[MERGE] per-user file properties

[Robert Collins]

On Tue, 2008-05-06 at 16:39 +1000, Ian Clatworthy wrote:
> This patch provides the plumbing for finding and reading per-user file
> properties. This feature is a building block for EOL support. However,
> it has been explicitly designed to be a generic capability and ought to
> be suitable for configuring other interesting things like custom diff
> and merge algorithms.

I think the other review feedback is good. I'd like to raise a few
things you may not have considered.

EOL support as far as I can tell has two components:

 - tree filtering
 - an EOL filter

And the EOL filter seems to break itself into two parts - a filter for
EOL transforms, and configuration for when that filter should do things.

It seems to me that you can't write tree filtering all that easily as a
plugin, but you could write the EOL filter as a plugin if tree filtering
has landed.

So I'd like to see tree filtering land before this - because I think it
immediately allows a bunch of interesting plugins.

Separately, the 'this is generic' concept tickles all sorts of knee-jerk
avoidance reactions in me. If this is generic, how does it scale. Is it
meant to be machine managed or human managed? Is it compilable or will
it require arbitrarily high queries on huge trees? (How much does it
cost to query every file in a mozilla tree? Once? Twice? Three times?)

When EOL transforms are being used this is going to be a critical part
of performance for large trees; if it really is the best option to write
a generic tool for that - great. However, it seems to me that the
current interface lends itself to being extremely slow and that concerns
me greatly.

If its not clear why it could be extremely slow (even without thousands
of entries in the properties file(s)), then we may have different
understandings of what code is going to do and how often this will get
checked.

Which is another reason this should come in after the core filtering
support - its hard to tell how this will be used with no users or pseudo
code for it.

-Rob

-- 
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