Merge branch 'pt/am-abort-fix' into maint

Various fixes around "git am" that applies a patch to a history
that is not there yet.

* pt/am-abort-fix:
  am --abort: keep unrelated commits on unborn branch
  am --abort: support aborting to unborn branch
  am --abort: revert changes introduced by failed 3way merge
  am --skip: support skipping while on unborn branch
  am -3: support 3way merge on unborn branch
  am --skip: revert changes introduced by failed 3way merge

1 files changed, 23 insertions, 8 deletions

diff --git a/git-am.sh b/git-am.sh
index a67d0f989..3103c0fc2 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -69,6 +69,8 @@ then
 	cmdline="$cmdline -3"
 fi
 
+empty_tree=4b825dc642cb6eb9a060e54bf8d69288fbee4904
+
 sq () {
 	git rev-parse --sq-quote "$@"
 }
@@ -85,7 +87,7 @@ safe_to_abort () {
 		return 1
 	fi
 
-	if ! test -s "$dotest/abort-safety"
+	if ! test -f "$dotest/abort-safety"
 	then
 		return 0
 	fi
@@ -177,7 +179,8 @@ It does not apply to blobs recorded in its index.")"
     then
 	    GIT_MERGE_VERBOSITY=0 && export GIT_MERGE_VERBOSITY
     fi
-    git-merge-recursive $orig_tree -- HEAD $his_tree || {
+    our_tree=$(git rev-parse --verify -q HEAD || echo $empty_tree)
+    git-merge-recursive $orig_tree -- $our_tree $his_tree || {
 	    git rerere $allow_rerere_autoupdate
 	    die "$(gettext "Failed to merge in the changes.")"
     }
@@ -502,10 +505,11 @@ then
 		;;
 	t,)
 		git rerere clear
-		git read-tree --reset -u HEAD HEAD
-		orig_head=$(cat "$GIT_DIR/ORIG_HEAD")
-		git reset HEAD
-		git update-ref ORIG_HEAD $orig_head
+		head_tree=$(git rev-parse --verify -q HEAD || echo $empty_tree) &&
+		git read-tree --reset -u $head_tree $head_tree &&
+		index_tree=$(git write-tree) &&
+		git read-tree -m -u $index_tree $head_tree
+		git read-tree $head_tree
 		;;
 	,t)
 		if test -f "$dotest/rebasing"
@@ -515,8 +519,19 @@ then
 		git rerere clear
 		if safe_to_abort
 		then
-			git read-tree --reset -u HEAD ORIG_HEAD
-			git reset ORIG_HEAD
+			head_tree=$(git rev-parse --verify -q HEAD || echo $empty_tree) &&
+			git read-tree --reset -u $head_tree $head_tree &&
+			index_tree=$(git write-tree) &&
+			orig_head=$(git rev-parse --verify -q ORIG_HEAD || echo $empty_tree) &&
+			git read-tree -m -u $index_tree $orig_head
+			if git rev-parse --verify -q ORIG_HEAD >/dev/null 2>&1
+			then
+				git reset ORIG_HEAD
+			else
+				git read-tree $empty_tree
+				curr_branch=$(git symbolic-ref HEAD 2>/dev/null) &&
+				git update-ref -d $curr_branch
+			fi
 		fi
 		rm -fr "$dotest"
 		exit ;;