RST reader: allow < 3 spaces indent under directives.

Closes #4579.

src/Text/Pandoc/Readers/RST.hs

@@ -651,11 +651,15 @@ directive' = do
   skipMany spaceChar
   top <- many $ satisfy (/='\n')
              <|> try (char '\n' <*
-                      notFollowedBy' (rawFieldListItem 3) <*
-                      count 3 (char ' ') <*
+                      notFollowedBy' (rawFieldListItem 1) <*
+                      many1 (char ' ') <*
                       notFollowedBy blankline)
   newline
-  fields <- many $ rawFieldListItem 3
+  fields <- do
+    fieldIndent <- length <$> lookAhead (many (char ' '))
+    if fieldIndent == 0
+       then return []
+       else many $ rawFieldListItem fieldIndent
   body <- option "" $ try $ blanklines >> indentedBlock
   optional blanklines
   let body' = body ++ "\n\n"

test/command/4579.md

@@ -0,0 +1,16 @@
+```
+% pandoc -f rst -t native
+.. list-table::
+  :header-rows: 1
+
+  * - Foo
+    - Bar
+  * - spam
+    - ham
+^D
+[Table [] [AlignDefault,AlignDefault] [0.0,0.0]
+ [[Plain [Str "Foo"]]
+ ,[Plain [Str "Bar"]]]
+ [[[Plain [Str "spam"]]
+  ,[Plain [Str "ham"]]]]]
+```