LaTeX reader: support `\expandafter`.

Closes #3983.

2 files changed, 48 insertions, 6 deletions

diff --git a/src/Text/Pandoc/Readers/LaTeX.hs b/src/Text/Pandoc/Readers/LaTeX.hs
index 089d3d741..37becf59f 100644
--- a/src/Text/Pandoc/Readers/LaTeX.hs
+++ b/src/Text/Pandoc/Readers/LaTeX.hs
@@ -372,11 +372,14 @@ totoks pos t =
          | otherwise ->
            Tok pos Symbol (T.singleton c) : totoks (incSourceColumn pos 1) rest
 
-  where isSpaceOrTab ' '  = True
-        isSpaceOrTab '\t' = True
-        isSpaceOrTab _    = False
-        isLetterOrAt '@'  = True
-        isLetterOrAt c    = isLetter c
+isSpaceOrTab :: Char -> Bool
+isSpaceOrTab ' '  = True
+isSpaceOrTab '\t' = True
+isSpaceOrTab _    = False
+
+isLetterOrAt :: Char -> Bool
+isLetterOrAt '@'  = True
+isLetterOrAt c    = isLetter c
 
 isLowerHex :: Char -> Bool
 isLowerHex x = x >= '0' && x <= '9' || x >= 'a' && x <= 'f'
@@ -411,10 +414,19 @@ doMacros n = do
          Tok spos (CtrlSeq "end") _ : Tok _ Symbol "{" :
           Tok _ Word name : Tok _ Symbol "}" : ts
             -> handleMacros spos ("end" <> name) ts
+         Tok _ (CtrlSeq "expandafter") _ : t : ts
+            -> do setInput ts
+                  doMacros n
+                  getInput >>= setInput . combineTok t
          Tok spos (CtrlSeq name) _ : ts
             -> handleMacros spos name ts
          _ -> return ()
-  where handleMacros spos name ts = do
+  where combineTok (Tok spos (CtrlSeq name) x) (Tok _ Word w : ts)
+          | T.all isLetterOrAt w =
+            Tok spos (CtrlSeq (name <> w)) (x1 <> w <> x2) : ts
+              where (x1, x2) = T.break isSpaceOrTab x
+        combineTok t ts = t:ts
+        handleMacros spos name ts = do
                 macros <- sMacros <$> getState
                 case M.lookup name macros of
                      Nothing -> return ()
@@ -439,6 +451,7 @@ doMacros n = do
                                  else doMacros (n + 1)
                             ExpandWhenDefined -> return ()
 
+
 setpos :: SourcePos -> Tok -> Tok
 setpos spos (Tok _ tt txt) = Tok spos tt txt
 
diff --git a/test/command/3983.md b/test/command/3983.md
new file mode 100644
index 000000000..7eaeb99f0
--- /dev/null
+++ b/test/command/3983.md
@@ -0,0 +1,29 @@
+```
+pandoc -f latex -t native
+\def\filename@area{foo:bar:baz}
+\makeatletter
+\graphicspath\expandafter{\expandafter{\filename@area}}%
+\makeatother
+^D
+[RawBlock (Format "latex") "\\makeatletter"
+,RawBlock (Format "latex") "\\makeatother"]
+```
+
+```
+pandoc -f latex -t native
+\makeatletter
+  \newcommand\urlfootnote@[1]{\footnote{\url@{#1}}}
+  \DeclareRobustCommand{\urlfootnote}{\hyper@normalise\urlfootnote@}
+\makeatother
+^D
+[RawBlock (Format "latex") "\\makeatletter"
+,RawBlock (Format "latex") "\\makeatother"]
+```
+
+```
+pandoc -f latex -t native
+\def\foo{bar}
+\expandafter\bam\foo
+^D
+[RawBlock (Format "latex") "\\bambar"]
+```