calc() it up — use Sass calculations more

[wlib]

Description

• I replaced all Sass +, -, and * math operators with Sass calc()ulations
  • note that the output CSS is simplified at compile time if possible; the output css is slightly smaller
• I removed calc() from the disallowed functions in stylelint
• I added a with-value() function
  • it ensures that the value has a unit, for calc() with addition or subtraction with potentially null or unitless values like zero
  • it makes some of the source scss more verbose than add() and subtract() but it is more explicit and the output css is slightly more optimized

Motivation & Context

I described the full motivation in #39507.

Also, a nice side-effect here is that the code is slightly less tedious to convert to use css variables.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-39606--twbs-bootstrap.netlify.app/

Related issues

#39507

[mdo]

Without reviewing in depth yet, I'll just add that this is the way and I'm glad you proposed it. Unsure what version we'll do this in just yet. Thoughts on v5.4 @julien-deramond?

[mdo]

You'll have to interpolate the Sass variables across all of these calc() functions.

[wlib]

oof... it looks like that is a requirement for node-sass in the failed CI, which uses LibSass (both deprecated in favor of Dart Sass).

See https://sass-lang.com/documentation/syntax/special-functions/#element-progid-and-expression

LibSass, Ruby Sass, and versions of Dart Sass prior to 1.40.0 parse calc() as special syntactic function like element().
Dart Sass versions 1.40.0 and later parse calc() as a calculation.

Does Bootstrap support LibSass builds in v5? I know that it was internally dropped but I mean for when people import and build the Sass themselves.

[mdo]

Yeah, v5 still supports it. We'll drop it in v6 I imagine.

[wlib]

This would probably have to hold off until then, because the calc simplification only happens when the variables are not interpolated. Switching everything to calc would probably make the output too large in most cases.

[mdo]

We could actually consider dropping LibSass in v5.4 or like a special v5.5. We'll be moving onto v6 dev at some point but TBD on actual timeline.

[julien-deramond]

I agree in terms of realistic timeline that we could consider dropping LibSass in v5.4/v5.5. I hope, however, that it wouldn't trigger a semver comments war.