`pkgconf`-provided `pkg-config` does `--modversion` differently; dependency resolution fails mysteriously

[jashank]

Describe the bug

On a system where pkgconf provides pkg-config, Cabal incorrectly reports dependency resolution failures. It turns out (modulo a bug in pkgconf), pkgconf --modversion only reports information about one package at a time, whereas Cabal happily tries the lot:

cabal/cabal-install-solver/src/Distribution/Solver/Types/PkgConfigDb.hs

Lines 70 to 72 in 3af1731

	(pkgVersions, _errs, exitCode) <-
	getProgramInvocationOutputAndErrors verbosity
	(programInvocation pkgConfig ("--modversion" : pkgNames))

(Whether that pkgconf behaviour is correct is another question, and one I'm certainly not qualified to answer.)

To Reproduce

(I use Pango as an example here, because it's where I started; however, this affects pretty much any package that has a pkg-config dependency.)

% pkg-config --about | head -n1
pkgconf 1.9.4

% pkg-config --modversion pango
1.50.14

% cabal v2-install --lib pango
Resolving dependencies...
Error: cabal: Could not resolve dependencies:
[__0] next goal: pango (user goal)
[__0] rejecting: pango-0.13.8.2, pango-0.13.8.1, pango-0.13.8.0,
pango-0.13.6.1, pango-0.13.6.0, pango-0.13.5.0, pango-0.13.4.0,
pango-0.13.3.1, pango-0.13.3.0, pango-0.13.2.0, pango-0.13.1.1,
pango-0.13.1.0, pango-0.13.0.5, pango-0.13.0.4, pango-0.13.0.3,
pango-0.13.0.2, pango-0.13.0.1, pango-0.13.0.0, pango-0.12.5.3,
pango-0.12.5.0, pango-0.12.4, pango-0.12.3, pango-0.12.2, pango-0.12.1,
pango-0.12.0, pango-0.11.2, pango-0.11.1, pango-0.11.0 (conflict: pkg-config
package pango>=1.0, not found in the pkg-config database)
[__0] fail (backjumping, conflict set: pango)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: pango

