottumukkala.27 at gmail dot com> ---
It is the duplicate of bug 111174. Arguments of function redeclared in the
function definition which is not possible.

[Bug c++/52953] function parameter name redeclarations not detected

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52953

--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, Bug 111174 is already closed as a duplicate of this one.