Disallow notes within notes in reST and markdown.

These previously caused infinite looping and stack overflows.
For example:

[^1]

[^1]: See [^1]

Note references are allowed in reST notes, so this isn't a full
implementation of reST. That can come later. For now we need to
prevent the stack overflows.

Partially resolves Issue #297.

2 files changed, 19 insertions, 6 deletions

diff --git a/src/Text/Pandoc/Readers/Markdown.hs b/src/Text/Pandoc/Readers/Markdown.hs
index d284fb25e..1b408dcb2 100644
--- a/src/Text/Pandoc/Readers/Markdown.hs
+++ b/src/Text/Pandoc/Readers/Markdown.hs
@@ -1187,7 +1187,14 @@ note = try $ do
   let notes = stateNotes state
   case lookup ref notes of
     Nothing   -> fail "note not found"
-    Just raw  -> liftM Note $ parseFromString parseBlocks raw
+    Just raw  -> do
+       -- We temporarily empty the note list while parsing the note,
+       -- so that we don't get infinite loops with notes inside notes...
+       -- Note references inside other notes do not work.
+       updateState $ \st -> st{ stateNotes = [] }
+       contents <- parseFromString parseBlocks raw
+       updateState $ \st -> st{ stateNotes = notes }
+       return $ Note contents
 
 inlineNote :: GenParser Char ParserState Inline
 inlineNote = try $ do
diff --git a/src/Text/Pandoc/Readers/RST.hs b/src/Text/Pandoc/Readers/RST.hs
index 04bb33023..844b4e5b8 100644
--- a/src/Text/Pandoc/Readers/RST.hs
+++ b/src/Text/Pandoc/Readers/RST.hs
@@ -866,10 +866,16 @@ note = try $ do
   case lookup ref notes of
     Nothing   -> fail "note not found"
     Just raw  -> do
+      -- We temporarily empty the note list while parsing the note,
+      -- so that we don't get infinite loops with notes inside notes...
+      -- Note references inside other notes are allowed in reST, but
+      -- not yet in this implementation.
+      updateState $ \st -> st{ stateNotes = [] }
       contents <- parseFromString parseBlocks raw
-      when (ref == "*" || ref == "#") $ do -- auto-numbered
-        -- delete the note so the next auto-numbered note
-        -- doesn't get the same contents:
-        let newnotes = deleteFirstsBy (==) notes [(ref,raw)]
-        updateState $ \st -> st{ stateNotes = newnotes }
+      let newnotes = if (ref == "*" || ref == "#") -- auto-numbered
+                        -- delete the note so the next auto-numbered note
+                        -- doesn't get the same contents:
+                        then deleteFirstsBy (==) notes [(ref,raw)]
+                        else notes
+      updateState $ \st -> st{ stateNotes = newnotes }
       return $ Note contents