Re: property co-existence problems.

kfogel@collab.net wrote:
> There are several different problems going on here, I think:
>
> 1) We determine textiness from mime-type.
> 2) We determine mergeability from textiness.

Determining mergeability from the MIME type (directly or indirectly) is
basically the right thing to do: that is exactly the sort of thing a MIME type
is for.

> 3) We determine eol-mungability from textiness.

One can see the attempted logic in that, but as we can't universally define
"textiness" this doesn't universally work.

> The proposal for the "svn:text" property solves problem number (1).
> Now we would have a way to determine textiness.
>
> But is "textiness" the right determinant for how to merge something?

Only in the limited world where there is just one merge algorithm - and we
already claim to support pluggable merges. So: no.

> And is an object's preferred merging behavior related to its proper
> diff behavior?

Related, yes, but not very closely. In practice we need to be able to specify
them independently.

> And are either of these two things related to whether
> svn:eol-style should be honored?

In my opinion: no. I think we need to move carefully but positively towards
obeying the EOL style regardless of MIME type and diffing and merging.

I see the problems as:

     A) We determine mergeability and diffability from MIME type regardless of
which merge or diff program is to be used. Thus pluggable diff/merge aren't
invoked when they should be.

     B) We ignore svn:eol-style for certain MIME types, though there is no need
to do so.

     C) Our interpretation of svn:mime-type is not extensible.

Proposal: we read and use a configurable mapping from MIME types to diff and
merge methods. This would initially be in the per-user configuration file
(though, as often before, this may bring up the desire for some way of
distributing such configuration from the repository). An example of a typical
configuration (syntax yet to be determined):

[[[
# For each list of MIME type patterns, a diff command and a merge command
# are specified. If a command is empty, no diff/merge is performed.
# For the built-in diff/merge, write svn_internal_diff/_merge.
# (n.b. We currently say "diff3" for "merge".)

# Plain text files. (There would be a built-in default configuration
# something like this, matching the old, built-in behaviour.)
For MIME types: text/*, blah/xml
   diff-cmd=/usr/bin/diff
   merge-cmd=svn_internal_merge

# Default (non-)actions. (This section need not be specified)
For MIME types: *
   diff-cmd=
   merge-cmd=
]]]

I think this addresses A and C. B would be addressed by phasing in
unconditional processing of svn:eol-style.

- Julian

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Received on Tue Oct 26 00:38:52 2004