html.renderCodeBlock and attributes

[maxatome]

Hello,

Is there any reason why html.renderCodeBlock and html.renderFencedCodeBlock do not allow to RenderAttributes as other HTML tags?

If not and a fix is accepted, how to distinguish the attributes targeting <pre> from those targetting <code>?

[yuin]

As you know, code blocks consist of pre and code tags. Because of this, it is impossible to determine which tag should receive attributes, so RenderAttributes is not supported. Since code blocks are defined as HTML Block type 1, please represent them simply in HTML.

[maxatome]

Hello,

I think it can be solved by changing a few things to the ast.Node interface: SetAttribute, SetAttributeString and Attribute methods could take a variadic tags parameter.

SetAttribute(name []byte, value interface{}, tags ...string)
SetAttributeString(name string, value interface{}, tags ...string)
Attribute(name []byte) (interface{}, bool), tags ...string
AttributeString(name string) (interface{}, bool, tags ...string)

So the SetAttribute* can store some optional tags for which the attribute applies. If no tags are passed, it applies to all tags rendered or, as today, to a specific tag among several used by the renderer for the node. If one or several tags are passed, it means the attribute applies only for these tags.

html.RenderAttributes could also take an optional tag parameter:

func RenderAttributes(w util.BufWriter, node ast.Node, filter util.BytesFilter, tag ...string) {

• if len(tag) == 0 it only writes the attributes not bound to a specific tag;
• if len(tag) == 1 it writes the attributes bound to tag[0] (and possibly merges them to the attributes not bound to a specific tag, to be discussed);
• len(tag) > 1 is IMHO an error, but it can also be handled using a merge…

Probably ast.Attribute should be changed to:

type Attribute struct {
	Name  []byte
	Value interface{}
	Tag string
}

(note Tag string and not Tags []string to facilitate SetAttribute* implementation.)

The chosen tag terminology does not directly refer to HTML, but to any subdivision a renderer can use to represent a node. It could be named differently.

Of course, changing a public interface and a public struct is a breaking change, but it is a small change with a very low impact as if tags are never used, nothing change in foreign code as the variadic tag/tags param is not used.

The following ast.Node implementations can benefit of this change for the HTML renderer:

• KindCodeBlock: tags pre + code
• KindFencedCodeBlock: tags pre + code
• KindFootnoteLink: tags sup + a
• KindFootnoteBacklink: tag a
• KindFootnoteList: tags div (already supported) + hr + ol
• KindTableHeader: tags thead (already supported) + tr + tbody

What do you think? If you are interested, I can provide a POC.