Implement record dot syntaxwip/joachim/bump-haddock

2 files changed, 136 insertions, 1 deletions

diff --git a/compiler/Language/Haskell/Syntax/Expr.hs b/compiler/Language/Haskell/Syntax/Expr.hs
index 3d6500d342..9967a78314 100644
--- a/compiler/Language/Haskell/Syntax/Expr.hs
+++ b/compiler/Language/Haskell/Syntax/Expr.hs
@@ -40,6 +40,7 @@ import Language.Haskell.Syntax.Binds
 -- others:
 import GHC.Tc.Types.Evidence
 import GHC.Core
+import GHC.Core.DataCon (FieldLabelString)
 import GHC.Types.Name
 import GHC.Types.Basic
 import GHC.Types.Fixity
@@ -59,6 +60,110 @@ import qualified Data.Data as Data (Fixity(..))
 import GHCi.RemoteTypes ( ForeignRef )
 import qualified Language.Haskell.TH as TH (Q)
 
+{- Note [RecordDotSyntax field updates]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The extensions @OverloadedRecordDot@ @OverloadedRecordUpdate@ together
+enable record updates like @a{foo.bar.baz = 1}@. Introducing this
+syntax slightly complicates parsing. This note explains how it's done.
+
+In the event a record is being constructed or updated, it's this
+production that's in play:
+@
+aexp1 -> aexp1 '{' fbinds '}' {
+  ...
+  mkHsRecordPV ... $1 (snd $3)
+}
+@
+@fbinds@ is a list of field bindings. @mkHsRecordPV@ is a function of
+the @DisambECP b@ typeclass, see Note [Ambiguous syntactic
+categories].
+
+The "normal" rules for an @fbind@ are:
+@
+fbind
+        : qvar '=' texp
+        | qvar
+@
+These rules compute values of @LHsRecField GhcPs (Located b)@. They
+apply in the context of record construction, record updates, record
+patterns and record expressions. That is, @b@ ranges over @HsExpr
+GhcPs@, @HsPat GhcPs@ and @HsCmd GhcPs@.
+
+When @OverloadedRecordDot@ and @OverloadedRecordUpdate@ are both
+enabled, two additional @fbind@ rules are admitted:
+@
+        | field TIGHT_INFIX_PROJ fieldToUpdate '=' texp
+        | field TIGHT_INFIX_PROJ fieldToUpdate
+@
+
+These rules only make sense when parsing record update expressions
+(that is, patterns and commands cannot be parsed by these rules and
+neither record constructions).
+
+The results of these new rules cannot be represented by @LHsRecField
+GhcPs (LHsExpr GhcPs)@ values as the type is defined today. We
+minimize modifying existing code by having these new rules calculate
+@LHsRecProj GhcPs (Located b)@ ("record projection") values instead:
+@
+newtype FieldLabelStrings = FieldLabelStrings [Located FieldLabelString]
+type RecProj arg = HsRecField' FieldLabelStrings arg
+type LHsRecProj p arg = Located (RecProj arg)
+@
+
+The @fbind@ rule is then given the type @fbind :: { forall b.
+DisambECP b => PV (Fbind b) }@ accomodating both alternatives:
+@
+type Fbind b = Either
+                  (LHsRecField GhcPs (Located b))
+                  ( LHsRecProj GhcPs (Located b))
+@
+
+In @data HsExpr p@, the @RecordUpd@ constuctor indicates regular
+updates vs. projection updates by means of the @rupd_flds@ member
+type, an @Either@ instance:
+@
+  | RecordUpd
+      { rupd_ext  :: XRecordUpd p
+      , rupd_expr :: LHsExpr p
+      , rupd_flds :: Either [LHsRecUpdField p] [LHsRecUpdProj p]
+      }
+@
+Here,
+@
+type RecUpdProj p = RecProj (LHsExpr p)
+type LHsRecUpdProj p = Located (RecUpdProj p)
+@
+and @Left@ values indicating regular record update, @Right@ values
+updates desugared to @setField@s.
+
+If @OverloadedRecordUpdate@ is enabled, any updates parsed as
+@LHsRecField GhcPs@ values are converted to @LHsRecUpdProj GhcPs@
+values (see function @mkRdrRecordUpd@ in 'GHC.Parser.PostProcess').
+-}
+
+-- | RecordDotSyntax field updates
+
+newtype FieldLabelStrings =
+  FieldLabelStrings [Located FieldLabelString]
+                               deriving (Data)
+
+instance Outputable FieldLabelStrings where
+  ppr (FieldLabelStrings flds) =
+    hcat (punctuate dot (map (ppr . unLoc) flds))
+
+-- Field projection updates (e.g. @foo.bar.baz = 1@). See Note
+-- [RecordDotSyntax field updates].
+type RecProj arg = HsRecField' FieldLabelStrings arg
+
+-- The phantom type parameter @p@ is for symmetry with @LHsRecField p
+-- arg@ in the definition of @data Fbind@ (see GHC.Parser.Process).
+type LHsRecProj p arg = Located (RecProj arg)
+
+-- These two synonyms are used in the definition of syntax @RecordUpd@
+-- below.
+type RecUpdProj p = RecProj (LHsExpr p)
+type LHsRecUpdProj p = Located (RecUpdProj p)
+
 {-
 ************************************************************************
 *                                                                      *
@@ -356,16 +461,44 @@ data HsExpr p
   --
   --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'{'@,
   --         'GHC.Parser.Annotation.AnnDotdot','GHC.Parser.Annotation.AnnClose' @'}'@
+  --         'GHC.Parser.Annotation.AnnComma, 'GHC.Parser.Annotation.AnnDot',
+  --         'GHC.Parser.Annotation.AnnClose' @'}'@
 
