Add quotes properly in markdown YAML metadata fields.

This fixes a bug, which caused the writer to look at the LAST
rather than the FIRST character in determining whether quotes
were needed.  So we got spurious quotes in some cases and
didn't get necessary quotes in others.

Closes #7245.  Updated a number of test cases accordingly.

1 files changed, 5 insertions, 6 deletions

diff --git a/src/Text/Pandoc/Writers/Markdown.hs b/src/Text/Pandoc/Writers/Markdown.hs
index daf45ed53..3295d9e6c 100644
--- a/src/Text/Pandoc/Writers/Markdown.hs
+++ b/src/Text/Pandoc/Writers/Markdown.hs
@@ -26,7 +26,7 @@ import Data.Default
 import Data.List (intersperse, sortOn, transpose)
 import Data.List.NonEmpty (nonEmpty, NonEmpty(..))
 import qualified Data.Map as M
-import Data.Maybe (fromMaybe, mapMaybe)
+import Data.Maybe (fromMaybe, mapMaybe, isNothing)
 import qualified Data.Set as Set
 import Data.Text (Text)
 import qualified Data.Text as T
@@ -142,18 +142,17 @@ valToYaml (SimpleVal x)
   | otherwise =
       if hasNewlines x
          then hang 0 ("|" <> cr) x
-         else if fst $ foldr needsDoubleQuotes (False, True) x
+         else if isNothing $ foldM needsDoubleQuotes True x
            then "\"" <> fmap escapeInDoubleQuotes x <> "\""
            else x
     where
-      needsDoubleQuotes t (positive, isFirst)
+      needsDoubleQuotes isFirst t
         = if T.any isBadAnywhere t ||
              (isFirst && T.any isYamlPunct (T.take 1 t))
-              then (True, False)
-              else (positive, False)
+              then Nothing
+              else Just False
       isBadAnywhere '#' = True
       isBadAnywhere ':' = True
-      isBadAnywhere '`' = False
       isBadAnywhere _   = False
       hasNewlines NewLine = True
       hasNewlines BlankLines{} = True