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plugin-transform-regenerator can produce infinite loop using async/await and nested try/catch/finally #9019

mgroenhoff opened this Issue Nov 13, 2018 · 4 comments


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mgroenhoff commented Nov 13, 2018

Bug Report

Current Behavior
The state machine produced by @babel/plugin-transform-regenerator is incorrect and can produce an infinite loop using nested try/catch/finally statements inside a loop together with async/await as shown in the example below.

If I run the code from the repl below with node it loops two times and then exits the loop. If I run the code produced by babel it loops 10 times.

Input Code

let call = 0;
async function callback() {
    if (call < 2) {
        throw new Error("err");
    call = 0;

async function main() {
    let retry;
    do {
      	retry = false;
        let result;
        try {
            try {
                result = await callback();
            } catch (error) {
                console.log("error 1");
                throw error;
            }/* finally {
                // If I enable this finally block and `await callback()` does not throw ("success"), it jumps to the outer catch block ("error 2") below
                console.log("finally 1");
        } catch (error) {
            console.log("error 2");
            retry = true;
        } finally {
            console.log("finally 2");
    } while (retry);


See repl

Expected behavior/code
If I uncomment the inner finally everything works as expected.
See repl


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babel-bot commented Nov 13, 2018

Hey @mgroenhoff! We really appreciate you taking the time to report an issue. The collaborators
on this project attempt to help as many people as possible, but we're a limited number of volunteers,
so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack
community that typically always has someone willing to help. You can sign-up here
for an invite.


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ulrichb commented Nov 23, 2018

@mgroenhoff Is the this._invoke() call in defineIteratorMethods() involved in this endless loop?

I'm also seeing an endless loop here (but only in the MS Edge (v18) browser, not in Chrome/Fx)...


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mgroenhoff commented Nov 27, 2018

@ulrichb I'm sorry but I don't see any references to this._invoke() or defineIteratorMethods() in my code or the generated code. Can you try to explain why you brought those up?


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ulrichb commented Nov 27, 2018

@mgroenhoff Sry. Forget my comment. I had an endless iterator in my user code (just affecting MS Edge).

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