Fix #41

src/Language/Docopt/Parser/Desc.purs

@@ -17,10 +17,12 @@ import Data.Function (on)
 import Data.String as Str
 import Control.Lazy (defer)
 import Control.Bind ((>=>))
+import Control.Monad (when)
 import Control.Alt ((<|>))
 import Control.Apply ((*>), (<*))
 import Control.MonadPlus (guard)
-import Data.List (List, (:), many, some, head, length, filter, catMaybes)
+import Data.List (List(..), (:), many, some, head, length, filter, catMaybes,
+                  reverse)
 import Text.Parsing.Parser (ParseError, fail) as P
 import Text.Parsing.Parser.Combinators ((<?>), try, choice, lookAhead, manyTill,
                                         option, optionMaybe, notFollowedBy,
@@ -193,8 +195,19 @@ parse :: (List L.PositionedToken) -> Either P.ParseError (List Desc)
 parse = flip L.runTokenParser descParser
 
 descParser :: L.TokenParser (List Desc)
-descParser = markIndent do many desc <* L.eof
+descParser = markIndent do
+  reverse <$> go Nil
+  <* L.eof
   where
+    go vs = do
+      v <- (Just <$> desc) <|> (descContent true $> Nothing)
+      case v of
+        Just v' -> go (v' : vs)
+        Nothing ->
+          P.choice [
+            desc >>= \v' -> go (v' : vs)
+          , pure vs
+          ]
 
     anyName :: L.TokenParser String
     anyName = L.angleName <|> L.shoutName <|> L.name
@@ -205,8 +218,8 @@ descParser = markIndent do many desc <* L.eof
                        , positionalsDesc
                        ]
 
-    descContent :: L.TokenParser (List Content)
-    descContent = do
+    descContent :: Boolean -> L.TokenParser (List Content)
+    descContent toplevel = do
       markIndent do
         catMaybes <$> (flip P.manyTill descEnd do
           P.choice $ P.try <$> [
@@ -221,7 +234,8 @@ descParser = markIndent do many desc <* L.eof
             L.eof
           , void $ P.lookAhead do
               L.newline
-              lessIndented
+              when (not toplevel)
+                lessIndented
               P.choice [
                 void L.sopt
               , void L.lopt
@@ -234,14 +248,14 @@ descParser = markIndent do many desc <* L.eof
     positionalsDesc = do
       L.angleName <|> L.shoutName
       repeatable <- P.option false $ L.tripleDot $> true
-      descContent
+      descContent false
       pure CommandDesc
 
     optionDesc :: L.TokenParser Desc
     optionDesc = do
 
       xopt        <- opt
-      description <- descContent
+      description <- descContent false
 
       let defaults = getDefaultValue <$> filter isDefaultTag description
           envs     = getEnvKey       <$> filter isEnvTag     description

test/Test/Spec/DescParserSpec.purs

@@ -141,6 +141,72 @@ descParserSpec = \_ ->
         , fail
               "-f=BAZ, --foo=qux"
               "Option-arguments mismatch: \"BAZ\" and \"qux\""
+        , pass (dedent
+          -- Fix #41
+          -- Should allow non-empty option sections that contain no options.
+          """
+          foo bar
+          """
+          ) []
+        , pass (dedent
+          -- Fix #41
+          -- Should allow non-empty option sections that contain no options.
+          """
+          foo bar
+          -f=BAZ, --foo=BAZ [default: 100]
+          -q=BAZ, --qux=BAZ [default: 200]
+          """
+          ) [ o { name:       Desc.Full 'f' "foo"
+                , arg:        Just $ arg "BAZ" (int 100)
+                , env:        Nothing
+                , repeatable: false
+                }
+            , o { name:       Desc.Full 'q' "qux"
+                , arg:        Just $ arg "BAZ" (int 200)
+                , env:        Nothing
+                , repeatable: false
+                }
+            ]
+        , pass (dedent
+          -- Fix #41
+          -- Should allow non-empty option sections that contain no options.
+          """
+          -f=BAZ, --foo=BAZ [default: 100]
+          foo bar
+          -q=BAZ, --qux=BAZ [default: 200]
+          """
+          ) [ o { name:       Desc.Full 'f' "foo"
+                , arg:        Just $ arg "BAZ" (int 100)
+                , env:        Nothing
+                , repeatable: false
+                }
+            , o { name:       Desc.Full 'q' "qux"
+                , arg:        Just $ arg "BAZ" (int 200)
+                , env:        Nothing
+                , repeatable: false
+                }
+            ]
+        , pass (dedent
+          -- Fix #41
+          -- Should allow non-empty option sections that contain no options.
+          """
+          foo bar
+          -f=BAZ, --foo=BAZ [default: 100]
+          foo bar
+          -q=BAZ, --qux=BAZ [default: 200]
+          foo bar
+          """
+          ) [ o { name:       Desc.Full 'f' "foo"
+                , arg:        Just $ arg "BAZ" (int 100)
+                , env:        Nothing
+                , repeatable: false
+                }
+            , o { name:       Desc.Full 'q' "qux"
+                , arg:        Just $ arg "BAZ" (int 200)
+                , env:        Nothing
+                , repeatable: false
+                }
+            ]
         , pass (dedent
             -- if an option is indented past the start of the description
             -- block for the previous option, it's considered part of the