sync: Provide a CLI command to opt in/out of smartsync for a user.v2.70

Add a boolean `sync.smartsync` setting in the per-user repo config
(~/.repoconfig/config):
* true: smart sync by default, as if -s were passed.
* false: never smart sync by default, even if the manifest enables it.
* unset: follow the manifest default, as before.

Add docs/repoconfig.md as the user facing documentation for
~/.repoconfig/config and its settings, and point smart-sync.md and the
`repo sync` help at it.

Bug: 569927750
Test: ./run_tests
Change-Id: Ideb4119fcb5e90f8bb35c493d9e4f8bec7878b77
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/643264
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Insaf Latypov <saferif@google.com>
Tested-by: Insaf Latypov <saferif@google.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/docs/smart-sync.md b/docs/smart-sync.md
index 24f37461b..905a004a0 100644
--- a/docs/smart-sync.md
+++ b/docs/smart-sync.md
@@ -204,6 +204,10 @@ still fails the sync, as before. Options that specify an explicit target or
 manifest source (such as `-t`/`--smart-tag`, `-m`/`--manifest-name` or
 `--superproject-revision`) will also disable the default Smart Sync behavior.
 
+Users can override this manifest default on their workstation with the
+`sync.smartsync` user setting; see
+[Per-user default](#Per_user-default-sync_smartsync) below.
+
 ### --smart-sync / -s
 
 Explicitly enables Smart Sync. Repo will call
@@ -231,6 +235,18 @@ match the settings Android build environments automatically setup.
 Explicitly disables Smart Sync, overriding any `sync-smartsync="true"` setting
 declared in the manifest `<default>` element.
 
+### Per-user default (sync.smartsync)
+
+A user can decide once, for all their checkouts, whether `repo sync` should
+Smart Sync by default by setting the boolean `sync.smartsync` key in their
+[per-user repo config](./repoconfig.md#smartsync).
+
+Command line flags (`-s`, `--no-smart-sync`, `-t`) override the user setting,
+which in turn overrides the manifest's `sync-smartsync` default.  A Smart Sync
+enabled this way is treated as an explicit request, so it is subject to the
+same restrictions as `-s` and fails the sync if no manifest can be obtained
+from the server instead of silently falling back to ToT.
+
 ### --smart-tag=TAG / -t
 
 Repo will call `GetManifest(TAG)`.