Support value/type namespaces on identifier links

Identifier links can be prefixed with a 'v' or 't' to indicate the value or
type namespace of the desired identifier. For example:

-- | Some link to a value: v'Data.Functor.Identity'
--
-- Some link to a type: t'Data.Functor.Identity'

The default is still the type (with a warning about the ambiguity)

2 files changed, 43 insertions, 15 deletions

diff --git a/haddock-api/src/Haddock/Interface/LexParseRn.hs b/haddock-api/src/Haddock/Interface/LexParseRn.hs
index 59ad4fdf..66083cf5 100644
--- a/haddock-api/src/Haddock/Interface/LexParseRn.hs
+++ b/haddock-api/src/Haddock/Interface/LexParseRn.hs
@@ -34,8 +34,8 @@ import Haddock.Types
 import Name
 import Outputable ( showPpr, showSDoc )
 import RdrName
+import RdrHsSyn (setRdrNameSpace)
 import EnumSet
-import RnEnv (dataTcOccs)
 
 processDocStrings :: DynFlags -> Maybe Package -> GlobalRdrEnv -> [HsDocString]
                   -> ErrMsgM (Maybe (MDoc Name))
@@ -89,24 +89,37 @@ processModuleHeader dflags pkgName gre safety mayStr = do
 -- fallbacks in case we can't locate the identifiers.
 --
 -- See the comments in the source for implementation commentary.
-rename :: DynFlags -> GlobalRdrEnv -> Doc RdrName -> ErrMsgM (Doc Name)
+rename :: DynFlags -> GlobalRdrEnv -> Doc NsRdrName -> ErrMsgM (Doc Name)
 rename dflags gre = rn
   where
     rn d = case d of
       DocAppend a b -> DocAppend <$> rn a <*> rn b
       DocParagraph doc -> DocParagraph <$> rn doc
-      DocIdentifier x -> do
+      DocIdentifier (NsRdrName ns x) -> do
+        let occ = rdrNameOcc x
+            isValueName = isDataOcc occ || isVarOcc occ
+
+        let valueNsChoices | isValueName = [x]
+                           | otherwise   = [] -- is this ever possible?
+            typeNsChoices  | isValueName = [setRdrNameSpace x tcName]
+                           | otherwise   = [x]
+
         -- Generate the choices for the possible kind of thing this
-        -- is.
-        let choices = dataTcOccs x
+        -- is. We narrow down the possibilities with the namespace (if
+        -- there is one).
+        let choices = case ns of
+                        Value -> valueNsChoices
+                        Type  -> typeNsChoices
+                        None  -> valueNsChoices ++ typeNsChoices
 
         -- Lookup any GlobalRdrElts that match the choices.
         case concatMap (\c -> lookupGRE_RdrName c gre) choices of
           -- We found no names in the env so we start guessing.
           [] ->
             case choices of
-              -- This shouldn't happen as 'dataTcOccs' always returns at least its input.
-              [] -> pure (DocMonospaced (DocString (showPpr dflags x)))
+              -- The only way this can happen is if a value namespace was
+              -- specified on something that cannot be a value.
+              [] -> invalidValue dflags x
 
               -- There was nothing in the environment so we need to
               -- pick some default from what's available to us. We
@@ -116,7 +129,7 @@ rename dflags gre = rn
               -- type constructor names (such as in #253). So now we
               -- only get type constructor links if they are actually
               -- in scope.
-              a:_ -> outOfScope dflags a
+              a:_ -> outOfScope dflags ns a
 
           -- There is only one name in the environment that matches so
           -- use it.
@@ -155,17 +168,23 @@ rename dflags gre = rn
 -- users shouldn't rely on this doing the right thing. See tickets
 -- #253 and #375 on the confusion this causes depending on which
 -- default we pick in 'rename'.
-outOfScope :: DynFlags -> RdrName -> ErrMsgM (Doc a)
-outOfScope dflags x =
+outOfScope :: DynFlags -> Namespace -> RdrName -> ErrMsgM (Doc a)
+outOfScope dflags ns x =
   case x of
     Unqual occ -> warnAndMonospace occ
     Qual mdl occ -> pure (DocIdentifierUnchecked (mdl, occ))
     Orig _ occ -> warnAndMonospace occ
     Exact name -> warnAndMonospace name  -- Shouldn't happen since x is out of scope
   where
+    prefix = case ns of
+               Value -> "the value "
+               Type -> "the type "
+               None -> ""
+
     warnAndMonospace a = do
-      tell ["Warning: '" ++ showPpr dflags a ++ "' is out of scope.\n" ++
-            "    If you qualify the identifier, haddock can try to link it anyway."]
+      tell ["Warning: " ++ prefix ++ "'" ++ showPpr dflags a ++ "' is out of scope.\n" ++
+            "    If you qualify the identifier, haddock can try to link it\n" ++
+            "    it anyway."]
       pure (monospaced a)
     monospaced a = DocMonospaced (DocString (showPpr dflags a))
 
@@ -184,7 +203,7 @@ ambiguous dflags x gres = do
       msg = "Warning: " ++ x_str ++ " is ambiguous. It is defined\n" ++
             concatMap (\n -> "    * " ++ defnLoc n ++ "\n") (map gre_name gres) ++
             "    You may be able to disambiguate the identifier by qualifying it or\n" ++
-            "    by hiding some imports.\n" ++
+            "    by specifying the type/value namespace explicitly.\n" ++
             "    Defaulting to " ++ x_str ++ " defined " ++ defnLoc dflt
   -- TODO: Once we have a syntax for namespace qualification (#667) we may also
   -- want to emit a warning when an identifier is a data constructor for a type
@@ -198,3 +217,13 @@ ambiguous dflags x gres = do
     isLocalName _ = False
     x_str = '\'' : showPpr dflags x ++ "'"
     defnLoc = showSDoc dflags . pprNameDefnLoc
+
+-- | Handle value-namespaced names that cannot be for values.
+--
+-- Emits a warning that the value-namespace is invalid on a non-value identifier.
+invalidValue :: DynFlags -> RdrName -> ErrMsgM (Doc a)
+invalidValue dflags x = do
+  tell ["Warning: '" ++ showPpr dflags x ++ "' cannot be value, yet it is\n" ++
+            "    namespaced as such. Did you mean to specify a type namespace\n" ++
+            "    instead?"]
+  pure (DocMonospaced (DocString (showPpr dflags x)))
diff --git a/haddock-api/src/Haddock/Interface/ParseModuleHeader.hs b/haddock-api/src/Haddock/Interface/ParseModuleHeader.hs
index 050901b6..802ea773 100644
--- a/haddock-api/src/Haddock/Interface/ParseModuleHeader.hs
+++ b/haddock-api/src/Haddock/Interface/ParseModuleHeader.hs
@@ -16,7 +16,6 @@ import Data.Char
 import DynFlags
 import Haddock.Parser
 import Haddock.Types
-import RdrName
 
 -- -----------------------------------------------------------------------------
 -- Parsing module headers
@@ -24,7 +23,7 @@ import RdrName
 -- NB.  The headers must be given in the order Module, Description,
 -- Copyright, License, Maintainer, Stability, Portability, except that
 -- any or all may be omitted.
-parseModuleHeader :: DynFlags -> Maybe Package -> String -> (HaddockModInfo RdrName, MDoc RdrName)
+parseModuleHeader :: DynFlags -> Maybe Package -> String -> (HaddockModInfo NsRdrName, MDoc NsRdrName)
 parseModuleHeader dflags pkgName str0 =
    let
       getKey :: String -> String -> (Maybe String,String)