[PATCH v3 2/3] fetch: add --prefetch option

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

From: Derrick Stolee <dstolee@microsoft.com>

The --prefetch option will be used by the 'prefetch' maintenance task
instead of sending refspecs explicitly across the command-line. The
intention is to modify the refspec to place all results in
refs/prefetch/ instead of anywhere else.

Create helper method filter_prefetch_refspec() to modify a given refspec
to fit the rules expected of the prefetch task:

 * Negative refspecs are preserved.
 * Refspecs without a destination are removed.
 * Refspecs whose source starts with "refs/tags/" are removed.
 * Other refspecs are placed within "refs/prefetch/".

Finally, we add the 'force' option to ensure that prefetch refs are
replaced as necessary.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/fetch-options.txt   |  5 +++
 builtin/fetch.c                   | 56 +++++++++++++++++++++++++++++++
 t/t5582-fetch-negative-refspec.sh | 30 +++++++++++++++++
 3 files changed, 91 insertions(+)

diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index 07783deee309..9e7b4e189ce0 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -110,6 +110,11 @@ ifndef::git-pull[]
 	setting `fetch.writeCommitGraph`.
 endif::git-pull[]
 
+--prefetch::
+	Modify the configured refspec to place all refs into the
+	`refs/prefetch/` namespace. See the `prefetch` task in
+	linkgit:git-maintenance[1].
+
 -p::
 --prune::
 	Before fetching, remove any remote-tracking references that no
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 0b90de87c7a2..30856b442b79 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -48,6 +48,7 @@ enum {
 static int fetch_prune_config = -1; /* unspecified */
 static int fetch_show_forced_updates = 1;
 static uint64_t forced_updates_ms = 0;
+static int prefetch = 0;
 static int prune = -1; /* unspecified */
 #define PRUNE_BY_DEFAULT 0 /* do we prune by default? */
 
@@ -158,6 +159,8 @@ static struct option builtin_fetch_options[] = {
 		    N_("do not fetch all tags (--no-tags)"), TAGS_UNSET),
 	OPT_INTEGER('j', "jobs", &max_jobs,
 		    N_("number of submodules fetched in parallel")),
+	OPT_BOOL(0, "prefetch", &prefetch,
+		 N_("modify the refspec to place all refs within refs/prefetch/")),
 	OPT_BOOL('p', "prune", &prune,
 		 N_("prune remote-tracking branches no longer on remote")),
 	OPT_BOOL('P', "prune-tags", &prune_tags,
@@ -436,6 +439,55 @@ static void find_non_local_tags(const struct ref *refs,
 	oidset_clear(&fetch_oids);
 }
 
+static void filter_prefetch_refspec(struct refspec *rs)
+{
+	int i;
+
+	if (!prefetch)
+		return;
+
+	for (i = 0; i < rs->nr; i++) {
+		struct strbuf new_dst = STRBUF_INIT;
+		char *old_dst;
+		const char *sub = NULL;
+
+		if (rs->items[i].negative)
+			continue;
+		if (!rs->items[i].dst ||
+		    (rs->items[i].src &&
+		     !strncmp(rs->items[i].src, "refs/tags/", 10))) {
+			int j;
+
+			free(rs->items[i].src);
+			free(rs->items[i].dst);
+
+			for (j = i + 1; j < rs->nr; j++) {
+				rs->items[j - 1] = rs->items[j];
+				rs->raw[j - 1] = rs->raw[j];
+			}
+			rs->nr--;
+			continue;
+		}
+
+		old_dst = rs->items[i].dst;
+		strbuf_addstr(&new_dst, "refs/prefetch/");
+
+		/*
+		 * If old_dst starts with "refs/", then place
+		 * sub after that prefix. Otherwise, start at
+		 * the beginning of the string.
+		 */
+		if (!skip_prefix(old_dst, "refs/", &sub))
+			sub = old_dst;
+		strbuf_addstr(&new_dst, sub);
+
+		rs->items[i].dst = strbuf_detach(&new_dst, NULL);
+		rs->items[i].force = 1;
+
+		free(old_dst);
+	}
+}
+
 static struct ref *get_ref_map(struct remote *remote,
 			       const struct ref *remote_refs,
 			       struct refspec *rs,
@@ -452,6 +504,10 @@ static struct ref *get_ref_map(struct remote *remote,
 	struct hashmap existing_refs;
 	int existing_refs_populated = 0;
 
+	filter_prefetch_refspec(rs);
+	if (remote)
+		filter_prefetch_refspec(&remote->fetch);
+
 	if (rs->nr) {
 		struct refspec *fetch_refspec;
 
diff --git a/t/t5582-fetch-negative-refspec.sh b/t/t5582-fetch-negative-refspec.sh
index f34509727702..030e6f978c4e 100755
--- a/t/t5582-fetch-negative-refspec.sh
+++ b/t/t5582-fetch-negative-refspec.sh
@@ -240,4 +240,34 @@ test_expect_success "push with matching +: and negative refspec" '
 	git -C two push -v one
 '
 
+test_expect_success '--prefetch correctly modifies refspecs' '
+	git -C one config --unset-all remote.origin.fetch &&
+	git -C one config --add remote.origin.fetch "refs/tags/*:refs/tags/*" &&
+	git -C one config --add remote.origin.fetch ^refs/heads/bogus/ignore &&
+	git -C one config --add remote.origin.fetch "refs/heads/bogus/*:bogus/*" &&
+
+	git tag -a -m never never-fetch-tag HEAD &&
+
+	git branch bogus/fetched HEAD~1 &&
+	git branch bogus/ignore HEAD &&
+
+	git -C one fetch --prefetch --no-tags &&
+	test_must_fail git -C one rev-parse never-fetch-tag &&
+	git -C one rev-parse refs/prefetch/bogus/fetched &&
+	test_must_fail git -C one rev-parse refs/prefetch/bogus/ignore &&
+
+	# correctly handle when refspec set becomes empty
+	# after removing the refs/tags/* refspec.
+	git -C one config --unset-all remote.origin.fetch &&
+	git -C one config --add remote.origin.fetch "refs/tags/*:refs/tags/*" &&
+
+	git -C one fetch --prefetch --no-tags &&
+	test_must_fail git -C one rev-parse never-fetch-tag &&
+
+	# The refspec for refs that are not fully qualified
+	# are filtered multiple times.
+	git -C one rev-parse refs/prefetch/bogus/fetched &&
+	test_must_fail git -C one rev-parse refs/prefetch/bogus/ignore
+'
+
 test_done
-- 
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