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import type { Token } from './tokenizer';
/**
* AST for the safe function expression language. Deliberately small:
* no assignment, no arbitrary function values, no `new`, no property calls.
*/
export type ExpressionNode =
| { type: 'literal'; value: unknown }
| { type: 'identifier'; name: string }
| { type: 'member'; object: ExpressionNode; property: string }
| { type: 'index'; object: ExpressionNode; index: ExpressionNode }
| {
type: 'call';
callee: string;
args: ExpressionNode[];
/** The receiver of an aggregate: `series` in `series.instances.max(x)`. */
receiver?: string;
}
| { type: 'unary'; operator: '!' | '-' | '+'; argument: ExpressionNode }
| {
type: 'binary';
operator: string;
left: ExpressionNode;
right: ExpressionNode;
}
| {
type: 'logical';
operator: '&&' | '||';
left: ExpressionNode;
right: ExpressionNode;
}
| {
type: 'conditional';
test: ExpressionNode;
consequent: ExpressionNode;
alternate: ExpressionNode;
}
| { type: 'array'; elements: ExpressionNode[] }
| {
type: 'template';
parts: Array<
{ kind: 'text'; text: string } | { kind: 'expr'; node: ExpressionNode }
>;
};
/**
* Property names that may never be accessed — they walk the prototype chain
* and would break out of the data sandbox.
*/
export const FORBIDDEN_PROPERTIES = new Set([
'__proto__',
'prototype',
'constructor',
]);
/**
* The literal `defined`: an operand of `==` and `!=` only. `X == defined` holds
* when `X` has a value (present and not empty).
*/
export const DEFINED_LITERAL: unique symbol = Symbol('defined');
const KEYWORD_LITERALS = new Map<string, unknown>([
['true', true],
['false', false],
['null', null],
['undefined', undefined],
['defined', DEFINED_LITERAL],
]);
/** Binary operator precedence (higher binds tighter). */
const BINARY_PRECEDENCE: Record<string, number> = {
'||': 1,
'&&': 2,
'==': 3,
'!=': 3,
'===': 3,
'!==': 3,
'<': 4,
'<=': 4,
'>': 4,
'>=': 4,
in: 4,
'+': 5,
'-': 5,
'*': 6,
'/': 6,
'%': 6,
};
/** The aggregates that a receiver can call: `series.instances.max(x)`. */
export const AGGREGATE_NAMES = new Set(['min', 'max', 'sum', 'count']);
/** The receivers of an aggregate. */
export const AGGREGATE_RECEIVERS = new Set([
'series',
'displaySet',
'displaySets',
]);
/**
* The receiver of `<receiver>.instances.<aggregate>`, or `undefined`. Only
* these four names on these receivers can be called as a method.
*/
function aggregateReceiver(node: ExpressionNode): string | undefined {
if (
node.type === 'member' &&
AGGREGATE_NAMES.has(node.property) &&
node.object.type === 'member' &&
node.object.property === 'instances' &&
node.object.object.type === 'identifier' &&
AGGREGATE_RECEIVERS.has(node.object.object.name)
) {
return node.object.object.name;
}
return undefined;
}
class Parser {
private tokens: Token[];
private position = 0;
private expression: string;
constructor(source: string, expression: string) {
this.expression = expression;
this.tokens = tokenize(source, expression);
}
private peek(): Token {
return this.tokens[this.position];
}
private next(): Token {
return this.tokens[this.position++];
}
private isPunct(value: string): boolean {
const token = this.peek();
return token.kind === 'punct' && token.value === value;
}
private isIdent(name: string): boolean {
const token = this.peek();
return token.kind === 'ident' && token.name === name;
}
private expectPunct(value: string): void {
Iif (!this.isPunct(value)) {
throw new ExpressionSyntaxError(`Expected '${value}'`, this.expression);
}
this.next();
}
private fail(message: string): never {
throw new ExpressionSyntaxError(message, this.expression);
}
parse(): ExpressionNode {
const node = this.parseConditional();
Iif (this.peek().kind !== 'end') {
this.fail('Unexpected trailing input');
}
return node;
}
/** Also used for template interpolations and call arguments. */
parseSubExpression(): ExpressionNode {
return this.parseConditional();
