[PATCH v3 14/28] upload-pack: make sure deepening preserves shallow roots

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

When "fetch --depth=N" where N exceeds the longest chain of history in
the source repo, usually we just send an "unshallow" line to the
client so full history is obtained.

When the source repo is shallow we need to make sure to "unshallow"
the current shallow point _and_ "shallow" again when the commit
reaches its shallow bottom in the source repo.

This should fix both cases: large <N> and --unshallow.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/fetch-options.txt |  8 ++++++--
 shallow.c                       |  6 +++++-
 t/t5536-fetch-shallow.sh        | 16 ++++++++++++++++
 upload-pack.c                   |  2 +-
 4 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index ba1fe49..a83d2b4 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -14,8 +14,12 @@
 	branch history. Tags for the deepened commits are not fetched.
 
 --unshallow::
-	Convert a shallow repository to a complete one, removing all
-	the limitations imposed by shallow repositories.
+	If the source repository is complete, convert a shallow
+	repository to a complete one, removing all the limitations
+	imposed by shallow repositories.
++
+If the source repository is shallow, fetch as much as possible so that
+the current repository has the same history as the source repository.
 
 ifndef::git-pull[]
 --dry-run::
diff --git a/shallow.c b/shallow.c
index 2ec0c8c..1baf6b5 100644
--- a/shallow.c
+++ b/shallow.c
@@ -73,6 +73,7 @@ struct commit_list *get_shallow_commits(struct object_array *heads, int depth,
 	struct commit_list *result = NULL;
 	struct object_array stack = OBJECT_ARRAY_INIT;
 	struct commit *commit = NULL;
+	struct commit_graft *graft;
 
 	while (commit || i < heads->nr || stack.nr) {
 		struct commit_list *p;
@@ -97,7 +98,10 @@ struct commit_list *get_shallow_commits(struct object_array *heads, int depth,
 		if (parse_commit(commit))
 			die("invalid commit");
 		cur_depth++;
-		if (cur_depth >= depth) {
+		if ((depth != INFINITE_DEPTH && cur_depth >= depth) ||
+		    (is_repository_shallow() && !commit->parents &&
+		     (graft = lookup_commit_graft(commit->object.sha1)) != NULL &&
+		     graft->nr_parent < 0)) {
 			commit_list_insert(commit, &result);
 			commit->object.flags |= shallow_flag;
 			commit = NULL;
diff --git a/t/t5536-fetch-shallow.sh b/t/t5536-fetch-shallow.sh
index 41de74d..e011ead 100755
--- a/t/t5536-fetch-shallow.sh
+++ b/t/t5536-fetch-shallow.sh
@@ -79,6 +79,22 @@ EOF
 	)
 '
 
+test_expect_success 'fetch --unshallow from shallow clone' '
+	(
+	cd shallow2 &&
+	git fetch --unshallow &&
+	git fsck &&
+	git log --format=%s origin/master >actual &&
+	cat <<EOF >expect &&
+6
+5
+4
+3
+EOF
+	test_cmp expect actual
+	)
+'
+
 test_expect_success 'fetch something upstream has but hidden by clients shallow boundaries' '
 	# the blob "1" is available in .git but hidden by the
 	# shallow2/.git/shallow and it should be resent
diff --git a/upload-pack.c b/upload-pack.c
index f082f06..28269c7 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -619,7 +619,7 @@ static void receive_needs(void)
 	if (depth > 0) {
 		struct commit_list *result = NULL, *backup = NULL;
 		int i;
-		if (depth == INFINITE_DEPTH)
+		if (depth == INFINITE_DEPTH && !is_repository_shallow())
 			for (i = 0; i < shallows.nr; i++) {
 				struct object *object = shallows.objects[i].item;
 				object->flags |= NOT_SHALLOW;
-- 
1.8.2.83.gc99314b