Add REPO_SKIP_SELF_UPDATE check in sync

The command _PostRepoFetch will try to self update
during repo sync. That is beneficial but adds
version uncertainty, fail potential and slow downs
in non-interactive scenarios.

Conditionally skip the update if env variable
REPO_SKIP_SELF_UPDATE is defined.

A call to selfupdate works as before, meaning even
with the variable set, it will run the update.

Change-Id: Iab0ef55dc3d3db3cbf1ba1f506c57fbb58a504c3
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/439967
Tested-by: Fredrik de Groot <[email protected]>
Commit-Queue: Josip Sokcevic <[email protected]>
Reviewed-by: Josip Sokcevic <[email protected]>

Author: SpecificityD3luxe

docs/release-process.md

@@ -96,6 +96,9 @@ If that tag is valid, then repo will warn and use that commit instead.
 
 If that tag cannot be verified, it gives up and forces the user to resolve.
 
+If env variable `REPO_SKIP_SELF_UPDATE` is defined, this will
+bypass the self update algorithm.
+
 ### Force an update
 
 The `repo selfupdate` command can be used to force an immediate update.

subcmds/sync.py

@@ -958,7 +958,9 @@ def _FetchMain(
         if not success:
             err_event.set()
 
-        _PostRepoFetch(rp, opt.repo_verify)
+        # Call self update, unless requested not to
+        if os.environ.get("REPO_SKIP_SELF_UPDATE", "0") == "0":
+            _PostRepoFetch(rp, opt.repo_verify)
         if opt.network_only:
             # Bail out now; the rest touches the working tree.
             if err_event.is_set():