outtroBlock issue causes dynamic components with each block to not be destroyed

[btakita]

My app seems to be running into this edge case. I don't yet have an isolated reproduction of the issue, but I do have some generated output that has the bug with the fix.

This causes the issue. The problem is each_blocks[i] is set to null & outroBlock is called two times. The first invocation does not have the fn argument and the second invocation does (however, each_blocks[i] is null).

function outroBlock(i, detach, fn) {
	if (each_blocks[i]) {
		each_blocks[i].o(function () {
			if (detach) {
				each_blocks[i].d(detach)
				each_blocks[i] = null
			}
			if (fn) { fn() }
		})
	}
}

This seems to work:

function outroBlock(i, detach, fn) {
	if (each_blocks[i]) {
		each_blocks[i].o(function () {
			if (detach) {
				each_blocks[i].d(detach)
				each_blocks[i] = null
			}
			if (fn) { fn() }
		})
	} else {
		if (fn) { fn() }
	}
}

[btakita]

#1512

[btakita]

I attempted to reproduce the issue. However, there is another error that occurs when you click 'Child2'

TypeError: switch_instance is undefined

TypeError: if_blocks[current_block_type_index] is undefined

https://svelte.technology/repl?version=2.11.0&gist=1942fddd9ef996aa566059a90b07df29

From my app, it seems like the issue has to do with the following:

if/else block or dynamic component
loads a child component
loads a grandchild component
has an each block which loads a great grandchild component

If the each block in the grandchild component does not load a component, then the issue does not manifest.

[btakita]

The order of method invocation is as follows:

for (; #i < ${iterations}.length; #i += 1) ${outroBlock}(#i, 1);

svelte/src/compile/nodes/EachBlock.ts

Line 454 in 26dfb9a

for (; #i < ${iterations}.length; #i += 1) ${outroBlock}(#i, 1);

then

for (let #i = 0; #i < ${iterations}.length; #i += 1) ${outroBlock}(#i, 0, ${countdown});`

svelte/src/compile/nodes/EachBlock.ts

Line 484 in 26dfb9a

for (let #i = 0; #i < ${iterations}.length; #i += 1) ${outroBlock}(#i, 0, ${countdown});`

Notice that the first time outroBlock is invoked, there is no fn passed in to outroBlock. The first invocation causes each_blocks[i] to be set to null, which prevents the countdown fn from being called. The PR calls the fn if passed in even if each_blocks[i] is null.
I'm still attempting to recreate this case in the REPL, but it definitely occurs in my app...

[btakita]

In the short term, setting

nestedTransitions: false

causes outroBlock to not be rendered.

[Rich-Harris]

I fixed the issue that was preventing the reproduction, in #1677. Any chance you can create a repro now that that's released? Your fix in #1662 looks good, but it'd be great to have a repro if possible so we can guard against regressions.

[jacwright]

#1693 and #1709 contain fixes for each blocks (the latter threw an error in the console, so I'm less sure that was for this issue). Agreed a repro would be nice to know if we can close this.

[Rich-Harris]

There was never a repro for this — is it still an issue, or was it fixed?

[Conduitry]

I'm going to assume this has been fixed, at least by the recent outro/detach stuff. Please reopen if you have a repro.