   -- For details on above see note [Api annotations] in GHC.Parser.Annotation
   | RecordUpd
       { rupd_ext  :: XRecordUpd p
       , rupd_expr :: LHsExpr p
-      , rupd_flds :: [LHsRecUpdField p]
+      , rupd_flds :: Either [LHsRecUpdField p] [LHsRecUpdProj p]
       }
   -- For a type family, the arg types are of the *instance* tycon,
   -- not the family tycon
 
+  -- | Record field selection e.g @z.x@.
+  --
+  --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnDot'
+  --
+  -- This case only arises when the OverloadedRecordDot langauge
+  -- extension is enabled.
+
+  | HsGetField {
+        gf_ext :: XGetField p
+      , gf_expr :: LHsExpr p
+      , gf_field :: Located FieldLabelString
+      }
+
+  -- | Record field selector. e.g. @(.x)@ or @(.x.y)@
+  --
+  --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpenP'
+  --         'GHC.Parser.Annotation.AnnDot', 'GHC.Parser.Annotation.AnnCloseP'
+  --
+  -- This case only arises when the OverloadedRecordDot langauge
+  -- extensions is enabled.
+
+  | HsProjection {
+        proj_ext :: XProjection p
+      , proj_flds :: [Located FieldLabelString]
+      }
+
   -- | Expression with an explicit type signature. @e :: type@
   --
   --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnDcolon'
diff --git a/compiler/Language/Haskell/Syntax/Extension.hs b/compiler/Language/Haskell/Syntax/Extension.hs
index 16b11b3e30..f843bee1a2 100644
--- a/compiler/Language/Haskell/Syntax/Extension.hs
+++ b/compiler/Language/Haskell/Syntax/Extension.hs
@@ -387,6 +387,8 @@ type family XDo             x
 type family XExplicitList   x
 type family XRecordCon      x
 type family XRecordUpd      x
+type family XGetField       x
+type family XProjection     x
 type family XExprWithTySig  x
 type family XArithSeq       x
 type family XBracket        x