Description:

The pappl PKGBUILD (1.2.0-1 in this instance) does not list a dependency on libpng so the HAVE_LIBPNG macro is not defined and the built-in base image/png to image/pwg-raster filter is not included in the package:

https://github.com/michaelrsweet/pappl/blob/dc8e97b021bf92fc1ecd74a983803dd19a58d812/pappl/system.c#L251

Interestingly, libjpeg-turbo is listed as a dependency so the other base filter (image/jpeg to image/pwg-raster) is available.

I discovered this when submitting png images to lprint and getting the unexpected log message "Unable to process job with format 'image/png'" instead of a printed label.

Steps to reproduce:

* lprint submit a PNG image
* A label is not printed
* Log message "Unable to process job with format 'image/png'." originating from pappl is written by lprint

Suggested patch:

diff --git a/PKGBUILD b/PKGBUILD
index 23b7c24..926741d 100644
--- a/PKGBUILD
+++ b/PKGBUILD
@@ -8,7 +8,7 @@ arch=('x86_64')
url="https://www.msweet.org/pappl/"
license=('Apache' 'custom')
depends=('libcups' 'libjpeg-turbo' 'pam' 'libusb'
- 'openssl' 'zlib' 'avahi' 'glibc')
+ 'openssl' 'zlib' 'avahi' 'glibc' 'libpng')
makedepends=('git')
source=(https://github.com/michaelrsweet/pappl/releases/download/v${pkgver}/${pkgname}-${pkgver}.tar.gz{,.sig})
sha256sums=('93b2fd7f8d4528fa655adc6174ed7eb925e80f417663acd8118fb04b61cc38d7'