[Libguestfs] [nbdkit PATCH] build: Allow 'make install' into non-root --prefix: bash-completion

[Eric Blake]

In general, autotooled packages are supposed to allow
'./configure --prefix=$HOME/subdir' as a way to then get
'make install' to run as non-root.  In fact, 'make distcheck'
tests that this scenario works; alas, we fail due to:

 /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

The culprit? We use pkg-config to ask bash-completion where it
would install user completion scripts.  bash-completion.pc states:

prefix=/usr
completionsdir=${prefix}/share/bash-completion/completions

but pkg-config --variable defaults to flattening the ${prefix}
in our use of the PKG_CHECK_VAR() macro, which in turn means
that './configure --prefix=$HOME/subdir' still uses an absolute
path pointing to a root-owned directory (rather than one relative
to our desired ${prefix}) in our definition of bashcompsdir.

The solution? Tell pkg-config to NOT flatten the prefix variable.

Signed-off-by: Eric Blake <eblake at redhat.com>
---

I'm posting this one for review, particularly since it means someone
running 'make install' with a non-root --prefix will now be stuck
with bash completion libraries that won't be loaded by default (the
user will have to probably edit their ~/.bashrc to load things), but
that still seems better than the alternative of failing to install
because the installation wants to override root-owned files in spite
of the non-root --prefix.

'make distcheck' still doesn't pass for me; the next failure is
due to attempts to overwrite root-owned ocaml files.  Similar symptoms
as what this patch addressed for bashcompsdir, but there we aren't
using pkg-config --variable.  Instaed, our definition of ocamllibdir
(based on ${OCAMLLIB} in m4/ocaml.m4) is coming from 'ocamlc -where',
and I have no idea how to coerce that to print a relative pathname,
or even if it is common to have ocaml libraries installed in a non-root
home directory but which can still be picked up by ocaml at runtime.

 configure.ac | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 33ed4d5..8c97ffb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -337,7 +337,15 @@ PKG_CHECK_MODULES([BASH_COMPLETION], [bash-completion >= 2.0], [
     bash_completion=yes
     AC_MSG_CHECKING([for bash-completions directory])
     m4_ifdef([PKG_CHECK_VAR],[
-        PKG_CHECK_VAR(bashcompdir, [bash-completion], [completionsdir])
+        dnl PKG_CHECK_VAR(bashcompdir, [bash-completion], [completionsdir])
+        dnl Unfortunately, PKG_CHECK_VAR flattens references to ${prefix},
+        dnl which in turn means './configure --prefix=...' to a location
+        dnl writable by non-root still fails when it comes to installing
+        dnl the bash completions.
+        dnl So here, we just run the same command as the macro would, but
+        dnl with an override for prefix to keep 'make distcheck' happy.
+        bashcompdir=`$PKG_CONFIG --define-variable=prefix='${prefix}' \
+          --variable=completionsdir bash-completion 2>/dev/null`
     ])
     AS_IF([test -z "$bashcompdir"], [
         bashcompdir="${sysconfdir}/bash_completion.d"
-- 
2.17.2