Fix migration script to use original SHA1 from tempest's commits

Use git log instead of git filter-branch - which rewrites the history - to get
SHA1 from the commits that touch the files to be migrated from tempest to
tempest_lib.

Change-Id: I321d78390991eb90fbb4a176a12187b78edc9f31
Closes-bug: #1386782

1 files changed, 9 insertions, 52 deletions

diff --git a/tools/migrate_from_tempest.sh b/tools/migrate_from_tempest.sh
index 2bf02d1..4751d0b 100755
--- a/tools/migrate_from_tempest.sh
+++ b/tools/migrate_from_tempest.sh
@@ -46,58 +46,15 @@ function count_commits {
 git clone $TEMPEST_GIT_URL $tmpdir
 cd $tmpdir
 
-# Build the grep pattern for ignoring files that we want to keep
-keep_pattern="\($(echo $files | sed -e 's/ /\\|/g')\)"
-# Prune all other files in every commit
-pruner="git ls-files | grep -v \"$keep_pattern\" | git update-index --force-remove --stdin; git ls-files > /dev/stderr"
-
-# Find all first commits with listed files and find a subset of them that
-# predates all others
-roots=""
-for file in $files; do
-    file_root="$(git rev-list --reverse HEAD -- $file | head -n1)"
-    fail=0
-    for root in $roots; do
-         if git merge-base --is-ancestor $root $file_root; then
-             fail=1
-             break
-         elif ! git merge-base --is-ancestor $file_root $root; then
-             new_roots="$new_roots $root"
-         fi
-     done
-     if [ $fail -ne 1 ]; then
-         roots="$new_roots $file_root"
-     fi
-done
-
-set_roots="
-if [ '' $(for root in $roots; do echo " -o \"\$GIT_COMMIT\" == '$root' "; done) ]; then
-    echo ''
-else
-    cat
-fi"
-
-# Enhance git_commit_non_empty_tree to skip merges with:
-# a) either two equal parents (commit that was about to land got purged as well
-# as all commits on mainline);
-# b) or with second parent being an ancestor to the first one (just as with a)
-# but when there are some commits on mainline).
-# In both cases drop second parent and let git_commit_non_empty_tree to decide
-# if commit worth doing (most likely not).
-
-skip_empty=$(cat << \EOF
-if [ $# = 5 ] && git merge-base --is-ancestor $5 $3; then
-    git_commit_non_empty_tree $1 -p $3
-else
-    git_commit_non_empty_tree "$@"
-fi
-EOF
-)
-
-# Prune just the commits relevant to what is being migrated
-git filter-branch --index-filter "$pruner" --parent-filter "$set_roots" --commit-filter "$skip_empty" HEAD
-
-SHA1_LIST=`git log --oneline`
+# get only commits that touch our files
+commits="$(git log --format=format:%h --no-merges --follow -- $files)"
+# then their merge commits - which works fina since we merge commits
+# individually.
+merge_commits="$(git log --format=format:%h --merges --first-parent -- $files)"
+pattern="\n$(echo $commits $merge_commits | sed -e 's/ /\\|/g')"
+
+# order them by filtering each one in the order it appears on rev-list
+SHA1_LIST=$(git rev-list --oneline HEAD | grep $pattern)
 
 # Move files and commit
 cd -