Allow line comments end with end of input

Close #119.

CHANGELOG.md

@@ -3,6 +3,9 @@
 * Defined `displayException` for `ParseError`, so exceptions are displayed
   in human-friendly form now. This works with GHC 7.10 and later.
 
+* Line comments parsed by `skipLineComment` now may end at the end of input
+  and do not necessarily require a newline to be parsed correctly. See #119.
+
 ## Megaparsec 5.0.1
 
 * Derived `NFData` instances for `Pos`, `InvalidPosException`, `SourcePos`,

Text/Megaparsec/Lexer.hs

@@ -158,7 +158,7 @@ skipLineComment :: (MonadParsec e s m, Token s ~ Char)
   -> m ()
 skipLineComment prefix = p >> void (manyTill C.anyChar n)
   where p = C.string prefix
-        n = lookAhead C.newline
+        n = lookAhead (void C.newline) <|> eof
 
 -- | @skipBlockComment start end@ skips non-nested block comment starting
 -- with @start@ and ending with @end@.

tests/Lexer.hs

@@ -71,6 +71,7 @@ tests = testGroup "Lexer"
   [ testProperty "space combinator"       prop_space
   , testProperty "symbol combinator"      prop_symbol
   , testProperty "symbol' combinator"     prop_symbol'
+  , testCase     "case_skipLineCommentEof" case_skipLineCommentEof
   , testCase     "skipBlockCommentNested" case_skipBlockCommentNested
   , testProperty "indentLevel"            prop_indentLevel
   , testProperty "incorrectIndent"        prop_incorrectIndent
@@ -165,6 +166,12 @@ parseSymbol p' f s' t = checkParser p r s
         g = takeWhile (not . isSpace) s
         s = s' ++ maybeToList t
 
+case_skipLineCommentEof :: Assertion
+case_skipLineCommentEof = checkCase p r s
+  where p = space (void C.spaceChar) (skipLineComment "//") empty <* eof
+        r = Right ()
+        s = "  // this line comment doesn't have a newline at the end "
+
 case_skipBlockCommentNested :: Assertion
 case_skipBlockCommentNested = checkCase p r s
   where p = space (void C.spaceChar) empty