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Re: [PATCH v4 2/2] git-version-gen: add --fallback option to use if git

From: Eric Blake
Subject: Re: [PATCH v4 2/2] git-version-gen: add --fallback option to use if git is not present
Date: Mon, 31 Dec 2012 15:45:31 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0

On 12/28/2012 03:13 PM, Peter Rosin wrote:
> When building in a git checkout, but from a system lacking git, it
> is useful to fall back to the version determined when the git
> checkout was last used from a system sporting git.
> * build-aux/git-version-gen: Add support for the new option --fallback,
> which comes into play when there is no $tarball_version_file and
> git is not working.

You didn't really document how to wire up makefiles to properly inject a
decent --fallback option into the script; but I'm at least satisfied
that this patch in isolation doesn't break existing packages that don't
use the --falback option, while leaving the door open for packages that
DO want to support the use of --fallback.

As I understand it, the idea is that you have a shared folder that can
be accessed via multiple machines; on some machines, you have git, and
can therefore do a git checkout that populates Makefile with the right
information for use as a fallback.  On other machines you lack git but
can see the .git directory in the shared directory; since it is still a
development build and you never ran 'make dist', you still want to have
the effect of a devel checkout, rather than building from a tarball, and
if all that git was needed for can be injected from the machine that has
git installed, then the other machine can benefit from the --falback.

I just now noticed v5, so I'll check that out before pushing anything.

I will point out that your script introduces yet another instance of a
non-portable construct:

test -z "$fallback"

Per the Autoconf manual:

     Posix also says that `test ! "STRING"', `test -n "STRING"' and
     `test -z "STRING"' work with any string, but many shells (such as
     Solaris, AIX 3.2, UNICOS, Digital Unix 4, etc.) get
     confused if STRING looks like an operator:

          $ test -n =
          test: argument expected
          $ test ! -n
          test: argument expected
          $ test -z ")"; echo $?

However, this idiom is already in use elsewhere in git-version-gen, so
it should be fixed in an independent patch.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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