How to enable code folding for markdown in TextMate?

Question

I would like to enable code folding for markdown in textmate.

Specifically, I would like any headings (text preceded by one or more '#' characters) to be the line that would toggle blocks between it and the next heading and/or horizontal rule. Example:

# Level 1 Heading - I'd like the block below to fold

The text I'd like to fold away

## Level 2 Heading

More text...

BBEdit seems to do this just fine for markdown. TextMate supports code folding just fine for languages that denote blocks with paired (and identically indented) curly braces.

I know TextMate offers two variables you can set in the language grammar file, but I'd need more talent with regular expressions than I possess to figure it out. Following is what currently resides in the markdown language grammar for the code folding settings:

foldingStartMarker = '(?x)
    (<(?i:head|body|table|thead|tbody|tfoot|tr|div|select|fieldset|style|script|ul|ol|form|dl)\b.*?>
    |<!--(?!.*-->)
    |\{\s*($|\?>\s*$|//|/\*(.*\*/\s*$|(?!.*?\*/)))
    )';
foldingStopMarker = '(?x)
    (</(?i:head|body|table|thead|tbody|tfoot|tr|div|select|fieldset|style|script|ul|ol|form|dl)>
    |^\s*-->
    |(^|\s)\}
    )';

Any help greatly appreciated!

Answer 1

TextMate flat-out can't do this.

TextMate's language parser reads files on a line-by-line basis. Which means that in order for code to be folded there needs to be a start marker AND an end marker. Like <ul> and </ul>. In this case, since the end of a section is not marked by anything other than the start of the next section, the line-by-line parser cannot go back and say an empty line should mark the end of a code folded block.

Does that make sense?

Answer 2

On the Macromates blog, they explain how to enable basic code folding for markdown. This lets you fold at the header level so long as you're using the "#" symbol for your headers.

For Markdown's folding settings (scoped to text.html.markdown), let's look at some more sneaky patterns:

{ foldingIndentedBlockStart = '^#+\s+'; foldingIndentedBlockIgnore = '^(?!#+\s+)'; }

We let a heading be a start marker and then we effectively ignore everything which is not a heading, causing those lines to be included in the foldable block despite not being indented. This allows you to collapse entire sections of a Markdown document down to just the headings.