[fix] Max call stack exceeded when large number of components are flushed

[AaronDDM]

This PR is in reference to the discussion here: #7032

Without this check, flush() is being invoked multiple times, even if the previous run has not yet completed. This occurs if/when you have a large number of components. Eventually, this repeated invocation results in a max call stack exceeded error.

(I shall add a test for the original issue ASAP, get a test/pass based on the change)

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• Prefix your PR title with [feat], [fix], [chore], or [docs].
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with npm test and lint the project with npm run lint

[dummdidumm]

This isn't the right fix because we would end up where we were previously to #6920 (you can see that the code prior to #6920 had exactly the check that you want to add now)

[kyrylkov]

@dummdidumm But it would also mean it's working again, while all versions since that commit break our app.

[AaronDDM]

This isn't the right fix because we would end up where we were previously to #6920 (you can see that the code prior to #6920 had exactly the check that you want to add now)

The while loop will actually keep going as dirty_components keeps getting added to (e.g. dirty_components.length keeps getting bigger and bigger), would it not? So this technically just prevents the same while loop being called multiple times when it is already running.

note: tests also pass with this fix, but I'll see about adding additional tests

Edit: I also tested this branch with the code from https://svelte.dev/repl/5c59fe6aa6354b03aea62c445836f2b1?version=3.44.3 which was used as a reproduction (#6760) for one of the fixes that #6920 addressed, and the fix still works, no regression.

[AaronDDM]

@dummdidumm mind having a 2nd look at this? Happy to pivot as needed to get a resolution. Thank you!

[ruslan-khomiak]

@bluwy @Conduitry Hi guys, please tell me what needs to be done to merge this PR? Because the problem remains relevant for us and we are still on svelte version 3.44.2.

[kyrylkov]

@dummdidumm See post above please

[dummdidumm]

Please provide a reproducible (REPL or github repo) so we can investigate this properly. This PR isn't doing anything, flushing is never set to true so I can't imagine this would fix your problem. The related issue is missing a minimum reproducible.

[ruslan-khomiak]

Please provide a reproducible (REPL or github repo) so we can investigate this properly. This PR isn't doing anything, flushing is never set to true so I can't imagine this would fix your problem. The related issue is missing a minimum reproducible.

ok, got it. I'll try to do a REPL

[AaronDDM]

Hey guys, apologies I’ll take a look at updating the PR again.

[ruslan-khomiak]

Please provide a reproducible (REPL or github repo) so we can investigate this properly. This PR isn't doing anything, flushing is never set to true so I can't imagine this would fix your problem. The related issue is missing a minimum reproducible.

@dummdidumm @Conduitry
I created a REPL and tried to simplify what I have as much as possible in order to reproduce the bug. For reproducing you need to click the "Toggle" button in the REPL.

https://svelte.dev/repl/86b8b83f2e2b475e8e92aaa4df9c7da2?version=3.44.2 - everything is good
https://svelte.dev/repl/86b8b83f2e2b475e8e92aaa4df9c7da2?version=3.44.3 - maximum call stack size exceeded error

Looks like the problem appeared after the merge of this PR: https://github.com/sveltejs/svelte/pull/6920/files

I hope this helps you find the problem and fix it.

[baseballyama]

Close in favor of #8114