`cabal v2-install --verbose --lib pango`

% cabal v2-install --verbose --lib pango
Reading available packages of hackage.haskell.org...
Using most recent state specified from most recent cabal update
index-state(hackage.haskell.org) = 2023-04-27T03:20:47Z
Running: /home/jashank/bin/local/ghc --numeric-version
looking for tool ghc-pkg near compiler in /home/jashank/bin/local
found ghc-pkg in /home/jashank/.ghcup/ghc/9.6.1/bin/ghc-pkg-9.6.1
Running: /home/jashank/.ghcup/ghc/9.6.1/bin/ghc-pkg-9.6.1 --version
Running: /home/jashank/bin/local/ghc --supported-languages
Running: /home/jashank/bin/local/ghc --info
creating /tmp/jashank/cabal-install.-1289081/dist-newstyle
creating /tmp/jashank/cabal-install.-1289081/dist-newstyle/cache
Compiler settings changed, reconfiguring...
Running: /home/jashank/bin/local/ghc --numeric-version
looking for tool ghc-pkg near compiler in /home/jashank/bin/local
found ghc-pkg in /home/jashank/.ghcup/ghc/9.6.1/bin/ghc-pkg-9.6.1
Running: /home/jashank/.ghcup/ghc/9.6.1/bin/ghc-pkg-9.6.1 --version
Running: /home/jashank/bin/local/ghc --supported-languages
Running: /home/jashank/bin/local/ghc --info
Running: /home/jashank/bin/local/ghc --print-global-package-db
Reading available packages of hackage.haskell.org...
Using most recent state specified from most recent cabal update
index-state(hackage.haskell.org) = 2023-04-27T03:20:47Z
Running: /usr/bin/pkg-config --version
Running: /usr/bin/pkg-config --variable pc_path pkg-config
Running: /usr/bin/pkg-config --version
Running: /usr/bin/pkg-config --list-all
Running: /usr/bin/pkg-config --modversion guile-3.0 libtcmalloc_debug polyml xcb-renderutil 'flac++' bullet libtasn1 freetype2 libxslt harfbuzz-subset edje panelw libpci wayland-cursor cairo-tee pamc xcb-icccm gmpxx webkit2gtk-4.0 orc-0.4 eo-cxx pangoot libidn2 fftw3q ector wayland-client gobject-2.0 xcb-aux efreet-mime ecore-wl2 gmodule-2.0 kadm-client fftw3f libsharpyuv xcb-damage fontconfig gdk-x11-3.0 xtst yajl bdw-gc libunwind-coredump eio-cxx libnl-route-3.0 xpm libselinux kdb libevent_extra xcb-util readline pangofc fftw3 libjpeg harfbuzz ecore-sdl tic tk xkbcommon-x11 xcb-record libwebpdecoder libpcre2-16 cddlib evas-cxx openssl libout123 expat libnl-nf-3.0 vips-cpp cairo-fc liblzma libpcre efl-ui xcb-dri3 evas xcb-keysyms m17n-shell efl-canvas-wl atf-sh sysprof-capture-4 PyImath hogweed python-3.11 xcb-randr kadm-server xcb-render xcb-xkb xfixes gsl z3 libcrypto libbrotlienc libsasl2 harfbuzz-icu jansson libpcre2-posix libnl-genl-3.0 xcb-sync wayland-server gobject-introspection-no-export-1.0 libxcrypt libgsasl elementary libstartup-notification-1.0 m17n-core xcb-xrm atspi-2 xcursor x11 ldap pixman-1 fribidi 'gtk+-broadway-3.0' libexslt vorbisfile lber jemalloc gl libuv ecore-x libbsd-overlay libprofiler xcb-dri2 poppler-glib cairo-script xcb-xinerama libunwind-ptrace libpcreposix libattr libffi cairo-ft libpulse-mainloop-glib cairo-xcb cairo-xlib blkid gmodule-no-export-2.0 efl-cxx glesv2 matio cairo-xlib-xrender harfbuzz-cairo atf-c xmuu libgsf-1 epoxy krb5-gssapi xau libidn libpng mit-krb5 eldbus-cxx libunwind verilator xcb-atom libpulse libusb-1.0 menu libevent xaw3d 'gtk+-3.0' xft audit xdamage eina-cxx libnl-idiag-3.0 xaw7 cairo-gobject pango mit-krb5-gssapi libpcre32 uuid ecore-ipc gmp guile-2.2 sqlite3 wayland-scanner 'ncurses++w' avahi-libevent libgit2 gssrpc icu-uc libacl m17n-flt libcrypt libssl gtk4-wayland 'atf-c++' efreet xt gdk-pixbuf-2.0 gtk4-x11 cairo-pdf python zlib xcb-event sm ethumb-client ecore-cxx mpfr m17n-gui xrender python3-embed xscrnsaver tcl ecore-imf-evas krb5 gpg-error libtcmalloc atk-bridge-2.0 graphene-gobject-1.0 xcb-cursor alsa avahi-core libnl-cli-3.0 cairo-script-interpreter ecore-imf gdk-broadway-3.0 xkbfile libpcrecpp libxml-2.0 opus xcb-glx xapian-core elput ecore-evas luajit xcb-xfixes libmpg123 libseccomp libavif libsystemd 'gtk+-x11-3.0' ogg pangoft2 efreet-trash opengl eio glesv1_cm xcb-screensaver libglvnd xrandr ecore xcb-xv ice libbrotlicommon xcb-image libtirpc gmodule-export-2.0 cairo-png xcb-xinput libwebpdemux xext nettle libwebp wayland-egl libgcrypt libpcre16 cairo-ps xcb-shape cloudproviders gtk4-unix-print xcb-res libunwind-generic libpcre2-8 fwupd-efi libsoup-2.4 egl libpulse-simple gdk-wayland-3.0 yaml-0.1 libsyn123 libopenjp2 cairo gobject-introspection-1.0 xcb-present liblz4 libcap-ng ecore-input-evas xcb-dpms pangocairo eo ecore-fb elua ncursesw xcb-composite xcb-xvmc xinerama gdlib cgif graphite2 gnutls-dane libcurl xcb-xselinux atk libwebpmux OpenEXR webkit2gtk-web-extension-4.0 sndfile xi gdk-3.0 libsepol re2 ethumb emile libtiff-4 valgrind eolian libmd xcb-ewmh cairo-xcb-shm flac gnutls libevent_openssl libmariadb gio-unix-2.0 lmdb sdl2 edje-cxx python-3.11-embed libinput eet emotion atomic_ops libevent_core gtk4 ecore-drm2 ephysics libbsd dbus-1 imagequant libnl-3.0 com_err ruby eldbus libpsl pam libverto efl-core tinfo efl-net libtcmalloc_minimal_debug ecore-file gthread-2.0 ecore-con fftw3l gmodule libpng16 eeze librsvg-2.0 'gtk+-wayland-3.0' panel vorbisenc spng eina cairo-svg glib-2.0 libkeyutils python2 ecore-input menuw orc-test-0.4 xcb-xtest harfbuzz-gobject graphene-1.0 libelf xdmcp eolian-cxx python3 javascriptcoregtk-4.0 bzip2 vorbis x11-xcb pangoxft libperf libpq auparse 'gtk+-unix-print-3.0' libarchive pthread-stubs hunspell icu-i18n glib libevent_pthreads eet-cxx libotf icu-io gio-2.0 xcb-xf86dri gtk4-broadway vips embryo 'ncurses++' tree-sitter alsa-topology lcms2 ethumb_client gthread glx poppler xcomposite ncurses libsoup-gnome-2.4 p11-kit-1 mount libedit libpcre2-32 history xcb ecore-buffer libzstd ecore-avahi avahi-client ecore-audio xkbcommon gnome-todo libexif libthai python-2.7 wayland-egl-backend fuse xkbregistry elementary-cxx formw libtcmalloc_minimal Imath pam_misc libudev datrie-0.2 gail-3.0 efl form cfitsio xcb-shm libnl-xfrm-3.0 libbrotlidec xmu compositeproto dri2proto videoproto shared-mime-info fixesproto xcb-proto udev xcmiscproto xf86dgaproto emacs fontsproto chemical-mime-data dri3proto resourceproto dmxproto randrproto recordproto xbitmaps xproto damageproto kbproto dpmsproto xextproto bash-completion dracut xineramaproto inputproto xwaylandproto glproto xtrans bigreqsproto xf86bigfontproto renderproto scrnsaverproto xorg-macros presentproto xf86vidmodeproto bodr xf86driproto eigen3 systemd
Resolving dependencies...
CallStack (from HasCallStack):
  withMetadata, called at src/Distribution/Simple/Utils.hs:368:14 in Cabal-3.10.1.0-inplace:Distribution.Simple.Utils
Error: cabal: Could not resolve dependencies:
[__0] next goal: pango (user goal)
[__0] rejecting: pango-0.13.8.2, pango-0.13.8.1, pango-0.13.8.0,
pango-0.13.6.1, pango-0.13.6.0, pango-0.13.5.0, pango-0.13.4.0,
pango-0.13.3.1, pango-0.13.3.0, pango-0.13.2.0, pango-0.13.1.1,
pango-0.13.1.0, pango-0.13.0.5, pango-0.13.0.4, pango-0.13.0.3,
pango-0.13.0.2, pango-0.13.0.1, pango-0.13.0.0, pango-0.12.5.3,
pango-0.12.5.0, pango-0.12.4, pango-0.12.3, pango-0.12.2, pango-0.12.1,
pango-0.12.0, pango-0.11.2, pango-0.11.1, pango-0.11.0 (conflict: pkg-config
package pango>=1.0, not found in the pkg-config database)
[__0] fail (backjumping, conflict set: pango)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: pango (29)

