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Merge branch 'ab/coding-guidelines-c99' into maint-2.38
Update CodingGuidelines to clarify what features to use and avoid in C99. * ab/coding-guidelines-c99: CodingGuidelines: recommend against unportable C99 struct syntax CodingGuidelines: mention C99 features we can't use CodingGuidelines: allow declaring variables in for loops CodingGuidelines: mention dynamic C99 initializer elements CodingGuidelines: update for C99
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@ -204,10 +204,19 @@ For C programs:
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by e.g. "echo DEVELOPER=1 >>config.mak".
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- We try to support a wide range of C compilers to compile Git with,
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including old ones. You should not use features from newer C
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including old ones. As of Git v2.35.0 Git requires C99 (we check
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"__STDC_VERSION__"). You should not use features from a newer C
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standard, even if your compiler groks them.
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There are a few exceptions to this guideline:
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New C99 features have been phased in gradually, if something's new
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in C99 but not used yet don't assume that it's safe to use, some
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compilers we target have only partial support for it. These are
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considered safe to use:
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. since around 2007 with 2b6854c863a, we have been using
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initializer elements which are not computable at load time. E.g.:
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const char *args[] = {"constant", variable, NULL};
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. since early 2012 with e1327023ea, we have been using an enum
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definition whose last element is followed by a comma. This, like
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@ -223,18 +232,24 @@ For C programs:
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. since early 2021 with 765dc168882, we have been using variadic
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macros, mostly for printf-like trace and debug macros.
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These used to be forbidden, but we have not heard any breakage
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report, and they are assumed to be safe.
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. since late 2021 with 44ba10d6, we have had variables declared in
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the for loop "for (int i = 0; i < 10; i++)".
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New C99 features that we cannot use yet:
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. %z and %zu as a printf() argument for a size_t (the %z being for
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the POSIX-specific ssize_t). Instead you should use
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printf("%"PRIuMAX, (uintmax_t)v). These days the MSVC version we
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rely on supports %z, but the C library used by MinGW does not.
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. Shorthand like ".a.b = *c" in struct initializations is known to
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trip up an older IBM XLC version, use ".a = { .b = *c }" instead.
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See the 33665d98 (reftable: make assignments portable to AIX xlc
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v12.01, 2022-03-28).
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- Variables have to be declared at the beginning of the block, before
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the first statement (i.e. -Wdeclaration-after-statement).
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- Declaring a variable in the for loop "for (int i = 0; i < 10; i++)"
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is still not allowed in this codebase. We are in the process of
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allowing it by waiting to see that 44ba10d6 (revision: use C99
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declaration of variable in for() loop, 2021-11-14) does not get
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complaints. Let's revisit this around November 2022.
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- NULL pointers shall be written as NULL, not as 0.
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- When declaring pointers, the star sides with the variable
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@ -47,13 +47,6 @@ static inline int want_ancestry(const struct rev_info *revs);
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void show_object_with_name(FILE *out, struct object *obj, const char *name)
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{
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fprintf(out, "%s ", oid_to_hex(&obj->oid));
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/*
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* This "for (const char *p = ..." is made as a first step towards
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* making use of such declarations elsewhere in our codebase. If
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* it causes compilation problems on your platform, please report
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* it to the Git mailing list at git@vger.kernel.org. In the meantime,
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* adding -std=gnu99 to CFLAGS may help if you are with older GCC.
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*/
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for (const char *p = name; *p && *p != '\n'; p++)
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fputc(*p, out);
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fputc('\n', out);
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