Make `plain` output plainer.

Previously we used the following Project Gutenberg conventions
for plain output:

- extra space before and after level 1 and 2 headings
- all-caps for strong emphasis `LIKE THIS`
- underscores surrounding regular emphasis `_like this_`

This commit makes `plain` output plainer. Strong and Emph
inlines are rendered without special formatting.  Headings
are also rendered without special formatting, and with only
one blank line following.

To restore the former behavior, use `-t plain+gutenberg`.

API change: Add `Ext_gutenberg` constructor to `Extension`.

See #5741.

2 files changed, 17 insertions, 5 deletions

diff --git a/src/Text/Pandoc/Extensions.hs b/src/Text/Pandoc/Extensions.hs
index 6cb87eef6..121b60e7b 100644
--- a/src/Text/Pandoc/Extensions.hs
+++ b/src/Text/Pandoc/Extensions.hs
@@ -155,6 +155,7 @@ data Extension =
     | Ext_tex_math_double_backslash  -- ^ TeX math btw \\(..\\) \\[..\\]
     | Ext_tex_math_single_backslash  -- ^ TeX math btw \(..\) \[..\]
     | Ext_yaml_metadata_block -- ^ YAML metadata block
+    | Ext_gutenberg           -- ^ Use Project Gutenberg conventions for plain
     deriving (Show, Read, Enum, Eq, Ord, Bounded, Data, Typeable, Generic)
 
 -- | Extensions to be used with pandoc-flavored markdown.
diff --git a/src/Text/Pandoc/Writers/Markdown.hs b/src/Text/Pandoc/Writers/Markdown.hs
index e298fafe9..fc25cde44 100644
--- a/src/Text/Pandoc/Writers/Markdown.hs
+++ b/src/Text/Pandoc/Writers/Markdown.hs
@@ -523,16 +523,22 @@ blockToMarkdown' opts (Header level attr inlines) = do
   contents <- inlineListToMarkdown opts $
                  -- ensure no newlines; see #3736
                  walk lineBreakToSpace $
-                 if level == 1 && plain
+                 if level == 1 && plain && isEnabled Ext_gutenberg opts
                     then capitalize inlines
                     else inlines
   let setext = writerSetextHeaders opts
       hdr = nowrap $ case level of
-            1 | plain -> blanklines 3 <> contents <> blanklines 2
+            1 | plain ->
+                if isEnabled Ext_gutenberg opts
+                   then blanklines 3 <> contents <> blanklines 2
+                   else contents <> blankline
               | setext ->
                   contents <> attr' <> cr <> text (replicate (offset contents) '=') <>
                   blankline
-            2 | plain -> blanklines 2 <> contents <> blankline
+            2 | plain ->
+                if isEnabled Ext_gutenberg opts
+                   then blanklines 2 <> contents <> blankline
+                   else contents <> blankline
               | setext ->
                   contents <> attr' <> cr <> text (replicate (offset contents) '-') <>
                   blankline
@@ -1036,13 +1042,18 @@ inlineToMarkdown opts (Emph lst) = do
   plain <- asks envPlain
   contents <- inlineListToMarkdown opts lst
   return $ if plain
-              then "_" <> contents <> "_"
+              then if isEnabled Ext_gutenberg opts
+                      then "_" <> contents <> "_"
+                      else contents
               else "*" <> contents <> "*"
 inlineToMarkdown _ (Strong []) = return empty
 inlineToMarkdown opts (Strong lst) = do
   plain <- asks envPlain
   if plain
-     then inlineListToMarkdown opts $ capitalize lst
+     then inlineListToMarkdown opts $
+          if isEnabled Ext_gutenberg opts
+             then capitalize lst
+             else lst
      else do
        contents <- inlineListToMarkdown opts lst
        return $ "**" <> contents <> "**"