@jesscss/plugin-less-compat

@jesscss/plugin-less-compat

A Less compatibility bridge for Jess.

Jess accepts typed AST-v2 Fn values here and provides the shared Jess-owned bridge for Less-style plugin function registration and Less-shaped function values.

The public compiler does not support Less 4 visitors, post-processors, file manager plugins, or a full Less tree AST adapter.

How it works

• Native functions only — pass Fn values from @jesscss/core/value; their bodies receive typed values and FnCtx capabilities.
• Less plugin function bridge — pass Less-style plugins with install(less, manager, functions) through plugins. The bridge supplies a Less-shaped functions.functionRegistry and the supported less.tree constructor facades, then lazily adapts function arguments and return values at the Jess boundary.

For example, migrate a Less functionRegistry.add('increment', fn) contribution to a typed function and register it through functions:

import { Compiler } from 'jess';
import { defineFunction, makeDimension } from '@jesscss/core/value';
import lessCompatPlugin from '@jesscss/plugin-less-compat';

const increment = defineFunction('increment', {
  params: [{ kinds: ['Dimension'] }] as const,
  body: value => makeDimension(value.number + 1, value.unit)
});

const compiler = new Compiler({
  compile: { plugins: [lessCompatPlugin({ functions: [increment] })] }
});

For legacy Less function plugins:

const legacyPlugin = {
  install(less, _manager, functions) {
    functions.add('increment', value =>
      new less.tree.Dimension(value.value + 1, value.unit)
    );
  }
};

const compiler = new Compiler({
  compile: { plugins: [lessCompatPlugin({ plugins: [legacyPlugin] })] }
});

Less-shaped values are boundary values only. Jess owns their conversion back into typed AST-v2 values.

Status

Alpha / experimental. The supported public routes are native function contribution and Less plugin function bridging. If you need Less visitors, post-processors, file managers, or broad Less tree AST mutation support today, use Less.js directly.

The programmatic plugin/compiler API is not yet stabilized — the jess CLI is the documented public surface for the alpha. Watch the docs site for the API once it settles. Current design notes live in DESIGN.md.

• Project overview & positioning: https://github.com/jesscss/jess#readme
• Docs: https://jesscss.github.io/ (currently pre-alpha content)
• Issues: https://github.com/jesscss/jess/issues
• License: MIT