Merge branch 'ps/fetch-atomic'

"git fetch" can make two separate fetches, but ref updates coming
from them were in two separate ref transactions under "--atomic",
which has been corrected.

* ps/fetch-atomic:
  fetch: make `--atomic` flag cover pruning of refs
  fetch: make `--atomic` flag cover backfilling of tags
  refs: add interface to iterate over queued transactional updates
  fetch: report errors when backfilling tags fails
  fetch: control lifecycle of FETCH_HEAD in a single place
  fetch: backfill tags before setting upstream
  fetch: increase test coverage of fetches

2 files changed, 103 insertions, 0 deletions

diff --git a/t/t5503-tagfollow.sh b/t/t5503-tagfollow.sh
index 195fc64..e72fdc2 100755
--- a/t/t5503-tagfollow.sh
+++ b/t/t5503-tagfollow.sh
@@ -160,4 +160,78 @@ test_expect_success 'new clone fetch main and tags' '
 	test_cmp expect actual
 '
 
+test_expect_success 'atomic fetch with failing backfill' '
+	git init clone3 &&
+
+	# We want to test whether a failure when backfilling tags correctly
+	# aborts the complete transaction when `--atomic` is passed: we should
+	# neither create the branch nor should we create the tag when either
+	# one of both fails to update correctly.
+	#
+	# To trigger failure we simply abort when backfilling a tag.
+	write_script clone3/.git/hooks/reference-transaction <<-\EOF &&
+		while read oldrev newrev reference
+		do
+			if test "$reference" = refs/tags/tag1
+			then
+				exit 1
+			fi
+		done
+	EOF
+
+	test_must_fail git -C clone3 fetch --atomic .. $B:refs/heads/something &&
+	test_must_fail git -C clone3 rev-parse --verify refs/heads/something &&
+	test_must_fail git -C clone3 rev-parse --verify refs/tags/tag2
+'
+
+test_expect_success 'atomic fetch with backfill should use single transaction' '
+	git init clone4 &&
+
+	# Fetching with the `--atomic` flag should update all references in a
+	# single transaction, including backfilled tags. We thus expect to see
+	# a single reference transaction for the created branch and tags.
+	cat >expected <<-EOF &&
+		prepared
+		$ZERO_OID $B refs/heads/something
+		$ZERO_OID $S refs/tags/tag2
+		$ZERO_OID $T refs/tags/tag1
+		committed
+		$ZERO_OID $B refs/heads/something
+		$ZERO_OID $S refs/tags/tag2
+		$ZERO_OID $T refs/tags/tag1
+	EOF
+
+	write_script clone4/.git/hooks/reference-transaction <<-\EOF &&
+		( echo "$*" && cat ) >>actual
+	EOF
+
+	git -C clone4 fetch --atomic .. $B:refs/heads/something &&
+	test_cmp expected clone4/actual
+'
+
+test_expect_success 'backfill failure causes command to fail' '
+	git init clone5 &&
+
+	write_script clone5/.git/hooks/reference-transaction <<-EOF &&
+		while read oldrev newrev reference
+		do
+			if test "\$reference" = refs/tags/tag1
+			then
+				# Create a nested tag below the actual tag we
+				# wanted to write, which causes a D/F conflict
+				# later when we want to commit refs/tags/tag1.
+				# We cannot just `exit 1` here given that this
+				# would cause us to die immediately.
+				git update-ref refs/tags/tag1/nested $B
+				exit \$!
+			fi
+		done
+	EOF
+
+	test_must_fail git -C clone5 fetch .. $B:refs/heads/something &&
+	test $B = $(git -C clone5 rev-parse --verify refs/heads/something) &&
+	test $S = $(git -C clone5 rev-parse --verify tag2) &&
+	test_must_fail git -C clone5 rev-parse --verify tag1
+'
+
 test_done
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index ef0da0a..48e14e2 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -343,6 +343,35 @@ test_expect_success 'fetch --atomic --append appends to FETCH_HEAD' '
 	test_cmp expected atomic/.git/FETCH_HEAD
 '
 
+test_expect_success 'fetch --atomic --prune executes a single reference transaction only' '
+	test_when_finished "rm -rf \"$D\"/atomic" &&
+
+	cd "$D" &&
+	git branch scheduled-for-deletion &&
+	git clone . atomic &&
+	git branch -D scheduled-for-deletion &&
+	git branch new-branch &&
+	head_oid=$(git rev-parse HEAD) &&
+
+	# Fetching with the `--atomic` flag should update all references in a
+	# single transaction.
+	cat >expected <<-EOF &&
+		prepared
+		$ZERO_OID $ZERO_OID refs/remotes/origin/scheduled-for-deletion
+		$ZERO_OID $head_oid refs/remotes/origin/new-branch
+		committed
+		$ZERO_OID $ZERO_OID refs/remotes/origin/scheduled-for-deletion
+		$ZERO_OID $head_oid refs/remotes/origin/new-branch
+	EOF
+
+	write_script atomic/.git/hooks/reference-transaction <<-\EOF &&
+		( echo "$*" && cat ) >>actual
+	EOF
+
+	git -C atomic fetch --atomic --prune origin &&
+	test_cmp expected atomic/actual
+'
+
 test_expect_success '--refmap="" ignores configured refspec' '
 	cd "$TRASH_DIRECTORY" &&
 	git clone "$D" remote-refs &&