RE: [PATCH] run-command.c: fix missing include under `NO_PTHREADS`

[<rsbecker@nexbridge.com>]

On Tuesday, May 16, 2023 3:12 PM, Junio C Hamano wrote:
>Taylor Blau <me@ttaylorr.com> writes:
>
>> When building git with `NO_PTHREADS=YesPlease`, we fail to build
>> run-command.o since we don't have a definition for ALLOC_GROW:
>>
>>     $ make NO_PTHREADS=1 DEVELOPER=1 run-command.o
>>     GIT_VERSION = 2.41.0.rc0.1.g787eb3beae.dirty
>>         CC run-command.o
>>     run-command.c: In function ‘git_atexit’:
>>     run-command.c:1103:9: error: implicit declaration of function ‘ALLOC_GROW’ [-
>Werror=implicit-function-declaration]
>>      1103 |         ALLOC_GROW(git_atexit_hdlrs.handlers, git_atexit_hdlrs.nr + 1,
>git_atexit_hdlrs.alloc);
>>           |         ^~~~~~~~~~
>>     cc1: all warnings being treated as errors
>>     make: *** [Makefile:2715: run-command.o] Error 1
>
>I am OK to give a reproduction recipe, i.e. the "$ make" command line, to make it
>easy for people, who cannot remember how to define make variables from the
>command line, to try out themselves, but I hate the "build transcript" in the log
>message, when a few lines of prose suffices.
>
>How about this?
>
>    Git 2.41-rc0 fails to compile run-command.c with NO_PTHREADS
>    defined, i.e.
>
>      $ make NO_PTHREADS=1 run-command.o
>
>    as ALLOC_GROW() macro is used in the atexit() emulation but the
>    macro definition is not available.
>
>> This bisects to 36bf195890 (alloc.h: move ALLOC_GROW() functions from
>> cache.h, 2023-02-24), which replaced includes of "cache.h" with
>> "alloc.h", which is the new home of `ALLOC_GROW()` (and
>> `ALLOC_GROW_BY()`).
>
>Good.
>Insert something like:
>
>    We can see that run-command.c is the only one that try to use
>    these macros without including <alloc.h>.
>
>      $ git grep -l -e '[^_]ALLOC_GROW(' -e 'ALLOC_GROW_BY(' \*.c | sort >/tmp/1
>      $ git grep -l 'alloc\.h' \*.c | sort >/tmp/2
>      $ comm -23 /tmp/[12]
>      compat/simple-ipc/ipc-unix-socket.c
>      run-command.c
>
>    The "compat/" file only talks about the macro in the comment,
>    and is not broken.
>
>here.  What I am aiming for is to tell readers what they do not have to spend their
>time on.  As we encourage people to make sure to look for other errors that come
>from the same root cause when making a fix, avoiding duplicated work by telling
>what they do not have to look at is rather important.
>
>> run-command.c compiles fine when `NO_PTHREADS` is undefined, since its
>> use of `ALLOC_GROW()` is behind a `#ifndef NO_PTHREADS`. (Everything
>> else compiles fine when NO_PTHREADS is defined, so this is the only
>> spot that needs fixing).
>
>I think we can say that, but is probably coered by the three-line summary I gave
>above.
>
>> We could fix this by conditionally including "alloc.h" when
>> `NO_PTHREADS` is defined.  But we have relatively few examples of
>> conditional includes throughout the tree[^1].
>>
>> Instead, include "alloc.h" unconditionally in run-command.c to allow
>> it to successfully compile even when NO_PTHREADS is defined.
>
>Good.
>
>> [^1]: With `git grep -E -A1 '#if(n)?def' -- **/*.c | grep '#include' -B1`.
>
>Good.

This all makes sense to me.