[PATCH] fetch: add --no-update-remote-refs

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <dstolee@microsoft.com>

To prevent long blocking time during a 'git fetch' call, a user
may want to set up a schedule for background 'git fetch' processes.
However, these runs will update the refs/remotes branches, and
hence the user will not notice when remote refs are updated during
their foreground fetches. In fact, they may _want_ those refs to
stay put so they can work with the refs from their last foreground
fetch call.

Add a --[no-]update-remote-refs option to 'git fetch' which defaults
to the existing behavior of updating the remote refs. This allows
a user to run

  git fetch <remote> --no-update-remote-refs +refs/heads/*:refs/hidden/*

to populate a custom ref space and download a pack of the new
reachable objects. This kind of call allows a few things to happen:

1. We download a new pack if refs have updated.
2. Since the refs/hidden branches exist, GC will not remove the
   newly-downloaded data.
3. With fetch.writeCommitGraph enabled, the refs/hidden refs are
   used to update the commit-graph file.

To avoid the refs/hidden directory from filling without bound, the
--prune option can be included. When providing a refspec like this,
the --prune option does not delete remote refs and instead only
deletes refs in the target refspace.

Note: with the default refpsec, the --prune option will override
the --no-update-remote-refs option and will delete the refs that
do not exist on the remote.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
    fetch: add --no-update-remote-refs
    
    Here is a new feature for git fetch that hopefully is useful to some
    users. We've been using a patch like this in microsoft/git for about a
    month now, and I've been testing it locally using the custom refspec
    mentioned in the commit message. It's quite refreshing to run git fetch
    --all in my Git repo and see all the branch updates but not actually
    wait for any pack downloads.
    
    There is one question about how --prune and --no-update-remote-refs 
    should interact. Since --prune is not the default, and it works the way
    I'd like with a non-default refspec, I'm currently proposing allowing it
    to delete remote refs even if --no-update-remote-refs is provided.
    
    Thanks, -Stolee

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-532%2Fderrickstolee%2Ffetch-no-update-remote-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-532/derrickstolee/fetch-no-update-remote-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/532

 Documentation/fetch-options.txt |  7 +++++++
 builtin/fetch.c                 |  6 ++++++
 t/t5510-fetch.sh                | 24 ++++++++++++++++++++++++
 3 files changed, 37 insertions(+)

diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index a2f78624a2..0939642dce 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -254,6 +254,13 @@ endif::git-pull[]
 	'git-pull' the --ff-only option will still check for forced updates
 	before attempting a fast-forward update. See linkgit:git-config[1].
 
+--no-update-remote-refs::
+	By default, git updates the `refs/remotes/` refspace with the refs
+	advertised by the remotes during a `git fetch` command. With this
+	option, those refs will be ignored. If the `--prune` option is
+	specified and the default refpsec is used, then a ref that does not
+	appear in the remote will still be deleted from refs/remotes.
+
 -4::
 --ipv4::
 	Use IPv4 addresses only, ignoring IPv6 addresses.
diff --git a/builtin/fetch.c b/builtin/fetch.c
index b4c6d921d0..bf8000adaf 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -78,6 +78,7 @@ static struct list_objects_filter_options filter_options;
 static struct string_list server_options = STRING_LIST_INIT_DUP;
 static struct string_list negotiation_tip = STRING_LIST_INIT_NODUP;
 static int fetch_write_commit_graph = -1;
+static int update_remote_refs = 1;
 
 static int git_fetch_config(const char *k, const char *v, void *cb)
 {
@@ -201,6 +202,8 @@ static struct option builtin_fetch_options[] = {
 		 N_("check for forced-updates on all updated branches")),
 	OPT_BOOL(0, "write-commit-graph", &fetch_write_commit_graph,
 		 N_("write the commit-graph after fetching")),
+	OPT_BOOL(0, "update-remote-refs", &update_remote_refs,
+		 N_("update the refs/remotes/ refspace")),
 	OPT_END()
 };
 
@@ -746,6 +749,9 @@ static int update_local_ref(struct ref *ref,
 	const char *pretty_ref = prettify_refname(ref->name);
 	int fast_forward = 0;
 
+	if (!update_remote_refs && starts_with(ref->name, "refs/remotes/"))
+		return 0;
+
 	type = oid_object_info(the_repository, &ref->new_oid, NULL);
 	if (type < 0)
 		die(_("object %s not found"), oid_to_hex(&ref->new_oid));
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 4b60282689..35b50b2047 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -174,6 +174,30 @@ test_expect_success 'fetch --prune --tags with refspec prunes based on refspec'
 	git rev-parse sometag
 '
 
+test_expect_success 'fetch --no-update-remote-refs keeps existing refs' '
+	cd "$TRASH_DIRECTORY" &&
+	git clone "$D" remote-refs &&
+	git -C remote-refs rev-parse remotes/origin/master >old &&
+	git -C remote-refs update-ref refs/remotes/origin/master master~1 &&
+	git -C remote-refs rev-parse remotes/origin/master >new &&
+	git -C remote-refs fetch --no-update-remote-refs origin &&
+	git -C remote-refs rev-parse remotes/origin/master >actual &&
+	test_cmp new actual &&
+	git -C remote-refs fetch origin &&
+	git -C remote-refs rev-parse remotes/origin/master >actual &&
+	test_cmp old actual
+'
+
+test_expect_success 'fetch --no-update-remote-refs --prune with refspec' '
+	git -C remote-refs update-ref refs/remotes/origin/foo/otherbranch master &&
+	git -C remote-refs update-ref refs/hidden/foo/otherbranch master &&
+	git -C remote-refs fetch --prune --no-update-remote-refs origin +refs/heads/*:refs/hidden/* &&
+	git -C remote-refs rev-parse remotes/origin/foo/otherbranch &&
+	test_must_fail git -C remote-refs rev-parse refs/hidden/foo/otherbranch &&
+	git -C remote-refs fetch --prune --no-update-remote-refs origin &&
+	test_must_fail git -C remote-refs rev-parse remotes/origin/foo/otherbranch
+'
+
 test_expect_success 'fetch tags when there is no tags' '
 
     cd "$D" &&

base-commit: d0654dc308b0ba76dd8ed7bbb33c8d8f7aacd783
-- 
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