Import suggestions for local modules

[pepeiborra]

Currently ghcide suggests missing imports for Package modules only.

I would do this by enhancing kick to update a ShakeExtras mutable state containing a mapping from names to local modules. Then this mapping can be used by the existing suggestImports code action handler to provide the suggestions. A slight downside of this approach is that removing names from the state would be difficult. Since the names are only used to provide suggestions, this is ok.

As a refinement, use only the parsed AST, not the typed one. For modules with export lists, we only need the mod summary.

As a second refinement, get around the issue with deleted names by validating the suggestions before producing them.

[pepeiborra]

I'm grabbing this.

[wz1000]

Might I suggest using hiedb for this? Module exports can be stored in the database (definitions of top level names are already stored, we just need an extra boolean flag in the table to indicate whether the definition is exported).

Actually, due to the possibility of re-exports, we would need a new table in the database.

[pepeiborra]

I'm happy for my solution to be simplified or replacd once hiedb lands