allow specifying db uri in config file

[CobaltCause]

Fixes #2945.

Currently doesn't work because

error[E0277]: the trait bound `either::Either<std::string::String, DatabaseConfig>: doku::Document` is not satisfied
 --> crates/utils/src/settings/structs.rs:7:62
  |
7 | #[derive(Debug, Deserialize, Serialize, Clone, SmartDefault, Document)]
  |                                                              ^^^^^^^^ the trait `doku::Document` is not implemented for `either::Either<std::string::String, DatabaseConfig>`

Options for fixing this:

1. Defining our own Either type and implementing Document for it
2. Submitting a patch upstream to support the either crate

I like the second option more.

[Nutomic]

I dont think it makes sense to pull in a dependency for something that can be implemented with a simple enum (unless Im missing something).

[CobaltCause]

Yeah, I was actually thinking about this a while after opening this PR while doing other stuff, and you're totally right. Something in my brain is just hard wired to go "Oh you want X xor Y? Better pull in either!" for whatever reason. This would also mean I don't have to add stuff to doku, which I tried, and I couldn't really figure out the right way to add either support to it 😅

[CobaltCause]

Is there some documentation somewhere that I need to update? Edit: I think CI found it ❤️

[CobaltCause]

Also, seems like a breaking release is about to happen. I don't know how y'all feel about doing breaking configuration changes, but this might be a good time to do one and just get rid of the Parts configuration method entirely.

[dessalines]

I'm getting this error with current lemmy.hjson setups:

thread 'main' panicked at 'Failed to load settings file, see documentation (https://join-lemmy.org/docs/en/administration/configuration.html): 
LemmyError { message: None, inner: "data did not match any variant of untagged enum DatabaseConnection" near 15:3, context: SpanTrace [] }', 
crates/utils/src/settings/mod.rs:20:20

[Nutomic]

Im not convinced that this should be removed, it seems much easier for users who are unfamiliar with postgres. Why not keep both options?

[CobaltCause]

I'd argue it would be best to remove Parts because:

• It's less flexible than Uri
• Lemmy already has an environment variable for configuring the database via a connection URI, so there is already precedent for supporting connection URIs in Lemmy
• People should know how to write/use connection URIs anyway since they're going to need to know how to administrate PostgreSQL anyway, and most tools for this (e.g. psql) accept URIs
• It will reduce the amount of "why can't I use the unix domain socket with the Parts configuration?" questions you'll get, since that's how I initially ran into this
• I'd guess that most smaller instances will have Lemmy and PostgreSQL running on the same machine, and Uri will allow them to use peer authentication which will save them the hassle of managing additional secrets

I'll change the doc comment to link to PostgreSQL's documentation for writing connection URIs though, which should help with the familiarity problem.

[CobaltCause]

Can't use deny_unknown_fields in combination with flatten: https://serde.rs/container-attrs.html#deny_unknown_fields

[CobaltCause]

@dessalines good catch; this change fixes that. Basically, the enum variant needs #[serde(default)] but you can't do that so I had to break it out into a struct and apply it, and now it works. Previously, serde wasn't substituting in default values on missing keys.

[dessalines]

Mmmk I tested this on an existing install, and it worked well. Once those CI issues get solved, I'm good to merge this. Thanks!

[CobaltCause]

(That force-push was just to reword the commit to include a link to the issue I opened on doku)

[CobaltCause]

Maybe we should wait to merge this until we have the results of anixe/doku#33 (comment)

[CobaltCause]

@Nutomic: this PR didn't include the new doku release and so the generated documentation is still malformed. Don't forget to update doku and regenerate it to fix that.

Edit: I see this hasn't been done yet so I opened a PR. Presumably you've got bigger fish to fry.