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macro.js
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macro.js
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const { createMacro } = require('babel-plugin-macros');
const { expression } = require('@babel/template');
const { rename } = require('./names');
const { concat, getNextStatement, getOnlyArgument } = require('./macro-utils');
/**
* This is a babel macro. Import and use these symbols in accordance with the examples below.
* They are replaced with one of two variants depending on whether the ASYNC environment
* variable is defined at compile time.
*
* SYNC TEMPLATE ASYNC
*
* $async(function() {})
* function() {} <---> async function() {}
*
*
* $async; function fn() {}
* function fn() {} <---> async function fn() {}
*
*
* $async`fn`
* 'fn' <---> 'asyncFn'
*
*
* class Class() { class Class() { class Class() {
* @$async
* method() {}
* method() {} <---> async method() {}
* } } }
*
*
* $await(anyExpression)
* anyExpression <---> await anyExpression
*
*
* $await; for(const foo of iterable) {}
* for(const foo of iterable) {} <---> for await(const foo of iterable) {}
*
*
* $isAsync
* false <---> true
*
*
* $isSync
* true <---> false
*
*
* $Promise<typeExpr>
* typeExpr <---> Promise<typeExpr>
*
*
* $MaybePromise<typeExpr>
* typeExpr <---> typeExpr || Promise<typeExpr>
*
* Note that conditional expressions with fixed conditions (such as the last two examples)
* will be further simplified by the dead code elimination babel plugin
*
* To read more about babel macros, take a look at their docs:
* https://github.com/kentcdodds/babel-plugin-macros
*/
const { ast } = expression;
function asyncMacro({ references, babel, state, config: { ASYNC } }) {
const t = babel.types;
const {
$isAsync = [],
$isSync = [],
$iteratorSymbol = [],
$Promise = [],
$MaybePromise = [],
$ = [],
$async = [],
$await = [],
} = references;
for (const reference of $isAsync) {
reference.replaceWith(t.booleanLiteral(!!ASYNC));
}
for (const reference of $isSync) {
reference.replaceWith(t.booleanLiteral(!ASYNC));
}
for (const reference of $iteratorSymbol) {
reference.replaceWith(ASYNC ? ast`Symbol.asyncIterator` : ast`Symbol.iterator`);
}
for (const reference of concat($Promise, $MaybePromise)) {
const { parentPath, parent, node } = reference;
const { name } = node;
if (t.isTSTypeReference(parent)) {
const promisedType = parent.typeParameters.params[0];
if (ASYNC) {
node.name = 'Promise';
if (name === '$MaybePromise') {
parentPath.replaceWith(t.TSUnionType([promisedType, parent]));
}
} else {
parentPath.replaceWith(promisedType);
}
}
}
if (/\.ts$/.test(state.filename)) {
// Unfortunately typescript types lack scope in babel, so we do this the brute force way
babel.traverse(state.file.ast.program, {
Identifier(path) {
const { parentPath, parent, node } = path;
const { name } = node;
if (t.isTSTypeReference(parent)) {
if (name === '$Promise' || name === '$MaybePromise') {
if (!references[name]) {
throw new Error(`Encountered ${name} but ${name} was not imported from async.macro`);
}
const promisedType = parent.typeParameters.params[0];
if (ASYNC) {
node.name = 'Promise';
if (name === '$MaybePromise') {
parentPath.replaceWith(t.TSUnionType([promisedType, parent]));
}
} else {
parentPath.replaceWith(promisedType);
}
}
}
},
});
}
for (const reference of $) {
const { node } = reference.parentPath;
if (node.type === 'TaggedTemplateExpression') {
// $`fnName`
const { quasi } = reference.parentPath.node;
if (!quasi.quasis.length === 1) {
throw new Error('Interpolation not supported for $`fnName`');
}
const name = quasi.quasis[0].value.raw;
reference.parentPath.replaceWith(t.stringLiteral(rename(name, ASYNC)));
}
}
for (const reference of concat($async, $await)) {
const { node, parent } = reference.parentPath;
const refName = reference.node.name;
switch (node.type) {
case 'ExpressionStatement': {
const nextStatement = getNextStatement(reference);
if (refName === '$async' && t.isFunctionDeclaration(nextStatement)) {
// $async; function foo() {}
if (ASYNC) nextStatement.async = true;
} else if (
refName === '$async' &&
t.isExportNamedDeclaration(nextStatement) &&
t.isFunctionDeclaration(nextStatement.declaration)
) {
// $async; export function foo() {}
if (ASYNC) nextStatement.declaration.async = true;
} else if (refName === '$await' && t.isForOfStatement(nextStatement)) {
// $await; for { const foo of bar }
if (ASYNC) nextStatement.await = true;
}
reference.remove();
break;
}
case 'CallExpression': {
let argument = getOnlyArgument(reference, refName);
if (
refName === '$async' &&
(t.isFunctionExpression(argument) || t.isArrowFunctionExpression(argument))
) {
// $async(function() {})
// $async(() => {})
if (ASYNC) {
argument.async = true;
}
} else if (refName === '$await') {
// $await(someExpression)
if (ASYNC) {
argument = t.awaitExpression(argument);
}
}
reference.parentPath.replaceWith(t.parenthesizedExpression(argument));
break;
}
case 'Decorator':
// class {
// @$async
// method() {}
// }
if (t.isClassMethod(parent)) {
if (ASYNC) {
parent.async = true;
}
parent.decorators = parent.decorators.filter((dec) => dec !== node);
}
break;
}
}
}
module.exports = createMacro(asyncMacro, { configName: 'async' });