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visitors.ts
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visitors.ts
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import * as virtualTypes from "./path/lib/virtual-types";
import { DEPRECATED_KEYS, FLIPPED_ALIAS_KEYS, TYPES } from "@babel/types";
import type { NodePath, Visitor } from "./index";
type VIRTUAL_TYPES = keyof typeof virtualTypes;
function isVirtualType(type: string): type is VIRTUAL_TYPES {
return type in virtualTypes;
}
/**
* explode() will take a visitor object with all of the various shorthands
* that we support, and validates & normalizes it into a common format, ready
* to be used in traversal
*
* The various shorthands are:
* * `Identifier() { ... }` -> `Identifier: { enter() { ... } }`
* * `"Identifier|NumericLiteral": { ... }` -> `Identifier: { ... }, NumericLiteral: { ... }`
* * Aliases in `@babel/types`: e.g. `Property: { ... }` -> `ObjectProperty: { ... }, ClassProperty: { ... }`
*
* Other normalizations are:
* * Visitors of virtual types are wrapped, so that they are only visited when
* their dynamic check passes
* * `enter` and `exit` functions are wrapped in arrays, to ease merging of
* visitors
*/
export function explode(visitor: Visitor) {
if (visitor._exploded) return visitor;
visitor._exploded = true;
// normalise pipes
for (const nodeType of Object.keys(visitor) as (keyof Visitor)[]) {
if (shouldIgnoreKey(nodeType)) continue;
const parts: Array<string> = nodeType.split("|");
if (parts.length === 1) continue;
const fns = visitor[nodeType];
delete visitor[nodeType];
for (const part of parts) {
// @ts-expect-error part will be verified by `verify` later
visitor[part] = fns;
}
}
// verify data structure
verify(visitor);
// make sure there's no __esModule type since this is because we're using loose mode
// and it sets __esModule to be enumerable on all modules :(
// @ts-expect-error ESModule interop
delete visitor.__esModule;
// ensure visitors are objects
ensureEntranceObjects(visitor);
// ensure enter/exit callbacks are arrays
ensureCallbackArrays(visitor);
// add type wrappers
for (const nodeType of Object.keys(visitor)) {
if (shouldIgnoreKey(nodeType)) continue;
if (!isVirtualType(nodeType)) continue;
// wrap all the functions
const fns = visitor[nodeType];
for (const type of Object.keys(fns)) {
// @ts-expect-error manipulating visitors
fns[type] = wrapCheck(nodeType, fns[type]);
}
// clear it from the visitor
delete visitor[nodeType];
const types = virtualTypes[nodeType];
if (types !== null) {
for (const type of types) {
// merge the visitor if necessary or just put it back in
if (visitor[type]) {
mergePair(visitor[type], fns);
} else {
// @ts-expect-error Expression produces too complex union
visitor[type] = fns;
}
}
} else {
mergePair(visitor, fns);
}
}
// add aliases
for (const nodeType of Object.keys(visitor) as (keyof Visitor)[]) {
if (shouldIgnoreKey(nodeType)) continue;
const fns = visitor[nodeType];
let aliases = FLIPPED_ALIAS_KEYS[nodeType];
const deprecatedKey = DEPRECATED_KEYS[nodeType];
if (deprecatedKey) {
console.trace(
`Visitor defined for ${nodeType} but it has been renamed to ${deprecatedKey}`,
);
aliases = [deprecatedKey];
}
if (!aliases) continue;
// clear it from the visitor
delete visitor[nodeType];
for (const alias of aliases) {
const existing = visitor[alias];
if (existing) {
mergePair(existing, fns);
} else {
// @ts-expect-error Expression produces a union type that is too complex to represent.
