Update the ghc-8.6 branch (#889)

* Revert "Bump GHC version to 8.6"

This was applied to the wrong branch; there's now a `ghc-8.6` branch;
ghc-head is always supposed to point to GHC HEAD, i.e. an odd major version.
The next version bump to `ghc-head` is supposed to go from e.g. 8.5 to 8.7

This reverts commit 5e3cf5d8868323079ff5494a8225b0467404a5d1.

* README updates (#856)

* README: Remove mentions of master branch

* README: Add instructions for using html-test

* README: Change command to run _all_ the testsuites

* README: Add project overview section

(cherry picked from commit 61d6f935da97eb96685f07bf385102c2dbc2a33c)

* Export more fixities for Hoogle (#871)

This exports fixities for more things, including class methods and
type-level operators.

(cherry picked from commit 88316b972e3d47197b1019111bae0f7f87275fce)

* Avoid line breaks due to line length in Hoogle (#868)

* Avoid line breaks due to line length in Hoogle

Hoogle operates in a line-oriented fashion, so we should avoid ever
breaking due to long lines.

One way of doing this non-intrusively is to modify the 'DynFlags' that
are threaded through the 'Hoogle' module (note this is anyways only
passed through for use in the various 'showSDoc' functions).

* Amend test case

(cherry picked from commit 657b1b3d519545f8d4ca048c06210d6cbf0f0da0)

* tyThingToLHsDecl: Preserve type synonyms that contain a forall (#880)

* tyThingToLHsDecls: Preserve type synonyms that contain a forall

Fixes #879.

* Add Note [Invariant: Never expand type synonyms]

* Clarify Note [Invariant: Never expand type synonyms]

(cherry picked from commit c3eb3f0581f69e816f9453b1747a9f2a3ba02bb9)

* Fix HEAD html-test (#860)

* Update tests for 'StarIsType'

* Accept tests

* Revert "Update tests for 'StarIsType'"

This reverts commit 7f0c01383bbba6dc5af554ee82988d2cf44e407a.

* Refactor handling of parens in types (#874)

* Fix type parenthesization in Hoogle backend

Ported the logic in the HTML and LaTeX backends for adding in parens
into something top-level in 'GhcUtil'. Calling that from the Hoogle
backend fixes #873.

* Remove parenthesizing logic from LaTeX and XHTML backends

Now, the only times that parenthesis in types are added in any backend
is through the explicit 'HsParTy' constructor. Precedence is also
represented as its own datatype.

* List out cases explicitly vs. catch-all

* Fix printing of parens for QuantifiedConstraints

The priority of printing 'forall' types was just one too high.

Fixes #877.

* Accept HTML output for quantified contexts test

* Preserve docs on type family instances (#867)

* Preserve docs on type family instances

The only problem was that the instance location was slightly off
for type family instances.

* Accept output

(cherry picked from commit 133e9c2c168db19c1135479f7ab144c4e33af2a4)

* Fix broken instance source links (#869)

The problem manifests itself in instances that are defined in
modules other than the module where the class is defined. The fix
is just to thread through the 'Module' of the instance further
along.

Since orphan instances appear to already have been working, I didn't
do anything there.

(cherry picked from commit 2de7c2acf9b1ec85b09027a8bb58bf8512e91c05)

* Add some more unicode related tests (#872)

This has been fixed for sure ever since we switched from attoparsec to
parsec. Parts of it may have been working before that, but there was a
point where this would have failed (see #191).

A regression test never hurt anyone. :)

(cherry picked from commit 5ec7715d418bfac0f26aec6039792a99a6e89370)

* Misc tests (#858)

* More tests

* spliced types
* constructor/pattern argument docs
* strictness marks on fields with argument docs

* latex test cases need seperate directory

* Accept tests

* Additional tests for the identifier parser (#816)

* Add tests for the identifier parser

* docs: Clarify how to delimit identifiers

(cherry picked from commit 0861affeca4d72938f05a2eceddfae2c19199071)

