Hover causes far too much memory

[mpickering]

The way that the types are collected from the AST by using syb uses a lot of memory. This was already identified when haddock started using HIE files for its hyperlinker. The solution is to
make the traversal smarter to only recover types at the leaves rather than for all subexpressions.

This issues makes HIE unusable with GHC (or any big project) as the process of traversing a single module is too expensive.

cc @wz1000

[mpickering]

This change makes a big difference. mpickering/ghc-mod@1544779

If someone wants to finish this off then they need to reimplement collectSpanTypes in Haskell.Ide.Engine.ArtifactMap in order to build the type map directly whilst performing the query rather than building an intermediate list and copy these changes into ArtifactMap so the type map generation doesn't depend on ghc-mod at all.

Another reference is - https://gitlab.haskell.org/ghc/ghc/blob/fef4a8dd65428cbcdc4aa58f0444eae9f5cc63ed/compiler/hieFile/HieAst.hs

[fendor]

I can take a look at it, this week!

[fendor]

Problem has been adressed and merged into #1126.