Support for out of the box $custom-colors variable being merged with $theme-colors map

[marceloverdijk]

Prerequisites

• I have searched for duplicate or closed feature requests
• I have read the contributing guidelines

Proposal

Following the Customize Sass documentation regarding Importing and Add to map to add a custom theme color one should do:

// 1. Include functions first (so you can manipulate colors, SVGs, calc, etc)
@import "bootstrap/scss/functions";

// 2. Include any default variable overrides here

$violet:  #7F00FF;

// 3. Include remainder of required Bootstrap stylesheets (including any separate color mode stylesheets)
@import "bootstrap/scss/variables";
@import "bootstrap/scss/variables-dark";

// 4. Include any default map overrides here

$custom-colors: (
  "violet": $violet
);

$theme-colors: map-merge($theme-colors, $custom-colors);

It would be nice if BS internally would define an empty $custom-colors map and merge that already with $theme-colors.
As it would be empty it causes no difference with current behaviour.

Except it would be much easier for users to add custom theme colors, as it would effectively reduce above code to:

// 1. Include functions first (so you can manipulate colors, SVGs, calc, etc)
@import "bootstrap/scss/functions";

// 2. Include any default variable overrides here

$violet:  #7F00FF;

$custom-colors: (
  "violet": $violet
);

// 3. Include remainder of required Bootstrap stylesheets (including any separate color mode stylesheets)
@import "bootstrap/scss/variables";
@import "bootstrap/scss/variables-dark";

// 4. Include any default map overrides here

// Nothing needed here as BS will automatically merge the $custom-colors into the @theme-colors.

Motivation and context

Making it easier for users customizing the Sass to add custom theme colors.

[julien-deramond]

Thanks for creating this feature request @marceloverdijk
This is an interesting idea that we could study more in-depth for v5.4 (as it could be implemented without breaking anything in v5). I've added to the v5.4 project to analyze after our v5.3.x patches.

[mdo]

Yeah this is a solid idea, thanks for suggesting it!