[Bug c/106929] New: declaration in switch-case doesn't fail since GCC 11

[Bug c/106929] New: declaration in switch-case doesn't fail since GCC 11

[sigmaepsilon92 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106929

            Bug ID: 106929
           Summary: declaration in switch-case doesn't fail since GCC 11
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sigmaepsilon92 at gmail dot com
  Target Milestone: ---

this code should fail because declarations inside switch-cases aren't allowed
without {}:
void fn(int a) {
    switch (a) {
        case 0:
            int c = 5;
            break;
    }
}

Starting with gcc 11 this doesn't fail to compile anymore though.
The expected error message would look like this:

<source>: In function 'fn':
<source>:4:13: error: a label can only be part of a statement and a declaration
is not a statement
    4 |             int c = 5;
      |             ^~~
Compiler returned: 1

[Bug c/106929] declaration in switch-case doesn't fail since GCC 11

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106929

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This changed with r11-4813 and is intentional:

C Parser: Implement mixing of labels and code.

Implement mixing of labels and code as adopted for C2X
and process some std-attributes on labels.

[Bug c/106929] declaration in switch-case doesn't fail since GCC 11

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106929

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
For C17 (and previous standards), if you use -pedantic you'll get a warning,
and -pedantic-errors will make it an error.

[Bug c/106929] declaration in switch-case doesn't fail since GCC 11

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106929

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It's also the documented behaviour:
https://gcc.gnu.org/onlinedocs/gcc-11.3.0/gcc/Mixed-Labels-and-Declarations.html
and in the release notes:
https://gcc.gnu.org/gcc-11/changes.html#c

So not a bug.

[Bug c/106929] declaration in switch-case doesn't fail since GCC 11

[sigmaepsilon92 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106929

--- Comment #4 from Michael Zimmermann <sigmaepsilon92 at gmail dot com> ---
Interesting, but IMO it should still fail if you specify an older C standard
e.g. using `-std=c89`, but currently it doesn't.

[Bug c/106929] declaration in switch-case doesn't fail since GCC 11

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106929

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

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

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
-std=c89 doesn't mean there aren't any extensions accepted, if you want the
compiler to be pedantic, -pedantic or -pedantic-errors are the options to use
as documented (the former just warns, the latter errors).