Add inlay hints idea

content/ideas/inlay-hints.md

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+---
+title: Inlay hints in haskell-language-server
+---
+
+Inlay hints are a relatively new langauge server protocol 
+feature that allow servers to display additional information
+inline in the user's editor, and in some cases triggering
+edits when clicked.
+
+They have a wide variety of uses, the [HLS issue](https://github.com/haskell/haskell-language-server/issues/2938)
+discusses some of them. For example:
+
+- Replacing the bulky import lens with a compact inlay hint
+- Type annotations on various kinds of binding
+- Explicit display of record field names when they are omitted
+- More we haven't thought of!
+
+This project would be to try and implement as many of these 
+inlay hint uses as possible in HLS.
+
+## Mentorship
+
+Michael Peyton Jones will mentor.
+
+## Difficulty and size
+
+Much of this project will not be too difficult, however it will
+require understanding and modifying many parts of HLS's codebase,
+which is non-trivial. We may also need to work out how to get
+additional information from GHC, which will require interacting
+with GHC, and possibly contributing fixes upstream.
+
+**Difficulty**: medium
+**Size**: A basic version is probably doable in 175 hours, but
+there is probably 350 hours worth of work, or the project could
+extend into implementing other missing LSP features.