[v8] C, ObjC: Add -Wunterminated-string-initialization

Warn about the following:

    char  s[3] = "foo";

Initializing a char array with a string literal of the same length as
the size of the array is usually a mistake.  Rarely is the case where
one wants to create a non-terminated character sequence from a string
literal.

In some cases, for writing faster code, one may want to use arrays
instead of pointers, since that removes the need for storing an array of
pointers apart from the strings themselves.

    char  *log_levels[]   = { "info", "warning", "err" };
vs.
    char  log_levels[][7] = { "info", "warning", "err" };

This forces the programmer to specify a size, which might change if a
new entry is later added.  Having no way to enforce null termination is
very dangerous, however, so it is useful to have a warning for this, so
that the compiler can make sure that the programmer didn't make any
mistakes.  This warning catches the bug above, so that the programmer
will be able to fix it and write:

    char  log_levels[][8] = { "info", "warning", "err" };

This warning already existed as part of -Wc++-compat, but this patch
allows enabling it separately.  It is also included in -Wextra, since
it may not always be desired (when unterminated character sequences are
wanted), but it's likely to be desired in most cases.

Since Wc++-compat now includes this warning, the test has to be modified
to expect the text of the new warning too, in <gcc.dg/Wcxx-compat-14.c>.

gcc/c-family/ChangeLog:

	* c.opt: Add -Wunterminated-string-initialization.

gcc/c/ChangeLog:

	* c-typeck.cc (digest_init): Separate warnings about character
	  arrays being initialized as unterminated character sequences
	  with string literals, from -Wc++-compat, into a new warning,
	  -Wunterminated-string-initialization.

gcc/ChangeLog:

	* doc/invoke.texi: Document the new
	  -Wunterminated-string-initialization.

gcc/testsuite/ChangeLog:

	* gcc.dg/Wcxx-compat-14.c: Adapt the test to match the new text
	  of the warning, which doesn't say anything about C++ anymore.
	* gcc.dg/Wunterminated-string-initialization.c: New test.

Link: <https://lists.gnu.org/archive/html/groff/2022-11/msg00059.html>
Link: <https://lists.gnu.org/archive/html/groff/2022-11/msg00063.html>
Link: <https://inbox.sourceware.org/gcc/36da94eb-1cac-5ae8-7fea-ec66160cf413@gmail.com/T/>
Acked-by: Doug McIlroy <douglas.mcilroy@dartmouth.edu>
[Sandra: The documentation parts of the patch are OK.]
Reviewed-by: Sandra Loosemore <sloosemore@baylibre.com>
Cc: "G. Branden Robinson" <g.branden.robinson@gmail.com>
Cc: Ralph Corderoy <ralph@inputplus.co.uk>
Cc: Dave Kemper <saint.snit@gmail.com>
Cc: Larry McVoy <lm@mcvoy.com>
Cc: Andrew Pinski <pinskia@gmail.com>
Cc: Jonathan Wakely <jwakely.gcc@gmail.com>
Cc: Andrew Clayton <andrew@digital-domain.net>
Cc: Martin Uecker <muecker@gwdg.de>
Cc: David Malcolm <dmalcolm@redhat.com>
Cc: Mike Stump <mikestump@comcast.net>
Cc: Joseph Myers <josmyers@redhat.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
---

Hi!

I've added a changelog to the commit message, as requested by Sandra,
and noted her review.

Have a lovely day!
Alex


Range-diff against v7:
1:  c0f3ffcca7a ! 1:  06236d0aa05 C, ObjC: Add -Wunterminated-string-initialization
    @@ Commit message
         Since Wc++-compat now includes this warning, the test has to be modified
         to expect the text of the new warning too, in <gcc.dg/Wcxx-compat-14.c>.
     
    +    gcc/c-family/ChangeLog:
    +
    +            * c.opt: Add -Wunterminated-string-initialization.
    +
    +    gcc/c/ChangeLog:
    +
    +            * c-typeck.cc (digest_init): Separate warnings about character
    +              arrays being initialized as unterminated character sequences
    +              with string literals, from -Wc++-compat, into a new warning,
    +              -Wunterminated-string-initialization.
    +
    +    gcc/ChangeLog:
    +
    +            * doc/invoke.texi: Document the new
    +              -Wunterminated-string-initialization.
    +
    +    gcc/testsuite/ChangeLog:
    +
    +            * gcc.dg/Wcxx-compat-14.c: Adapt the test to match the new text
    +              of the warning, which doesn't say anything about C++ anymore.
    +            * gcc.dg/Wunterminated-string-initialization.c: New test.
    +
         Link: <https://lists.gnu.org/archive/html/groff/2022-11/msg00059.html>
         Link: <https://lists.gnu.org/archive/html/groff/2022-11/msg00063.html>
         Link: <https://inbox.sourceware.org/gcc/36da94eb-1cac-5ae8-7fea-ec66160cf413@gmail.com/T/>
         Acked-by: Doug McIlroy <douglas.mcilroy@dartmouth.edu>
    +    [Sandra: The documentation parts of the patch are OK.]
    +    Reviewed-by: Sandra Loosemore <sloosemore@baylibre.com>
         Cc: "G. Branden Robinson" <g.branden.robinson@gmail.com>
         Cc: Ralph Corderoy <ralph@inputplus.co.uk>
         Cc: Dave Kemper <saint.snit@gmail.com>
    @@ Commit message
         Cc: David Malcolm <dmalcolm@redhat.com>
         Cc: Mike Stump <mikestump@comcast.net>
         Cc: Joseph Myers <josmyers@redhat.com>
    -    Cc: Sandra Loosemore <sloosemore@baylibre.com>
         Signed-off-by: Alejandro Colomar <alx@kernel.org>
     
      ## gcc/c-family/c.opt ##

 gcc/c-family/c.opt                            |  4 ++++
 gcc/c/c-typeck.cc                             |  6 +++---
 gcc/doc/invoke.texi                           | 20 ++++++++++++++++++-
 gcc/testsuite/gcc.dg/Wcxx-compat-14.c         |  2 +-
 .../Wunterminated-string-initialization.c     |  6 ++++++
 5 files changed, 33 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/Wunterminated-string-initialization.c

Ping.

I see that GCC-14 has been released recently.  This is a gentle ping to
see if this is a better time for this patch.

Have a lovely day!
Alex