Bug 921601 – x11-wm/fvwm-2.7.0-r4 fails to compile (GCC-14-SYSTEM): PictureImageLoader.c:482:13: error: implicit declaration of function png_get_color_type [-Wimplicit-function-declaration]

• Product: Gentoo Linux
• Status: CONFIRMED ---

[Description Agostino Sarubbo 2024-01-08 08:26:53 UTC]

https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/

Issue: x11-wm/fvwm-2.7.0-r2 fails to compile (GCC-14-SYSTEM).
Discovered on: amd64 (internal ref: gcc14_tinderbox)

NOTE:
(GCC-14-SYSTEM) in the summary means that the bug was found on a machine that runs gcc-14 but this bug MAY or MAY NOT BE related to the new compiler

[Comment 1 Agostino Sarubbo 2024-01-08 08:26:55 UTC]

Created attachment 881669 [details]
build.log

build log and emerge --info

[Comment 2 Agostino Sarubbo 2024-05-06 06:51:10 UTC]

gcc14_tinderbox has reproduced this issue with version 2.7.0-r4 - Updating summary.

[Comment 3 Eli Schwartz 2024-05-16 05:17:31 UTC]

This only occurs when USE=png is disabled.

In /var/tmp/portage/x11-wm/fvwm-2.7.0-r4/work/fvwm-2.7.0/libs/Fpng.h

There is a fair amount of code to abstract away png support using glorious technology such as:

#if PngSupport
typedef png_uint_32 Fpng_uint_32;
#define Fpng_destroy_read_struct(a,b,c) png_destroy_read_struct(a,b,c)
#else
typedef unsigned long Fpng_uint_32;
#define Fpng_destroy_read_struct(a,b,c)
#endif


It also exposes png.h to consumers of Fpng.h.

In /var/tmp/portage/x11-wm/fvwm-2.7.0-r4/work/fvwm-2.7.0/libs/PictureImageLoader.c

static Bool PImageLoadPng(FIMAGE_CMD_ARGS)
{ 
        if (!PngSupport)
        {
                return False;
        }
[...]


And later on in the function, it uses various typedef'ed Fpng* typedefs and defines, but also uses, unconditionally,

png_get_color_type(Fpng_ptr, Finfo_ptr)

no define to hide it.

I personally think the entire thing is silly and standard technology here is to ifdef out the entire function to a stub.

Note: the linked PR is broken. It unconditionally depends on png.h which is quite missing the point. We can just as easily remove the USE flag and unconditionally enable png support.

[Comment 4 Brahmajit Das 2024-05-16 11:29:31 UTC]

Eli, does something like this look alright to you? I reason that since PNG support is not enabled, we shouldn't be needing this. 

diff --git a/libs/PictureImageLoader.c b/libs/PictureImageLoader.c
index c615081..0a91400 100644
--- a/libs/PictureImageLoader.c
+++ b/libs/PictureImageLoader.c
@@ -468,6 +468,7 @@ Bool PImageLoadPng(FIMAGE_CMD_ARGS)
 		Fpng_set_expand(Fpng_ptr);
 	}
 
+#if PngSupport
 	/* TA:  XXX:  (2011-02-14) -- Happy Valentines Day.
 	 *
 	 * png_get_color_type() defined in libpng 1.5 now hides a data member
@@ -492,6 +493,7 @@ Bool PImageLoadPng(FIMAGE_CMD_ARGS)
 	{
 		hasg = 1;
 	}
+#endif
 
 	if (hasa)
 		Fpng_set_expand(Fpng_ptr);