Allow enforcing tabs over spaces

[JoshuaKGoldberg]

For teams where the code style is tabs instead of spaces, linting needs a way to enforce that 4x gets replaced with tabs.

[DavidAnson]

That would seem to be in conflict with: https://github.com/DavidAnson/markdownlint/blob/master/doc/Rules.md#md010

I prefer tabs semantically, but tend to feel that documentation (Markdown) should render as uniformly as possible (spaces). Do you have a specific example of where tabs would be necessary in Markdown?

[JoshuaKGoldberg]

Not necessary, but practical. My use case is that my team at work uses tabs everywhere and wants to keep it standard in all our files.

[sensibleish]

The Markdown spec at https://daringfireball.net/projects/markdown/basics contains the string "4 spaces or 1 tab" twice. Lint rule MD010 doesn't seem valid, at least not as a blanket rule.

[DavidAnson]

@giskard22 I agree with your reading of the specification. That said, there are many projects that impose additional standards and forbidding tab characters like MD010 does is somewhat common. Linking tools will often go beyond what’s allowed by the specification in order to standardize, avoid unwanted practices, and so on. For scenarios where rule MD010 does not apply, it can be disabled.

[NatoBoram]

You having seen "many projects" imposing different standards shouldn't undermine the usability of your project. Linting tools shouldn't promote unwanted practices nor force different standards.

MD010 simply never applies. It should be a toggle between spaces or tabs.

[DavidAnson]

I’ll look at deprecating/replacing this rule in a future release.

[DavidAnson]

As I research this more, rule MD010 seems easy to define and implement - but the opposite rule to enforce tabs instead of spaces seems more ambiguous and open to debate.

http://spec.commonmark.org/0.28/#tabs

Many places where a tab could be used are not places I think everyone would agree it should be used, so I think the proposed rule to enforce tabs may need multiple options to support every scenario.

So I will leave this issue as a request to add a new rule for tabs. And separately, I will look at disabling MD010 by default to avoid being too opinionated out of the box.

[sww1235]

I would like to chime in on this, even though it is over 2 years old at this point and add a request for supporting tabs as well.

I would propose that the following rules are modified with a rule to check for tabs, spaces, or consistent styling.

• MD007
• MD010
• MD030

adding a consistent option to MD010 might be easier than dealing with a bunch of language specific options like in #383

Thank you

[groenroos]

+1 for implementing a new rule for enforcing indentation with tabs instead of spaces!

While space indentation may be more common in Markdown, I think in a large multi-language project, it's more important that the coding style is fairly consistent across the whole project, rather than orthodox to each individual language.

[AramZS]

+1 to tabs over spaces though I will note that YAML requires spaces, so as long as it doesn't mess with the YAML blocks.

[NomarCub]

I also have a use case that ul-indent is insufficient for as-is, and would need support for tabs. I use Obsidian, which has issues rendering space indentation consistently.

(see
Support Indentation Guides for all tab sizes (2 and 3 spaces) - Feature requests - Obsidian Forum
Custom list indent width with indentation guides - Feature archive - Obsidian Forum
Live Preview: improve vertical alignment of multiple paragraphs in lists - Feature requests - Obsidian Forum
Customise indent characters - Feature requests - Obsidian Forum)

[JoshuaKGoldberg]

Huh, I'd forgotten that I filed this issue. Since filing it I've come to the conclusion that a linter should not be used for formatting concerns such as enforcing tabs vs spaces. Closing this issue and unsubscribing from it, as I use Prettier or dprint to enforce formatting instead of markdownlint.

As of #594, you can use a built-in Markdownlint style/prettier.json (equivalent to eslint-config-prettier) to disable all formatting rules in Markdownlint:

// .markdownlint.json
{
    "extends": "markdownlint/style/prettier"
}

I've got a longer blog post about it here: https://blog.joshuakgoldberg.com/configuring-markdownlint-alongside-prettier (apologies for the shameless self promotion).

If someone else wants to file a new version of this issue, nothing's stopping you. Just know that I'll silently judge you for using a linter for formatting! 😉

[NomarCub]

I appreciate your post, but I disagree.

• I don't want one more tool just to enforce this rule.
• Tabs are not purely syntactic in markdown, they are basically significant whitespace, so this rule is a linting issue, not a formatting one only.
• Prettier is too opinionated, generic, and not configurable enough for markdown - see this example.

There's been some valuable discussion on this here, and others still want the feature, so please reopen this issue @JoshuaKGoldberg.
Also, thank you for the useful links, never heard of dprint before!