2 files changed, 69 insertions, 94 deletions

diff --git a/haddock-api/src/Haddock/Backends/Xhtml/Decl.hs b/haddock-api/src/Haddock/Backends/Xhtml/Decl.hs
index fdb80141..cc271fef 100644
--- a/haddock-api/src/Haddock/Backends/Xhtml/Decl.hs
+++ b/haddock-api/src/Haddock/Backends/Xhtml/Decl.hs
@@ -620,9 +620,9 @@ ppInstances links origin instances splice unicode pkg qual
   -- force Splice = True to use line URLs
   where
     instName = getOccString origin
-    instDecl :: Int -> DocInstance DocNameI -> (SubDecl,Located DocName)
+    instDecl :: Int -> DocInstance DocNameI -> (SubDecl, Maybe Module, Located DocName)
     instDecl no (inst, mdoc, loc, mdl) =
-        ((ppInstHead links splice unicode qual mdoc origin False no inst mdl), loc)
+        ((ppInstHead links splice unicode qual mdoc origin False no inst mdl), mdl, loc)
 
 
 ppOrphanInstances :: LinksInfo
@@ -635,9 +635,9 @@ ppOrphanInstances links instances splice unicode pkg qual
     instOrigin :: InstHead name -> InstOrigin (IdP name)
     instOrigin inst = OriginClass (ihdClsName inst)
 
-    instDecl :: Int -> DocInstance DocNameI -> (SubDecl,Located DocName)
+    instDecl :: Int -> DocInstance DocNameI -> (SubDecl, Maybe Module, Located DocName)
     instDecl no (inst, mdoc, loc, mdl) =
-        ((ppInstHead links splice unicode qual mdoc (instOrigin inst) True no inst mdl), loc)
+        ((ppInstHead links splice unicode qual mdoc (instOrigin inst) True no inst Nothing), mdl, loc)
 
 
 ppInstHead :: LinksInfo -> Splice -> Unicode -> Qualification
@@ -1101,38 +1101,18 @@ sumParens = ubxSumList
 -- * Rendering of HsType
 --------------------------------------------------------------------------------
 
-
-pREC_TOP, pREC_CTX, pREC_FUN, pREC_OP, pREC_CON :: Int
-
-pREC_TOP = 0 :: Int   -- type in ParseIface.y in GHC
-pREC_CTX = 1 :: Int   -- Used for single contexts, eg. ctx => type
-                      -- (as opposed to (ctx1, ctx2) => type)
-pREC_FUN = 2 :: Int   -- btype in ParseIface.y in GHC
-                      -- Used for LH arg of (->)
-pREC_OP  = 3 :: Int   -- Used for arg of any infix operator
-                      -- (we don't keep their fixities around)
-pREC_CON = 4 :: Int   -- Used for arg of type applicn:
-                      -- always parenthesise unless atomic
-
-maybeParen :: Int           -- Precedence of context
-           -> Int           -- Precedence of top-level operator
-           -> Html -> Html  -- Wrap in parens if (ctxt >= op)
-maybeParen ctxt_prec op_prec p | ctxt_prec >= op_prec = parens p
-                               | otherwise            = p
-
-
 ppLType, ppLParendType, ppLFunLhType :: Unicode -> Qualification -> HideEmptyContexts -> Located (HsType DocNameI) -> Html
 ppLType       unicode qual emptyCtxts y = ppType unicode qual emptyCtxts (unLoc y)
 ppLParendType unicode qual emptyCtxts y = ppParendType unicode qual emptyCtxts (unLoc y)
 ppLFunLhType  unicode qual emptyCtxts y = ppFunLhType unicode qual emptyCtxts (unLoc y)
 
 ppCtxType :: Unicode -> Qualification -> HsType DocNameI -> Html
-ppCtxType unicode qual ty = ppr_mono_ty pREC_CTX ty unicode qual HideEmptyContexts
+ppCtxType unicode qual ty = ppr_mono_ty (reparenTypePrec PREC_CTX ty) unicode qual HideEmptyContexts
 
 ppType, ppParendType, ppFunLhType :: Unicode -> Qualification -> HideEmptyContexts -> HsType DocNameI -> Html
-ppType       unicode qual emptyCtxts ty = ppr_mono_ty pREC_TOP ty unicode qual emptyCtxts
-ppParendType unicode qual emptyCtxts ty = ppr_mono_ty pREC_CON ty unicode qual emptyCtxts
-ppFunLhType  unicode qual emptyCtxts ty = ppr_mono_ty pREC_FUN ty unicode qual emptyCtxts
+ppType       unicode qual emptyCtxts ty = ppr_mono_ty (reparenTypePrec PREC_TOP ty) unicode qual emptyCtxts
+ppParendType unicode qual emptyCtxts ty = ppr_mono_ty (reparenTypePrec PREC_CON ty) unicode qual emptyCtxts
+ppFunLhType  unicode qual emptyCtxts ty = ppr_mono_ty (reparenTypePrec PREC_FUN ty) unicode qual emptyCtxts
 
