Fix import suggestions when dot is typed

[lazamar]

Fixes #613 and #342 at haskell-language-server.

Before

After

[lazamar]

I tried adding a completion test, but for some reason module suggestions are not being captured. It is not clear to me why.
The test added is here lazamar@4aefe73 and fails with

test/exe/Main.hs:2466:
expected: [("Control.Applicative",Just CiModule)]
but got: []

[pepeiborra]

Thank you sir!

While this fixes the bug in ghcide, I suspect the bug is upstream. What to do? I'm happy to merge this now and roll it back later if the fix is replicated in haskell-lsp. Equally happy to wait for the fix to land in haskell-lsp. Your choice

[pepeiborra]

Can we get a test, so that this will not break silently again?

[wz1000]

@lazamar are you planning to add tests in this PR? I need this commit for a merge of my hls-3 branch, so if you aren't keen on doing this soon, I can try to include some tests in the upcoming and merge this as is.

[lazamar]

@wz1000 I wrote a brief test here lazamar@4aefe73 but couldn't get completions to show up.
I can only look at it tomorrow night. If you decide to merge it as is I can make another PR for the test.

[wz1000]

I believe the issue with that test is that the Position is 0-indexed, so you need to subtract 1 from the coordinates.

[wz1000]

Also, we need a stale parsed module to generate completions, so the module has to compile initially, and then the partial import line has to be added in.