[Proposal] Extend multipart properties in mixins

[SevenOutman]

There're several CSS properties that supports multiple parts, e.g. transition. Sometime we want to write mixins that extends these properties, for example, below is a mixin meant to add background-color transition to a class.

.add-background-transition() {
  transition: background-color 0.3s;
}

But applying this mixin will not result in transition to be extended but overwritten:

.class {
  transition: color 0.3s;
  .add-background-transition(); // resulting in missing text-color transition
}

So I think it would be great if Less supports extending properties like transition:

.add-background-transition() {
  +transition: background-color 0.3s; // a leading plus sign indicates extending
}

.class {
  transition: color 0.3s;
  .add-background-transition(); // resulting in transition: color 0.3s, background-color 0.3s;
}

[matthew-dean]

You can already do this.

.add-background-transition() {
  transition+: background-color 0.3s;
}

.class {
  transition+: color 0.3s;
  .add-background-transition();
}

Result:

.class {
  transition: color 0.3s, background-color 0.3s;
}

[SevenOutman]

That's cool! But I don't see it in documentation. Did I miss something?

[iChenLei]

@SevenOutman https://lesscss.org/features/#merge-feature

[SevenOutman]

@iChenLei Thanks!

[SevenOutman]

One further question: is there ability to de-merge such properties? Like:

.no-text-transition() {
  transition-: color;
}