Comments following function included in function pattern about tree-sitter-haskell HOT 6 CLOSED

Same thing happens for class and instance patterns, for example:

instance Class Data where
  f = a

-- | haddock
g = a

class Class where
  f :: Data

-- | haddock
g = a

(class) @class.around
(instance (where)? . _ @class.inside) @class.around

from tree-sitter-haskell.

I'm not sure that it's feasible to implement this, since comments are allowed to break indentation:

f = do
  g

-- foo
  pure 1

so in order to decide whether the comment should terminate the do layout, we'd need to parse the indent of the following line, which would require us to either

• jump back to after g if indentation decreases to terminate the do node
• jump back to after foo if indentation stays the same so that the leading spaces of the next line won't be included in the comment (and we need them to determine the indent again for the next node)

and this won't work since we can't store two positions at once ☹️

(in case that is unclear: comments and indent are parsed manually in the C extension)

The only way I can imagine now would be to compromise and use -- | as an indicator, but since that isn't Haskell syntax, but Haddock, it could break valid code. Though it's probably unlikely to occur in an invalid position.

I'll think a bit more about this but I'm fairly pessimistic.

from tree-sitter-haskell.

@414owen do you have an idea maybe?

from tree-sitter-haskell.

I guess I'm unsure why it works without the do block. I would have thought the lexer would only detect the end of f when it sees function g, which would be after the comment.

from tree-sitter-haskell.

indeed, that's curious

from tree-sitter-haskell.

ok so in the case without do the function is entirely contained in the range a = b, so tree-sitter is conservative and uses the smallest tree that works, leaving the comment on its own since there's no reason to associate it with any neighboring node more than the others.

for the do case, the layout end is part of the function rhs, so the comment cannot escape that tree.

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