Incorrectly generates local selectors when using postcss-nested

[joepie91]

Test case (all dependencies at latest):

"use strict";

const postcss = require("postcss");

let input = `
:global {
	.foo {
		color: blue;
	}
}

:global .foo {
	color: red;
}
`;

let instance = postcss([
	require("postcss-nested"),
	// require("postcss-modules-local-by-default", { mode: "local" })
]);

instance.process(input).then((result) => {
	console.log(result.css);
});

Output when run as-is:

Without `from` option PostCSS could generate wrong source map and will not find Browserslist config. Set it to CSS file path or to `undefined` to prevent this warning.

:global .foo {
                color: blue;
        }

:global .foo {
        color: red;
}

Output when uncommenting (ie. enabling) postcss-modules-local-by-default:

Without `from` option PostCSS could generate wrong source map and will not find Browserslist config. Set it to CSS file path or to `undefined` to prevent this warning.

 :local(.foo) {
                color: blue;
        }

.foo {
        color: red;
}

Both selectors should be global selectors considering that's how they both reduce down when using postcss-nested, but somehow the one with block-scoped :global incorrectly becomes a local.

I'm not quite sure why - when disabling postcss-modules-local-by-default and inspecting the result AST when only postcss-nested is used, both nodes appear to be identically structured... but maybe I'm missing some PostCSS subtlety here.

[Bygaga63]

postcss/postcss-nested#157 also Andrey Sitnik recommended to move everything from Once method to proper Rule