Better handling of \makeatletter in parsing raw LaTeX.

Closes #11270.

src/Text/Pandoc/Readers/LaTeX.hs

@@ -144,7 +144,8 @@ rawLaTeXBlock = do
   toks <- getInputTokens
   snd <$> (
           rawLaTeXParser toks
-             (macroDef (const mempty) <|>
+             (makeAtLetterSection <|>
+              macroDef (const mempty) <|>
               do choice (map controlSeq
                    ["include", "input", "subfile", "usepackage"])
                  skipMany opt
@@ -154,6 +155,17 @@ rawLaTeXBlock = do
            (void (environment <|> blockCommand))
            (mconcat <$> many (block <|> beginOrEndCommand)))
 
+makeAtLetterSection :: PandocMonad m => LP m ()
+makeAtLetterSection = try $ do
+  controlSeq "makeatletter"
+  void $ manyTill
+    (   whitespace
+    <|> newlineTok
+    <|> macroDef (const ())
+    <|> void environment
+    <|> void blockCommand
+    ) (controlSeq "makeatother")
+
 -- See #4667 for motivation; sometimes people write macros
 -- that just evaluate to a begin or end command, which blockCommand
 -- won't accept.

test/command/11270.md

@@ -0,0 +1,25 @@
+```
+% pandoc -f markdown -t native -s
+---
+header-includes: |
+    \makeatletter
+    \beamer@ignorenonframefalse
+    \makeatother
+...
+
+^D
+Pandoc
+  Meta
+    { unMeta =
+        fromList
+          [ ( "header-includes"
+            , MetaBlocks
+                [ RawBlock
+                    (Format "tex")
+                    "\\makeatletter\n\\beamer@ignorenonframefalse\n\\makeatother"
+                ]
+            )
+          ]
+    }
+  []
+```