On 6/2/24 06:53, Markus Armbruster wrote:
Daniel P. Berrangé <berra...@redhat.com> writes:
On Mon, Feb 05, 2024 at 12:18:19PM -0500, Stefan Hajnoczi wrote:
C99 mixed declarations support interleaving of local variable
declarations and code.
The coding style "generally" forbids C99 mixed declarations with some
exceptions to the rule. This rule is not checked by checkpatch.pl and
naturally there are violations in the source tree.
While contemplating adding another exception, I came to the conclusion
that the best location for declarations depends on context. Let the
programmer declare variables where it is best for legibility. Don't try
to define all possible scenarios/exceptions.
...
Even if the compiler does reliably warn, I think the code pattern
remains misleading to contributors, as the flow control flaw is
very non-obvious.
Yup. Strong dislike.
Rather than accept the status quo and remove the coding guideline,
I think we should strengthen the guidelines, such that it is
explicitly forbidden in any method that uses 'goto'. Personally
I'd go all the way to -Werror=declaration-after-statement, as
I support this.
while C99 mixed decl is appealing,
Not to me.
I much prefer declarations and statements to be visually distinct.
Putting declarations first and separating from statements them with a
blank line accomplishes that. Less necessary in languages where
declarations are syntactically obvious.
But we already implicitly suggest C99, see commit ae7c80a7bd
("error: New macro ERRP_GUARD()"):
* To use ERRP_GUARD(), add it right at the beginning of the function.
* @errp can then be used without worrying about the argument being
* NULL or &error_fatal.
#define ERRP_GUARD() \
g_auto(ErrorPropagator) _auto_errp_prop = {.errp = errp}; \
do { \
if (!errp || errp == &error_fatal) { \
errp = &_auto_errp_prop.local_err; \
} \
} while (0)
Or commit 5626f8c6d4 ("rcu: Add automatically released rcu_read_lock
variants") with WITH_RCU_READ*:
util/aio-posix.c:540:5: error: mixing declarations and code is
incompatible with standards before C99
[-Werror,-Wdeclaration-after-statement]
RCU_READ_LOCK_GUARD();
^
include/qemu/rcu.h:189:28: note: expanded from macro 'RCU_READ_LOCK_GUARD'
g_autoptr(RCUReadAuto) _rcu_read_auto __attribute__((unused)) =
rcu_read_auto_lock()
^
