fetch: add a --prune-tags option and fetch.pruneTags config

Add a --prune-tags option to git-fetch, along with fetch.pruneTags
config option and a -P shorthand (-p is --prune). This allows for
doing any of:

    git fetch -p -P
    git fetch --prune --prune-tags
    git fetch -p -P origin
    git fetch --prune --prune-tags origin

Or simply:

    git config fetch.prune true &&
    git config fetch.pruneTags true &&
    git fetch

Instead of the much more verbose:

    git fetch --prune origin 'refs/tags/*:refs/tags/*' '+refs/heads/*:refs/remotes/origin/*'

Before this feature it was painful to support the use-case of pulling
from a repo which is having both its branches *and* tags deleted
regularly, and have our local references to reflect upstream.

At work we create deployment tags in the repo for each rollout, and
there's *lots* of those, so they're archived within weeks for
performance reasons.

Without this change it's hard to centrally configure such repos in
/etc/gitconfig (on servers that are only used for working with
them). You need to set fetch.prune=true globally, and then for each
repo:

    git -C {} config --replace-all remote.origin.fetch "refs/tags/*:refs/tags/*" "^\+*refs/tags/\*:refs/tags/\*$"

Now I can simply set fetch.pruneTags=true in /etc/gitconfig as well,
and users running "git pull" will automatically get the pruning
semantics I want.

Even though "git remote" has corresponding "prune" and "update
--prune" subcommands I'm intentionally not adding a corresponding
prune-tags or "update --prune --prune-tags" mode to that command.

It's advertised (as noted in my recent "git remote doc: correct
dangerous lies about what prune does") as only modifying remote
tracking references, whereas any --prune-tags option is always going
to modify what from the user's perspective is a local copy of the tag,
since there's no such thing as a remote tracking tag.

Ideally add_prune_tags_to_fetch_refspec() would be something that
would use ALLOC_GROW() to grow the 'fetch` member of the 'remote'
struct. Instead I'm realloc-ing remote->fetch and adding the
tag_refspec to the end.

The reason is that parse_{fetch,push}_refspec which allocate the
refspec (ultimately remote->fetch) struct are called many places that
don't have access to a 'remote' struct. It would be hard to change all
their callsites to be amenable to carry around the bookkeeping
variables required for dynamic allocation.

All the other callers of the API first incrementally construct the
string version of the refspec in remote->fetch_refspec via
add_fetch_refspec(), before finally calling parse_fetch_refspec() via
some variation of remote_get().

It's less of a pain to deal with the one special case that needs to
modify already constructed refspecs than to chase down and change all
the other callsites. The API I'm adding is intentionally not
generalized because if we add more of these we'd probably want to
re-visit how this is done.

See my "Re: [BUG] git remote prune removes local tags, depending on
fetch config" (87po6ahx87.fsf@evledraar.gmail.com;
https://public-inbox.org/git/87po6ahx87.fsf@evledraar.gmail.com/) for
more background info.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 29 insertions, 3 deletions

diff --git a/builtin/fetch.c b/builtin/fetch.c
index a7705bc150..55a0fc37be 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -38,6 +38,10 @@ static int fetch_prune_config = -1; /* unspecified */
 static int prune = -1; /* unspecified */
 #define PRUNE_BY_DEFAULT 0 /* do we prune by default? */
 
+static int fetch_prune_tags_config = -1; /* unspecified */
+static int prune_tags = -1; /* unspecified */
+#define PRUNE_TAGS_BY_DEFAULT 0 /* do we prune tags by default? */
+
 static int all, append, dry_run, force, keep, multiple, update_head_ok, verbosity, deepen_relative;
 static int progress = -1;
 static int tags = TAGS_DEFAULT, unshallow, update_shallow, deepen;
@@ -64,6 +68,11 @@ static int git_fetch_config(const char *k, const char *v, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(k, "fetch.prunetags")) {
+		fetch_prune_tags_config = git_config_bool(k, v);
+		return 0;
+	}
+
 	if (!strcmp(k, "submodule.recurse")) {
 		int r = git_config_bool(k, v) ?
 			RECURSE_SUBMODULES_ON : RECURSE_SUBMODULES_OFF;
@@ -126,6 +135,8 @@ static struct option builtin_fetch_options[] = {
 		    N_("number of submodules fetched in parallel")),
 	OPT_BOOL('p', "prune", &prune,
 		 N_("prune remote-tracking branches no longer on remote")),
+	OPT_BOOL('P', "prune-tags", &prune_tags,
+		 N_("prune local tags no longer on remote and clobber changed tags")),
 	{ OPTION_CALLBACK, 0, "recurse-submodules", &recurse_submodules, N_("on-demand"),
 		    N_("control recursive fetching of submodules"),
 		    PARSE_OPT_OPTARG, option_fetch_parse_recurse_submodules },
@@ -1212,6 +1223,8 @@ static void add_options_to_argv(struct argv_array *argv)
 		argv_array_push(argv, "--dry-run");
 	if (prune != -1)
 		argv_array_push(argv, prune ? "--prune" : "--no-prune");
+	if (prune_tags != -1)
+		argv_array_push(argv, prune_tags ? "--prune-tags" : "--no-prune-tags");
 	if (update_head_ok)
 		argv_array_push(argv, "--update-head-ok");
 	if (force)
@@ -1265,7 +1278,7 @@ static int fetch_multiple(struct string_list *list)
 	return result;
 }
 
-static int fetch_one(struct remote *remote, int argc, const char **argv)
+static int fetch_one(struct remote *remote, int argc, const char **argv, int prune_tags_ok)
 {
 	static const char **refs = NULL;
 	struct refspec *refspec;
@@ -1288,6 +1301,19 @@ static int fetch_one(struct remote *remote, int argc, const char **argv)
 			prune = PRUNE_BY_DEFAULT;
 	}
 
+	if (prune_tags < 0) {
+		/* no command line request */
+		if (0 <= remote->prune_tags)
+			prune_tags = remote->prune_tags;
+		else if (0 <= fetch_prune_tags_config)
+			prune_tags = fetch_prune_tags_config;
+		else
+			prune_tags = PRUNE_TAGS_BY_DEFAULT;
+	}
+
+	if (prune_tags_ok && prune_tags && remote_is_configured(remote, 0))
+		add_prune_tags_to_fetch_refspec(remote);
+
 	if (argc > 0) {
 		int j = 0;
 		int i;
@@ -1368,7 +1394,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	} else if (argc == 0) {
 		/* No arguments -- use default remote */
 		remote = remote_get(NULL);
-		result = fetch_one(remote, argc, argv);
+		result = fetch_one(remote, argc, argv, 1);
 	} else if (multiple) {
 		/* All arguments are assumed to be remotes or groups */
 		for (i = 0; i < argc; i++)
@@ -1386,7 +1412,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 		} else {
 			/* Zero or one remotes */
 			remote = remote_get(argv[0]);
-			result = fetch_one(remote, argc-1, argv+1);
+			result = fetch_one(remote, argc-1, argv+1, argc == 1);
 		}
 	}