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

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 ;;

t/t4151-am-abort.sh

@@ -14,6 +14,7 @@ test_expect_success setup '
 	git add file-1 file-2 &&
 	git commit -m initial &&
 	git tag initial &&
+	git format-patch --stdout --root initial >initial.patch &&
 	for i in 2 3 4 5 6
 	do
 		echo $i >>file-1 &&
@@ -63,6 +64,28 @@ do
 
 done
 
+test_expect_success 'am -3 --skip removes otherfile-4' '
+	git reset --hard initial &&
+	test_must_fail git am -3 0003-*.patch &&
+	test 3 -eq $(git ls-files -u | wc -l) &&
+	test 4 = "$(cat otherfile-4)" &&
+	git am --skip &&
+	test_cmp_rev initial HEAD &&
+	test -z "$(git ls-files -u)" &&
+	test_path_is_missing otherfile-4
+'
+
+test_expect_success 'am -3 --abort removes otherfile-4' '
+	git reset --hard initial &&
+	test_must_fail git am -3 0003-*.patch &&
+	test 3 -eq $(git ls-files -u | wc -l) &&
+	test 4 = "$(cat otherfile-4)" &&
+	git am --abort &&
+	test_cmp_rev initial HEAD &&
+	test -z $(git ls-files -u) &&
+	test_path_is_missing otherfile-4
+'
+
 test_expect_success 'am --abort will keep the local commits intact' '
 	test_must_fail git am 0004-*.patch &&
 	test_commit unrelated &&
@@ -72,4 +95,62 @@ test_expect_success 'am --abort will keep the local commits intact' '
 	test_cmp expect actual
 '
 
+test_expect_success 'am -3 stops on conflict on unborn branch' '
+	git checkout -f --orphan orphan &&
+	git reset &&
+	rm -f otherfile-4 &&
+	test_must_fail git am -3 0003-*.patch &&
+	test 2 -eq $(git ls-files -u | wc -l) &&
+	test 4 = "$(cat otherfile-4)"
+'
+
+test_expect_success 'am -3 --skip clears index on unborn branch' '
+	test_path_is_dir .git/rebase-apply &&
+	echo tmpfile >tmpfile &&
+	git add tmpfile &&
+	git am --skip &&
+	test -z "$(git ls-files)" &&
+	test_path_is_missing otherfile-4 &&
+	test_path_is_missing tmpfile
+'
+
+test_expect_success 'am -3 --abort removes otherfile-4 on unborn branch' '
+	git checkout -f --orphan orphan &&
+	git reset &&
+	rm -f otherfile-4 file-1 &&
+	test_must_fail git am -3 0003-*.patch &&
+	test 2 -eq $(git ls-files -u | wc -l) &&
+	test 4 = "$(cat otherfile-4)" &&
+	git am --abort &&
+	test -z "$(git ls-files -u)" &&
+	test_path_is_missing otherfile-4
+'
+
+test_expect_success 'am -3 --abort on unborn branch removes applied commits' '
+	git checkout -f --orphan orphan &&
+	git reset &&
+	rm -f otherfile-4 otherfile-2 file-1 file-2 &&
+	test_must_fail git am -3 initial.patch 0003-*.patch &&
+	test 3 -eq $(git ls-files -u | wc -l) &&
+	test 4 = "$(cat otherfile-4)" &&
+	git am --abort &&
+	test -z "$(git ls-files -u)" &&
+	test_path_is_missing otherfile-4 &&
+	test_path_is_missing file-1 &&
+	test_path_is_missing file-2 &&
+	test 0 -eq $(git log --oneline 2>/dev/null | wc -l) &&
+	test refs/heads/orphan = "$(git symbolic-ref HEAD)"
+'
+
+test_expect_success 'am --abort on unborn branch will keep local commits intact' '
+	git checkout -f --orphan orphan &&
+	git reset &&
+	test_must_fail git am 0004-*.patch &&
+	test_commit unrelated2 &&
+	git rev-parse HEAD >expect &&
+	git am --abort &&
+	git rev-parse HEAD >actual &&
+	test_cmp expect actual
+'
+
 test_done