Adam Gundry authored Dec 17, 2015 and Ben Gamari committed Dec 17, 2015

See `Note [Reifying field labels]` in `TcSplice`. This makes
typical uses of TH work better with `DuplicateRecordFields`.
If `reify` is called on the `Name` of a field label produced by
the output of a previous `reify`, and there are multiple  fields
with that label defined in the same module, it may fail with
an ambiguity error.

Test Plan:
Added tests, and manually tested that this makes
Aeson's `deriveJSON` avoid the `$sel:` prefixes.

Reviewers: simonpj, goldfire, austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1586

GHC Trac Issues: #11103