sheaf authored Feb 19, 2025 and Marge Bot committed Feb 25, 2025

This commit ensures that we propagate the enclosing long distance
information to let bindings inside guards, in order to get accurate
pattern-match checking warnings, in particular incomplete record
selector warnings.

Example:

  data D = K0 | K1 { fld :: Int }
  f :: D -> Int
  f d@(K1 {})
    | let i = fld d
    = i
  f _ = 3

We now correctly recognise that the field selector 'fld' cannot fail,
due to the outer pattern match which guarantees that the value 'd' has
the field 'fld'.

Fixes #25749