Added --strip-comments option, readerStripComments in ReaderOptions.

* Options:  Added readerStripComments to ReaderOptions.
* Added `--strip-comments` command-line option.
* Made `htmlTag` from the HTML reader sensitive to this feature.

This affects Markdown and Textile input.

Closes #2552.

MANUAL.txt

@@ -655,6 +655,14 @@ General writer options
     of contents.  The default is 3 (which means that level 1, 2, and 3
     headers will be listed in the contents).
 
+`--strip-comments`
+
+:   Strip out HTML comments in the Markdown or Textile source,
+    rather than passing them on to Markdown, Textile or HTML
+    output as raw HTML.  This does not apply to HTML comments
+    inside raw HTML blocks when the `markdown_in_html_blocks`
+    extension is not set.
+
 `--no-highlight`
 
 :   Disables syntax highlighting for code blocks and inlines, even when

src/Text/Pandoc/App.hs

@@ -483,6 +483,7 @@ convertWithOpts opts = do
           , readerTrackChanges = optTrackChanges opts
           , readerAbbreviations = abbrevs
           , readerExtensions = readerExts
+          , readerStripComments = optStripComments opts
           }
 
     let transforms = (case optBaseHeaderLevel opts of
@@ -666,6 +667,7 @@ data Opt = Opt
     , optIncludeInHeader       :: [FilePath]       -- ^ Files to include in header
     , optResourcePath          :: [FilePath] -- ^ Path to search for images etc
     , optEol                   :: LineEnding -- ^ Style of line-endings to use
+    , optStripComments          :: Bool       -- ^ Skip HTML comments
     } deriving (Generic, Show)
 
 instance ToJSON Opt where
@@ -742,6 +744,7 @@ defaultOpts = Opt
     , optIncludeInHeader       = []
     , optResourcePath          = ["."]
     , optEol                   = Native
+    , optStripComments          = False
     }
 
 addMetadata :: (String, String) -> Pandoc -> Pandoc
@@ -1114,6 +1117,11 @@ options =
                  "NUMBER")
                  "" -- "Length of line in characters"
 
+    , Option "" ["strip-comments"]
+                (NoArg
+                 (\opt -> return opt { optStripComments = True }))
+               "" -- "Strip HTML comments"
+
     , Option "" ["toc", "table-of-contents"]
                 (NoArg
                  (\opt -> return opt { optTableOfContents = True }))

src/Text/Pandoc/Options.hs

@@ -65,7 +65,8 @@ data ReaderOptions = ReaderOptions{
                                        -- indented code blocks
        , readerAbbreviations         :: Set.Set String -- ^ Strings to treat as abbreviations
        , readerDefaultImageExtension :: String -- ^ Default extension for images
-       , readerTrackChanges          :: TrackChanges
+       , readerTrackChanges          :: TrackChanges -- ^ Track changes setting for docx
+       , readerStripComments         :: Bool -- ^ Strip HTML comments instead of parsing as raw HTML
 } deriving (Show, Read, Data, Typeable, Generic)
 
 instance ToJSON ReaderOptions where
@@ -82,6 +83,7 @@ instance Default ReaderOptions
                , readerAbbreviations         = defaultAbbrevs
                , readerDefaultImageExtension = ""
                , readerTrackChanges          = AcceptChanges
+               , readerStripComments         = False
                }
 
 defaultAbbrevs :: Set.Set String

src/Text/Pandoc/Readers/HTML.hs

@@ -46,9 +46,10 @@ import qualified Text.Pandoc.Builder as B
 import Text.Pandoc.Builder (Blocks, Inlines, trimInlines, HasMeta(..))
 import Text.Pandoc.Shared ( extractSpaces, addMetaField
                           , escapeURI, safeRead, crFilter )
-import Text.Pandoc.Options (ReaderOptions(readerExtensions), extensionEnabled,
-                               Extension (Ext_epub_html_exts,
-                               Ext_raw_html, Ext_native_divs, Ext_native_spans))
+import Text.Pandoc.Options (
+         ReaderOptions(readerExtensions,readerStripComments), extensionEnabled,
+         Extension (Ext_epub_html_exts,
+                    Ext_raw_html, Ext_native_divs, Ext_native_spans))
 import Text.Pandoc.Logging
 import Text.Pandoc.Parsing hiding ((<|>))
 import Text.Pandoc.Walk
@@ -1070,7 +1071,7 @@ _ `closes` _ = False
 --- parsers for use in markdown, textile readers
 
 -- | Matches a stretch of HTML in balanced tags.
-htmlInBalanced :: (Monad m)
+htmlInBalanced :: (HasReaderOptions st, Monad m)
                => (Tag String -> Bool)
                -> ParserT String st m String
 htmlInBalanced f = try $ do
@@ -1118,7 +1119,7 @@ hasTagWarning (TagWarning _:_) = True
 hasTagWarning _ = False
 
 -- | Matches a tag meeting a certain condition.
-htmlTag :: Monad m
+htmlTag :: (HasReaderOptions st, Monad m)
         => (Tag String -> Bool)
         -> ParserT [Char] st m (Tag String, String)
 htmlTag f = try $ do
@@ -1153,7 +1154,10 @@ htmlTag f = try $ do
           count (length s + 4) anyChar
           skipMany (satisfy (/='>'))
           char '>'
-          return (next, "<!--" <> s <> "-->")
+          stripComments <- getOption readerStripComments
+          if stripComments
+             then return (next, "")
+             else return (next, "<!--" <> s <> "-->")
          | otherwise -> fail "bogus comment mode, HTML5 parse error"
        TagOpen tagname attr -> do
          guard $ all (isName . fst) attr

src/Text/Pandoc/Readers/Markdown.hs

@@ -1079,7 +1079,9 @@ htmlBlock' = try $ do
     first <- htmlElement
     skipMany spaceChar
     optional blanklines
-    return $ return $ B.rawBlock "html" first
+    return $ if null first
+                then mempty
+                else return $ B.rawBlock "html" first
 
 strictHtmlBlock :: PandocMonad m => MarkdownParser m String
 strictHtmlBlock = htmlInBalanced (not . isInlineTag)

test/command/2552.md

@@ -0,0 +1,14 @@
+```
+% pandoc --strip-comments
+Foo
+
+bar
+
+<!-- comment -->
+
+baz<!-- bim -->boop
+^D
+<p>Foo</p>
+<p>bar</p>
+<p>bazboop</p>
+```