Questions about git-rev-parse

["Theodore Ts'o" <tytso@mit.edu>]

So I was looking at git-rev-parse trying to understand the man page, as
I was trying to understand how various commands can accept lists (or
ranges) of commits, and the man page raised a number of questions.
First of all, the DESCRIPTION section doesn't quite parse as English:

       Many  git  porcelainish commands take mixture of flags (i.e. parameters
       that  begin  with  a  dash  -)  and  parameters  meant  for  underlying
       git-rev-list  command  they use internally and flags and parameters for
       other commands they use as the downstream of git-rev-list. 

But, as best as I can gather that it's a helper function meant to do
some basic options parsing for those git porcelain commands that expect
to take a set of revision ID's.

This raises some additional questions, though.  If the goal of this
command is to parse out those options and arguments which are meant for
git-rev-list, why does it translate tag names to SHA id's:

% git-rev-parse v1.5.0..v1.5.0.1
dedb0faa48787839dbc47b7ca2507bda5924ec2c
^6db027ffe03210324939b3dd655c4223ca023b45

After all, git-rev-list can just as easily accept:

	git-rev-list dedb0faa48787839dbc47b7ca2507bda5924ec2c \
		^6db027ffe03210324939b3dd655c4223ca023b45

as

	git-rev-list v1.5.0..v1.5.0.1

Also, there are a number of options in git-rev-list which make it appear
to be a general dumping ground of miscellaneous options.  

For example, it's not clear what 

	git-rev-parse --show-prefix

and

	git-rev-parse --show-cdup

have to do with the description of git-rev-parse as described in the
DESCRIPTION section.  It seems to be completely miscellaneous extras
that were tacked on.  Or am I missing something?

Finally, it seems rather unfortunate that certain bits of functionality
such as --since and --until were hidden into git-rev-parse, since it
means that some commands which are implemented as shell scripts are more
likely to use git-rev-parse, and will therefore support --since and
--until, where as other commands which are implemented as built-in's,
such as git-log, don't accept --since and --until.

So I'm wondering if I'm missing something about historical context,
since from looking at git-rev-parse, it looks like not a lot of thought
went into its design, and it has a bunch of stuff that grew via
accretion; or maybe I'm not understanding why it was designed the way it
was?

Regards,

						- Ted