include-files: support recursive includes

Closes: #101

Author: tarleb

include-files/README.md

@@ -31,6 +31,14 @@ will want to include files written in a different format. An
 alternative format can be specified via the `format` attribute.
 Only plain-text formats are accepted.
 
+### Recursive transclusion
+
+Included files can in turn include other files. Note that all
+filenames must be relative to the directory from which pandoc is
+run. I.e., if a file `a/b.md` is included in the main document,
+and another file `a/b/c.md` should be included, the full relative
+path must be used. Writing `b/c.md` in `a/b.md` would *not* work.
+
 ## Example
 
 Let's assume we are writing a longer document, like a thesis.

include-files/expected.native

@@ -7,6 +7,9 @@
 ,Header 1 ("different-format",[],[]) [Str "Different",Space,Str "format"]
 ,Header 2 ("org-header",[],[]) [Str "Org",Space,Str "header"]
 ,Para [Str "This",Space,Str "is",Space,Emph [Str "emphasized"],Str "."]
+,Header 1 ("recursive-transclusion",[],[]) [Str "Recursive",Space,Str "transclusion"]
+,Para [Str "This",Space,Str "is",Space,Code ("",[],[]) "file-f.md",Str "."]
+,Para [Str "This",Space,Str "is",Space,Code ("",[],[]) "file-a.md",Str "."]
 ,Header 1 ("appendix",[],[]) [Str "Appendix"]
 ,Para [Str "More",Space,Str "info",Space,Str "goes",Space,Str "here."]
 ,Header 2 ("questionaire",[],[]) [Str "Questionaire"]

include-files/include-files.lua

@@ -7,7 +7,7 @@
 local List = require 'pandoc.List'
 
 --- Shift headings in block list by given number
-function shift_headings(blocks, shift_by)
+local function shift_headings(blocks, shift_by)
   if not shift_by then
     return blocks
   end
@@ -23,7 +23,8 @@ function shift_headings(blocks, shift_by)
 end
 
 --- Filter function for code blocks
-function CodeBlock(cb)
+local transclude
+function transclude (cb)
   -- ignore code blocks which are not of class "include".
   if not cb.classes:includes 'include' then
     return
@@ -40,9 +41,18 @@ function CodeBlock(cb)
     if line:sub(1,2) ~= '//' then
       local fh = io.open(line)
       local contents = pandoc.read(fh:read '*a', format).blocks
+      -- recursive transclusion
+      contents = pandoc.walk_block(
+        pandoc.Div(contents),
+        {CodeBlock = transclude}
+      ).content
       blocks:extend(shift_headings(contents, shift_heading_level_by))
       fh:close()
     end
   end
   return blocks
 end
+
+return {
+  {CodeBlock = transclude}
+}

include-files/sample.md

@@ -21,6 +21,13 @@ file-b.md
 file-d.org
 ```
 
+# Recursive transclusion
+
+``` {.include}
+// this will also include file-a.md
+file-f.md
+```
+
 # Appendix
 
 More info goes here.