Subject: [PATCH v4] fetch: allow adding a filter after initial clone.

From: Xin Li <[email-masked]>
Date: Thu, 28 May 2020 17:04:32 -0700

Retroactively adding filter can be useful for existing shallow clones as
they allow users to see earlier change histories without downloading all
git objects in a regular --unshallow fetch.

Without this patch, users can make a clone partial by editing the
repository configuration to convert the remote into a promisor, like:

  git config core.repositoryFormatVersion 1
  git config extensions.partialClone origin
  git fetch --unshallow --filter=blob:none origin

Since the hard part of making this work is already in place and such
edits can be error-prone, teach Git to perform the required configuration
change automatically instead.

Instead of bailing out immediately when no promisor is available, make
the code perform a more precise check for any potential problems
(extensions became special in repository version 1, while it can have
any value in version 0, so upgrade should not happen if the repository
have an unsupported configuration that would render it invalid if we
upgraded).

Signed-off-by: Xin Li <[email-masked]>
Reviewed-by: Jonathan Nieder <[email-masked]>
---
 builtin/fetch.c                  |  3 --
 builtin/sparse-checkout.c        |  2 +
 cache.h                          |  2 +
 list-objects-filter-options.c    |  3 +-
 repository.h                     |  6 +++
 setup.c                          | 77 ++++++++++++++++++++++++++++++--
 t/t0410-partial-clone.sh         | 23 ++++++++++
 t/t1090-sparse-checkout-scope.sh |  1 -
 t/t2404-worktree-config.sh       |  4 +-
 t/t5500-fetch-pack.sh            |  1 -
 t/t5702-protocol-v2.sh           |  1 -
 11 files changed, 111 insertions(+), 12 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index b5788c16bf..3347d578ea 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1790,9 +1790,6 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	if (depth || deepen_since || deepen_not.nr)
 		deepen = 1;
 
-	if (filter_options.choice && !has_promisor_remote())
-		die("--filter can only be used when extensions.partialClone is set");
-
 	if (all) {
 		if (argc == 1)
 			die(_("fetch --all does not take a repository argument"));
diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index 95d0882417..95669815d4 100644
--- a/builtin/sparse-checkout.c
+++ b/builtin/sparse-checkout.c
@@ -249,6 +249,8 @@ static int set_config(enum sparse_checkout_mode mode)
 {
 	const char *config_path;
 
+	if (upgrade_repository_format(1) < 0)
+		die(_("unable to upgrade repository format to enable worktreeConfig"));
 	if (git_config_set_gently("extensions.worktreeConfig", "true")) {
 		error(_("failed to set extensions.worktreeConfig setting"));
 		return 1;
diff --git a/cache.h b/cache.h
index 0f0485ecfe..66dcd2f219 100644
--- a/cache.h
+++ b/cache.h
@@ -1042,6 +1042,7 @@ struct repository_format {
 	int worktree_config;
 	int is_bare;
 	int hash_algo;
+	int has_extensions;
 	char *work_tree;
 	struct string_list unknown_extensions;
 };
@@ -1056,6 +1057,7 @@ struct repository_format {
 	.version = -1, \
 	.is_bare = -1, \
 	.hash_algo = GIT_HASH_SHA1, \
+	.has_extensions = 0, \
 	.unknown_extensions = STRING_LIST_INIT_DUP, \
 }
 
diff --git a/list-objects-filter-options.c b/list-objects-filter-options.c
index 256bcfbdfe..3553ad7b0a 100644
--- a/list-objects-filter-options.c
+++ b/list-objects-filter-options.c
@@ -326,7 +326,8 @@ void partial_clone_register(
 
 	/* Check if it is already registered */
 	if (!promisor_remote_find(remote)) {
-		git_config_set("core.repositoryformatversion", "1");
+		if (upgrade_repository_format(1) < 0)
+			die(_("unable to upgrade repository format to support partial clone"));
 
 		/* Add promisor config for the remote */
 		cfg_name = xstrfmt("remote.%s.promisor", remote);
diff --git a/repository.h b/repository.h
index 6534fbb7b3..40cc12c7cf 100644
--- a/repository.h
+++ b/repository.h
@@ -196,4 +196,10 @@ void repo_update_index_if_able(struct repository *, struct lock_file *);
 
 void prepare_repo_settings(struct repository *r);
 
