From 20704d86a0ae043664f3facca84a61eded05de6e Mon Sep 17 00:00:00 2001
From: Ben Williams <bwilliams@gryphonnetworks.com>
Date: Thu, 15 Nov 2012 15:48:44 -0500
Subject: [PATCH] Switch to expression-based folding.

Syntax-based folding was way too slow in very large Markdown files. Add
a new file after/ftplugin/mkd.vim with a foldexpr function to determine
folds. The function is based on Steve Losh's gist at
https://gist.github.com/1038710
---
 after/ftplugin/mkd.vim | 51 ++++++++++++++++++++++++++++++++++++++++++
 syntax/mkd.vim         | 21 -----------------
 2 files changed, 51 insertions(+), 21 deletions(-)
 create mode 100644 after/ftplugin/mkd.vim

diff --git a/after/ftplugin/mkd.vim b/after/ftplugin/mkd.vim
new file mode 100644
index 0000000..f04ae2b
--- /dev/null
+++ b/after/ftplugin/mkd.vim
@@ -0,0 +1,51 @@
+" folding for Markdown headers, both styles (atx- and setex-)
+" http://daringfireball.net/projects/markdown/syntax#header
+"
+" this code can be placed in file
+"   $HOME/.vim/after/ftplugin/markdown.vim
+"
+" original version from Steve Losh's gist: https://gist.github.com/1038710
+
+func! Foldexpr_markdown(lnum)
+    if (a:lnum == 0)
+        let l0 = getline(a:lnum)
+    else
+        let l0 = getline(a:lnum-1)
+    endif
+
+    let l1 = getline(a:lnum)
+
+    let l2 = getline(a:lnum+1)
+
+    if  l2 =~ '^==\+\s*'
+        " next line is underlined (level 1)
+        return '>1'
+    elseif l2 =~ '^--\+\s*'
+        " next line is underlined (level 2)
+        return '>2'
+    elseif l1 =~ '^#'
+        " don't include the section title in the fold
+        return '-1'
+    elseif l0 =~ '^#'
+        " current line starts with hashes
+        return '>'.matchend(l0, '^#\+')
+    elseif a:lnum == 1
+        " fold any 'preamble'
+        return '>1'
+    else
+        " keep previous foldlevel
+        return '='
+    endif
+endfunc
+
+setlocal foldexpr=Foldexpr_markdown(v:lnum)
+setlocal foldmethod=expr
+
+"---------- everything after this is optional -----------------------
+" change the following fold options to your liking
+" see ':help fold-options' for more
+setlocal foldenable
+setlocal foldlevel=0
+setlocal foldcolumn=0
+set foldmethod=expr
+set foldopen-=search
diff --git a/syntax/mkd.vim b/syntax/mkd.vim
index 8f3fd86..c99968d 100644
--- a/syntax/mkd.vim
+++ b/syntax/mkd.vim
@@ -86,27 +86,6 @@ syn region htmlH6       start="^\s*######"              end="\($\|#\+\)" contain
 syn match  htmlH1       /^.\+\n=\+$/ contains=@Spell
 syn match  htmlH2       /^.\+\n-\+$/ contains=@Spell
 
-
-
-" fold region for headings
-syn region mkdHeaderFold
-    \ start="^\s*\z(#\+\)"
-    \ skip="^\s*\z1#\+"
-    \ end="^\(\s*#\)\@="
-    \ fold contains=TOP
-
-" fold region for lists
-syn region mkdListFold
-    \ start="^\z(\s*\)\*\z(\s*\)"
-    \ skip="^\z1 \z2\s*[^#]"
-    \ end="^\(.\)\@="
-    \ fold contains=TOP
-
-syn sync fromstart
-setlocal foldmethod=syntax
-
-
-
 "highlighting for Markdown groups
 HtmlHiLink mkdString	    String
 HtmlHiLink mkdCode          String
-- 
2.39.2