nix-in-node/src/transformers/attribute-sets.js

"use strict";

const assert = require("assert");
const types = require("@babel/types");
const template = require("@babel/template").default;
const splitFilter = require("split-filter");

const unpackExpression = require("./util/unpack-expression");
const templateExpression = require("./util/template-expression");
const NoChange = require("../astformer/actions/no-change");
const printAst = require("../print-ast");
const lazyWrapper = require("./templates/lazy-wrapper");
const callLazyWrapper = require("./templates/call-lazy-wrapper");
const objectLiteral = require("./templates/object-literal");

// TODO: Optimize lazy evaluation wrappers by only unpacking them selectively when used in an actual expression; in particular, that avoids the "wrapper that just calls another wrapper" overhead when passing attributes as function arguments
// TODO: Change to a prototype-based scope object chain? This should produce more consistent output regardless of whether a given set of bindings is static vs. dynamic and recursive vs. non-recursive

let tmplAssertKeys = template(`
	$assertUniqueKeys( %%keyList%% )
`);

let tmplObjectNormal = templateExpression(`
	(() => {
		%%keyAssertion%%;

		return %%object%%;
	})()
`);

let tmplScopeWrapper = templateExpression(`(
	(() => {
		%%bindings%%;

		return %%object%%;
	})()
)`);

let tmplDynamicScopeWrapper = templateExpression(`(
	(() => {
		%%keyAssertion%%;

		let $attributes = {};

		with ($attributes) {
			/* Static and overrides */
			Object.assign($attributes, {
				%%bindings%%;
			});
		}

		return $attributes;
	})()
)`);

// FIXME: Verify that this always works, and that we don't need `var` for hoisting!
let tmplRecursiveBinding = template(`
	const %%name%% = %%expression%%;
`);


function isDynamicBinding(binding) {
	return binding.attrpath.attr[0].type !== "NixAttributeIdentifier";
}

function objectNormal(bindings) {
	return tmplObjectNormal({
		object: objectLiteral(bindings.map(({ name, expression }) => {
			return [ name, expression ];
		})),
		keyAssertion: bindings.some((binding) => typeof binding.name !== "string")
			// Only needed when dealing with dynamic keys
			? assertKeys(bindings.map(({ name }) => implicitStringLiteral(name)))
			: null
	});
}

function objectRecursiveStatic(bindings) {
	return tmplScopeWrapper({
		bindings: bindings.map(({ name, expression }) => {
			return tmplRecursiveBinding({
				name: name,
				expression: expression
			});
		}),
		object: objectLiteral(bindings.map(({ name }) => {
			assert(typeof name === "string");
			return [ name, types.identifier(name) ];
		}))
	});
}

function objectRecursiveDynamic(bindings) {
	throw new Error(`UNIMPLEMENTED: Dynamic bindings are not supported yet`); 
	return tmplDynamicScopeWrapper({
		
	});
}

function implicitStringLiteral(node) {
	if (typeof node === "string") {
		return types.stringLiteral(node);
	} else {
		return node;
	}
}

function assertKeys(keys) {
	return tmplAssertKeys({ keyList: types.arrayExpression(keys) });
}

module.exports = {
	name: "attribute-sets",
	visitors: {
		Program: (_node, { setContext }) => {
			setContext(null, "attributeSets_inRecursiveSet", false);
			return NoChange;
		},
		NixAttributeSelection: (_node, { defer }) => {
			// TODO: Optimize dynamic attribute access by translating builtins.getAttr to dynamic property access at compile time? This requires scope analysis!
			return defer((node) => {
				assert(node.attrpath.type === "NixAttributePath");

				return node.attrpath.attr.reduce((last, identifier) => {
					assert(identifier.type === "NixAttributeIdentifier");

					return callLazyWrapper(types.memberExpression(last, types.identifier(identifier.name)));
				}, node.expression);
			});
		},
		NixAttributeSet: (node, { defer, setContext, getContext }) => {
			// if (node.recursive) {
			// 	setContext(null, "attributeSets_inRecursiveSet", true);
			// }

			return defer((node) => {
				let isRecursive = node.recursive;

				// let [ dynamicNodes, staticNodes ] = splitFilter(node.bind, (binding) => isDynamicBinding(binding));

				// let staticBindings = staticNodes.map((binding) => {
				// 	assert(binding.attrpath.attr.length === 1); // Nested attributes should have been desugared by this point

				// 	return {
				// 		name: binding.attrpath.attr[0].name,
				// 		expression: lazyWrapper(binding.expression)
				// 	};
				// });

				let bindings = node.bind.map((binding) => {
					assert(binding.attrpath.attr.length === 1); // Nested attributes should have been desugared by this point

					return {
						name: (isDynamicBinding(binding))
							? binding.attrpath.attr[0]
							: binding.attrpath.attr[0].name,
						expression: lazyWrapper(binding.expression)
					};
				});

				let hasDynamicBindings = bindings.some((binding) => typeof binding.name !== "string");

				if (isRecursive) {
					if (hasDynamicBindings) {
						return objectRecursiveDynamic(bindings);
					} else {
						return objectRecursiveStatic(bindings);
					}
				} else {
					return objectNormal(bindings);
				}
			});
		},
	}
};