Completion for Cabal Files

[VeryMilkyJoe]

When writing cabal files, developers often don't know the actual specification and it is tedious to have to look up the field names and which kinds of values to write for each field whenever one writes such a file.
Additionally, completion for any file-type is a good quality of life enhancement.

Completion of field-names

• Simple completion of available field names in cabal file.
• Completion of within stanza
• No completion of top level field names after stanza has been written

Completion of cabal values

• Suggest sensible inputs for values of field names.
• Implement for: cabal-version, license, testsuite > type, source-repository > type, filepath values, directory path values
• Implement for build-type, default-language, name, ghc-options, exposed-modules, other-modules, main-is.

Scoring for completions

• Score required fields higher than optional ones
• Scoring for licenses based on usage

Field descriptions

• Provide doc strings which inform users of what kinds of values are expected for a given field.