Add policy on plugin support tiers

[michaelpj]

Following discussion in
#3123.

This aims to make it more obvious what it means when we say we support a version of GHC.

[July541]

Very detailed description!

[July541]

So, we can announce "fully" support of ghc-9.2 and drop the support of 8.6.5 and 8.8.4?

[michaelpj]

So, we can announce "fully" support of ghc-9.2 and drop the support of 8.6.5 and 8.8.4?

I'm not sure. We have said that we won't do this until there is a 9.2 LTS stackage. I don't know if that's something we want to stick to, given that we're not using stack really for building or distribution any more. But we can discuss that separately, maybe at the HLS meeting?

[pepeiborra]

So, we can announce "fully" support of ghc-9.2 and drop the support of 8.6.5 and 8.8.4?

I'm not sure. We have said that we won't do this until there is a 9.2 LTS stackage. I don't know if that's something we want to stick to, given that we're not using stack really for building or distribution any more. But we can discuss that separately, maybe at the HLS meeting?

In case I don't make it to the HLS meeting, I am going to voice my concerns here:

1. We currently support and test GHC 8.6, 8.8, 8.10, 9.0, 9.2 and 9.4
2. It is extremely expensive, in terms of code maintainability, CI, and release cost, to support a GHC version
3. In addition to user experience, we need to consider HLS sustainability as a fully volunteer-driven effort. The current situation with 6 GHC versions is imho leaning too far on the user side.

[pepeiborra]

I can see how this is a good thing, but unless we automatically generate the plugins table, I can also see user issues in the future when the plugins table becomes outdated

[pepeiborra]

Suggested change

	| `hls-retrie-plugin` | 3 | 9.2 |
	| `hls-retrie-plugin` | 3 | 9.2, 9.4 |

[pepeiborra]

This table needs to be autogenerated, right? It should be not hard using the cabal-syntax package

[michaelpj]

It's not currently, and we do have trouble keeping it up-to-date. But it's still useful information, and I volunteer to maintain it until/unless we get to a point that we can auto-generate it.

The tier information also is manual and I don't think could be emitted from the plugin. Conceivably we could record all this information in the plugins and then have a haskell-language-server describe-plugins command that dumped it out, and then do that for all versions...

[michaelpj]

Let's give this a try at least.