Re: git-svn show-externals and svn version

From: Andreas Stricker <astricker@futurelab.ch>
Date: Mar 7, 2012, 09:39 UTC
Message-ID: <4F572CDC.6060303@futurelab.ch>
In-Reply-To: <5B8386D7-3C01-4A58-A7AB-9AA43BB45572@nikolaus-demmel.de>

Nikolaus Demmel <nikolaus@nikolaus-demmel.de> 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...

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> 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.

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> 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

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> 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?

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> 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