 ppHsTyVarBndr :: Unicode -> Qualification -> HsTyVarBndr DocNameI -> Html
 ppHsTyVarBndr _       qual (UserTyVar _ (L _ name)) =
@@ -1146,7 +1126,7 @@ ppLKind :: Unicode -> Qualification -> LHsKind DocNameI -> Html
 ppLKind unicode qual y = ppKind unicode qual (unLoc y)
 
 ppKind :: Unicode -> Qualification -> HsKind DocNameI -> Html
-ppKind unicode qual ki = ppr_mono_ty pREC_TOP ki unicode qual HideEmptyContexts
+ppKind unicode qual ki = ppr_mono_ty (reparenTypePrec PREC_TOP ki) unicode qual HideEmptyContexts
 
 patSigContext :: LHsType name -> HideEmptyContexts
 patSigContext typ | hasNonEmptyContext typ && isFirstContextEmpty typ =  ShowEmptyToplevelContexts
@@ -1177,57 +1157,56 @@ ppPatSigType unicode qual typ =
 ppForAllPart :: Unicode -> Qualification -> [LHsTyVarBndr DocNameI] -> Html
 ppForAllPart unicode qual tvs = hsep (forallSymbol unicode : ppTyVars unicode qual tvs) +++ dot
 
-ppr_mono_lty :: Int -> LHsType DocNameI -> Unicode -> Qualification -> HideEmptyContexts -> Html
-ppr_mono_lty ctxt_prec ty = ppr_mono_ty ctxt_prec (unLoc ty)
+ppr_mono_lty :: LHsType DocNameI -> Unicode -> Qualification -> HideEmptyContexts -> Html
+ppr_mono_lty ty = ppr_mono_ty (unLoc ty)
 
 
-ppr_mono_ty :: Int -> HsType DocNameI -> Unicode -> Qualification -> HideEmptyContexts -> Html
-ppr_mono_ty ctxt_prec (HsForAllTy _ tvs ty) unicode qual emptyCtxts
-  = maybeParen ctxt_prec pREC_FUN $
-    ppForAllPart unicode qual tvs <+> ppr_mono_lty pREC_TOP ty unicode qual emptyCtxts
+ppr_mono_ty :: HsType DocNameI -> Unicode -> Qualification -> HideEmptyContexts -> Html
+ppr_mono_ty (HsForAllTy _ tvs ty) unicode qual emptyCtxts
+  = ppForAllPart unicode qual tvs <+> ppr_mono_lty ty unicode qual emptyCtxts
 
-ppr_mono_ty ctxt_prec (HsQualTy _ ctxt ty) unicode qual emptyCtxts
-  = maybeParen ctxt_prec pREC_FUN $
-    ppLContext ctxt unicode qual emptyCtxts <+> ppr_mono_lty pREC_TOP ty unicode qual emptyCtxts
+ppr_mono_ty (HsQualTy _ ctxt ty) unicode qual emptyCtxts
+  = ppLContext ctxt unicode qual emptyCtxts <+> ppr_mono_lty ty unicode qual emptyCtxts
 
 -- UnicodeSyntax alternatives
-ppr_mono_ty _ (HsTyVar _ _ (L _ name)) True _ _
+ppr_mono_ty (HsTyVar _ _ (L _ name)) True _ _
   | getOccString (getName name) == "(->)" = toHtml "(→)"
 
