LaTeX reader: handle ## macro arguments properly.

These turn into regular `#` arguments when expanded.

Closes #8243.

src/Text/Pandoc/Readers/LaTeX/Macro.hs

@@ -216,7 +216,7 @@ newenvironment = do
     let result = (name,
                     Macro GroupScope ExpandWhenUsed argspecs optarg
                       (bg:startcontents),
-                    Macro GroupScope ExpandWhenUsed [] Nothing
+                    Macro GroupScope ExpandWhenUsed argspecs optarg
                       (endcontents ++ [eg]))
     (do lookupMacro name
         case mtype of

src/Text/Pandoc/Readers/LaTeX/Parsing.hs

@@ -414,14 +414,24 @@ tokenize = totoks
                       Tok pos (CtrlSeq (T.singleton d)) (T.pack [c,d])
                       : totoks (incSourceColumn pos 2) rest'
          | c == '#' ->
-           let (t1, t2) = T.span (\d -> d >= '0' && d <= '9') rest
-           in  case safeRead t1 of
-                    Just i ->
-                       Tok pos (Arg i) ("#" <> t1)
-                       : totoks (incSourceColumn pos (1 + T.length t1)) t2
-                    Nothing ->
-                       Tok pos Symbol "#"
-                       : totoks (incSourceColumn pos 1) t2
+           case T.uncons rest of
+             Just ('#', t3) ->
+               let (t1, t2) = T.span (\d -> d >= '0' && d <= '9') t3
+               in  case safeRead t1 of
+                        Just i ->
+                           Tok pos (DeferredArg i) ("##" <> t1)
+                           : totoks (incSourceColumn pos (2 + T.length t1)) t2
+                        Nothing -> Tok pos Symbol "#"
+                                  : Tok (incSourceColumn pos 1) Symbol "#"
+                                  : totoks (incSourceColumn pos 1) t2
+             _ ->
+               let (t1, t2) = T.span (\d -> d >= '0' && d <= '9') rest
+               in  case safeRead t1 of
+                        Just i ->
+                           Tok pos (Arg i) ("#" <> t1)
+                           : totoks (incSourceColumn pos (1 + T.length t1)) t2
+                        Nothing -> Tok pos Symbol "#"
+                                  : totoks (incSourceColumn pos 1) rest
          | c == '^' ->
            case T.uncons rest of
                 Just ('^', rest') ->
@@ -571,6 +581,8 @@ doMacros' n inp =
       x <- try $ spaces >> bracedOrToken
       getargs (M.insert i x argmap) rest
 
+    addTok False _args spos (Tok _ (DeferredArg i) txt) acc =
+      Tok spos (Arg i) txt : acc
     addTok False args spos (Tok _ (Arg i) _) acc =
        case M.lookup i args of
             Nothing -> mzero

src/Text/Pandoc/Readers/LaTeX/Types.hs

@@ -25,7 +25,7 @@ import Text.Pandoc.Sources
 import Data.List (groupBy)
 
 data TokType = CtrlSeq Text | Spaces | Newline | Symbol | Word | Comment |
-               Esc1    | Esc2   | Arg Int
+               Esc1    | Esc2   | Arg Int  | DeferredArg Int
      deriving (Eq, Ord, Show)
 
 data Tok = Tok SourcePos TokType Text

test/command/8243.md

@@ -0,0 +1,23 @@
+```
+% pandoc -f latex
+\newenvironment{topics}{
+\newcommand{\topic}[2]{ \item{##1 / ##2} }
+Topics:
+\begin{itemize}
+}
+{
+\end{itemize}
+}
+
+\begin{topics}
+\topic{Foo}{Bar}
+\topic{Baz}{Bim}
+\end{topics}
+^D
+<p>Topics:</p>
+<ul>
+<li><p><span>Foo / Bar</span></p></li>
+<li><p><span>Baz / Bim</span></p></li>
+</ul>
+```
+