feat: add infinite loop effect callstack

[dummdidumm]

This adds a new dev-time only dev_effect_stack variable, which executed effects are pushed to and eventually cleared out after everything's settled. If it doesn't settle however, i.e. you run into an infinite loop, the last ten effects are printed out so you get an idea where the error is coming from. For proper source mapping I also had to add location info to the generated effects.

Closes #13192

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Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint

[changeset-bot]

🦋 Changeset detected

Latest commit: c046928

The changes in this PR will be included in the next version bump.

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[trueadm]

Do you have a screenshot what this looks like?

[dummdidumm]

Try for yourself 🙂

[paoloricciuti]

Love this!

[trueadm]

We should probably disable this in node, as now I get this when running tests lol:

stderr | packages/svelte/tests/signals/test.ts > signals > schedules rerun when writing to signal before reading it (runes mode)
Last ten effects were:  [
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect]
]

stderr | packages/svelte/tests/signals/test.ts > signals > schedules rerun when writing to signal before reading it (runes mode)
Last ten effects were:  [
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect],
  [Function: $effect]
]

[dummdidumm]

Are these tests triggering the infinite loop guard on purpose? If not, why is this showing up?

[trueadm]

Just happens when you run all tests?

[RickRyan26]

5.0.0-next.244 is working great for me, performant and everything, 5.0.0-next.246 is throwing this error so I had to go back to 244. The the last ten effects are printed out but theyre all different normal things so I have no idea what to fix...

[paoloricciuti]

5.0.0-next.244 is working great for me, performant and everything, 5.0.0-next.246 is throwing this error so I had to go back to 244. The the last ten effects are printed out but theyre all different normal things so I have no idea what to fix...

That's weird...do you have a reproduction?

[RickRyan26]

5.0.0-next.244 is working great for me, performant and everything, 5.0.0-next.246 is throwing this error so I had to go back to 244. The the last ten effects are printed out but theyre all different normal things so I have no idea what to fix...

That's weird...do you have a reproduction?

Nevermind, I apologize, 246 works for me now.
I foolishly added reverse() to {#each products.reverse() as product (product.id)} at the same time I updated Svelte and was tricked by the coincidence.

The last 10 effects don't point me to that file tho.

[Rich-Harris]

Looks like there's an off-by-one error in Firefox:

To be honest I'm not sure how much use the transformed function body is in the browsers where it does work — unless I'm well versed in how the compiler transforms code, I'm liable to be confused by this and waste time looking for an occurrence of update(count) in my source code:

Feels like we might be better off attaching location information to the effect in development, so that we can do something like this instead:

Uncaught Svelte error: effect_update_depth_exceeded
Maximum update depth exceeded in App.svelte:3:1. This can happen when a reactive block or effect repeatedly sets a new value. Svelte limits the number of nested updates to prevent infinite loops

I'll open an issue