-ppr_mono_ty _ (HsBangTy _ b ty) u q _ =
+ppr_mono_ty (HsBangTy _ b ty) u q _ =
   ppBang b +++ ppLParendType u q HideEmptyContexts ty
-ppr_mono_ty _ (HsTyVar _ _ (L _ name)) _ q _ =
+ppr_mono_ty (HsTyVar _ _ (L _ name)) _ q _ =
   ppDocName q Prefix True name
-ppr_mono_ty _ (HsStarTy _ isUni) u _ _ =
+ppr_mono_ty (HsStarTy _ isUni) u _ _ =
   toHtml (if u || isUni then "★" else "*")
-ppr_mono_ty ctxt_prec (HsFunTy _ ty1 ty2) u q e =
-  ppr_fun_ty ctxt_prec ty1 ty2 u q e
-ppr_mono_ty _ (HsTupleTy _ con tys) u q _ =
+ppr_mono_ty (HsFunTy _ ty1 ty2) u q e =
+  hsep [ ppr_mono_lty ty1 u q HideEmptyContexts
+       , arrow u <+> ppr_mono_lty ty2 u q e
+       ]
+ppr_mono_ty (HsTupleTy _ con tys) u q _ =
   tupleParens con (map (ppLType u q HideEmptyContexts) tys)
-ppr_mono_ty _ (HsSumTy _ tys) u q _ =
+ppr_mono_ty (HsSumTy _ tys) u q _ =
   sumParens (map (ppLType u q HideEmptyContexts) tys)
-ppr_mono_ty _ (HsKindSig _ ty kind) u q e =
-  parens (ppr_mono_lty pREC_TOP ty u q e <+> dcolon u <+> ppLKind u q kind)
-ppr_mono_ty _         (HsListTy _ ty)       u q _ = brackets (ppr_mono_lty pREC_TOP ty u q HideEmptyContexts)
-ppr_mono_ty ctxt_prec (HsIParamTy _ (L _ n) ty) u q _ =
-    maybeParen ctxt_prec pREC_CTX $ ppIPName n <+> dcolon u <+> ppr_mono_lty pREC_TOP ty u q HideEmptyContexts
-ppr_mono_ty _         (HsSpliceTy {})     _ _ _ = error "ppr_mono_ty HsSpliceTy"
-ppr_mono_ty _         (HsRecTy {})        _ _ _ = toHtml "{..}"
+ppr_mono_ty (HsKindSig _ ty kind) u q e =
+  parens (ppr_mono_lty ty u q e <+> dcolon u <+> ppLKind u q kind)
+ppr_mono_ty (HsListTy _ ty)       u q _ = brackets (ppr_mono_lty ty u q HideEmptyContexts)
+ppr_mono_ty (HsIParamTy _ (L _ n) ty) u q _ =
+  ppIPName n <+> dcolon u <+> ppr_mono_lty ty u q HideEmptyContexts
+ppr_mono_ty (HsSpliceTy {})     _ _ _ = error "ppr_mono_ty HsSpliceTy"
+ppr_mono_ty (HsRecTy {})        _ _ _ = toHtml "{..}"
        -- Can now legally occur in ConDeclGADT, the output here is to provide a
        -- placeholder in the signature, which is followed by the field
        -- declarations.
-ppr_mono_ty _         (XHsType (NHsCoreTy {})) _ _ _ = error "ppr_mono_ty HsCoreTy"
-ppr_mono_ty _         (HsExplicitListTy _ Promoted tys) u q _ = promoQuote $ brackets $ hsep $ punctuate comma $ map (ppLType u q HideEmptyContexts) tys
-ppr_mono_ty _         (HsExplicitListTy _ NotPromoted tys) u q _ = brackets $ hsep $ punctuate comma $ map (ppLType u q HideEmptyContexts) tys
-ppr_mono_ty _         (HsExplicitTupleTy _ tys) u q _ = promoQuote $ parenList $ map (ppLType u q HideEmptyContexts) tys
-
-ppr_mono_ty ctxt_prec (HsAppTy _ fun_ty arg_ty) unicode qual _
-  = maybeParen ctxt_prec pREC_CON $
-    hsep [ppr_mono_lty pREC_FUN fun_ty unicode qual HideEmptyContexts, ppr_mono_lty pREC_CON arg_ty unicode qual HideEmptyContexts]
-
-ppr_mono_ty ctxt_prec (HsOpTy _ ty1 op ty2) unicode qual _
-  = maybeParen ctxt_prec pREC_FUN $
-    ppr_mono_lty pREC_OP ty1 unicode qual HideEmptyContexts <+> ppr_op <+> ppr_mono_lty pREC_OP ty2 unicode qual HideEmptyContexts
+ppr_mono_ty (XHsType (NHsCoreTy {})) _ _ _ = error "ppr_mono_ty HsCoreTy"
+ppr_mono_ty (HsExplicitListTy _ Promoted tys) u q _ = promoQuote $ brackets $ hsep $ punctuate comma $ map (ppLType u q HideEmptyContexts) tys
+ppr_mono_ty (HsExplicitListTy _ NotPromoted tys) u q _ = brackets $ hsep $ punctuate comma $ map (ppLType u q HideEmptyContexts) tys
+ppr_mono_ty (HsExplicitTupleTy _ tys) u q _ = promoQuote $ parenList $ map (ppLType u q HideEmptyContexts) tys
+
+ppr_mono_ty (HsAppTy _ fun_ty arg_ty) unicode qual _
+  = hsep [ ppr_mono_lty fun_ty unicode qual HideEmptyContexts
+         , ppr_mono_lty arg_ty unicode qual HideEmptyContexts ]
+
+ppr_mono_ty (HsOpTy _ ty1 op ty2) unicode qual _
+  = ppr_mono_lty ty1 unicode qual HideEmptyContexts <+> ppr_op <+> ppr_mono_lty ty2 unicode qual HideEmptyContexts
   where
     -- `(:)` is valid in type signature only as constructor to promoted list
     -- and needs to be quoted in code so we explicitly quote it here too.
@@ -1236,24 +1215,17 @@ ppr_mono_ty ctxt_prec (HsOpTy _ ty1 op ty2) unicode qual _
         | otherwise = ppr_op'
     ppr_op' = ppLDocName qual Infix op
 
