Re: [PATCH] git-compat-util(msvc): C11 does not imply support for zero-sized arrays
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Dec 9, 2021, 01:39 UTC
- Message-ID
- <xmqqee6mv9no.fsf@gitster.g>
- In-Reply-To
- <pull.1094.git.1638823724410.gitgitgadget@gmail.com>
"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com> writes:
Show 5 quoted lines
> From: Johannes Schindelin <johannes.schindelin@gmx.de> > > This seems to be required to define `FLEX_ARRAY` in a manner that MSVC > in C11 mode accepts. Without this fix, building Git for Windows' > experimental FSCache code would fail thusly:
So, what's the final verdict on this one, after a few back and forth to clarify the "seems to be required" above?
In the meantime, I am tempted to queue the following as a pure clean-up.
Thoughts?
----- >8 --------- >8 --------- >8 --------- >8 --------- >8 ----- Subject: [PATCH] flex-array: simplify compiler-specific workaround
We use "type array[];" syntax for the flex-array member at the end of a struct under C99 or later, except when we are building with older SUNPRO_C compilers. As we find more vendor compilers that claim to grok C99 but not understand ts flex-array syntax, the existing "If we are using C99, but not with these compilers..." conditional will keep growing.
Make it more manageable by listing vendor-specific exceptions earlier, with the expectation that new exceptions will not be combined into existing ones to make the condition longer, and instead will be implemented as a new "#elif" in the cascade of #if/#elif/#else/#endif. E.g. if MSC is found to have a quirk similar to old SUNPRO_C, we can just add a single line
#elif defined(_MSC_VER)
immediately before "#elif defined(__GNUC__)" to cause us to fallback to the safer but a bit wasteful version.
Signed-off-by: Junio C Hamano <gitster@pobox.com> --- git-compat-util.h | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
diff --git c/git-compat-util.h w/git-compat-util.h index c6bd2a84e5..9ba047a58e 100644 --- c/git-compat-util.h +++ w/git-compat-util.h @@ -33,14 +33,23 @@ /* * See if our compiler is known to support flexible array members. */ -#if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L) && (!defined(__SUNPRO_C) || (__SUNPRO_C > 0x580)) -# define FLEX_ARRAY /* empty */ + +/* + * Check vendor specific quirks first, before checking the + * __STDC_VERSION__, as vendor compilers can lie and we need to be + * able to work them around. Note that by not defining FLEX_ARRAY + * here, we can fall back to use the "safer but a bit wasteful" one + * later. + */ +#if defined(__SUNPRO_C) && (__SUNPRO_C <= 0x580) #elif defined(__GNUC__) # if (__GNUC__ >= 3) # define FLEX_ARRAY /* empty */ # else # define FLEX_ARRAY 0 /* older GNU extension */ # endif +#elif defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L) +# define FLEX_ARRAY /* empty */ #endif /*