scalar: make GVFS Protocol a forced choice

Documentation/scalar.txt

@@ -103,6 +103,26 @@ clone), and `~/.scalarCache` on macOS.
     Retrieve missing objects from the specified remote, which is expected to
     understand the GVFS protocol.
 
+--[no-]gvfs-protocol::
+	When cloning from a `<url>` with either `dev.azure.com` or
+	`visualstudio.com` in the name, `scalar clone` will attempt to use the GVFS
+	Protocol to access Git objects, specifically from a cache server when
+	available, and will fail to clone if there is an error over that protocol.
+
+	To enable the GVFS Protocol regardless of the origin `<url>`, use
+	`--gvfs-protocol`. This will cause `scalar clone` to fail when the origin
+	server fails to provide a valid response to the `gvfs/config` endpoint.
+
+	To disable the GVFS Protocol, use `--no-gvfs-protocol` and `scalar clone`
+	will only use the Git protocol, starting with a partial clone. This can be
+	helpful if your `<url>` points to Azure Repos but the repository does not
+	have GVFS cache servers enabled. It is likely more efficient to use its
+	partial clone functionality through the Git protocol.
+
+	Previous versions of `scalar clone` could fall back to a partial clone over
+	the Git protocol if there is any issue gathering GVFS configuration
+	information from the origin server.
+
 List
 ~~~~
 

scalar.c

@@ -708,6 +708,8 @@ static int cmd_clone(int argc, const char **argv)
 	int src = 1;
 	const char *cache_server_url = NULL, *local_cache_root = NULL;
 	char *default_cache_server_url = NULL, *local_cache_root_abs = NULL;
+	int gvfs_protocol = -1;
+
 	struct option clone_options[] = {
 		OPT_STRING('b', "branch", &branch, N_("<branch>"),
 			   N_("branch to checkout after clone")),
@@ -718,6 +720,8 @@ static int cmd_clone(int argc, const char **argv)
 			    "be checked out")),
 		OPT_BOOL(0, "src", &src,
 			 N_("create repository within 'src' directory")),
+		OPT_BOOL(0, "gvfs-protocol", &gvfs_protocol,
+			 N_("force enable (or disable) the GVFS Protocol")),
 		OPT_STRING(0, "cache-server-url", &cache_server_url,
 			   N_("<url>"),
 			   N_("the url or friendly name of the cache server")),
@@ -737,7 +741,6 @@ static int cmd_clone(int argc, const char **argv)
 	char *enlistment = NULL, *dir = NULL;
 	struct strbuf buf = STRBUF_INIT;
 	int res;
-	int gvfs_protocol;
 
 	argc = parse_options(argc, argv, NULL, clone_options, clone_usage, 0);
 
@@ -845,8 +848,18 @@ static int cmd_clone(int argc, const char **argv)
 		goto cleanup;
 	}
 
-	gvfs_protocol = cache_server_url ||
-			supports_gvfs_protocol(url, &default_cache_server_url);
+	/* Is --[no-]gvfs-protocol unspecified? Infer from url. */
+	if (gvfs_protocol < 0) {
+		if (cache_server_url ||
+		    strstr(url, "dev.azure.com") ||
+		    strstr(url, "visualstudio.com"))
+			gvfs_protocol = 1;
+		else
+			gvfs_protocol = 0;
+	}
+
+	if (gvfs_protocol && !supports_gvfs_protocol(url, &default_cache_server_url))
+		die(_("failed to contact server via GVFS Protocol"));
 
 	if (gvfs_protocol) {
 		if ((res = init_shared_object_cache(url, local_cache_root)))

t/t9210-scalar.sh

@@ -314,7 +314,12 @@ test_expect_success '`scalar clone` with GVFS-enabled server' '
 	# We must set credential.interactive=true to bypass a setting
 	# in "scalar clone" that disables interactive credentials during
 	# an unattended command.
-	scalar -c credential.interactive=true clone --single-branch -- http://$HOST_PORT/ using-gvfs &&
+	GIT_TRACE2_EVENT="$(pwd)/clone-trace-with-gvfs" scalar \
+		-c credential.interactive=true \
+		clone --gvfs-protocol \
+		--single-branch -- http://$HOST_PORT/ using-gvfs &&
+
+	grep "GET/config(main)" <clone-trace-with-gvfs &&
 
 	: verify that the shared cache has been configured &&
 	cache_key="url_$(printf "%s" http://$HOST_PORT/ |
@@ -336,6 +341,24 @@ test_expect_success '`scalar clone` with GVFS-enabled server' '
 	)
 '
 
+test_expect_success '`scalar clone --no-gvfs-protocol` skips gvfs/config' '
+	# the fake cache server requires fake authentication &&
+	git config --global core.askPass true &&
+
+	# We must set credential.interactive=true to bypass a setting
+	# in "scalar clone" that disables interactive credentials during
+	# an unattended command.
+	GIT_TRACE2_EVENT="$(pwd)/clone-trace-no-gvfs" scalar \
+		-c credential.interactive=true \
+		clone --no-gvfs-protocol \
+		--single-branch -- http://$HOST_PORT/ skipping-gvfs &&
+
+	! grep "GET/config(main)" <clone-trace-no-gvfs &&
+	! git config -C skipping-gvfs/src core.gvfs &&
+
+	test_config -C skipping-gvfs/src remote.origin.partialclonefilter blob:none
+'
+
 test_expect_success '`scalar register` parallel to worktree is unsupported' '
 	git init test-repo/src &&
 	mkdir -p test-repo/out &&