+/*
+ * Return 1 if upgrade repository format to target_version succeeded,
+ * 0 if no upgrade is necessary; returns -1 when upgrade is not possible.
+ */
+int upgrade_repository_format(int target_version);
+
 #endif /* REPOSITORY_H */
diff --git a/setup.c b/setup.c
index 65fe5ecefb..0759e9f8f9 100644
--- a/setup.c
+++ b/setup.c
@@ -13,6 +13,9 @@ static int work_tree_config_is_bogus;
 static struct startup_info the_startup_info;
 struct startup_info *startup_info = &the_startup_info;
 
+static int verify_repository_format_eligibility(const struct repository_format *,
+    struct strbuf *, int);
+
 /*
  * The input parameter must contain an absolute path, and it must already be
  * normalized.
@@ -455,6 +458,7 @@ static int check_repo_format(const char *var, const char *value, void *vdata)
 	if (strcmp(var, "core.repositoryformatversion") == 0)
 		data->version = git_config_int(var, value);
 	else if (skip_prefix(var, "extensions.", &ext)) {
+		data->has_extensions = 1;
 		/*
 		 * record any known extensions here; otherwise,
 		 * we fall through to recording it as unknown, and
@@ -506,9 +510,15 @@ static int check_repository_format_gently(const char *gitdir, struct repository_
 		die("%s", err.buf);
 	}
 
-	repository_format_precious_objects = candidate->precious_objects;
-	set_repository_format_partial_clone(candidate->partial_clone);
-	repository_format_worktree_config = candidate->worktree_config;
+	if (candidate->version >= 1) {
+		repository_format_precious_objects = candidate->precious_objects;
+		set_repository_format_partial_clone(candidate->partial_clone);
+		repository_format_worktree_config = candidate->worktree_config;
+	} else {
+		repository_format_precious_objects = 0;
+		set_repository_format_partial_clone(NULL);
+		repository_format_worktree_config = 0;
+	}
 	string_list_clear(&candidate->unknown_extensions, 0);
 
 	if (repository_format_worktree_config) {
@@ -538,6 +548,34 @@ static int check_repository_format_gently(const char *gitdir, struct repository_
 	return 0;
 }
 
+int upgrade_repository_format(int target_version)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct strbuf err = STRBUF_INIT;
+	struct strbuf repo_version = STRBUF_INIT;
+	struct repository_format repo_fmt = REPOSITORY_FORMAT_INIT;
+
+	strbuf_git_common_path(&sb, the_repository, "config");
+	read_repository_format(&repo_fmt, sb.buf);
+	strbuf_release(&sb);
+
+	if (repo_fmt.version >= target_version)
+		return 0;
+
+	if (verify_repository_format_eligibility(&repo_fmt, &err,
+	    target_version) < 0) {
+		warning("unable to upgrade repository format from %d to %d: %s",
+		    repo_fmt.version, target_version, err.buf);
+		strbuf_release(&err);
+		return -1;
+	}
+
+	strbuf_addf(&repo_version, "%d", target_version);
+	git_config_set("core.repositoryformatversion", repo_version.buf);
+	strbuf_release(&repo_version);
+	return 1;
+}
+
 static void init_repository_format(struct repository_format *format)
 {
 	const struct repository_format fresh = REPOSITORY_FORMAT_INIT;
@@ -562,7 +600,7 @@ void clear_repository_format(struct repository_format *format)
 	init_repository_format(format);
 }
 
-int verify_repository_format(const struct repository_format *format,
+static int verify_repository_format_version(const struct repository_format *format,
 			     struct strbuf *err)
 {
 	if (GIT_REPO_VERSION_READ < format->version) {
@@ -571,6 +609,18 @@ int verify_repository_format(const struct repository_format *format,
 		return -1;
 	}
 
+	return 0;
+}
+
+int verify_repository_format(const struct repository_format *format,
+			     struct strbuf *err)
+{
+	int result;
+
+	result = verify_repository_format_version(format, err);
+	if (result != 0)
+		return (result);
+
 	if (format->version >= 1 && format->unknown_extensions.nr) {
 		int i;
 
@@ -585,6 +635,25 @@ int verify_repository_format(const struct repository_format *format,
 	return 0;
 }
 
+static int verify_repository_format_eligibility(const struct repository_format
+    *format, struct strbuf *err, int target_version)
+{
+	int result;
+
+	result = verify_repository_format_version(format, err);
+	if (result != 0)
+		return (result);
+
+	if (format->version <= 0 && format->has_extensions &&
+	    target_version >= 1) {
+		strbuf_addf(err, _("extensions found for repository version %d"),
+			      format->version);
+		return -1;
+	}
+
+	return 0;
+}
+
 void read_gitfile_error_die(int error_code, const char *path, const char *dir)
 {
 	switch (error_code) {
diff --git a/t/t0410-partial-clone.sh b/t/t0410-partial-clone.sh
index a3988bd4b8..463dc3a8be 100755
--- a/t/t0410-partial-clone.sh
+++ b/t/t0410-partial-clone.sh
@@ -30,6 +30,29 @@ test_expect_success 'extensions.partialclone without filter' '
 	git -C client fetch origin
 '
 
