build_clone: git clean newly cloned trees

This may seem redundant, however:

git does not track empty directories.  So it can happen that a
directory is created as part of `git clone', but is empty in the
revision switched to with `git checkout'.

In this situation, the tree we are going to build ought not to contain
this directory, because that directory will not (in general) be
produced, eg when the revision being switched to becomes master.

We can use git clean to produce a working tree whose contents -
including the presence or absence of empty directories - depends only
on the commit we are trying to check out, and not on the previous
states of the git history or working tree.

For example, if a directory is made empty (ie, deleted, since git does
not distinguish) in xen.git#staging, osstest's clones of
xen.git#master will produce the directory, but `git checkout' of
staging won't delete it.  If the xen.git build system mistakenly
depends on this directory, we won't detect this until the deletion
reaches master.  This situation actually occurred with xen.git#598e97f
"tools/python: remove broken xl binding" (fixed in b261366f).

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/Osstest/TestSupport.pm b/Osstest/TestSupport.pm
index f9eba6bb37920baa4a08f85f630af7bf1a5df2dc..aa41952e0141ddd3169bf44345d58545d1dca50e 100644 (file)
--- a/Osstest/TestSupport.pm
+++ b/Osstest/TestSupport.pm
@@ -1231,6 +1231,7 @@ END
 END
                          (length($r{"revision_$which"}) ? <<END : ''));
            git checkout '$r{"revision_$which"}'
+           git clean -xdf
 END
     } else {
         die "$vcs $which $tree ?";