From e0290fd18bb523f5f08e2d5f5d2a8b89916654d2 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Wed, 31 Oct 2018 21:51:20 -0700
Subject: LaTeX writer: add newline if math ends in a comment.

This prevents the closing delimiter from being swalled
up in the comment.

Closes #4880.
---
 src/Text/Pandoc/Writers/LaTeX.hs | 14 ++++++++++++--
 test/command/4880.md             |  7 +++++++
 2 files changed, 19 insertions(+), 2 deletions(-)
 create mode 100644 test/command/4880.md

diff --git a/src/Text/Pandoc/Writers/LaTeX.hs b/src/Text/Pandoc/Writers/LaTeX.hs
index 11d58b90a..a2c7ac34f 100644
--- a/src/Text/Pandoc/Writers/LaTeX.hs
+++ b/src/Text/Pandoc/Writers/LaTeX.hs
@@ -1168,10 +1168,10 @@ inlineToLaTeX (Str str) = do
   liftM text $ stringToLaTeX TextString str
 inlineToLaTeX (Math InlineMath str) = do
   setEmptyLine False
-  return $ "\\(" <> text str <> "\\)"
+  return $ "\\(" <> text (handleMathComment str) <> "\\)"
 inlineToLaTeX (Math DisplayMath str) = do
   setEmptyLine False
-  return $ "\\[" <> text str <> "\\]"
+  return $ "\\[" <> text (handleMathComment str) <> "\\]"
 inlineToLaTeX il@(RawInline f str)
   | f == Format "latex" || f == Format "tex"
                         = do
@@ -1272,6 +1272,16 @@ inlineToLaTeX (Note contents) = do
        -- note: a \n before } needed when note ends with a Verbatim environment
        else "\\footnote" <> beamerMark <> braces noteContents
 
+-- A comment at the end of math needs to be followed by a newline,
+-- or the closing delimiter gets swallowed.
+handleMathComment :: String -> String
+handleMathComment s =
+  let (xs, ys) = break (\c -> c == '\n' || c == '%') $ reverse s
+  in  case ys of
+         '%':'\\':_ -> s
+         '%':_      -> s ++ "\n"
+         _          -> s
+
 protectCode :: [Inline] -> [Inline]
 protectCode [] = []
 protectCode (x@(Code ("",[],[]) _) : xs) = x : protectCode xs
diff --git a/test/command/4880.md b/test/command/4880.md
new file mode 100644
index 000000000..638e3edee
--- /dev/null
+++ b/test/command/4880.md
@@ -0,0 +1,7 @@
+```
+% pandoc -t latex
+$x=y%comment$
+^D
+\(x=y%comment
+\)
+```
-- 
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