scalar: make GVFS Protocol a forced choice

* Add --[no-]gvfs-protocol option.
* Remove fallback.

TODO: expand this message.

Signed-off-by: Derrick Stolee <stolee@gmail.com>

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 &&