Output pattern synonyms in Hoogle backend (#947)

* Output pattern synonyms in Hoogle backend

We were previously weren't outputting _any_ pattern synonyms, bundled or
not. Now, we output both.

Fixes #946.

* Update changelog

4 files changed, 50 insertions, 8 deletions

diff --git a/CHANGES.md b/CHANGES.md
index c1801716..7ed90cdc 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -4,6 +4,8 @@
 
  * Support type and data families in the LaTeX backend (#734)
 
+ * Support pattern synonyms in the Hoogle backend (#947)
+
 ## Changes in version 2.21.0
 
  * Overhaul handling of data declarations in XHTML and LaTeX. Adds support for
diff --git a/haddock-api/src/Haddock/Backends/Hoogle.hs b/haddock-api/src/Haddock/Backends/Hoogle.hs
index 885c608b..5f77c38c 100644
--- a/haddock-api/src/Haddock/Backends/Hoogle.hs
+++ b/haddock-api/src/Haddock/Backends/Hoogle.hs
@@ -122,10 +122,14 @@ commaSeparate dflags = showSDocUnqual dflags . interpp'SP
 
 ppExport :: DynFlags -> ExportItem GhcRn -> [String]
 ppExport dflags ExportDecl { expItemDecl    = L _ decl
-                           , expItemMbDoc   = (dc, _)
+                           , expItemPats    = bundledPats
+                           , expItemMbDoc   = mbDoc
                            , expItemSubDocs = subdocs
                            , expItemFixities = fixities
-                           } = ppDocumentation dflags dc ++ f decl ++ ppFixities
+                           } = concat [ ppDocumentation dflags dc ++ f d
+                                      | (d, (dc, _)) <- (decl, mbDoc) : bundledPats
+                                      ] ++
+                               ppFixities
     where
         f (TyClD _ d@DataDecl{})  = ppData dflags d subdocs
         f (TyClD _ d@SynDecl{})   = ppSynonym dflags d
@@ -140,12 +144,13 @@ ppExport dflags ExportDecl { expItemDecl    = L _ decl
 ppExport _ _ = []
 
 ppSigWithDoc :: DynFlags -> Sig GhcRn -> [(Name, DocForDecl Name)] -> [String]
-ppSigWithDoc dflags (TypeSig _ names sig) subdocs
-    = concatMap mkDocSig names
-    where
-        mkDocSig n = mkSubdoc dflags n subdocs [pp_sig dflags [n] (hsSigWcType sig)]
-
-ppSigWithDoc _ _ _ = []
+ppSigWithDoc dflags sig subdocs = case sig of
+    TypeSig _ names t -> concatMap (mkDocSig "" (hsSigWcType t)) names
+    PatSynSig _ names t -> concatMap (mkDocSig "pattern " (hsSigType t)) names
+    _ -> []
+  where
+    mkDocSig leader typ n = mkSubdoc dflags n subdocs
+                                     [leader ++ pp_sig dflags [n] typ]
 
 ppSig :: DynFlags -> Sig GhcRn -> [String]
 ppSig dflags x  = ppSigWithDoc dflags x []
diff --git a/hoogle-test/ref/Bug946/test.txt b/hoogle-test/ref/Bug946/test.txt
new file mode 100644
index 00000000..ff63a766
--- /dev/null
+++ b/hoogle-test/ref/Bug946/test.txt
@@ -0,0 +1,19 @@
+-- Hoogle documentation, generated by Haddock
+-- See Hoogle, http://www.haskell.org/hoogle/
+
+@package test
+@version 0.0.0
+
+module Bug946
+
+-- | A wrapper around <a>Int</a>
+data AnInt
+
+-- | some <a>Int</a>
+AnInt :: Int -> AnInt
+
+-- | The <a>Int</a> 0
+pattern Zero :: AnInt
+
+-- | The double 2.5
+pattern TwoPointFive :: Double
diff --git a/hoogle-test/src/Bug946/Bug946.hs b/hoogle-test/src/Bug946/Bug946.hs
new file mode 100644
index 00000000..606b5ac4
--- /dev/null
+++ b/hoogle-test/src/Bug946/Bug946.hs
@@ -0,0 +1,16 @@
+{-# LANGUAGE PatternSynonyms #-}
+module Bug946 (
+  AnInt(AnInt, Zero),
+  pattern TwoPointFive,
+) where
+
+-- | A wrapper around 'Int'
+data AnInt = AnInt Int -- ^ some 'Int'
+
+-- | The 'Int' 0
+pattern Zero :: AnInt
+pattern Zero = AnInt 0
+
+-- | The double 2.5
+pattern TwoPointFive :: Double
+pattern TwoPointFive = 2.5