Expected behavior

Packages with pkg-config dependencies, such as Pango, work.

System information

% lsb_release -d
Description:	Fedora release 39 (Rawhide)
% cabal --version
cabal-install version 3.10.1.0
compiled using version 3.10.1.0 of the Cabal library 
% ghc --version
The Glorious Glasgow Haskell Compilation System, version 9.6.1
% ghcup --version
The GHCup Haskell installer, version 0.1.19.2

Additional context

• Cabal 3.8 checks for literally all pkg-config packages in the system #8494: a previous adventure in pkgconf-vs-pkg-config problems.
• maximum_package_count is off by one when limiting number of packages to consider pkgconf/pkgconf#295: --modversion actually yields two versions at a time, which is a strict improvement over one.

[Dretch]

I have worked around this issue for my use case by wrapping pkg-config with a script that fails when given more than one argument, so triggering the fallback code path in cabal that calls pkg-config once for each package:

#!/bin/bash
# workaround https://github.com/haskell/cabal/issues/8923 by making pkg-config fail
# when given more than one package, instead of silently using only the first package 
mkdir -p pkg-config-hack
cat <<'EOF' > pkg-config-hack/pkg-config
#!/bin/bash
if [ "$1" == "--modversion" ] && [ "$2" != "" ] && [ "$3" != "" ]; then
  exit 1
fi
exec /usr/bin/pkg-config $@
EOF
chmod +x pkg-config-hack/pkg-config
export PATH=$(pwd)/pkg-config-hack:$PATH

[juhp]

(I believe this was actually caused by a change of behavior of pkgconf-1.9 relative to 1.8 which still supported outputting many package versions (though admittedly that use-case feature made less sense.)

[juhp]

I think the safest would be just to run pkgconf individually on each pkg always?
(though reading all pkgs makes less sense anyway)

[juhp]

Fortunately the behavior seems reverted in pkgconf-2.0, but many distros are still on 1.8 or 1.9...

[juhp]

As a first step I applied this simple patch to Fedora cabal-install-3.8.1 - if anyone else wants this.