fix(download): correctly handle download = false and implementationn = "rust"

[stefanboca]

Previously, this set of options would result in the lua implementation being used. The new flow should be more linear and easy to follow, with more descriptive and specialized error messages.

[Saghen]

Much cleaner, thank you!

[konradmalik]

hmm, after this PR I get this warning:

[blink.cmp]: Falling back to Lua implementation due to error while downloading pre-built binary:
...es/start/blink-cmp/lua/blink/cmp/fuzzy/download/init.lua:73: No fuzzy matching library found, but downloading from github is disabled.
Either run `cargo build --release` via your package manager, or set `fuzzy.prebuilt_binaries.download = true` in config.
See the docs for more info.
[blink.cmp]: Set `fuzzy.implementation = 'prefer_rust' | 'lua'` to suppress this warning.

But I'm using nix, and the binary is provided by just using blink-cmp plugin from this repo's flake.
In my settings I have download=false because it won't work on Nix. Also I'm using the version from main, not a tag.

Before lua implementation all worked fine, so I suspect that it still does but now I get this warning.
But then it's not clear how I can ensure that it indeed is using Rust implementation and not Lua if I disable this warning 🤔 I'd also like to know in the future if it breaks.
Any ideas on how to solve this?

PS setting implementation = "rust" results in this error:

...es/start/blink-cmp/lua/blink/cmp/fuzzy/download/init.lua:73: No fuzzy matching library found, but downloading from github is disabled.
Either run `cargo build --release` via your package manager, or set `fuzzy.prebuilt_binaries.download = true` in config.
See the docs for more info.

[Saghen]

The latest change should bypass the prebuilt binaries entirely when on nix (no need to set download false). Lmk if that works for you

[debugloop]

Something is still of with the v0.13 line and also current main. I'm getting

.../nixpkgs/blink-cmp/lua/blink/cmp/fuzzy/download/init.lua:90: No fuzzy matching library found, but can't download from github due to not being on a git tag and no fuzzy.prebuilt_binaries.force_version is set.
Either run cargo build --release via your package manager, switch to a git tag, or set fuzzy.prebuilt_binaries.force_version in config.
See the docs for more info.

I think whatever the issue around downloads was, there's still something off about the path resolution of the .so file, even if it's included with the flake. Any way to provide a path statically? I'll try to find you some more info to work with.

[konradmalik]

yeah, still the same issue, but I'm pretty sure the so file is properly loaded.
I can force the implementation into be rust by a hack (require + set_implementation).
I will have a PR shortly.

[konradmalik]

watch out, this is a big one 😄 #1356