refactor: carve out modules from Main.hs

[monacoremo]

This will reduce the amount of code under conditional CCP compilation, making the code easier to reason about. Carving out modules will also increase unit testing opportunities.

Very WIP.

Edit: I converged to the following structure, to summarize:

• PostgREST.AppState encapsulate all stateful pieces of our application. It's now the only module handling MVars, IORefs etc. This makes it very obvious where state is used in other modules, and makes it easier to refactor the state further.
• PostgREST.Workers contains all current workers. They seem a bit convoluted right now, I tried to clarify the current setup by avoiding passing around connWorker :: IO () etc. More work to be done here to simplify
• PostgREST.Config has a simplified interface - parsing the config is now one function, not puzzling together with the right incantation of multiple functions. Config could be signifcantly refactored now that most (soon: all?) options are optional and we have several config sources (env, config file, db..)
• PostgREST.Config.Database contains a few of the config from db pieces (e.g. the statement, that was a bit out of place with the request/query stuff) - more to come as we refactor Config down the line
• PostgREST.Unix now contains all the unix-specific functionality (from UnixSocket and things in old Main)
• PostgREST.CLI absorbed a bit more of the miscellaneous functionality of the executable. To be further sorted out as we go
• Main now is quite minimal, also regarding external dependencies. Minimal code is under conditional CPP compilation

[monacoremo]

I've added a summary of what changed to the top comment. Suggest that we make a cut here, WDYT @wolfgangwalther ? Thank you for all the review!!

[wolfgangwalther]

I did it! My head is burning a bit, because this a bit harder to review, but I'm still alive.

It's a bit annoying that this is one of the areas where we're really missing a few tests. Need to review a bit more carefully to make sure there is no change in behaviour. Refactoring with 100% coverage is a lot more fun ;)

[wolfgangwalther]

Suggest that we make a cut here, WDYT @wolfgangwalther ?

Yes, please! :D

[monacoremo]

Suggest that we make a cut here, WDYT @wolfgangwalther ?

Yes, please! :D

Thank you so much for your thorough review! Working on the fixes

[monacoremo]

@wolfgangwalther I think that's it! All review comments should be adressed, in individual commits since you reviewed. I didn't touch the history. Shall we merge?

[wolfgangwalther]

@wolfgangwalther I think that's it! All review comments should be adressed, in individual commits since you reviewed. I didn't touch the history. Shall we merge?

Apart from the still wrong comment, everything else looks good.

Could you rebase/squash in a way, that everything is in one refactor: commit, except:

• fix: Improve log message on config reload
• fix: Close unix socket properly
• fix: Panic when running on windows with unix socket enabled

(I hope I got all of those?)

Would be good to separate those in the history, because they change behaviour. And we can then put them in the changelog, too, when they are properly prefixed and separated.

[monacoremo]

Would be good to separate those in the history, because they change behaviour.

Yes, that's good! Everything else was just reshuffling stuff around.

@wolfgangwalther, I hope you will not be too sad, I think this was the last mega-refactor for now. Now that we have split up a lot of stuff, the further changes will be more localized. Thank you so much for bearing with me on this!

[wolfgangwalther]

Something went wrong with rebasing. The always pass is back on the windows branch.

[monacoremo]

Something went wrong with rebasing. The always pass is back on the windows branch.

Yes, weird - must have slipped by as I reordered the commits, would have expected a rebase conflict. Added it back in.