visitor[alias] = { ...fns };
}
}
}
for (const nodeType of Object.keys(visitor)) {
if (shouldIgnoreKey(nodeType)) continue;
ensureCallbackArrays(
// @ts-expect-error nodeType must present in visitor after previous validations
visitor[nodeType],
);
}
return visitor;
}
export function verify(visitor: Visitor) {
if (visitor._verified) return;
if (typeof visitor === "function") {
throw new Error(
"You passed `traverse()` a function when it expected a visitor object, " +
"are you sure you didn't mean `{ enter: Function }`?",
);
}
for (const nodeType of Object.keys(visitor) as (keyof Visitor)[]) {
if (nodeType === "enter" || nodeType === "exit") {
validateVisitorMethods(nodeType, visitor[nodeType]);
}
if (shouldIgnoreKey(nodeType)) continue;
if (TYPES.indexOf(nodeType) < 0) {
throw new Error(
`You gave us a visitor for the node type ${nodeType} but it's not a valid type`,
);
}
const visitors = visitor[nodeType];
if (typeof visitors === "object") {
for (const visitorKey of Object.keys(visitors)) {
if (visitorKey === "enter" || visitorKey === "exit") {
// verify that it just contains functions
validateVisitorMethods(
`${nodeType}.${visitorKey}`,
visitors[visitorKey],
);
} else {
throw new Error(
"You passed `traverse()` a visitor object with the property " +
`${nodeType} that has the invalid property ${visitorKey}`,
);
}
}
}
}
visitor._verified = true;
}
function validateVisitorMethods(
path: string,
val: any,
): asserts val is Function | Function[] {
const fns = [].concat(val);
for (const fn of fns) {
if (typeof fn !== "function") {
throw new TypeError(
`Non-function found defined in ${path} with type ${typeof fn}`,
);
}
}
}
export function merge<State>(visitors: Visitor<State>[]): Visitor<State>;
export function merge(
visitors: Visitor<unknown>[],
states?: any[],
wrapper?: Function | null,
): Visitor<unknown>;
export function merge(
visitors: any[],
states: any[] = [],
wrapper?: Function | null,
) {
const rootVisitor: Visitor = {};
for (let i = 0; i < visitors.length; i++) {
const visitor = visitors[i];
const state = states[i];
explode(visitor);
for (const type of Object.keys(visitor) as (keyof Visitor)[]) {
let visitorType = visitor[type];
// if we have state or wrapper then overload the callbacks to take it
if (state || wrapper) {
visitorType = wrapWithStateOrWrapper(visitorType, state, wrapper);
}
// @ts-expect-error: Expression produces a union type that is too complex to represent.
const nodeVisitor = (rootVisitor[type] ||= {});
mergePair(nodeVisitor, visitorType);
}
}
return rootVisitor;
}
function wrapWithStateOrWrapper<State>(
oldVisitor: Visitor<State>,
state: State,
wrapper?: Function | null,
) {
const newVisitor: Visitor = {};
for (const key of Object.keys(oldVisitor) as (keyof Visitor<State>)[]) {
let fns = oldVisitor[key];
// not an enter/exit array of callbacks
if (!Array.isArray(fns)) continue;
// @ts-expect-error manipulating visitors
fns = fns.map(function (fn) {
let newFn = fn;
if (state) {
newFn = function (path: NodePath) {
return fn.call(state, path, state);
};
}
if (wrapper) {
// @ts-expect-error Fixme: document state.key
newFn = wrapper(state.key, key, newFn);
}
// Override toString in case this function is printed, we want to print the wrapped function, same as we do in `wrapCheck`
if (newFn !== fn) {
newFn.toString = () => fn.toString();
}
return newFn;
});
// @ts-expect-error: Expression produces a union type that is too complex to represent.
newVisitor[key] = fns;
}
return newVisitor;
}
function ensureEntranceObjects(obj: Visitor) {
for (const key of Object.keys(obj) as (keyof Visitor)[]) {
if (shouldIgnoreKey(key)) continue;
const fns = obj[key];
if (typeof fns === "function") {
// @ts-expect-error: Expression produces a union type that is too complex to represent.
obj[key] = { enter: fns };
}
}
}
function ensureCallbackArrays(obj: Visitor) {
// @ts-expect-error normalizing enter property
if (obj.enter && !Array.isArray(obj.enter)) obj.enter = [obj.enter];
// @ts-expect-error normalizing exit property
if (obj.exit && !Array.isArray(obj.exit)) obj.exit = [obj.exit];
}
function wrapCheck(nodeType: VIRTUAL_TYPES, fn: Function) {
const newFn = function (this: unknown, path: NodePath) {
if (path[`is${nodeType}`]()) {
return fn.apply(this, arguments);
}
};
newFn.toString = () => fn.toString();
return newFn;
}
function shouldIgnoreKey(
key: string,
): key is
| "enter"
| "exit"
| "shouldSkip"
| "denylist"
| "noScope"
| "skipKeys"
| "blacklist" {
// internal/hidden key
if (key[0] === "_") return true;
// ignore function keys
if (key === "enter" || key === "exit" || key === "shouldSkip") return true;
// ignore other options
if (
key === "denylist" ||
key === "noScope" ||
key === "skipKeys" ||
// TODO: Remove in Babel 8
key === "blacklist"
) {
return true;
}
return false;
}
function mergePair(dest: any, src: any) {
for (const key of Object.keys(src)) {
dest[key] = [].concat(dest[key] || [], src[key]);
}
}