fetch: allow explicit --refmap to override configuration

Since the introduction of opportunisitic updates of remote-tracking
branches, started at around f269048 (fetch: opportunistically
update tracking refs, 2013-05-11) with a few updates in v1.8.4 era,
the remote.*.fetch configuration always kicks in even when a refspec
to specify what to fetch is given on the command line, and there is
no way to disable or override it per-invocation.

Teach the command to pay attention to the --refmap=<lhs>:<rhs>
command-line options that can be used to override the use of
configured remote.*.fetch as the refmap.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

Documentation/fetch-options.txt

@@ -72,6 +72,14 @@ endif::git-pull[]
 	setting. See linkgit:git-config[1].
 
 ifndef::git-pull[]
+--refmap=<refspec>::
+	When fetching refs listed on the command line, use the
+	specified refspec (can be given more than once) to map the
+	refs to remote-tracking branches, instead of the values of
+	`remote.*.fetch` configuration variables for the remote
+	repository.  See section on "Configured Remote-tracking
+	Branches" for details.
+
 -t::
 --tags::
 	Fetch all tags from the remote (i.e., fetch remote tags

Documentation/git-fetch.txt

@@ -95,6 +95,10 @@ This configuration is used in two ways:
   only used to decide _where_ the refs that are fetched are stored
   by acting as a mapping.
 
+The latter use of the `remote.<repository>.fetch` values can be
+overridden by giving the `--refmap=<refspec>` parameter(s) on the
+command line.
+
 
 EXAMPLES
 --------

builtin/fetch.c

@@ -45,6 +45,8 @@ static struct transport *gsecondary;
 static const char *submodule_prefix = "";
 static const char *recurse_submodules_default;
 static int shown_url = 0;
+static int refmap_alloc, refmap_nr;
+static const char **refmap_array;
 
 static int option_parse_recurse_submodules(const struct option *opt,
 				   const char *arg, int unset)
@@ -69,6 +71,19 @@ static int git_fetch_config(const char *k, const char *v, void *cb)
 	return 0;
 }
 
+static int parse_refmap_arg(const struct option *opt, const char *arg, int unset)
+{
+	ALLOC_GROW(refmap_array, refmap_nr + 1, refmap_alloc);
+
+	/*
+	 * "git fetch --refmap='' origin foo"
+	 * can be used to tell the command not to store anywhere
+	 */
+	if (*arg)
+		refmap_array[refmap_nr++] = arg;
+	return 0;
+}
+
 static struct option builtin_fetch_options[] = {
 	OPT__VERBOSITY(&verbosity),
 	OPT_BOOL(0, "all", &all,
@@ -107,6 +122,8 @@ static struct option builtin_fetch_options[] = {
 		   N_("default mode for recursion"), PARSE_OPT_HIDDEN },
 	OPT_BOOL(0, "update-shallow", &update_shallow,
 		 N_("accept refs that update .git/shallow")),
+	{ OPTION_CALLBACK, 0, "refmap", NULL, N_("refmap"),
+	  N_("specify fetch refmap"), PARSE_OPT_NONEG, parse_refmap_arg },
 	OPT_END()
 };
 
@@ -278,6 +295,9 @@ static struct ref *get_ref_map(struct transport *transport,
 	const struct ref *remote_refs = transport_get_remote_refs(transport);
 
 	if (refspec_count) {
+		struct refspec *fetch_refspec;
+		int fetch_refspec_nr;
+
 		for (i = 0; i < refspec_count; i++) {
 			get_fetch_map(remote_refs, &refspecs[i], &tail, 0);
 			if (refspecs[i].dst && refspecs[i].dst[0])
@@ -307,12 +327,21 @@ static struct ref *get_ref_map(struct transport *transport,
 		 * by ref_remove_duplicates() in favor of one of these
 		 * opportunistic entries with FETCH_HEAD_IGNORE.
 		 */
-		for (i = 0; i < transport->remote->fetch_refspec_nr; i++)
-			get_fetch_map(ref_map, &transport->remote->fetch[i],
-				      &oref_tail, 1);
+		if (refmap_array) {
+			fetch_refspec = parse_fetch_refspec(refmap_nr, refmap_array);
+			fetch_refspec_nr = refmap_nr;
+		} else {
+			fetch_refspec = transport->remote->fetch;
+			fetch_refspec_nr = transport->remote->fetch_refspec_nr;
+		}
+
+		for (i = 0; i < fetch_refspec_nr; i++)
+			get_fetch_map(ref_map, &fetch_refspec[i], &oref_tail, 1);
 
 		if (tags == TAGS_SET)
 			get_fetch_map(remote_refs, tag_refspec, &tail, 0);
+	} else if (refmap_array) {
+		die("--refmap option is only meaningful with command-line refspec(s).");
 	} else {
 		/* Use the defaults */
 		struct remote *remote = transport->remote;

t/t5510-fetch.sh

@@ -447,6 +447,43 @@ test_expect_success 'explicit pull should update tracking' '
 	)
 '
 
+test_expect_success 'explicit --refmap is allowed only with command-line refspec' '
+	cd "$D" &&
+	(
+		cd three &&
+		test_must_fail git fetch --refmap="*:refs/remotes/none/*"
+	)
+'
+
+test_expect_success 'explicit --refmap option overrides remote.*.fetch' '
+	cd "$D" &&
+	git branch -f side &&
+	(
+		cd three &&
+		git update-ref refs/remotes/origin/master base-origin-master &&
+		o=$(git rev-parse --verify refs/remotes/origin/master) &&
+		git fetch --refmap="refs/heads/*:refs/remotes/other/*" origin master &&
+		n=$(git rev-parse --verify refs/remotes/origin/master) &&
+		test "$o" = "$n" &&
+		test_must_fail git rev-parse --verify refs/remotes/origin/side &&
+		git rev-parse --verify refs/remotes/other/master
+	)
+'
+
+test_expect_success 'explicitly empty --refmap option disables remote.*.fetch' '
+	cd "$D" &&
+	git branch -f side &&
+	(
+		cd three &&
+		git update-ref refs/remotes/origin/master base-origin-master &&
+		o=$(git rev-parse --verify refs/remotes/origin/master) &&
+		git fetch --refmap="" origin master &&
+		n=$(git rev-parse --verify refs/remotes/origin/master) &&
+		test "$o" = "$n" &&
+		test_must_fail git rev-parse --verify refs/remotes/origin/side
+	)
+'
+
 test_expect_success 'configured fetch updates tracking' '
 
 	cd "$D" &&