From 9352750cb24b672e869e7351df9875d5fa8bf7f9 Mon Sep 17 00:00:00 2001
From: John MacFarlane <fiddlosopher@gmail.com>
Date: Sat, 24 Mar 2012 15:53:57 -0700
Subject: RST writer:  Better handling of inline formatting.

* `hi*there*hi` now gets rendered properly as `hi\ *there*\ hi`
* Unnecessary '\ ' are avoided around :math:, :sub:, :sup:
* Implemented most of the rules in
  http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#inline-markup-recognition-rules,
  though some unnecessary '\ ' may be inserted when unicode quotes
  are used.
---
 src/Text/Pandoc/Writers/RST.hs | 55 +++++++++++++++++++++++++++++++++++++++---
 tests/writer.rst               |  6 ++---
 2 files changed, 54 insertions(+), 7 deletions(-)

diff --git a/src/Text/Pandoc/Writers/RST.hs b/src/Text/Pandoc/Writers/RST.hs
index d6e5b5c9e..e6c84760e 100644
--- a/src/Text/Pandoc/Writers/RST.hs
+++ b/src/Text/Pandoc/Writers/RST.hs
@@ -38,6 +38,7 @@ import Data.List ( isPrefixOf, intersperse, transpose )
 import Text.Pandoc.Pretty
 import Control.Monad.State
 import Control.Applicative ( (<$>) )
+import Data.Char (isSpace)
 
 type Refs = [([Inline], Target)]
 
@@ -253,7 +254,52 @@ blockListToRST blocks = mapM blockToRST blocks >>= return . vcat
 
 -- | Convert list of Pandoc inline elements to RST.
 inlineListToRST :: [Inline] -> State WriterState Doc
-inlineListToRST lst = mapM inlineToRST lst >>= return . hcat
+inlineListToRST lst = mapM inlineToRST (insertBS lst) >>= return . hcat
+  where insertBS :: [Inline] -> [Inline] -- insert '\ ' where needed
+        insertBS (x:y:z:zs)
+          | isComplex y && surroundComplex x z =
+             x : y : RawInline "rst" "\\ " : insertBS (z:zs)
+        insertBS (x:y:zs)
+          | isComplex x && not (okAfterComplex y) =
+              x : RawInline "rst" "\\ " : insertBS (y : zs)
+          | isComplex y && not (okBeforeComplex x) =
+              x : RawInline "rst" "\\ " : insertBS (y : zs)
+          | otherwise =
+              x : insertBS (y : zs)
+        insertBS (x:ys) = x : insertBS ys
+        insertBS [] = []
+        surroundComplex :: Inline -> Inline -> Bool
+        surroundComplex (Str s@(_:_)) (Str s'@(_:_)) =
+          case (last s, head s') of
+             ('\'','\'') -> True
+             ('"','"')   -> True
+             ('<','>')   -> True
+             ('[',']')   -> True
+             ('{','}')   -> True
+             _           -> False
+        surroundComplex _ _ = False
+        okAfterComplex :: Inline -> Bool
+        okAfterComplex Space = True
+        okAfterComplex LineBreak = True
+        okAfterComplex (Str (c:_)) = isSpace c || c `elem` "-.,:;!?\\/'\")]}>–—"
+        okAfterComplex _ = False
+        okBeforeComplex :: Inline -> Bool
+        okBeforeComplex Space = True
+        okBeforeComplex LineBreak = True
+        okBeforeComplex (Str (c:_)) = isSpace c || c `elem` "-:/'\"<([{–—"
+        okBeforeComplex _ = False
+        isComplex :: Inline -> Bool
+        isComplex (Emph _) = True
+        isComplex (Strong _) = True
+        isComplex (SmallCaps _) = True
+        isComplex (Strikeout _) = True
+        isComplex (Superscript _) = True
+        isComplex (Subscript _) = True
+        isComplex (Link _ _) = True
+        isComplex (Image _ _) = True
+        isComplex (Code _ _) = True
+        isComplex (Math _ _) = True
+        isComplex _ = False
 
 -- | Convert Pandoc inline element to RST.
 inlineToRST :: Inline -> State WriterState Doc
@@ -268,10 +314,10 @@ inlineToRST (Strikeout lst) = do
   return $ "[STRIKEOUT:" <> contents <> "]"
 inlineToRST (Superscript lst) = do 
   contents <- inlineListToRST lst
-  return $ "\\ :sup:`" <> contents <> "`\\ "
+  return $ ":sup:`" <> contents <> "`"
 inlineToRST (Subscript lst) = do 
   contents <- inlineListToRST lst
-  return $ "\\ :sub:`" <> contents <> "`\\ "
+  return $ ":sub:`" <> contents <> "`"
 inlineToRST (SmallCaps lst) = inlineListToRST lst
 inlineToRST (Quoted SingleQuote lst) = do
   contents <- inlineListToRST lst
@@ -286,11 +332,12 @@ inlineToRST (Str str) = return $ text $ escapeString str
 inlineToRST (Math t str) = do
   modify $ \st -> st{ stHasMath = True }
   return $ if t == InlineMath
-              then ":math:`" <> text str <> "`" <> beforeNonBlank "\\ "
+              then ":math:`" <> text str <> "`"
               else if '\n' `elem` str
                    then blankline $$ ".. math::" $$
                         blankline $$ nest 3 (text str) $$ blankline
                    else blankline $$ (".. math:: " <> text str) $$ blankline
+inlineToRST (RawInline "rst" x) = return $ text x
 inlineToRST (RawInline _ _) = return empty
 inlineToRST (LineBreak) = return cr -- there's no line break in RST
 inlineToRST Space = return space
diff --git a/tests/writer.rst b/tests/writer.rst
index 09fd8dcb3..8d7c7915c 100644
--- a/tests/writer.rst
+++ b/tests/writer.rst
@@ -563,7 +563,7 @@ This is code: ``>``, ``$``, ``\``, ``\$``, ``<html>``.
 
 [STRIKEOUT:This is *strikeout*.]
 
-Superscripts: a\ :sup:`bc`\ d a\ :sup:`*hello*`\  a\ :sup:`hello there`\ .
+Superscripts: a\ :sup:`bc`\ d a\ :sup:`*hello*` a\ :sup:`hello there`.
 
 Subscripts: H\ :sub:`2`\ O, H\ :sub:`23`\ O, H\ :sub:`many of them`\ O.
 
@@ -602,12 +602,12 @@ LaTeX
 -  :math:`x \in y`
 -  :math:`\alpha \wedge \omega`
 -  :math:`223`
--  :math:`p`\ -Tree
+-  :math:`p`-Tree
 -  Here’s some display math:
 
    .. math:: \frac{d}{dx}f(x)=\lim_{h\to 0}\frac{f(x+h)-f(x)}{h}
 
--  Here’s one that has a line break in it: :math:`\alpha + \omega \times x^2`\ .
+-  Here’s one that has a line break in it: :math:`\alpha + \omega \times x^2`.
 
 These shouldn’t be math:
 
-- 
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