Properly handle boolean values in writing YAML metadata.

(Markdown writer.)
This requires doctemplates >= 0.9.
Closes #6388.

pandoc.cabal

@@ -410,7 +410,7 @@ library
                  deepseq               >= 1.3      && < 1.5,
                  directory             >= 1.2.3    && < 1.4,
                  doclayout             >= 0.3      && < 0.4,
-                 doctemplates          >= 0.8.2    && < 0.9,
+                 doctemplates          >= 0.9      && < 0.10,
                  emojis                >= 0.1      && < 0.2,
                  exceptions            >= 0.8      && < 0.11,
                  file-embed            >= 0.0      && < 0.1,
@@ -767,7 +767,7 @@ test-suite test-pandoc
                   bytestring        >= 0.9     && < 0.12,
                   containers        >= 0.4.2.1 && < 0.7,
                   directory         >= 1.2.3   && < 1.4,
-                  doctemplates      >= 0.8.2   && < 0.9,
+                  doctemplates      >= 0.9     && < 0.10,
                   exceptions        >= 0.8     && < 0.11,
                   executable-path   >= 0.0     && < 0.1,
                   filepath          >= 1.1     && < 1.5,

src/Text/Pandoc/Writers/Markdown.hs

@@ -174,6 +174,8 @@ valToYaml :: Val Text -> Doc Text
 valToYaml (ListVal xs) =
   vcat $ map (\v -> hang 2 "- " (valToYaml v)) xs
 valToYaml (MapVal c) = contextToYaml c
+valToYaml (BoolVal True) = "true"
+valToYaml (BoolVal False) = "false"
 valToYaml (SimpleVal x)
   | isEmpty x = empty
   | otherwise =

src/Text/Pandoc/Writers/Shared.hs

@@ -109,8 +109,7 @@ metaValueToVal blockWriter inlineWriter (MetaMap metamap) =
   MapVal . Context <$> mapM (metaValueToVal blockWriter inlineWriter) metamap
 metaValueToVal blockWriter inlineWriter (MetaList xs) = ListVal <$>
   mapM (metaValueToVal blockWriter inlineWriter) xs
-metaValueToVal _ _ (MetaBool True) = return $ SimpleVal "true"
-metaValueToVal _ _ (MetaBool False) = return NullVal
+metaValueToVal _ _ (MetaBool b) = return $ BoolVal b
 metaValueToVal _ inlineWriter (MetaString s) =
    SimpleVal <$> inlineWriter (Builder.toList (Builder.text s))
 metaValueToVal blockWriter _ (MetaBlocks bs) = SimpleVal <$> blockWriter bs

stack.yaml

@@ -16,7 +16,10 @@ extra-deps:
 - commonmark-0.1.1.2
 - commonmark-extensions-0.2.0.4
 - commonmark-pandoc-0.2.0.1
-- doctemplates-0.8.3
+# - doctemplates-0.8.3
+- doctemplates:
+  git: https://github.com/jgm/doctemplates.git
+  commit: 6cb8d09264f7c1f4b59ac67ff98b1a664a85e36a
 - citeproc-0.2.0.1
 # - citeproc:
 #   git: https://github.com/jgm/citeproc.git

test/command/6388.md

@@ -0,0 +1,16 @@
+```
+% pandoc -t markdown -s
+---
+nvalue: false
+value: true
+---
+
+text
+^D
+---
+nvalue: false
+value: true
+---
+
+text
+```