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Implement NoFieldSelectors

Closed Fumiaki Kinoshita requested to merge fumieval/ghc:fieldselectors-fumieval into master

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  • are either individually buildable or squashed
  • have commit messages which describe what they do (referring to Notes and tickets using #NNNN syntax when appropriate)
  • have added source comments describing your change. For larger changes you likely should add a Note and cross-reference it from the relevant places.
  • add a testcase to the testsuite.
  • This MR implements the NoFieldSelectors proposal.

Summary of the changes

(Items with bold texts are the key parts of the implementation.)

  • A new language extension, FieldSelectors, is added and enabled by default.
  • NoFieldSelectors negates FieldSelectors.
  • We added a new field in FieldLabel indicating whether FieldSelectors is enabled in the definition. As a result, we had to update the use sites of FieldLabel.
  • Previously, whether DuplicateRecordFields is in effect is represented by Bool; we replaced it by an explicit datatype instead.
  • lookupOccRn_overloaded has been renamed to lookupOccRn_overloaded_expr.
    • It is used to look up variables in expressions.
    • Selector functions created with NoFieldSelectors are hidden from this function.
  • lookupGlobalOccRn_overloaded has been renamed to lookupGlobalOccRn_overloaded_pat.
    • It is used to find field names in record patterns, updates, and constructions.
    • It can find selector functions with NoFieldSelectors.
  • Created a new datatype LookupOccRnOverloadedResult in place of Either Name [Name]
  • Fixed the bug #18729 (closed) preventing it work on GHCi
Edited by Adam Gundry