packages/babel-traverse/src/path/evaluation.js
import type NodePath from "./index";
// This file contains Babels metainterpreter that can evaluate static code.
const VALID_CALLEES = ["String", "Number", "Math"];
const INVALID_METHODS = ["random"];
/**
* Walk the input `node` and statically evaluate if it's truthy.
*
* Returning `true` when we're sure that the expression will evaluate to a
* truthy value, `false` if we're sure that it will evaluate to a falsy
* value and `undefined` if we aren't sure. Because of this please do not
* rely on coercion when using this method and check with === if it's false.
*
* For example do:
*
* if (t.evaluateTruthy(node) === false) falsyLogic();
*
* **AND NOT**
*
* if (!t.evaluateTruthy(node)) falsyLogic();
*
*/
export function evaluateTruthy(): boolean {
const res = this.evaluate();
if (res.confident) return !!res.value;
}
/**
* Deopts the evaluation
*/
function deopt(path, state) {
if (!state.confident) return;
state.deoptPath = path;
state.confident = false;
}
/**
* We wrap the _evaluate method so we can track `seen` nodes, we push an item
* to the map before we actually evaluate it so we can deopt on self recursive
* nodes such as:
*
* var g = a ? 1 : 2,
* a = g * this.foo
*/
function evaluateCached(path, state) {
const { node } = path;
const { seen } = state;
if (seen.has(node)) {
const existing = seen.get(node);
if (existing.resolved) {
return existing.value;
} else {
deopt(path, state);
return;
}
} else {
const item = { resolved: false };
seen.set(node, item);
const val = _evaluate(path, state);
if (state.confident) {
item.resolved = true;
item.value = val;
}
return val;
}
}
function _evaluate(path, state) {
if (!state.confident) return;
const { node } = path;
if (path.isSequenceExpression()) {
const exprs = path.get("expressions");
return evaluateCached(exprs[exprs.length - 1], state);
}
if (
path.isStringLiteral() ||
path.isNumericLiteral() ||
path.isBooleanLiteral()
) {
return node.value;
}
if (path.isNullLiteral()) {
return null;
}
if (path.isTemplateLiteral()) {
return evaluateQuasis(path, node.quasis, state);
}
if (
path.isTaggedTemplateExpression() &&
path.get("tag").isMemberExpression()
) {
const object = path.get("tag.object");
const {
node: { name },
} = object;
const property = path.get("tag.property");
if (
object.isIdentifier() &&
name === "String" &&
!path.scope.getBinding(name, true) &&
property.isIdentifier &&
property.node.name === "raw"
) {
return evaluateQuasis(path, node.quasi.quasis, state, true);
}
}
if (path.isConditionalExpression()) {
const testResult = evaluateCached(path.get("test"), state);
if (!state.confident) return;
if (testResult) {
return evaluateCached(path.get("consequent"), state);
} else {
return evaluateCached(path.get("alternate"), state);
}
}
if (path.isExpressionWrapper()) {
// TypeCastExpression, ExpressionStatement etc
return evaluateCached(path.get("expression"), state);
}
// "foo".length
if (
path.isMemberExpression() &&
!path.parentPath.isCallExpression({ callee: node })
) {
const property = path.get("property");
const object = path.get("object");
if (object.isLiteral() && property.isIdentifier()) {
const value = object.node.value;
const type = typeof value;
if (type === "number" || type === "string") {
return value[property.node.name];
}
}
}
if (path.isReferencedIdentifier()) {
const binding = path.scope.getBinding(node.name);
if (binding && binding.constantViolations.length > 0) {
return deopt(binding.path, state);
}
if (binding && path.node.start < binding.path.node.end) {
return deopt(binding.path, state);
}
if (binding?.hasValue) {
return binding.value;
} else {
if (node.name === "undefined") {
return binding ? deopt(binding.path, state) : undefined;
} else if (node.name === "Infinity") {
return binding ? deopt(binding.path, state) : Infinity;
} else if (node.name === "NaN") {
return binding ? deopt(binding.path, state) : NaN;
}
const resolved = path.resolve();
if (resolved === path) {
return deopt(path, state);
} else {
return evaluateCached(resolved, state);
}
}
}
if (path.isUnaryExpression({ prefix: true })) {
if (node.operator === "void") {
// we don't need to evaluate the argument to know what this will return
return undefined;
}
const argument = path.get("argument");
if (
node.operator === "typeof" &&
(argument.isFunction() || argument.isClass())
) {
return "function";
}
const arg = evaluateCached(argument, state);
if (!state.confident) return;
switch (node.operator) {
case "!":
return !arg;
case "+":
return +arg;
case "-":
return -arg;
case "~":
return ~arg;
case "typeof":
return typeof arg;
}
}
if (path.isArrayExpression()) {
const arr = [];
const elems: Array<NodePath> = path.get("elements");
for (const elem of elems) {
const elemValue = elem.evaluate();
if (elemValue.confident) {
arr.push(elemValue.value);
} else {
return deopt(elem, state);
}
}
return arr;
}
if (path.isObjectExpression()) {
const obj = {};
const props: Array<NodePath> = path.get("properties");
for (const prop of props) {
if (prop.isObjectMethod() || prop.isSpreadElement()) {
return deopt(prop, state);
}
const keyPath = prop.get("key");
let key = keyPath;
if (prop.node.computed) {
key = key.evaluate();
if (!key.confident) {
return deopt(keyPath, state);
}
key = key.value;
} else if (key.isIdentifier()) {
key = key.node.name;
} else {
key = key.node.value;
}
const valuePath = prop.get("value");
let value = valuePath.evaluate();
if (!value.confident) {
return deopt(valuePath, state);
}
value = value.value;
obj[key] = value;
}
return obj;
}
if (path.isLogicalExpression()) {
// If we are confident that the left side of an && is false, or the left
// side of an || is true, we can be confident about the entire expression
const wasConfident = state.confident;
const left = evaluateCached(path.get("left"), state);
const leftConfident = state.confident;
state.confident = wasConfident;
const right = evaluateCached(path.get("right"), state);
const rightConfident = state.confident;
switch (node.operator) {
case "||":
// TODO consider having a "truthy type" that doesn't bail on
// left uncertainty but can still evaluate to truthy.