-ppr_mono_ty ctxt_prec (HsParTy _ ty) unicode qual emptyCtxts
---  = parens (ppr_mono_lty pREC_TOP ty)
-  = ppr_mono_lty ctxt_prec ty unicode qual emptyCtxts
+ppr_mono_ty (HsParTy _ ty) unicode qual emptyCtxts
+  = parens (ppr_mono_lty ty unicode qual emptyCtxts)
+--  = parens (ppr_mono_lty ctxt_prec ty unicode qual emptyCtxts)
 
-ppr_mono_ty ctxt_prec (HsDocTy _ ty _) unicode qual emptyCtxts
-  = ppr_mono_lty ctxt_prec ty unicode qual emptyCtxts
+ppr_mono_ty (HsDocTy _ ty _) unicode qual emptyCtxts
+  = ppr_mono_lty ty unicode qual emptyCtxts
 
-ppr_mono_ty _ (HsWildCardTy (AnonWildCard _)) _ _ _ = char '_'
-ppr_mono_ty _ (HsTyLit _ n) _ _ _ = ppr_tylit n
+ppr_mono_ty (HsWildCardTy (AnonWildCard _)) _ _ _ = char '_'
+ppr_mono_ty (HsTyLit _ n) _ _ _ = ppr_tylit n
 
 ppr_tylit :: HsTyLit -> Html
 ppr_tylit (HsNumTy _ n) = toHtml (show n)
 ppr_tylit (HsStrTy _ s) = toHtml (show s)
 
-ppr_fun_ty :: Int -> LHsType DocNameI -> LHsType DocNameI -> Unicode -> Qualification -> HideEmptyContexts -> Html
-ppr_fun_ty ctxt_prec ty1 ty2 unicode qual emptyCtxts
-  = let p1 = ppr_mono_lty pREC_FUN ty1 unicode qual HideEmptyContexts
-        p2 = ppr_mono_lty pREC_TOP ty2 unicode qual emptyCtxts
-    in
-    maybeParen ctxt_prec pREC_FUN $
-    hsep [p1, arrow unicode <+> p2]
diff --git a/haddock-api/src/Haddock/Backends/Xhtml/Layout.hs b/haddock-api/src/Haddock/Backends/Xhtml/Layout.hs
index 501caa4b..1c44ffda 100644
--- a/haddock-api/src/Haddock/Backends/Xhtml/Layout.hs
+++ b/haddock-api/src/Haddock/Backends/Xhtml/Layout.hs
@@ -40,7 +40,6 @@ module Haddock.Backends.Xhtml.Layout (
   topDeclElem, declElem,
 ) where
 
-
 import Haddock.Backends.Xhtml.DocMarkup
 import Haddock.Backends.Xhtml.Types
 import Haddock.Backends.Xhtml.Utils
@@ -48,6 +47,7 @@ import Haddock.Types
 import Haddock.Utils (makeAnchorId, nameAnchorId)
 import qualified Data.Map as Map
 import Text.XHtml hiding ( name, title, quote )
+import Data.Maybe (fromMaybe)
 
 import FastString            ( unpackFS )
 import GHC
@@ -151,20 +151,22 @@ subTable pkg qual decls = Just $ table << aboves (concatMap subRow decls)
 
