When fetching with --recurse-submodules, git currently exits with a
non-zero status if any submodule references an OID that is not reachable
from the submodule's remote.  This situation arises naturally when an
upstream branch is still in preparation (e.g. a topic branch in a merge
window): the local branch does not depend on the missing commit, so a
hard failure is unnecessarily disruptive.

Patch 1 fixes a pre-existing NEEDSWORK in submodule.c where a phase-1
fetch failure was recorded immediately, even when a phase-2 OID-based
retry was about to be scheduled.  After this fix the existing fatal
behaviour is preserved but the logic is now structured so that errors
are only recorded when the phase-2 retry actually fails, or when there
is no phase-2 retry to fall back on.

Patch 2 introduces fetch.submoduleErrors (fail|warn) and
--submodule-errors=(fail|warn) to let users opt into non-fatal
behaviour.  The default remains fail for full backwards compatibility.

Changes in v4:
- Forward an explicit --submodule-errors=fail to child fetches as well,
  so the command line overrides fetch.submoduleErrors=warn config in
  the per-remote children of fetch --all/--multiple (noticed by Junio)

Changes in v3:
- Report a phase-1 failure also when the gitlink commits are already
  present locally, instead of silently succeeding
- Route "Could not access submodule" through record_fetch_error() so it
  shows up in the error summary and honors the warn mode
- Forward --submodule-errors to child fetches so it takes effect for
  fetch --all/--multiple and nested submodule recursion
- Add tests for all of the above
- Documentation: don't imply git pull takes --submodule-errors, minor
  wording and placement fixes

Changes in v2:
- Fix option synopsis to use (fail|warn) instead of <fail|warn>
- Add --submodule-errors documentation to Documentation/fetch-options.adoc

Paulius Zaleckas (2):
  submodule: fix premature failure in recursive submodule fetch
  fetch: add fetch.submoduleErrors to make submodule fetch errors
    non-fatal

 Documentation/config/fetch.adoc  |  14 +++
 Documentation/fetch-options.adoc |   8 ++
 builtin/fetch.c                  |  46 ++++++++-
 submodule.c                      |  58 ++++++++---
 submodule.h                      |   7 +-
 t/t5526-fetch-submodules.sh      | 161 +++++++++++++++++++++++++++++++
 6 files changed, 277 insertions(+), 17 deletions(-)

-- 
2.54.0