+test_expect_success 'convert shallow clone to partial clone' '
+	rm -fr server client &&
+	test_create_repo server &&
+	test_commit -C server my_commit 1 &&
+	test_commit -C server my_commit2 1 &&
+	git clone --depth=1 "file://$(pwd)/server" client &&
+	git -C client fetch --unshallow --filter="blob:none" &&
+	test_cmp_config -C client true remote.origin.promisor &&
+	test_cmp_config -C client blob:none remote.origin.partialclonefilter &&
+	test_cmp_config -C client 1 core.repositoryformatversion
+'
+
+test_expect_success 'convert shallow clone to partial clone must fail with any extension' '
+	rm -fr server client &&
+	test_create_repo server &&
+	test_commit -C server my_commit 1 &&
+	test_commit -C server my_commit2 1 &&
+	git clone --depth=1 "file://$(pwd)/server" client &&
+	test_cmp_config -C client 0 core.repositoryformatversion &&
+	git -C client config extensions.partialclone origin &&
+	test_must_fail git -C client fetch --unshallow --filter="blob:none"
+'
+
 test_expect_success 'missing reflog object, but promised by a commit, passes fsck' '
 	rm -rf repo &&
 	test_create_repo repo &&
diff --git a/t/t1090-sparse-checkout-scope.sh b/t/t1090-sparse-checkout-scope.sh
index 40cc004326..f35a73dd20 100755
--- a/t/t1090-sparse-checkout-scope.sh
+++ b/t/t1090-sparse-checkout-scope.sh
@@ -63,7 +63,6 @@ test_expect_success 'in partial clone, sparse checkout only fetches needed blobs
 	git -C server commit -m message &&
 
 	test_config -C client core.sparsecheckout 1 &&
-	test_config -C client extensions.partialclone origin &&
 	echo "!/*" >client/.git/info/sparse-checkout &&
 	echo "/a" >>client/.git/info/sparse-checkout &&
 	git -C client fetch --filter=blob:none origin &&
diff --git a/t/t2404-worktree-config.sh b/t/t2404-worktree-config.sh
index 286121d8de..9536d10919 100755
--- a/t/t2404-worktree-config.sh
+++ b/t/t2404-worktree-config.sh
@@ -23,8 +23,10 @@ test_expect_success 'config --worktree without extension' '
 '
 
 test_expect_success 'enable worktreeConfig extension' '
+	git config core.repositoryformatversion 1 &&
 	git config extensions.worktreeConfig true &&
-	test_cmp_config true extensions.worktreeConfig
+	test_cmp_config true extensions.worktreeConfig &&
+	test_cmp_config 1 core.repositoryformatversion
 '
 
 test_expect_success 'config is shared as before' '
diff --git a/t/t5500-fetch-pack.sh b/t/t5500-fetch-pack.sh
index 8c54e34ef1..0f5ff25179 100755
--- a/t/t5500-fetch-pack.sh
+++ b/t/t5500-fetch-pack.sh
@@ -999,7 +999,6 @@ fetch_filter_blob_limit_zero () {
 	test_config -C "$SERVER" uploadpack.allowfilter 1 &&
 
 	git clone "$URL" client &&
-	test_config -C client extensions.partialclone origin &&
 
 	test_commit -C "$SERVER" two &&
 
diff --git a/t/t5702-protocol-v2.sh b/t/t5702-protocol-v2.sh
index 5039e66dc4..8b27fad6cd 100755
--- a/t/t5702-protocol-v2.sh
+++ b/t/t5702-protocol-v2.sh
@@ -348,7 +348,6 @@ test_expect_success 'partial fetch' '
 	rm -rf client "$(pwd)/trace" &&
 	git init client &&
 	SERVER="file://$(pwd)/server" &&
-	test_config -C client extensions.partialClone "$SERVER" &&
 
 	GIT_TRACE_PACKET="$(pwd)/trace" git -C client -c protocol.version=2 \
 		fetch --filter=blob:none "$SERVER" master:refs/heads/other &&
-- 
2.27.0.rc0.183.gde8f92d652-goog