Re: git-svn show-externals and svn version

Nikolaus Demmel [off-list ref] wrote:

I feel a bit like I am talking to myself, but I see from the high
traffic on this list that people are busy doing great things :-). I will
write anyway in case someone interested in git-svn listens.

Um I'm always a bit behind in reading this list. A long time ago my
colleague and I implemented a parser for the new svn:externals format
as a proof of concept[1]. I never took the time to finish it.

So I've investigated the matter a bit further. Turns out in the
subversion SWIG language bindings there is an API function that parses
svn:externals definitions for you.

This looks like a sane approach. I ended with a bunch of complicated
parsing code [2].

How could this be used in git-svn show-externals? As layed out before, I
believe that the current output for the svn1.5 syntax is inherently
broken and we should not worry about backwards compatibility for
that.

I second that. The output for the new syntax is just plain broken and
can't be used in a sane way. I know that because I tried...

To maintain backwards compatibility with the output for the old
format and to give a canonical, easy to parse, output for any external
definition, I suggest sticking to the current format, just inserting the
parsed definition at the appropriate place with relative URLs completely
resolved to absolute ones.

This is exactly what my proof of concept does. The output format keeps
the same as for pre subversion 1.5 format.

The pre-svn1.5 syntax for external definitions was:

LOCAL-PATH [-r REVISION] ABSOLUTE-URL

The output for show-externals was thus (note that there is no parsing of
the external definition going on yet):

DIRECTORY-PREFIX/LOCAL-PATH [-rREVISION] ABSOLUTE-URL

Wasn't there also a line commented with a hash "#" before that? Like:
# DIRECTORY-PREFIX

The DIRECTORY-PREFIX was added because show-externals shows the external
definitions for all subdirectories recursively. With this prefix, every
line can be processed on its own. I suggest extending this output to:

DIRECTORY-PREFIX/LOCAL-PATH [-rREVISION] ABSOLUTE-URL[@PEG-REV]

Again, as mentioned above, show-externals should parse the definitions
and resolve relative URLs. Any lines that the svn API call cannot parse
should be completely ommited (e.g. commented lines and empty lines).

A sane approach. What about a warning about lines skipped?

As I understand it show-externals is intended primarily for scripts for
further processing. With this extension existing scripts for the old
syntax should keep working also long as they don't feature
peg-revisions. With relative URLs resolved and a standard ordering old
and new syntax cannot be distinguished in terms of show-externals output
(except when there are peg-revsion are there).

True. So external tools like git-svn-clone-externals will still work
with this. I verified this with my proof of concept.

Regards, Andy

[1] https://github.com/AndyStricker/git
[2]
https://github.com/AndyStricker/git/commit/9981b3b8313fb831247a16a04d5040bd6a8660b1