Runtime error with nested components, {{#if}}s, and {{yield}}

[TehShrike]

Very similar to #625 - observed in Svelte 1.22.3.

I got a reproduction in the REPL here but then downloaded it locally to fiddle with it some more, so you can find an even slimmer reproduction in https://github.com/TehShrike/svelte-1-22-3-nested-yield-issue-repro

When the state changes and causes some elements to be cleaned up, an error is thrown Uncaught TypeError: Cannot read property 'unmount' of null

Seems to happen when there is a loop that contains a component with {{yield}} inside of an {{#if}} block, but only when there is another Svelte component nested inside of the yielding component.

[PaulBGD]

Hitting the same error in one of my projects using Svelte when I upgraded from a 5 month old version. Only difference is that while it's the same error (calling unmount on null fragment) my project doesn't use loops. Your example is much smaller than mine, so I'll try to debug it and figure out what's going on.

[TehShrike]

yeah, it may be possible to trigger the issue with a destroy() or otherwise causing the nested components to not be needed any more. I only spent a little time slimming down the reproduction case.

[PaulBGD]

Found it:

svelte/src/generators/dom/visitors/IfBlock.ts

Lines 274 to 278 in fe75570

	block.builders.destroy.addLine(
	`${if_name}{
	${name}.unmount();
	${name}.destroy();
	}`

${name}.unmount needs to be added to the unmount block.

[laszbalo]

Is this issue fixed? Tried to run the Modal example from the guide, but got the same error. Tried it locally, and also in the REPL. I am on version 1.23.4.

[TehShrike]

My reproduction cases above don't throw errors any more with 1.27.0.

[PaulBGD]

I've updated to latest version in my large project and no issues.

[Rich-Harris]

Fixed in 1.28