 -- | Sub table with source information (optional).
 subTableSrc :: Maybe Package -> Qualification -> LinksInfo -> Bool
-            -> [(SubDecl,Located DocName)] -> Maybe Html
+            -> [(SubDecl, Maybe Module, Located DocName)] -> Maybe Html
 subTableSrc _ _ _ _ [] = Nothing
 subTableSrc pkg qual lnks splice decls = Just $ table << aboves (concatMap subRow decls)
   where
-    subRow ((decl, mdoc, subs),L loc dn) =
+    subRow ((decl, mdoc, subs), mdl, L loc dn) =
       (td ! [theclass "src clearfix"] <<
         (thespan ! [theclass "inst-left"] << decl)
-        <+> linkHtml loc dn
+        <+> linkHtml loc mdl dn
       <->
       docElement td << fmap (docToHtml Nothing pkg qual) mdoc
       )
       : map (cell . (td <<)) subs
-    linkHtml loc@(RealSrcSpan _) dn = links lnks loc splice dn
-    linkHtml _ _ = noHtml
+
+    linkHtml :: SrcSpan -> Maybe Module -> DocName -> Html
+    linkHtml loc@(RealSrcSpan _) mdl dn = links lnks loc splice mdl dn
+    linkHtml _ _ _ = noHtml
 
 subBlock :: [Html] -> Maybe Html
 subBlock [] = Nothing
@@ -197,7 +199,7 @@ subEquations pkg qual = divSubDecls "equations" "Equations" . subTable pkg qual
 subInstances :: Maybe Package -> Qualification
              -> String -- ^ Class name, used for anchor generation
              -> LinksInfo -> Bool
-             -> [(SubDecl,Located DocName)] -> Html
+             -> [(SubDecl, Maybe Module, Located DocName)] -> Html
 subInstances pkg qual nm lnks splice = maybe noHtml wrap . instTable
   where
     wrap contents = subSection (collapseDetails id_ DetailsOpen (summary +++ contents))
@@ -209,7 +211,7 @@ subInstances pkg qual nm lnks splice = maybe noHtml wrap . instTable
 
 subOrphanInstances :: Maybe Package -> Qualification
                    -> LinksInfo -> Bool
-                   -> [(SubDecl,Located DocName)] -> Html
+                   -> [(SubDecl, Maybe Module, Located DocName)] -> Html
 subOrphanInstances pkg qual lnks splice  = maybe noHtml wrap . instTable
   where
     wrap = ((h1 << "Orphan instances") +++)
@@ -268,13 +270,13 @@ declElem = paragraph ! [theclass "src"]
 -- it adds a source and wiki link at the right hand side of the box
 topDeclElem :: LinksInfo -> SrcSpan -> Bool -> [DocName] -> Html -> Html
 topDeclElem lnks loc splice names html =
-    declElem << (html <+> (links lnks loc splice $ head names))
+    declElem << (html <+> (links lnks loc splice Nothing $ head names))
         -- FIXME: is it ok to simply take the first name?
 
 -- | Adds a source and wiki link at the right hand side of the box.
 -- Name must be documented, otherwise we wouldn't get here.
-links :: LinksInfo -> SrcSpan -> Bool -> DocName -> Html
-links ((_,_,sourceMap,lineMap), (_,_,maybe_wiki_url)) loc splice docName@(Documented n mdl) =
+links :: LinksInfo -> SrcSpan -> Bool -> Maybe Module -> DocName -> Html
+links ((_,_,sourceMap,lineMap), (_,_,maybe_wiki_url)) loc splice mdl' docName@(Documented n mdl) =
   srcLink <+> wikiLink <+> (selfLink ! [theclass "selflink"] << "#")
   where selfLink = linkedAnchor (nameAnchorId (nameOccName (getName docName)))
 
@@ -298,12 +300,13 @@ links ((_,_,sourceMap,lineMap), (_,_,maybe_wiki_url)) loc splice docName@(Docume
 
         -- For source links, we want to point to the original module,
         -- because only that will have the source.
-        -- TODO: do something about type instances. They will point to
-        -- the module defining the type family, which is wrong.
-        origMod = nameModule n
+        --
+        -- 'mdl'' is a way of "overriding" the module. Without it, instances
+        -- will point to the module defining the class/family, which is wrong.
+        origMod = fromMaybe (nameModule n) mdl'
         origPkg = moduleUnitId origMod
 
         fname = case loc of
           RealSrcSpan l -> unpackFS (srcSpanFile l)
           UnhelpfulSpan _ -> error "links: UnhelpfulSpan"
-links _ _ _ _ = noHtml
+links _ _ _ _ _ = noHtml