LaTeX reader: add support for LaTeX subfiles package.

Closes #3530.

src/Text/Pandoc/Readers/LaTeX.hs

@@ -1008,6 +1008,7 @@ include = do
               char '\\'
               name <- try (string "include")
                   <|> try (string "input")
+                  <|> try (string "subfile")
                   <|> string "usepackage"
               -- skip options
               skipMany $ try $ char '[' *> manyTill anyChar (char ']')

test/command/3530.md

@@ -0,0 +1,22 @@
+```
+% pandoc -f latex -t native
+\subfile{command/sub-file-chapter-1}
+\subfile{command/sub-file-chapter-2}
+^D
+[Header 1 ("chapter-1",[],[]) [Str "Chapter",Space,Str "1"]
+,Para [Str "This",Space,Str "is",Space,Str "Chapter",Space,Str "1,",Space,Str "provided",Space,Str "in",Space,Str "a",Space,Str "sub",Space,Str "file."]
+,Header 1 ("chapter-2",[],[]) [Str "Chapter",Space,Str "2"]
+,Para [Str "This",Space,Str "is",Space,Str "Chapter",Space,Str "2,",Space,Str "provided",Space,Str "in",Space,Str "a",Space,Str "second",Space,Str "sub",Space,Str "file."]]
+```
+
+```
+% pandoc -flatex+raw_tex -t native
+\subfile{command/sub-file-chapter-1}
+\subfile{command/sub-file-chapter-2}
+^D
+[Header 1 ("chapter-1",[],[]) [Str "Chapter",Space,Str "1"]
+,Para [Str "This",Space,Str "is",Space,Str "Chapter",Space,Str "1,",Space,Str "provided",Space,Str "in",Space,Str "a",Space,Str "sub",Space,Str "file."]
+,Header 1 ("chapter-2",[],[]) [Str "Chapter",Space,Str "2"]
+,Para [Str "This",Space,Str "is",Space,Str "Chapter",Space,Str "2,",Space,Str "provided",Space,Str "in",Space,Str "a",Space,Str "second",Space,Str "sub",Space,Str "file."]]
+
+```

test/command/sub-file-chapter-1.tex

@@ -0,0 +1,8 @@
+\documentclass[main.tex]{subfiles}
+\begin{document}
+
+\section{Chapter 1}
+
+This is Chapter 1, provided in a sub file. 
+
+\end{document}

test/command/sub-file-chapter-2.tex

@@ -0,0 +1,8 @@
+\documentclass[main.tex]{subfiles}
+\begin{document}
+
+\section{Chapter 2}
+
+This is Chapter 2, provided in a second sub file. 
+
+\end{document}