recommended use of PKG_CHECK_VAR for bashcompdir causes 'make distcheck' failures

[ebblake]

The main page for this project suggests that other projects wanting to add third-party drop-ins should use:
"For packages using GNU autotools the installation can be handled for example like this in configure.ac:

PKG_CHECK_VAR(bashcompdir, [bash-completion], [completionsdir], ,
bashcompdir="${sysconfdir}/bash_completion.d")
AC_SUBST(bashcompdir)

...accompanied by this in Makefile.am:

bashcompdir = @bashcompdir@
dist_bashcomp_DATA = # completion files go here
"

However, the nbdkit project did just that, and it causes 'make distcheck' to fail. The problem is that even though bash-completion.pc contains:
prefix=/usr
completionsdir=${prefix}/share/bash-completion/completions

the result of the PKG_CHECK_VAR macro, which really is merely a call to:

bashcompdir=`$PKG_CONFIG --variable=completionsdir bash-completion 2>/dev/null

is always absolute ("/usr/share/bash-completion/completions", that is, ${prefix} was resolved before output) instead of --prefix-relative (as in a literal '${prefix}/share/bash-completion/completions'). Then when 'make distcheck' invokes './configure --prefix=/path/to/nonroot/_inst', it expects that 'make install' can be run as non-root with no files being installed outside of that jail, but that expectation is broken because the absolute name stored in bashcompdir is not prefix-relative, resulting in:

/usr/bin/install -c -m 644 ../../../bash/nbdkit '/usr/share/bash-completion/completions' /usr/bin/install: cannot remove '/usr/share/bash-completion/completions/nbdkit': Permission denied

It can be worked around by doing:

bashcompdir=$PKG_CONFIG --define-variable=prefix='${prefix}' \ --variable=completionsdir bash-completion 2>/dev/null

but I don't know if that is the right approach to take, especially since the PKG_CHECK_VAR() macro does not easily allow that type of rewrite. Are there any other best-practice ideas out there on working around this sort of issue?

The nbdkit thread can be found here: https://www.redhat.com/archives/libguestfs/2018-December/msg00103.html

See also https://git.dereferenced.org/pkgconf/pkgconf/issues/17

[kaniini]

As mentioned there:

The issue is that the bash-completion pkgconfig file defines completionsdir with the ${prefix} variable. As you probably already know, the prefix is typically set to /usr or similar, and is a system-wide path that requires root. This is something you should work around yourself, it is probably not an issue in either software.

This means the prefix should be overwritten by your build system if you are installing elsewhere, such as the prefix you are building your local copy with.