state.confident = leftConfident && (!!left || rightConfident);
if (!state.confident) return;
return left || right;
case "&&":
state.confident = leftConfident && (!left || rightConfident);
if (!state.confident) return;
return left && right;
}
}
if (path.isBinaryExpression()) {
const left = evaluateCached(path.get("left"), state);
if (!state.confident) return;
const right = evaluateCached(path.get("right"), state);
if (!state.confident) return;
switch (node.operator) {
case "-":
return left - right;
case "+":
return left + right;
case "/":
return left / right;
case "*":
return left * right;
case "%":
return left % right;
case "**":
return left ** right;
case "<":
return left < right;
case ">":
return left > right;
case "<=":
return left <= right;
case ">=":
return left >= right;
case "==":
return left == right; // eslint-disable-line eqeqeq
case "!=":
return left != right;
case "===":
return left === right;
case "!==":
return left !== right;
case "|":
return left | right;
case "&":
return left & right;
case "^":
return left ^ right;
case "<<":
return left << right;
case ">>":
return left >> right;
case ">>>":
return left >>> right;
}
}
if (path.isCallExpression()) {
const callee = path.get("callee");
let context;
let func;
// Number(1);
if (
callee.isIdentifier() &&
!path.scope.getBinding(callee.node.name, true) &&
VALID_CALLEES.indexOf(callee.node.name) >= 0
) {
func = global[node.callee.name];
}
if (callee.isMemberExpression()) {
const object = callee.get("object");
const property = callee.get("property");
// Math.min(1, 2)
if (
object.isIdentifier() &&
property.isIdentifier() &&
VALID_CALLEES.indexOf(object.node.name) >= 0 &&
INVALID_METHODS.indexOf(property.node.name) < 0
) {
context = global[object.node.name];
func = context[property.node.name];
}
// "abc".charCodeAt(4)
if (object.isLiteral() && property.isIdentifier()) {
const type = typeof object.node.value;
if (type === "string" || type === "number") {
context = object.node.value;
func = context[property.node.name];
}
}
}
if (func) {
const args = path.get("arguments").map(arg => evaluateCached(arg, state));
if (!state.confident) return;
return func.apply(context, args);
}
}
deopt(path, state);
}
function evaluateQuasis(path, quasis: Array<Object>, state, raw = false) {
let str = "";
let i = 0;
const exprs = path.get("expressions");
for (const elem of quasis) {
// not confident, evaluated an expression we don't like
if (!state.confident) break;
// add on element
str += raw ? elem.value.raw : elem.value.cooked;
// add on interpolated expression if it's present
const expr = exprs[i++];
if (expr) str += String(evaluateCached(expr, state));
}
if (!state.confident) return;
return str;
}
/**
* Walk the input `node` and statically evaluate it.
*
* Returns an object in the form `{ confident, value }`. `confident` indicates
* whether or not we had to drop out of evaluating the expression because of
* hitting an unknown node that we couldn't confidently find the value of.
*
* Example:
*
* t.evaluate(parse("5 + 5")) // { confident: true, value: 10 }
* t.evaluate(parse("!true")) // { confident: true, value: false }
* t.evaluate(parse("foo + foo")) // { confident: false, value: undefined }
*
*/
export function evaluate(): { confident: boolean, value: any } {
const state = {
confident: true,
deoptPath: null,
seen: new Map(),
};
let value = evaluateCached(this, state);
if (!state.confident) value = undefined;
return {
confident: state.confident,
deopt: state.deoptPath,
value: value,
};
}