Handle records in the renamer

This patch moves the field-based logic for disambiguating record updates
to the renamer. The type-directed logic, scheduled for removal, remains
in the typechecker.

To do this properly (and fix the myriad of bugs surrounding the treatment
of duplicate record fields), we took the following main steps:

  1. Create GREInfo, a renamer-level equivalent to TyThing which stores
     information pertinent to the renamer.
     This allows us to uniformly treat imported and local Names in the
     renamer, as described in Note [GREInfo].

  2. Remove GreName. Instead of a GlobalRdrElt storing GreNames, which
     distinguished between normal names and field names, we now store
     simple Names in GlobalRdrElt, along with the new GREInfo information
     which allows us to recover the FieldLabel for record fields.

  3. Add namespacing for record fields, within the OccNames themselves.
     This allows us to remove the mangling of duplicate field selectors.

     This change ensures we don't print mangled names to the user in
     error messages, and allows us to handle duplicate record fields
     in Template Haskell.

  4. Move record disambiguation to the renamer, and operate on the
     level of data constructors instead, to handle #21443.

     The error message text for ambiguous record updates has also been
     changed to reflect that type-directed disambiguation is on the way
     out.

(3) means that OccEnv is now a bit more complex: we first key on the
textual name, which gives an inner map keyed on NameSpace:

  OccEnv a ~ FastStringEnv (UniqFM NameSpace a)

Note that this change, along with (2), both increase the memory residency
of GlobalRdrEnv = OccEnv [GlobalRdrElt], which causes a few tests to
regress somewhat in compile-time allocation.

Even though (3) simplified a lot of code (in particular the treatment of
field selectors within Template Haskell and in error messages), it came
with one important wrinkle: in the situation of

  -- M.hs-boot
  module M where { data A; foo :: A -> Int }
  -- M.hs
  module M where { data A = MkA { foo :: Int } }

we have that M.hs-boot exports a variable foo, which is supposed to match
with the record field foo that M exports. To solve this issue, we add a
new impedance-matching binding to M

  foo{var} = foo{fld}

This mimics the logic that existed already for impedance-binding DFunIds,
but getting it right was a bit tricky.
See Note [Record field impedance matching] in GHC.Tc.Module.

We also needed to be careful to avoid introducing space leaks in GHCi.
So we dehydrate the GlobalRdrEnv before storing it anywhere, e.g. in
ModIface. This means stubbing out all the GREInfo fields, with the
function forceGlobalRdrEnv.
When we read it back in, we rehydrate with rehydrateGlobalRdrEnv.
This robustly avoids any space leaks caused by retaining old type
environments.

Fixes #13352 #14848 #17381 #17551 #19664 #21443 #21444 #21720 #21898 #21946 #21959 #22125 #22160 #23010 #23062 #23063

Updates haddock submodule

-------------------------
Metric Increase:
    MultiComponentModules
    MultiLayerModules
    MultiLayerModulesDefsGhci
    MultiLayerModulesNoCode
    T13701
    T14697
    hard_hole_fits
-------------------------

2 files changed, 30 insertions, 0 deletions

diff --git a/docs/users_guide/9.6.1-notes.rst b/docs/users_guide/9.6.1-notes.rst
index eaed67da22..5cf40a310b 100644
--- a/docs/users_guide/9.6.1-notes.rst
+++ b/docs/users_guide/9.6.1-notes.rst
@@ -215,6 +215,11 @@ Runtime system
 - Add `Foreign.C.Types.ConstPtr` was added to encode ``const``-qualified pointer return
   types in foreign declarations when using ``CApiFFI`` extension.
 
+- The ``RecordUpd`` constructor of ``HsExpr`` now takes an ``HsRecUpdFields``
+  instead of ``Either [LHsRecUpdField p] [LHsRecUpdProj p]``.
+  Instead of ``Left ..``, use the constructor ``RegularRecUpdFields``, and instead
+  of ``Right ..``, use the constructor ``OverloadedRecUpdFields``.
+
 ``ghc-heap`` library
 ~~~~~~~~~~~~~~~~~~~~
 
diff --git a/docs/users_guide/9.8.1-notes.rst b/docs/users_guide/9.8.1-notes.rst
index 97d7829ce3..003e3ed78b 100644
--- a/docs/users_guide/9.8.1-notes.rst
+++ b/docs/users_guide/9.8.1-notes.rst
@@ -46,6 +46,20 @@ Compiler
   A new warning group :ghc-flag:`-Wextended-warnings` includes all such warnings
   regardless of category.  See :ref:`warning-deprecated-pragma`.
 
+- GHC is now better at disambiguating record updates in the presence of duplicate
+  record fields. The following program is now accepted ::
+
+     {-# LANGUAGE DuplicateRecordFields #-}
+
+     data R = MkR1 { foo :: Int }
+            | MkR2 { bar :: Int }
+
+     data S = MkS { foo :: Int, bar :: Int }
+
+     blah x = x { foo = 5, bar = 6 }
+
+  The point is that only the type S has a constructor with both fields "foo"
+  and "bar", so this record update is unambiguous.
 
 GHCi
 ~~~~
@@ -82,6 +96,17 @@ Runtime system
 ``ghc-heap`` library
 ~~~~~~~~~~~~~~~~~~~~
 
+``template-haskell`` library
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- The ``GadtC`` and ``RecGadtC`` constructors of the ``Con`` datatype now take
+  non-empty lists of constructors. This means that the ``gadtC`` and ``recGadtC``
+  smart constructors also expect non-empty lists as arguments.
+
+- Record fields now belong to separate ``NameSpace``s, keyed by the parent of
+  the record field. This is the name of the first constructor of the parent type,
+  even if this constructor does not have the field in question.
+  This change enables TemplateHaskell support for ``DuplicateRecordFields``.
 
 Included libraries
 ------------------