RST reader: change treatment of number-lines directives.

Directives of this type without numeric inputs should not have a
`startFrom` attribute; with a blank value, the writers can produce
extra whitespace.

pandoc.cabal

@@ -189,6 +189,7 @@ extra-source-files:
                  test/command/*.md
                  test/command/3533-rst-csv-tables.csv
                  test/command/3880.txt
+                 test/command/5182.txt
                  test/command/abbrevs
                  test/command/SVG_logo-without-xml-declaration.svg
                  test/command/SVG_logo.svg

src/Text/Pandoc/Readers/RST.hs

@@ -505,7 +505,11 @@ includeDirective top fields body = do
          let numberLines = lookup "number-lines" fields
          let classes = trimr lang : ["numberLines" | isJust numberLines] ++
                           maybe [] words (lookup "class" fields)
-         let kvs = maybe [] (\n -> [("startFrom", trimr n)]) numberLines
+         let kvs = maybe [] (\n -> let tn = trimr n
+                                   in if tn == ""
+                                        then []
+                                        else [("startFrom", tn)])
+                            numberLines
          let ident = maybe "" trimr $ lookup "name" fields
          let attribs = (ident, classes, kvs)
          return $ B.codeBlockWith attribs contents'
@@ -999,9 +1003,11 @@ codeblock ident classes numberLines lang body =
                     : maybe [] (const ["numberLines"]) numberLines
                     ++ classes
           kvs     = case numberLines of
-                          Just "" -> []
                           Nothing -> []
-                          Just n  -> [("startFrom",trim n)]
+                          Just n
+                            | trn == "" -> []
+                            | otherwise -> [("startFrom", trn)]
+                            where trn = trimr n
 
 ---
 --- note block

test/Tests/Readers/RST.hs

@@ -112,15 +112,15 @@ tests = [ "line block with blank line" =:
                   "def func(x):\n  return y")
         , "Code directive with number-lines, no line specified" =: T.unlines
             [ ".. code::python"
-            , "   :number-lines: "
+            , "   :number-lines:"
             , ""
             , "  def func(x):"
             , "    return y"
             ]  =?>
               doc (codeBlockWith
                   ( ""
                   , ["python", "numberLines"]
-                  , [ ("startFrom", "") ]
+                  , []
                   )
                   "def func(x):\n  return y")
         , testGroup "literal / line / code blocks"

test/command/5182.md

@@ -0,0 +1,6 @@
+```
+pandoc -f rst -t native
+.. include:: command/5182.txt
+^D
+[CodeBlock ("",["python","numberLines"],[]) "def func(x):\n  return y"]
+```

test/command/5182.txt

@@ -0,0 +1,5 @@
+.. code::python
+   :number-lines:
+
+  def func(x):
+    return y