}
private parseConditional(): ExpressionNode {
const test = this.parseBinary(0);
Eif (!this.isPunct('?')) {
return test;
}
this.next();
const consequent = this.parseConditional();
this.expectPunct(':');
const alternate = this.parseConditional();
return { type: 'conditional', test, consequent, alternate };
}
private parseBinary(minPrecedence: number): ExpressionNode {
let left = this.parseUnary();
for (;;) {
const token = this.peek();
let operator: string | undefined;
if (token.kind === 'punct' && BINARY_PRECEDENCE[token.value]) {
operator = token.value;
} else if (token.kind === 'ident' && token.name === 'in') {
operator = 'in';
}
if (!operator) {
return left;
}
const precedence = BINARY_PRECEDENCE[operator];
if (precedence <= minPrecedence) {
return left;
}
this.next();
const right = this.parseBinary(precedence);
left =
operator === '&&' || operator === '||'
? { type: 'logical', operator, left, right }
: { type: 'binary', operator, left, right };
}
}
private parseUnary(): ExpressionNode {
const token = this.peek();
if (
token.kind === 'punct' &&
(token.value === '!' || token.value === '-' || token.value === '+')
) {
this.next();
return {
type: 'unary',
operator: token.value,
argument: this.parseUnary(),
};
}
return this.parsePostfix();
}
private parsePostfix(): ExpressionNode {
let node = this.parsePrimary();
for (;;) {
if (this.isPunct('.')) {
this.next();
const property = this.next();
Iif (property.kind !== 'ident') {
this.fail("Expected a property name after '.'");
}
Iif (FORBIDDEN_PROPERTIES.has(property.name)) {
this.fail(`Access to '${property.name}' is not allowed`);
}
node = { type: 'member', object: node, property: property.name };
continue;
}
Iif (this.isPunct('[')) {
this.next();
const index = this.parseSubExpression();
this.expectPunct(']');
node = { type: 'index', object: node, index };
continue;
}
if (this.isPunct('(')) {
const receiver = aggregateReceiver(node);
Iif (node.type !== 'identifier' && !receiver) {
this.fail('Only whitelisted helper functions may be called');
}
const callee =
node.type === 'identifier'
? node.name
: (node as { property: string }).property;
this.next();
const args: ExpressionNode[] = [];
if (!this.isPunct(')')) {
for (;;) {
args.push(this.parseSubExpression());
Iif (this.isPunct(',')) {
this.next();
continue;
}
break;
}
}
this.expectPunct(')');
node = receiver
? { type: 'call', callee, args, receiver }
: { type: 'call', callee, args };
continue;
}
return node;
}
}
private parsePrimary(): ExpressionNode {
const token = this.next();
if (token.kind === 'number') {
return { type: 'literal', value: token.value };
}
if (token.kind === 'string') {
return { type: 'literal', value: token.value };
}
Iif (token.kind === 'template') {
return {
type: 'template',
parts: token.parts.map((part) =>
part.kind === 'text'
? part
: {
kind: 'expr' as const,
node: parseExpressionSource(part.source, this.expression),
}
),
};
}
if (token.kind === 'ident') {
if (KEYWORD_LITERALS.has(token.name)) {
return { type: 'literal', value: KEYWORD_LITERALS.get(token.name) };
}
Iif (token.name === 'in') {
this.fail("Unexpected 'in'");
}
Iif (FORBIDDEN_PROPERTIES.has(token.name)) {
this.fail(`Access to '${token.name}' is not allowed`);
}
return { type: 'identifier', name: token.name };
}
Eif (token.kind === 'punct') {
if (token.value === '(') {
const node = this.parseSubExpression();
this.expectPunct(')');
return node;
}
Eif (token.value === '[') {
const elements: ExpressionNode[] = [];
Eif (!this.isPunct(']')) {
for (;;) {
elements.push(this.parseSubExpression());
if (this.isPunct(',')) {
this.next();
continue;
}
break;
}
}
this.expectPunct(']');
return { type: 'array', elements };
}
}
this.fail('Unexpected token');
}
}
/** Parses a raw expression source string into an AST. */
export function parseExpressionSource(
source: string,
expression = source
): ExpressionNode {
return new Parser(source, expression).parse();
}
|