From 55c524e83cda8ab90b3b202e32b79106b408efb0 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Sat, 13 Aug 2022 12:57:28 -0700
Subject: [PATCH] Support --strip-comments in commonmark/gfm.

This change makes the commonmark reader sensitive to
`readerStripComments`.

Closes #8222.
---
 src/Text/Pandoc/Readers/CommonMark.hs | 47 ++++++++++++++++++++++-----
 1 file changed, 38 insertions(+), 9 deletions(-)

diff --git a/src/Text/Pandoc/Readers/CommonMark.hs b/src/Text/Pandoc/Readers/CommonMark.hs
index ecc6505f8..528d84dbf 100644
--- a/src/Text/Pandoc/Readers/CommonMark.hs
+++ b/src/Text/Pandoc/Readers/CommonMark.hs
@@ -34,7 +34,10 @@ import Text.Pandoc.Parsing (runParserT, getInput, getPosition,
                             runF, defaultParserState, option, many1, anyChar,
                             Sources(..), ToSources(..), ParserT, Future,
                             sourceName, sourceLine, incSourceLine)
+import Text.Pandoc.Walk (walk)
 import qualified Data.Text as T
+import qualified Data.Attoparsec.Text as A
+import Control.Applicative ((<|>))
 
 -- | Parse a CommonMark formatted string into a 'Pandoc' structure.
 readCommonMark :: (PandocMonad m, ToSources a)
@@ -86,15 +89,41 @@ metaValueParser opts = do
      Right (Cm bls :: Cm () Blocks) -> return $ return $ B.toMetaValue bls
 
 readCommonMarkBody :: PandocMonad m => ReaderOptions -> Sources -> [Tok] -> m Pandoc
-readCommonMarkBody opts s toks
-  | isEnabled Ext_sourcepos opts =
-    case runIdentity (parseCommonmarkWith (specFor opts) toks) of
-      Left err -> throwError $ PandocParsecError s err
-      Right (Cm bls :: Cm SourceRange Blocks) -> return $ B.doc bls
-  | otherwise =
-    case runIdentity (parseCommonmarkWith (specFor opts) toks) of
-      Left err -> throwError $ PandocParsecError s err
-      Right (Cm bls :: Cm () Blocks) -> return $ B.doc bls
+readCommonMarkBody opts s toks =
+  (if readerStripComments opts
+      then walk stripBlockComments . walk stripInlineComments
+      else id) <$>
+  if isEnabled Ext_sourcepos opts
+     then case runIdentity (parseCommonmarkWith (specFor opts) toks) of
+            Left err -> throwError $ PandocParsecError s err
+            Right (Cm bls :: Cm SourceRange Blocks) -> return $ B.doc bls
+     else case runIdentity (parseCommonmarkWith (specFor opts) toks) of
+            Left err -> throwError $ PandocParsecError s err
+            Right (Cm bls :: Cm () Blocks) -> return $ B.doc bls
+
+stripBlockComments :: Block -> Block
+stripBlockComments (RawBlock (B.Format "html") s) =
+  RawBlock (B.Format "html") (removeComments s)
+stripBlockComments x = x
+
+stripInlineComments :: Inline -> Inline
+stripInlineComments (RawInline (B.Format "html") s) =
+  RawInline (B.Format "html") (removeComments s)
+stripInlineComments x = x
+
+removeComments :: Text -> Text
+removeComments s =
+  either (const s) id $ A.parseOnly pRemoveComments s
+ where
+  pRemoveComments = mconcat <$> A.many'
+    ("" <$ (A.string "<!--" *> A.scan (0 :: Int) scanChar <* A.char '>') <|>
+     (A.takeWhile1 (/= '<')) <|>
+     (A.string "<"))
+  scanChar st c =
+    case c of
+      '-' -> Just (st + 1)
+      '>' | st >= 2 -> Nothing
+      _ -> Just 0
 
 specFor :: (Monad m, Typeable m, Typeable a,
             Rangeable (Cm a Inlines), Rangeable (Cm a Blocks))