Thanks everyone! Here's an updated v2 following Peff's suggestions on
how to write the advice part.

Making submodule.alternateErrorStrategy default to 'info' is reasonable,
but I don't know how much it matters in practice - here,
submodule.alternateLocation was set because of "clone
--recurse-submodules --reference", which also sets
submodule.alternateErrorStrategy. I don't know when
submodule.alternateLocation would ever be set alone, but then again, I'm
not very familiar with this part. I've left that alone for now.

Jonathan Tan (2):
  Doc: explain submodule.alternateErrorStrategy
  submodule--helper: advise on fatal alternate error

 Documentation/config/advice.txt    |  3 +++
 Documentation/config/submodule.txt |  4 +++-
 advice.c                           |  2 ++
 advice.h                           |  1 +
 builtin/submodule--helper.c        | 10 ++++++++++
 5 files changed, 19 insertions(+), 1 deletion(-)

-- 
2.24.0.393.g34dc348eaf-goog