patch 9.1.1537: helptoc: still some issues when markdown code blocks

Problem:  helptoc: still some issues when parsing markdown code blocks
          (VimWei)
Solution: assign nextline to curline before starting the next loop
          iteration; when processing fenced code blocks, flip the
          skip_fence variable, update the test to be more comprehensive

related: https://github.com/vim/vim/issues/17699#issuecomment-3055603968
closes: #17716

Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/pack/dist/opt/helptoc/autoload/helptoc.vim

@@ -3,7 +3,7 @@ vim9script noclear
 # the Vim HelpTOC plugin, creates a table of contents in a popup
 # Maintainer: Vim project
 # Original Author: @lacygoill
-# Latest Change: 2025 Jul 09
+# Latest Change: 2025 Jul 10
 #
 # Config {{{1
 # g:helptoc {{{2
@@ -523,12 +523,14 @@ def SetToc() #{{{2
 
         # Special handling for markdown filetype using setext headings
         if g:helptoc.type == 'markdown'
+            # ignore fenced codeblock lines
             if curline =~ '^```.'
                 skip_fence = true
             elseif curline =~ '^```$'
-                skip_fence = false
+                skip_fence = !skip_fence
             endif
             if skip_fence
+                curline = nextline
                 continue
             endif
             # Check for setext formatted headings (= or - underlined)

src/testdir/dumps/Test_helptoc_markdown_01.dump

@@ -1,20 +1,20 @@
-|#+0#e000e06#ffffff0| |M|y| |D|o|c|u|m|e|n|t| +0#0000000&@27|┌| |1|/|1| |(|1|/|1|)| @2|p|r|e|s@1| |?| |f|o|r| |h|e|l|p| |─@1|┐
+|#+0#e000e06#ffffff0| |H|e|a|d|i|n|g| |1| +0#0000000&@29|┌| |3|/|3| |(|1|/|1|)| @2|p|r|e|s@1| |?| |f|o|r| |h|e|l|p| |─@1|┐
-| @40|│| |M+0#0000001#e0e0e08|y| |D|o|c|u|m|e|n|t| @18| +0#0000000#ffffff0|│
+| @40|│| |H|e|a|d|i|n|g| |1| @21|│
-|S|o|m|e| |t|e|x|t|.| @30|│| | +0#4040ff13&@29| +0#0000000&|│
+|S|o|m|e| |t|e|x|t|.| @30|│| |A|n|o|t|h|e|r| |H|e|a|d|i|n|g| |1| @13|│
-| @40|│| | +0#4040ff13&@29| +0#0000000&|│
+| @40|│| |L+0#0000001#e0e0e08|a|s|t| |H|e|a|d|i|n|g| |1| @15| +0#0000000#ffffff0|│
 |`+0#e000e06&@2|v|i|m| +0#0000000&@34|│| | +0#4040ff13&@29| +0#0000000&|│
 |#| |T|h|i|s| |i|s| |a| |V|i|m|9|S|c|r|i|p|t| |c|o|m@1|e|n|t| @10|│| | +0#4040ff13&@29| +0#0000000&|│
 |d|e|f| |M|y|F|u|n|c|(|)| @28|│| | +0#4040ff13&@29| +0#0000000&|│
 | @1|#| |A|n|o|t|h|e|r| |c|o|m@1|e|n|t| @21|│| | +0#4040ff13&@29| +0#0000000&|│
 |e|n|d@1|e|f| @34|│| | +0#4040ff13&@29| +0#0000000&|│
 |`+0#e000e06&@2| +0#0000000&@37|│| | +0#4040ff13&@29| +0#0000000&|│
+|#+0#e000e06&| |A|n|o|t|h|e|r| |H|e|a|d|i|n|g| |1| +0#0000000&@21|│| | +0#4040ff13&@29| +0#0000000&|│
+| @40|│| | +0#4040ff13&@29| +0#0000000&|│
+|`+0#e000e06&@2| +0#0000000&@37|│| | +0#4040ff13&@29| +0#0000000&|│
+|#| |T|h|i|s| |i|s| |a| |c|o|m@1|e|n|t| |i|n| |a| |c|o|d|e|b|l|o|c|k| @6|│| | +0#4040ff13&@29| +0#0000000&|│
+|`+0#e000e06&@2| +0#0000000&@37|│| | +0#4040ff13&@29| +0#0000000&|│
+|#+0#e000e06&| |L|a|s|t| |H|e|a|d|i|n|g| |1| +0#0000000&@24|│| | +0#4040ff13&@29| +0#0000000&|│
+|a|n|d| |m|o|r|e| |t|e|x|t| @27|│| | +0#4040ff13&@29| +0#0000000&|│
 > @40|│| | +0#4040ff13&@29| +0#0000000&|│
-|~+0#4040ff13&| @39|│+0#0000000&| | +0#4040ff13&@29| +0#0000000&|│
-|~+0#4040ff13&| @39|│+0#0000000&| | +0#4040ff13&@29| +0#0000000&|│
-|~+0#4040ff13&| @39|│+0#0000000&| | +0#4040ff13&@29| +0#0000000&|│
-|~+0#4040ff13&| @39|│+0#0000000&| | +0#4040ff13&@29| +0#0000000&|│
-|~+0#4040ff13&| @39|│+0#0000000&| | +0#4040ff13&@29| +0#0000000&|│
-|~+0#4040ff13&| @39|│+0#0000000&| | +0#4040ff13&@29| +0#0000000&|│
-|~+0#4040ff13&| @39|│+0#0000000&| | +0#4040ff13&@29| +0#0000000&|│
 |~+0#4040ff13&| @39|└+0#0000000&|─@31|┘
-|:|H|e|l|p|T|o|c| @48|1@1|,|0|-|1| @7|A|l@1| 
+|:|H|e|l|p|T|o|c| @48|1|8|,|0|-|1| @7|A|l@1| 

src/testdir/test_plugin_helptoc.vim

@@ -8,15 +8,23 @@ func Test_helptoc_markdown_with_comments()
     packadd helptoc
     e Xmarkdown.md
     call append(0, [
-          \ '# My Document',
+          \ '# Heading 1',
-          \ '', 'Some text.',
+          \ '',
+          \ 'Some text.',
           \ '',
           \ '```vim',
           \ '# This is a Vim9Script comment',
           \ 'def MyFunc()',
           \ '  # Another comment',
           \ 'enddef',
-          \ '```'
+          \ '```',
+          \ '# Another Heading 1',
+          \ '',
+          \ '```',
+          \ '# This is a comment in a codeblock',
+          \ '```',
+          \ '# Last Heading 1',
+          \ 'and more text'
           \])
   END
 

src/version.c

@@ -719,6 +719,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1537,
 /**/
     1536,
 /**/