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.

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

test/command/1279.md

@@ -9,7 +9,7 @@ title: My Article
 [^1]: Dept. of This and That
 ^D
 ---
-author: "John Doe[^1]"
+author: John Doe[^1]
 date: 2014
 title: My Article
 ---

test/command/biblatex-inproceedings.md

@@ -63,7 +63,7 @@ references:
   publisher-place: Cambridge
   title: "Le *De Anima* dans la tradition grècque: Quelques aspects de
     l'interpretation du traité, de Theophraste à Themistius"
-  title-short: *De Anima* dans la tradition grècque
+  title-short: "*De Anima* dans la tradition grècque"
   type: paper-conference
 - author:
   - family: Salam

test/command/biblatex-jaffe.md

@@ -72,8 +72,8 @@ references:
   language: la
   number-of-volumes: 2
   publisher-place: Leipzig
-  title: "Regesta Pontificum Romanorum ab condita ecclesia ad annum post
-    Christum natum [mcxcviii]{.smallcaps}"
+  title: Regesta Pontificum Romanorum ab condita ecclesia ad annum post
+    Christum natum [mcxcviii]{.smallcaps}
   title-short: Regesta Pontificum Romanorum
   type: book
 ---

test/command/biblatex-moraux.md

@@ -86,7 +86,7 @@ references:
   publisher-place: Cambridge
   title: "Le *De Anima* dans la tradition grècque: Quelques aspects de
     l'interpretation du traité, de Theophraste à Themistius"
-  title-short: *De Anima* dans la tradition grècque
+  title-short: "*De Anima* dans la tradition grècque"
   type: paper-conference
 ---
 

test/command/biblatex-quotes.md

@@ -36,7 +36,7 @@ references:
   language: en-US
   publisher: Princeton University Press
   publisher-place: Princeton
-  title: "Aristotle's \"De Motu Animalium\""
+  title: Aristotle's "De Motu Animalium"
   type: book
 ---
 

test/command/biblatex-spiegelberg.md

@@ -63,8 +63,8 @@ references:
   issued: 1969
   language: de-DE
   page: 189-216
-  title: "Intention" und "Intentionalität" in der Scholastik, bei
-    Brentano und Husserl
+  title: "\"Intention\" und \"Intentionalität\" in der Scholastik, bei
+    Brentano und Husserl"
   title-short: Intention und Intentionalität
   type: article-journal
   volume: 29

test/command/biblatex-test-case-conversion.md

@@ -63,9 +63,9 @@ references:
   id: item1
   issued: 2013
   language: en-US
-  title: "A title, in English, with a Proper Name and an ACRONYM and a
+  title: A title, in English, with a Proper Name and an ACRONYM and a
     [camelCase]{.nocase} word and some units, 400 [nm]{.nocase},
-    3 [cm]{.nocase}, and a quote, *Alea [iacta est]{.nocase}*"
+    3 [cm]{.nocase}, and a quote, *Alea [iacta est]{.nocase}*
   type: article-journal
 ---
 

test/command/biblatex-textnormal.md

@@ -9,7 +9,7 @@
 nocite: "[@*]"
 references:
 - id: item1
-  title: "The title [of this book]{.nodecor}"
+  title: The title [of this book]{.nodecor}
   type: book
 ---