Docx reader: Avoid 0-level headers.

We used to parse paragraphs styled with "HeadingN" as "nth-level
header." But if a document has a custom style named "Heading0", this
will produce a 0-level header, which shouldn't exist. We only parse
this style if N>0. Otherwise we treat it as a normal style name, and
follow its dependencies, if any.

Closes #3830.

1 files changed, 5 insertions, 6 deletions

diff --git a/src/Text/Pandoc/Readers/Docx/Parse.hs b/src/Text/Pandoc/Readers/Docx/Parse.hs
index 24615ba94..05ce691a6 100644
--- a/src/Text/Pandoc/Readers/Docx/Parse.hs
+++ b/src/Text/Pandoc/Readers/Docx/Parse.hs
@@ -61,7 +61,7 @@ import Control.Monad.Reader
 import Control.Monad.State.Strict
 import Data.Bits ((.|.))
 import qualified Data.ByteString.Lazy as B
-import Data.Char (chr, isDigit, ord, readLitChar)
+import Data.Char (chr, ord, readLitChar)
 import Data.List
 import qualified Data.Map as M
 import Data.Maybe
@@ -939,19 +939,18 @@ elemToRunStyle ns element parentStyle
         }
 elemToRunStyle _ _ _ = defaultRunStyle
 
-isNumericNotNull :: String -> Bool
-isNumericNotNull str = (str /= []) && (all isDigit str)
-
 getHeaderLevel :: NameSpaces -> Element -> Maybe (String,Int)
 getHeaderLevel ns element
   | Just styleId <- findAttrByName ns "w" "styleId" element
   , Just index   <- stripPrefix "Heading" styleId
-  , isNumericNotNull index = Just (styleId, read index)
+  , Just n       <- stringToInteger index
+  , n > 0 = Just (styleId, fromInteger n)
   | Just styleId <- findAttrByName ns "w" "styleId" element
   , Just index   <- findChildByName ns "w" "name" element >>=
                     findAttrByName ns "w" "val" >>=
                     stripPrefix "heading "
-  , isNumericNotNull index = Just (styleId, read index)
+  , Just n <- stringToInteger index
+  , n > 0 = Just (styleId, fromInteger n)
 getHeaderLevel _ _ = Nothing
 
 blockQuoteStyleIds :: [String]