static/assert.ts

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import stacktrace from '../lib/stacktrace';

// This file defines three assert utilities:
// assert(condition, message?, extra_info...?): asserts condition
// unwrap(x: T | undefined | null, message?, extra_info...?): T
// assert_type(x, class, message?, extra_info...?)

function get_diagnostic() {
    const e = new Error(); // eslint-disable-line unicorn/error-message
    const trace = stacktrace.parse(e);
    if (trace.length >= 4) {
        const invoker_frame = trace[3];
        if (invoker_frame.fileName && invoker_frame.lineNumber) {
            return {
                file: invoker_frame.fileName,
                line: invoker_frame.lineNumber,
            };
        }
    }
}

function fail(fail_message: string, user_message: string | undefined, args: any[]): never {
    // Assertions will look like:
    // Assertion failed
    // Assertion failed: Foobar
    // Assertion failed: Foobar, [{"foo": "bar"}]
    let assert_line = fail_message;
    if (user_message) {
        assert_line += `: ${user_message}`;
    }
    if (args.length > 0) {
        try {
            assert_line += ', ' + JSON.stringify(args);
        } catch (e) {}
    }

    const diagnostic = get_diagnostic();
    if (diagnostic) {
        throw new Error(assert_line + `, at ${diagnostic.file}:${diagnostic.line}`);
    } else {
        throw new Error(assert_line);
    }
}

export function assert<C>(c: C, message?: string, ...extra_info: any[]): asserts c {
    if (!c) {
        fail('Assertion failed', message, extra_info);
    }
}

export function unwrap<T>(x: T | undefined | null, message?: string, ...extra_info: any[]): T {
    if (x === undefined || x === null) {
        fail('Unwrap failed', message, extra_info);
    }
    return x;
}