Rule Change: Add check for missing spaces before closing hashes in ATX headings

[xbinaryx]

What rule do you want to change?

no-missing-atx-heading-space

What change do you want to make?

Generate more warnings

How do you think the change should be implemented?

A new default behavior

Example code

#Heading 1#

What does the rule currently do for this code?

Currently, the rule only reports an error for #Heading (missing space after opening hash) but ignores 1# (missing space before closing hash).

What will the rule do after it's changed?

After the change, the rule will report errors for missing space before closing hash

Participation

• I am willing to submit a pull request to implement this change.

Additional comments

This behavior aligns with Markdownlint's implementation (rule MD018), which also checks for spaces both before and after hash sequences in ATX headings.

[lumirlumir]

This suggestion looks good to me. Markdownlint checks for this behavior as well.

• Reference: https://github.com/DavidAnson/markdownlint/blob/main/lib/md018.mjs#L23

[nzakas]

I don't think MD018 actually checks this. It's not mentioned in the docs:
https://github.com/DavidAnson/markdownlint/blob/main/doc/md018.md

This suggestion looks good to me. Markdownlint checks for this behavior as well.

* Reference: https://github.com/DavidAnson/markdownlint/blob/main/lib/md018.mjs#L23

I think you're misreading this code. This regex checks that there aren't any spaces after the # and before the end of the line.

There is actually a separate rule, MD020, that checks both leading and trailing:
https://github.com/DavidAnson/markdownlint/blob/main/doc/md020.md

So, I'm not sure this makes sense as a default behavior for this rule. We could potentially add an option to say that the user prefers closed atx style?

As a note: closed ATX style is just that, a stylistic choice, whereas the missing space after the opening # actually changes the node from a heading to a paragraph.

[lumirlumir]

Sorry, I misread the code. I thought the behavior belonged to MD018, but it actually belongs to MD020.

We could potentially add an option to say that the user prefers closed atx style?

Adding an option makes sense to me.

[Tanujkanti4441]

I am in favor of adding an option for checking spaces in closed atx headings. I think we can name it checkSpaceInClosedATX or checkSpaceInClosedATXHeading which will be a boolean option?

@eslint/eslint-team, any thoughts on this?

[xbinaryx]

It seems I got the Markdownlint rule numbers mixed up earlier. You're right, the behavior we're discussing actually aligns with MD020, not MD018. Given that, I'm in favor of implementing this as a new option rather than a default behavior.

[snitin315]

I'm not sure if we need an option if this is just a stylistic choice, that is not the scope for this plugin

[nzakas]

@snitin315 I think in this case adding an option to allow folks to transition easily from Markdownlint makes sense.

@Tanujkanti4441 maybe checkedClosedHeadings. We already have "space" and "atx" in the rule name so I don't think we have to repeat those.

[lumirlumir]

Considering the previous conversations and reactions, marking this suggestion as accepted.