Codeaction for exporting unused top-level bindings

[sureyeaah]

This codeaction lets you export unused top-level functions, data types, newtypes, type synonyms, type classes, type families and pattern synonyms.

• When exporting data types/newtypes/typeclasses/type families, we export all (e.g. Foo(..)).
• We don't support extracting the data constructor/fields when the corresponding type is already exported. e.g.

module X(Foo) where
Foo = Foo {foo :: ()}

This is done because it would require us to find the corresponding type in the export list.

Fixes haskell/haskell-language-server#157

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All committers have signed the CLA.

[cocreature]

Nice work, thanks a lot!
One question: I would have expected the code action to add the export at the end whereas your implementation adds it add the beginning. Was that an intentional choice or just because it was easier to implement?

[sureyeaah]

I did that because it was easier to implement but now that I think about it, it would be just as easy to append it at the end (in the same line as the closing bracket). I'll update the PR.

@cocreature I've updated it :)

[sureyeaah]

I just realized there is an edge case when appending to the export list -module X(foo,) where and module X(foo) where. We'll have to look for that last comma.
EDIT: Fixed.

[cocreature]

Thank you!

[cocreature]

I wonder how clever we should be in terms of inserting line breaks. At some point we venture into autoformatter territory which a code action is definitely not the right place for but maybe there is some middleground. E.g., insert a line break if the opening and closing parentheses are on different lines.

Let’s merge it like this but keep this in mind for a possible future extension.

[sureyeaah]

When writing codeactions, I prefer to offload as much work as possible to the formatter.
If we were to insert a line break, we would also have to get the indentation right.