packages/babel-plugin-proposal-async-generator-functions/src/index.js
import { declare } from "@babel/helper-plugin-utils";
import remapAsyncToGenerator from "@babel/helper-remap-async-to-generator";
import syntaxAsyncGenerators from "@babel/plugin-syntax-async-generators";
import { types as t } from "@babel/core";
import rewriteForAwait from "./for-await";
export default declare(api => {
api.assertVersion(7);
const yieldStarVisitor = {
Function(path) {
path.skip();
},
YieldExpression({ node }, state) {
if (!node.delegate) return;
const callee = state.addHelper("asyncGeneratorDelegate");
node.argument = t.callExpression(callee, [
t.callExpression(state.addHelper("asyncIterator"), [node.argument]),
state.addHelper("awaitAsyncGenerator"),
]);
},
};
const forAwaitVisitor = {
Function(path) {
path.skip();
},
ForOfStatement(path, { file }) {
const { node } = path;
if (!node.await) return;
const build = rewriteForAwait(path, {
getAsyncIterator: file.addHelper("asyncIterator"),
});
const { declar, loop } = build;
const block = loop.body;
// ensure that it's a block so we can take all its statements
path.ensureBlock();
// add the value declaration to the new loop body
if (declar) {
block.body.push(declar);
}
// push the rest of the original loop body onto our new body
block.body = block.body.concat(node.body.body);
t.inherits(loop, node);
t.inherits(loop.body, node.body);
if (build.replaceParent) {
path.parentPath.replaceWithMultiple(build.node);
} else {
path.replaceWithMultiple(build.node);
}
},
};
const visitor = {
Function(path, state) {
if (!path.node.async) return;
path.traverse(forAwaitVisitor, state);
if (!path.node.generator) return;
path.traverse(yieldStarVisitor, state);
remapAsyncToGenerator(path, {
wrapAsync: state.addHelper("wrapAsyncGenerator"),
wrapAwait: state.addHelper("awaitAsyncGenerator"),
});
},
};
return {
name: "proposal-async-generator-functions",
inherits: syntaxAsyncGenerators,
visitor: {
Program(path, state) {
// We need to traverse the ast here (instead of just vising Function
// in the top level visitor) because for-await needs to run before the
// async-to-generator plugin. This is because for-await is transpiled
// using "await" expressions, which are then converted to "yield".
//
// This is bad for performance, but plugin ordering will allow as to
// directly visit Function in the top level visitor.
path.traverse(visitor, state);
},
},
};
});