[boost] [git] Effects of git submodule update

Subject: [boost] [git] Effects of git submodule update
From: Beman Dawes (bdawes_at_[hidden])
Date: 2013-12-23 11:47:21

There has been a lot of concern expressed about updating submodules, so
I've updated the applicable section of "Getting Started with Modular Boost
Library Maintenance" to include reassurance that uncommitted changes will
not be overwritten.

See https://svn.boost.org/trac/boost/wiki/StartModMaint

A table has been added describing the effects of git submodule update.
Actual tests were run to determine the effects, using git 1.8.2.msysgit.0.

See
https://svn.boost.org/trac/boost/wiki/StartModMaint#Effectsofgitsubmoduleupdate

In looking at the table, a couple of things stand out:

* git submodule update, like git checkout, will not normally overwrite
uncommitted changes, regardless of whether the working copy is detached or
on a branch. See the table for the specific error message. From the error
message it appears checkout may actually be being called.

* The case of an update applied to a submodule that is on branch master and
at a commit behind the super-project's commit for that submodule just does
a pull without a detach. That is the only case where a" checkout --detach"
isn't done before a pull. I'm unsure whether this is a feature or a bug.

Comments welcome,

--Beman