Refactor renamer datastructures

This patch significantly refactors key renamer datastructures (primarily Avail
and GlobalRdrElt) in order to treat DuplicateRecordFields in a more robust way.
In particular it allows the extension to be used with pattern synonyms (fixes
where mangled record selector names could be printed instead of field labels
(e.g. with -Wpartial-fields or hole fits, see new tests).

The key idea is the introduction of a new type GreName for names that may
represent either normal entities or field labels.  This is then used in
GlobalRdrElt and AvailInfo, in place of the old way of representing fields
using FldParent (yuck) and an extra list in AvailTC.

Updates the haddock submodule.

1 files changed, 7 insertions, 3 deletions

diff --git a/compiler/GHC/Hs/Type.hs b/compiler/GHC/Hs/Type.hs
index 1b1e56b314..2c64d7a491 100644
--- a/compiler/GHC/Hs/Type.hs
+++ b/compiler/GHC/Hs/Type.hs
@@ -1898,9 +1898,13 @@ type LFieldOcc pass = XRec pass (FieldOcc pass)
 
 -- | Field Occurrence
 --
--- Represents an *occurrence* of an unambiguous field.  We store
--- both the 'RdrName' the user originally wrote, and after the
--- renamer, the selector function.
+-- Represents an *occurrence* of an unambiguous field.  This may or may not be a
+-- binding occurrence (e.g. this type is used in 'ConDeclField' and
+-- 'RecordPatSynField' which bind their fields, but also in 'HsRecField' for
+-- record construction and patterns, which do not).
+--
+-- We store both the 'RdrName' the user originally wrote, and after the renamer,
+-- the selector function.
 data FieldOcc pass = FieldOcc { extFieldOcc     :: XCFieldOcc pass
                               , rdrNameFieldOcc :: Located RdrName
                                  -- ^ See Note [Located RdrNames] in "GHC.Hs.Expr"