Minimum C Version

[Yay295]

While looking through the C code I noticed that loop variables are always declared before the loop

int x;
for (x = 0; x < size; ++x) {

instead of in it

for (int x = 0; x < size; ++x) {

except in /src/thirdparty/raqm/raqm.c and in this one location

Pillow/src/display.c

Line 519 in 4c59f77

for (UINT i = 0; formats[i] != 0; i++) {

C added support for this in C99, and a lot of this code is older than that so it makes sense that it wasn't used. But 1999 was also 23 years ago now. Should we still be trying to code to pre-C99, or should we start using a more modern standard? The makefile doesn't specify a standard to use.

[nulano]

Re raqm, that is a third party library included as-is (except for a small fribidi header included patch), and only used if you specify a specific build flag when installing Pillow. When I tried making that the default, I found a lot of the Linux systems tested in CI use a GCC version that defaults to C89 standard causing several compile errors in raqm. The line you found in display.c is also Windows-only, so will never be seen by GCC, only MSVC which now supports C99 by default (but didn't in the past).

But 1999 was also 23 years ago

I would say take that up with the GCC devs, but they have finally made the default a newer standard somewhat recently.

[hugovk]

We don't have a minimum C version as such, other than this:

Binary distributions are contributed for each release on a volunteer basis, but the source should compile and run everywhere platform support is listed. In general, we aim to support all current versions of Linux, macOS, and Windows.

---

A quick test after changing a couple of them, all CI jobs passed except for CentOS 7:

      src/libImaging/Convert.c: In function 'bit2l':
      src/libImaging/Convert.c:59:5: error: 'for' loop initial declarations are only allowed in C99 mode
           for (int x = 0; x < xsize; x++) *out++ = (*in++ != 0) ? 255 : 0;
           ^
      src/libImaging/Convert.c:59:5: note: use option -std=c99 or -std=gnu99 to compile your code

https://github.com/hugovk/Pillow/actions/runs/2902666901

CentOS 7 is still supported, until EOL on 30 Jun 2024.

[Yay295]

I found these two lines:

Pillow/src/libImaging/Draw.c

Line 38 in 196210b

#include <stdint.h>

Pillow/src/libImaging/QuantTypes.h

Line 19 in 196210b

#include <stdint.h>

stdint.h is technically a C99 addition, though it could have been provided earlier. Also both of those files can be disabled with defines (WITH_IMAGEDRAW and WITH_QUANTIZE). But if this include is working on all supported platforms, we could simplify this section:

Pillow/src/libImaging/ImPlatform.h

Lines 41 to 71 in 196210b

	/* For System that are not Windows, we'll need to define these. */
	#if SIZEOF_SHORT == 2
	#define INT16 short
	#elif SIZEOF_INT == 2
	#define INT16 int
	#else
	#define INT16 short /* most things works just fine anyway... */
	#endif
	#if SIZEOF_SHORT == 4
	#define INT32 short
	#elif SIZEOF_INT == 4
	#define INT32 int
	#elif SIZEOF_LONG == 4
	#define INT32 long
	#else
	#error Cannot find required 32-bit integer type
	#endif
	#if SIZEOF_LONG == 8
	#define INT64 long
	#elif SIZEOF_LONG_LONG == 8
	#define INT64 long
	#endif
	#define INT8 signed char
	#define UINT8 unsigned char
	#define UINT16 unsigned INT16
	#define UINT32 unsigned INT32

[raygard]

Still not clear to me if C99 should be considered minimum version for building Pillow. As I mentioned in #5367 (comment) I believe these lines in Quant.c uses a compound literal, which came in C99:

            dwi[j] = (DistanceWithIndex){
                &(avgDist[i * nEntries + j]),
                j
            };

Correct me if I am mistaken. Maybe GCC supports this without specifying C99? Are there other places that use compound literals?

[Yay295]

Maybe GCC supports this without specifying C99?

Yes https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html

Also https://gcc.gnu.org/onlinedocs/gcc/Standards.html

I believe the default standard used by GCC on CentOS 7 is gnu90.