Build: Make dependency on git change more robust

It can sometimes happen that .git/HEAD or .git/refs/head/*, which
are added as config.status dependencies during configure, do not
exist anymore at build time.  For instance, when the current branch
is deleted after switching to a different one.

Wrap the dependencies inside $(wildcard ...) to avoid this problem.
Note that this is a GNU make feature.  However, it should be fine
as it is only used for git builds.  Even if a non-GNU make is used,
the construct will hopefully just expand to nothing.

diff --git a/configure.ac b/configure.ac
index cd563c18dbe3c2da110da343755ccfe756ccaf10..6a692b20665b15449c5f4a617574b3f19c5ededc 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -69,10 +69,16 @@ SR_PACKAGE_VERSION="AC_PACKAGE_VERSION"
 sr_head=`git -C "$srcdir" rev-parse --verify --short HEAD 2>&AS_MESSAGE_LOG_FD`
 
 AS_IF([test "$?" -eq 0 && test -n "$sr_head"], [
-       CONFIG_STATUS_DEPENDENCIES='$(top_srcdir)/.git/HEAD'
+       sr_git_deps=
+       test ! -f "$srcdir/.git/HEAD" || sr_git_deps=' $(top_srcdir)/.git/HEAD'
+
        sr_head_name=`git -C "$srcdir" rev-parse --symbolic-full-name HEAD 2>&AS_MESSAGE_LOG_FD`
        AS_IF([test "$?" -eq 0 && test -f "$srcdir/.git/$sr_head_name"],
-               [CONFIG_STATUS_DEPENDENCIES="$CONFIG_STATUS_DEPENDENCIES \$(top_srcdir)/.git/$sr_head_name"])
+               [sr_git_deps="$sr_git_deps \$(top_srcdir)/.git/$sr_head_name"])
+
+       # Use $(wildcard) so that things do not break if for whatever
+       # reason these files do not exist anymore at make time.
+       test -z "$sr_git_deps" || CONFIG_STATUS_DEPENDENCIES="\$(wildcard$sr_git_deps)"
 
        # Append the revision hash unless we are exactly on a tagged release.
        git -C "$srcdir" describe --match 'AC_PACKAGE_NAME-AC_PACKAGE_VERSION' \