The hls-2 branch is ghcide head plus some changes intended to be upstreamed. As per #173, it seems once they are upstreamed hls can use ghcide master. These changes aren't too major, they mainly consist of

• This PR: Use stale information if it's available to answer requests quickly ghcide#624
• A backport of .hie files to ghc 8.6
• A rewrite of definition/typedefinition/hover using .hie files
• documentSymbols using .hie files
• A module graph
• Propagating changes to parent modules on save using the module graph
• @bubba's patch to add hyperlinks to hover
• Initial support for telemetry thanks to @mpardalos

The hiedb changes are not included because I don't think they are ready yet.

Taken from a list by @wz1000 in #173 (comment)