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Re: pkg-config "Requires" fields and propagated inputs

From: Taylan Ulrich Bayırlı/Kammer
Subject: Re: pkg-config "Requires" fields and propagated inputs
Date: Wed, 29 Apr 2015 22:17:42 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Picking this topic back up after some things got in between:

address@hidden (Ludovic Courtès) writes:

> address@hidden (Taylan Ulrich "Bayırlı/Kammer") skribis:
>> Maybe I should try to move to a strategy that calls pkg-config instead
>> of parsing the files in Guile, but it might be nontrivial to get the
>> PKG_CONFIG_PATH right for each call, and doing many execs might be too
>> slow, so I'll first see how much further I can get with this strategy.
> Yeah forking would be slow; parsing sounds good.  However, the ‘satisfy’
> predicates could be based on actual package contents (when available):
> looking for actual .pc files and libraries.

I overhauled the strategy somewhat, and indeed look for actual .pc files
(under $prefix/lib/pkgconfig directories) and files (under
$prefix/lib directories) now.  For .pc files, the extension is stripped,
for files, the foo part is taken.  These then serve as exact
pkg-config package names and library names respectively, making
everything more robust.  Thanks for the idea!

>> $ ./pre-inst-env guile -c '((@ (guix missing-propagated-inputs) 
>> print-missing-propagated-inputs))'
>> "fftw": ("-lfftw3" "-lm")
>> "fftwf": ("-lfftw3f" "-lm")
> This is a false positives: -lfftw3* is actually provided by the package
> itself, and -lm is part of libc, so it’s always found (libc libraries
> will have to be special-cased.)

Libc components are now handled.  The fftw3 stuff is handled fine under
the new strategy.

>> "apr": ("-ldl" "-lpthread" "-lcrypt" "-lrt" "-lapr-${APR_MAJOR_VERSION}")
> Again libc libraries, and the library of APR itself.  Problem is that
> this one requires almost a full reimplementation of pkg-config, to be
> able to do variable substitution (probably not insurmountable though.)

Implementing variable substitution was fairly straightforward, so these
are fine now.

>> "guile": ("-lgc" "-lffi")
> guile-2.0.pc has this:
>   Libs: -L${libdir} -lguile-2.0 
> -L/gnu/store/dxfv00pgmnhxkj5jh3yxyp0q94l6i2ch-libgc-7.4.2/lib -lgc
> So here -lgc is a false positive: libgc is found by virtue of the -L
> flag.

The -L flags are handled too now; the directory they point at is handled
equivalently to $prefix/lib directories under the new strategy.
(I.e. they're scanned for files.)

> ‘-lffi’ only appears in ‘Libs.private’ (static linking) so I would just
> ignore it.

You're right; unlike Requires.private, Libs.private has no effect on
e.g. pkg-config --exists, so it's really only for static linking; I
removed the parsing of Libs.private fields.

> It looks like there are 3 classes of false positives here that would
> need to be addressed to make the report more directly readable.

I think all these false positives are fixed now!

New sample output from my machine:

portaudio: pkg-config: () libs: ("asound")
avahi: pkg-config: ("glib-2.0" "gobject-2.0" "glib-2.0") libs: ()
libatomic-ops: pkg-config: () libs: ("atomic_ops")
ijs: pkg-config: () libs: ("ijs")
mesa: pkg-config: ("xcb-dri3" "xcb-dri2" "libudev" "xcb-dri3" "xcb-dri2") libs: 
dbus-glib: pkg-config: ("gobject-2.0" "glib-2.0" "dbus-1") libs: ()
libcroco: pkg-config: ("libxml-2.0" "glib-2.0") libs: ()
gst-plugins-base: pkg-config: ("gio-2.0" "glib-2.0" "gio-2.0") libs: ()
harfbuzz: pkg-config: ("icu-uc") libs: ()
gtk+: pkg-config: ("gio-2.0" "cairo" "gio-2.0" "cairo" "gio-2.0" "cairo") libs: 
pango: pkg-config: ("gobject-2.0" "glib-2.0" "gmodule-no-export-2.0" 
"fontconfig" "freetype2" "xft") libs: ()
cairo: pkg-config: ("xcb-shm" "xcb-render" "xcb-render") libs: ("z" "z")
eudev: pkg-config: ("gobject-2.0" "glib-2.0") libs: ()
qpdf: pkg-config: ("zlib") libs: ()
poppler: pkg-config: ("cairo" "cairo" "gio-2.0" "gobject-2.0" "glib-2.0") libs: 
pulseaudio: pkg-config: ("glib-2.0") libs: ()
libdvdnav: pkg-config: ("dvdread") libs: ()
libxslt: pkg-config: ("libxml-2.0" "libxml-2.0") libs: ("z" "z")
libxv: pkg-config: ("xproto" "xext" "x11") libs: ()
libx11: pkg-config: ("xproto") libs: ()
libxmu: pkg-config: ("xt" "x11" "xproto" "xext" "xt" "x11" "x11" "xproto" 
"x11") libs: ()
libxinerama: pkg-config: ("xext" "x11") libs: ()
libxft: pkg-config: ("xproto") libs: ()
libxext: pkg-config: ("x11") libs: ()
libxaw: pkg-config: ("xproto" "x11" "xproto" "x11") libs: ()
libxdmcp: pkg-config: ("xproto") libs: ()
libxpm: pkg-config: ("x11" "x11") libs: ()
libxkbfile: pkg-config: ("kbproto" "x11") libs: ()
xkbcomp: pkg-config: ("x11") libs: ()
libxxf86vm: pkg-config: ("x11") libs: ()
libxrender: pkg-config: ("x11" "xproto" "x11") libs: ()
libxfixes: pkg-config: ("xproto" "x11") libs: ()
libxt: pkg-config: ("xproto") libs: ()
libsm: pkg-config: ("xproto") libs: ()


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