Add dangling changes from branches ghc-8.6 and ghc-8.8 (#1243)

* Fix multiple typos and inconsistencies in doc/markup.rst

Note: I noticed some overlap with #1112 from @wygulmage and #1081 from
@parsonsmatt after creating these proposed changes - mea culpa for not
looking at the open PRs sooner.

* Fix #1113 If no Signatures, no section of index.html

* Change the formatting of missing link destinations

The current formatting of the missing link destination does not really
help user to understand the reasons of the missing link.

To address this, I've changed the formatting in two ways:

- the missing link symbol name is now fully qualified. This way you
immediately know which haskell module cannot be linked. It is then easier
to understand why this module does not have documentation (hidden module
or broken documentation).
- one line per missing link, that's more readable now that symbol name
can be longer due to qualification.

For example, before haddock was listing missing symbol such as:

```
could not find link destinations for:
  Word8 Word16 mapMaybe
```

Now it is listed as:

```
could not find link destinations for:
  - Data.Word.Word8
  - Data.Word.Word16
  - Data.Maybe.mapMaybe
```

* Add `--ignore-link-symbol` command line argument

This argument can be used multiples time. A missing link to a symbol
listed by `--ignore-link-symbol` won't trigger "missing link" warning.

* Forbid spaces in anchors (#1148)

* Improve error messages with context information (#1060)

Co-authored-by: Matt Audesse <matt@mattaudesse.com>
Co-authored-by: Mike Pilgrem <mpilgrem@users.noreply.github.com>
Co-authored-by: Guillaume Bouchard <guillaume.bouchard@tweag.io>
Co-authored-by: Pepe Iborra <pepeiborra@gmail.com>

1 files changed, 18 insertions, 9 deletions

diff --git a/haddock-api/src/Haddock/Interface/Create.hs b/haddock-api/src/Haddock/Interface/Create.hs
index 5a58e1ac..d554eeb3 100644
--- a/haddock-api/src/Haddock/Interface/Create.hs
+++ b/haddock-api/src/Haddock/Interface/Create.hs
@@ -39,6 +39,7 @@ import Data.Ord
 import Control.Applicative
 import Control.Monad
 import Data.Traversable
+import GHC.Stack (HasCallStack)
 
 import Avail hiding (avail)
 import qualified Avail
@@ -58,16 +59,21 @@ import FastString ( unpackFS, bytesFS )
 import BasicTypes ( StringLiteral(..), SourceText(..), PromotionFlag(..) )
 import qualified Outputable as O
 
+mkExceptionContext :: TypecheckedModule -> String
+mkExceptionContext =
+  ("creating Haddock interface for " ++) . moduleNameString . ms_mod_name . pm_mod_summary . tm_parsed_module
 
 -- | Use a 'TypecheckedModule' to produce an 'Interface'.
 -- To do this, we need access to already processed modules in the topological
 -- sort. That's what's in the 'IfaceMap'.
-createInterface :: TypecheckedModule
+createInterface :: HasCallStack
+                => TypecheckedModule
                 -> [Flag]       -- Boolean flags
                 -> IfaceMap     -- Locally processed modules
                 -> InstIfaceMap -- External, already installed interfaces
                 -> ErrMsgGhc Interface
-createInterface tm flags modMap instIfaceMap = do
+createInterface tm flags modMap instIfaceMap =
+ withExceptionContext (mkExceptionContext tm) $ do
 
   let ms             = pm_mod_summary . tm_parsed_module $ tm
       mi             = moduleInfo tm
@@ -207,7 +213,6 @@ createInterface tm flags modMap instIfaceMap = do
   , ifaceDynFlags          = dflags
   }
 
-
 -- | Given all of the @import M as N@ declarations in a package,
 -- create a mapping from the module identity of M, to an alias N
 -- (if there are multiple aliases, we pick the last one.)  This
@@ -652,7 +657,8 @@ collectDocs = go Nothing []
 -- We create the export items even if the module is hidden, since they
 -- might be useful when creating the export items for other modules.
 mkExportItems
-  :: Bool               -- is it a signature
+  :: HasCallStack
+  => Bool               -- is it a signature
   -> IfaceMap
   -> Maybe Package      -- this package
   -> Module             -- this module
@@ -711,7 +717,8 @@ mkExportItems
       availExportItem is_sig modMap thisMod semMod warnings exportedNames
         maps fixMap splices instIfaceMap dflags avail
 
-availExportItem :: Bool               -- is it a signature
+availExportItem :: HasCallStack
+                => Bool               -- is it a signature
                 -> IfaceMap
                 -> Module             -- this module
                 -> Module             -- semantic module
@@ -804,7 +811,7 @@ availExportItem is_sig modMap thisMod semMod warnings exportedNames
             Just synifiedDecl -> pure synifiedDecl
             Nothing -> O.pprPanic "availExportItem" (O.text err)
 
-    availExportDecl :: AvailInfo -> LHsDecl GhcRn
+    availExportDecl :: HasCallStack => AvailInfo -> LHsDecl GhcRn
                     -> (DocForDecl Name, [(Name, DocForDecl Name)])
                     -> ErrMsgGhc [ ExportItem GhcRn ]
     availExportDecl avail decl (doc, subs)
@@ -1075,7 +1082,8 @@ fullModuleContents is_sig modMap pkgName thisMod semMod warnings gre exportedNam
 -- This function looks through the declarations in this module to try to find
 -- the one with the right name.
 extractDecl
-  :: DeclMap                   -- ^ all declarations in the file
+  :: HasCallStack
+  => DeclMap                   -- ^ all declarations in the file
   -> Name                      -- ^ name of the declaration to extract
   -> LHsDecl GhcRn             -- ^ parent declaration
   -> Either ErrMsg (LHsDecl GhcRn)
@@ -1159,10 +1167,11 @@ extractDecl declMap name decl
               _ -> Left "internal: extractDecl (ClsInstD)"
       _ -> Left ("extractDecl: Unhandled decl for " ++ getOccString name)
 
-extractPatternSyn :: Name -> Name -> [LHsTypeArg GhcRn] -> [LConDecl GhcRn] -> Either ErrMsg (LSig GhcRn)
+extractPatternSyn :: HasCallStack => Name -> Name -> [LHsTypeArg GhcRn] -> [LConDecl GhcRn] -> Either ErrMsg (LSig GhcRn)
 extractPatternSyn nm t tvs cons =
   case filter matches cons of
-    [] -> Left "extractPatternSyn: constructor pattern not found"
+    [] -> Left . O.showSDocUnsafe $
+          O.text "constructor pattern " O.<+> O.ppr nm O.<+> O.text "not found in type" O.<+> O.ppr t
     con:_ -> pure (extract <$> con)
  where
   matches :: LConDecl GhcRn -> Bool