From a2c4261b32d3ed3fd6562a5260d25a82d9f75e9b Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Fri, 24 Aug 2018 18:04:00 -0700
Subject: [PATCH] HTML reader: allow enabling `raw_tex` extension.

This now allows raw LaTeX environments, `\ref`, and `\eqref` to
be parsed (which is helpful for translation HTML documents using
MathJaX).

Closes #1126.
---
 MANUAL.txt                      |  3 ++-
 src/Text/Pandoc/Readers/HTML.hs | 31 ++++++++++++++++++++++++++++---
 test/command/1126.md            | 29 +++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 4 deletions(-)
 create mode 100644 test/command/1126.md

diff --git a/MANUAL.txt b/MANUAL.txt
index 7ba9e188e..4c68bfa86 100644
--- a/MANUAL.txt
+++ b/MANUAL.txt
@@ -1917,7 +1917,8 @@ This extension can be enabled/disabled for the following formats
 (in addition to `markdown`):
 
 input formats
-:  `latex`, `org`, `textile`
+:  `latex`, `org`, `textile`, `html` (environments, `\ref`, and
+   `\eqref` only)
 
 output formats
 :  `textile`, `commonmark`
diff --git a/src/Text/Pandoc/Readers/HTML.hs b/src/Text/Pandoc/Readers/HTML.hs
index 697ab89e9..ea62bfcbf 100644
--- a/src/Text/Pandoc/Readers/HTML.hs
+++ b/src/Text/Pandoc/Readers/HTML.hs
@@ -68,11 +68,13 @@ import qualified Text.Pandoc.Builder as B
 import Text.Pandoc.Class (PandocMonad (..))
 import Text.Pandoc.CSS (foldOrElse, pickStyleAttrProps)
 import Text.Pandoc.Definition
+import Text.Pandoc.Readers.LaTeX (rawLaTeXInline)
+import Text.Pandoc.Readers.LaTeX.Types (Macro)
 import Text.Pandoc.Error
 import Text.Pandoc.Logging
 import Text.Pandoc.Options (
     Extension (Ext_epub_html_exts, Ext_empty_paragraphs, Ext_native_divs,
-               Ext_native_spans, Ext_raw_html, Ext_line_blocks),
+               Ext_native_spans, Ext_raw_html, Ext_line_blocks, Ext_raw_tex),
     ReaderOptions (readerExtensions, readerStripComments),
     extensionEnabled)
 import Text.Pandoc.Parsing hiding ((<|>))
@@ -102,7 +104,8 @@ readHtml opts inp = do
                                          (m:_) -> messageString m
   result <- flip runReaderT def $
        runParserT parseDoc
-       (HTMLState def{ stateOptions = opts } [] Nothing Set.empty M.empty [])
+       (HTMLState def{ stateOptions = opts }
+         [] Nothing Set.empty M.empty [] M.empty)
        "source" tags
   case result of
     Right doc -> return doc
@@ -124,7 +127,8 @@ data HTMLState =
      baseHref    :: Maybe URI,
      identifiers :: Set.Set String,
      headerMap   :: M.Map Inlines String,
-     logMessages :: [LogMessage]
+     logMessages :: [LogMessage],
+     macros      :: M.Map Text Macro
   }
 
 data HTMLLocal = HTMLLocal { quoteContext :: QuoteContext
@@ -907,9 +911,25 @@ pTagContents =
   <|> pStr
   <|> pSpace
   <|> smartPunctuation pTagContents
+  <|> pRawTeX
   <|> pSymbol
   <|> pBad
 
+pRawTeX :: PandocMonad m => InlinesParser m Inlines
+pRawTeX = do
+  lookAhead $ try $ do
+    char '\\'
+    choice $ map (try . string) ["begin", "eqref", "ref"]
+  guardEnabled Ext_raw_tex
+  inp <- getInput
+  st <- getState
+  res <- lift $ runParserT (withRaw rawLaTeXInline) st "chunk" (T.unpack inp)
+  case res of
+       Left _                -> mzero
+       Right (contents, raw) -> do
+         _ <- count (length raw) anyChar
+         return $ B.rawInline "tex" contents
+
 pStr :: PandocMonad m => InlinesParser m Inlines
 pStr = do
   result <- many1 $ satisfy $ \c ->
@@ -923,6 +943,7 @@ isSpecial '\''    = True
 isSpecial '.'     = True
 isSpecial '-'     = True
 isSpecial '$'     = True
+isSpecial '\\'    = True
 isSpecial '\8216' = True
 isSpecial '\8217' = True
 isSpecial '\8220' = True
@@ -1249,6 +1270,10 @@ isSpace _    = False
 
 -- Instances
 
+instance HasMacros HTMLState where
+  extractMacros        = macros
+  updateMacros f st    = st{ macros = f $ macros st }
+
 instance HasIdentifierList HTMLState where
   extractIdentifierList = identifiers
   updateIdentifierList f s = s{ identifiers = f (identifiers s) }
diff --git a/test/command/1126.md b/test/command/1126.md
new file mode 100644
index 000000000..014a8ae2d
--- /dev/null
+++ b/test/command/1126.md
@@ -0,0 +1,29 @@
+```
+% pandoc -f html -t latex
+\begin{eqnarray}
+A&=&B,\\
+C&=&D
+\end{eqnarray}
+^D
+\textbackslash{}begin\{eqnarray\}
+A\&=\&B,\textbackslash{}\textbackslash{} C\&=\&D
+\textbackslash{}end\{eqnarray\}
+```
+
+```
+% pandoc -f html+raw_tex -t latex
+<p>See \eqref{myeq}.</p>
+\begin{eqnarray}
+A&=&B,\\
+C&amp;=&amp;D
+\\label{myeq}
+\end{eqnarray}
+^D
+See \eqref{myeq}.
+
+\begin{eqnarray}
+A&=&B,\\
+C&=&D
+\\label{myeq}
+\end{eqnarray}
+```