Implement spin plugin list

[itowlson]

Fixes #937.

I'd really value comments on the structure of this - even more than usual, because I kind of felt that a bunch of this must already be in there but I wasn't sure where to find it. So please do flag up if logic is in the wrong places or are already done somewhere else.

The output with this code is loosely based on how apt looks on my WSL Ubuntu system, and looks like this:

$ spin plugin list
arm-only 0.1.0 [incompatible]
example 0.1.0
example 0.2.0
js2wasm 0.1.0 [installed]
not-spin-ver 9.1.0 [incompatible]
not-spin-ver 10.2.0 [requires other Spin version]
windows-only 0.1.0 [incompatible]

$ spin plugin list --installed
js2wasm 0.1.0 [installed]

It could alternatively be printed in tabular format, and/or with colour highlighting, and/or with emoticons - the PluginDescriptor hopefully decouples the printing logic enough that this would be easy to fiddle with.

At the moment, this glides silently over plugins that are in such a corrupted state that we can't even load them. This is preferable to being unable to list plugins at all just because one got mangled while I was trying to exit vi. It would be nice to print a warning if any were skipped, but it's a bit fiddly to do without losing the friendly ? syntax - I can have a noodle on it if people think it's worth it though.

Signed-off-by: itowlson ivan.towlson@fermyon.com

[kate-goldenring]

Just some minor comments but this is great! I love how you implemented this to look similar with apt and make it clear the "status" of a plugin (compatible with host, compatible with Spin, installed, etc) and how easy it will be to add the different print styles in future if desired.

I think glossing over invalidly formatted plugins is okay. They shouldn't be able to be merged into the plugins repo as they would fail the json schema workflow. Something could get through but as you mention, it is likely not worth the syntactical disruption.

[kate-goldenring]

Looks like a Rust fmt fix and this is good to go

[itowlson]

Huh. cargo fmt isn't requiring any changes for me...

[itowlson]

OH IT'S A NEW CLIPPY THANKS FOR THE BREAKING CHANGE ON A MINOR VERSION RUST