feat: add hex intelligence

[dbernheisel]

Adds hex package intelligence to mix.exs — package name completion, version completion, dep option suggestions, and hover documentation. Works across the public hex.pm registry and custom self-hosted repos like Oban with no configuration beyond what Mix already knows.

This is fairly self-contained with a few integrated points, so because of that, I felt a large PR would be ok for completeness. Happy to refactor/reorganize modules as you see fit.

Generally, this is porting hex-cmp

What it does

• Package completion — type {:phoe and get phoenix, phoenix_live_view, etc. with download counts and descriptions. Custom repo packages (like oban_pro) appear alongside hexpm results with their repo labeled.
• Version completion — type {:phoenix, "~> 1. and get filtered version candidates sorted newest-first. Retired versions are annotated with the retirement reason. Works for custom repos without needing repo: typed first.
• Dep option completion — type {:phoenix, "~> 1.7", and get only, runtime, override, repo, etc.
• Hover docs — hover a package atom to see description, installed vs latest version, license, download count, and links. For custom repos, metadata is extracted from locally-cached tarballs.

How it works

• Engine.Deps runs in the project's Mix context (where the Hex archive is loaded) and exposes repo config, dep versions, project files, and cached tarball paths over RPC.
• Hex.Context detects the cursor slot (name/version/opts) inside a deps function tuple using Sourceror's error-recovering parser, with a regex line fallback for cases where both parsers fail (unclosed strings). This assumes the conventional "deps" function within the project file (eg, mix.exs), and will not offer intelligence otherwise.
• Hex.Api routes through the hex.pm HTTP API via :hex_core dep for public packages and the repo protocol (:hex_repo) for custom repos. Custom repo responses are enriched with tarball metadata if they're already cached.
• Hex.Cache is a DETS-backed GenServer with 1-hour TTL and stale-on-error fallback so completions survive network failures and LSP restarts. This helps relieve the server from being hammered with repeated known info from the user.

Testing

• Verified with a custom repo, eg, oban.
• Verified with public packages
• Verified with private hex repos.
• Verified with umbrella apps, but it should work since it uses the engine's current InProject helpers.
• Verified with projects with a non-standard project file, eg, not named mix.exs

[dbernheisel]

not related, but a duplicated call (document is set on line 20 already)

[andyl]

@dbernheisel - if this is accepted, will we still need hex-cmp ?

ps hex-cmp has been very handy thanks for this great tool!

[dbernheisel]

Nope! It's more complete within Expert; supports custom repos, displays the installed version of the dep, and has access to the projects actual hex to know these things rather than reinventing what mix/hex do.