Headers ignore the `extend` font face attribute

[cyrus-and]

Expected Behavior

The extend attribute should be respected, just like it happens for markdown-code-face. That is, the background color of the markdown-header-face-* should extend to the whole width of the buffer when extend is t.

Actual Behavior

The background does not extend:

Steps to Reproduce

1. Place the following in /tmp/emacs/.emacs:

   (setq custom-file "/dev/null")
   
   (package-initialize)
   (add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/"))
   
   (package-install 'markdown-mode)
   
   (custom-set-faces
    `(markdown-header-face-1 ((t (:background "#ff0000" :extend t)))))

2. Start Emacs with HOME=/tmp/emacs emacs;

3. Create or open a Markdown file with at least one top-level header:

   # Header
   
   ```
   code
   ```

Backtrace

There are no errors.

Software Versions

• Markdown Mode: version 2.6-dev
• Emacs: GNU Emacs 29.0.50 (build 1, x86_64-apple-darwin20.6.0, NS appkit-2022.60 Version 11.6.5 (Build 20G527)) of 2022-04-29
• OS: macOS Big Sur 11.6.5

[syohex]

markdown-mode does not ignore extend attribute for header faces. extend attribute works only when the face is set from some point to end of the line. And markdown-mode does not set the header faces to end of the line.

Why markdown-mode is implemented like that, because Markdown allows to put closing sequences of # at header lines(Specification is here). To support both non closing sequences and closing sequences cases, markdown-mode does not set face to end of the line.

For example

# This is Header #

markdown-mode sets

• Set first # as markdown-header-delimiter-face
• Set This is Header as markdown-header-face-1
• Set last # as markdown-header-delimiter-face

By the way, extend attribute does not work as you expected for org-level-*, outline-* etc. Because those faces are not set to end of the line as well.

[cyrus-and]

To support both non closing sequences and closing sequences cases, markdown-mode does not set face to end of the line.

But it could when there is no closing sequence, no? If the detection is tricky (I don't think so), one could only do that if markdown-asymmetric-header (or a new setting, see below) is set to t.

By the way, extend attribute does not work as you expected for org-level-, outline- etc. Because those faces are not set to end of the line as well.

They do actually, at least org-mode, if org-fontify-whole-heading-line is set to t, markdown-mode could have a similar setting.

[syohex]

Ah, I see. I'll consider to introduce such variable. BTW markdown-asymmetric-header is used only for inserting headers, so I suppose it cannot be used for fontification flag.

[cyrus-and]

BTW markdown-asymmetric-header is used only for inserting headers, so I suppose it cannot be used for fontification flag.

Yeah, it makes sense, I was only suggesting that in case you didn't want to introduce a new variable.

[syohex]

@cyrus-and How about #706 ?

[cyrus-and]

@cyrus-and How about #706 ?

Just tried it and seems to work perfectly! Thank you.

[syohex]

I have merged #706