Fix parsing of identifiers written in infix way

4 files changed, 23 insertions, 12 deletions

diff --git a/CHANGES b/CHANGES
index 3a08424c..79a7e657 100644
--- a/CHANGES
+++ b/CHANGES
@@ -10,6 +10,8 @@ Changes in version 2.15.1
 
  * Fix re-exports of built-in type families (#310)
 
+ * Fix parsing of infix identifiers such as ``elem``.
+
 Changes in version 2.15.0
 
  * Always read in prologue files as UTF8 (#286 and Cabal #1721)
diff --git a/doc/haddock.xml b/doc/haddock.xml
index 618e19f2..3b58f824 100644
--- a/doc/haddock.xml
+++ b/doc/haddock.xml
@@ -1897,7 +1897,9 @@ module A where
         <para>Nothing special is needed to hyperlink identifiers which
         contain apostrophes themselves: to hyperlink
         <literal>foo'</literal> one would simply type
-        <literal>'foo''</literal>.</para>
+        <literal>'foo''</literal>. To hyperlink identifiers written in
+        infix form, simply put them in quotes as always:
+        <literal>'`elem`'</literal>.</para>
 
         <para>For compatibility with other systems, the following
         alternative form of markup is accepted<footnote><para>
diff --git a/haddock-library/src/Documentation/Haddock/Parser.hs b/haddock-library/src/Documentation/Haddock/Parser.hs
index 99010897..bea1803a 100644
--- a/haddock-library/src/Documentation/Haddock/Parser.hs
+++ b/haddock-library/src/Documentation/Haddock/Parser.hs
@@ -507,25 +507,26 @@ autoUrl = mkLink <$> url
 -- deems to be valid in an identifier. Note that it simply blindly consumes
 -- characters and does no actual validation itself.
 parseValid :: Parser String
-parseValid = do
-  vs' <- many' $ utf8String "⋆" <|> return <$> idChar
-  let vs = concat vs'
-  c <- peekChar
-  case c of
-    Just '`' -> return vs
-    Just '\'' -> (\x -> vs ++ "'" ++ x) <$> ("'" *> parseValid)
-                 <|> return vs
-    _ -> fail "outofvalid"
+parseValid = p some
   where
     idChar = satisfy (`elem` "_.!#$%&*+/<=>?@\\|-~:^")
              <|> digit <|> letter_ascii
+    p p' = do
+      vs' <- p' $ utf8String "⋆" <|> return <$> idChar
+      let vs = concat vs'
+      c <- peekChar
+      case c of
+        Just '`' -> return vs
+        Just '\'' -> (\x -> vs ++ "'" ++ x) <$> ("'" *> p many')
+                     <|> return vs
+        _ -> fail "outofvalid"
 
 -- | Parses UTF8 strings from ByteString streams.
 utf8String :: String -> Parser String
 utf8String x = decodeUtf8 <$> string (encodeUtf8 x)
 
--- | Parses identifiers with help of 'parseValid'. Asks GHC for 'String' from the
--- string it deems valid.
+-- | Parses identifiers with help of 'parseValid'. Asks GHC for
+-- 'String' from the string it deems valid.
 identifier :: Parser (DocH mod Identifier)
 identifier = do
   o <- idDelim
diff --git a/haddock-library/test/Documentation/Haddock/ParserSpec.hs b/haddock-library/test/Documentation/Haddock/ParserSpec.hs
index a228a956..5550e836 100644
--- a/haddock-library/test/Documentation/Haddock/ParserSpec.hs
+++ b/haddock-library/test/Documentation/Haddock/ParserSpec.hs
@@ -85,6 +85,12 @@ spec = do
         " don't use apostrophe's in the wrong place's" `shouldParseTo`
           "don't use apostrophe's in the wrong place's"
 
+      it "doesn't parse empty identifiers" $ do
+        "``" `shouldParseTo` "``"
+
+      it "can parse infix identifiers" $ do
+        "``infix``" `shouldParseTo` "`" <> DocIdentifier "infix" <> "`"
+
     context "when parsing URLs" $ do
       it "parses a URL" $ do
         "<http://example.com/>" `shouldParseTo` hyperlink "http://example.com/" Nothing