nix-in-node/src/transformers/desugar-inherits.js

"use strict";

const splitFilter = require("split-filter");
const assert = require("assert");

const NoChange = require("../astformer/actions/no-change");
const nixTypes = require("./_nix-types");

module.exports = {
	name: "desugar-inherits",
	visitors: {
		NixAttributeSet: (node) => {
			let [ inherits, regularBindings ] = splitFilter(node.bind, (binding) => binding.type === "NixInherit");

			if (inherits.length === 0) {
				return NoChange;
			} else {
				let tempCounter = 0;
				let inherits_ = inherits.map((inherit) => {
					return {
						tempName: `$$jsNix$temp$${tempCounter++}`,
						sourceExpression: inherit.expression,
						names: inherit.attrs.attr.map((attribute) => {
							assert(attribute.type === "NixAttributeIdentifier");
							return attribute.name;
						})
					};
				});

				let letBindings = inherits_.map((inherit) => {
					return nixTypes.NixBinding(
						[ nixTypes.NixAttributeIdentifier(inherit.tempName) ],
						inherit.sourceExpression
					);
				});

				let body = {
					... node,
					bind: [
						... regularBindings,
						... inherits_.flatMap((inherit) => {
							return inherit.names.map((name) => {
								return nixTypes.NixBinding(
									[ nixTypes.NixAttributeIdentifier(name) ],
									nixTypes.NixAttributeSelection(
										nixTypes.NixIdentifier(inherit.tempName),
										[ nixTypes.NixAttributeIdentifier(name) ]
									)
								);
							});
						})
					]
				};

				return nixTypes.NixLetIn(
					letBindings,
					body
				);
			}
		}
	}
};