(rfc) recommend installing a plugin when needed

[Martin Albisetti]

This is actually a late follow up on the IRC conversation about how to
implement this.

As I see it now, the plugin would be divided in the following:

1) Database of available plugins  (in the core?)
2) Code infrastructure to catch "not found" commands and suggest
plugins (in the core)
3) Pluggable abstraction class to download and install plugins
automagically  (in the core)
4) Default plugin to download plugins via checkouts (in the core?)

All of those are necessary for this spec to work, although we could at
a first stage, not include the automatic install infrastructure and
just point users to URLs for the missing plugins.

Now, the problems. The database of plugins will change
semi-frequently. This means we have to provide some way of updating
the local database. This also means we need to ship a DB with bzr
itself, so we can recommend plugins out of the box.
The idea would that there would be a plugin for each method of
installing plugins (debs, rpm, etc), which would also have it's DB,
overriding the default one, and falling back to the default if it
doesn't provide it. This way we can make sure this feature works
fairly well con all platforms.
lifeless mentioned that shipping something like a plugin DB with the
core isn't something we want, and that the DB itself should be
provided by the install plugins, but we shouldn't ship the checkout
plugin by default. This makes sense in some levels, but, on the other
hand, makes the feature completely useless by default and delegates
it's implementation to per-distro packaging or making the user install
a plugin manually, which is what we are trying to avoid in the first
place.

So...  ideas?



Martin