Svelte uses same yield content when it's in a if block

[PaulBGD]

I created a test repo with more info: https://github.com/PaulBGD/svelte-uses-same-yield

Comes down to:
This bug only occurs when there is a 2nd component with a yield in it and the 1st component has an if statement that uses the 2nd component in each block. The content of the yield will be the same passed from the 1st if block.

[PaulBGD]

This is a pretty major issue, as the following common code doesn't work:

{{#if false}}
<Component>Hello</Component>
{{else}}
<Component>Goodbye</Component>
{{/if}}

Shows Hello, the string Goodbye isn't even included in the final bundle.

[PaulBGD]

So changing

svelte/src/generators/dom/visitors/Component.js

Line 34 in 1868334

const yieldName = generator.current.getUniqueName( `render${name}YieldFragment` );

to generator.current.parent.getUniqueName fixes the issue, because before the different yield blocks were getting the same name and so svelte was only using the 1st one.

The only thing is, I don't understand why we need to use the parent there because I'm not super familiar with this piece of code. Any advice @Rich-Harris?

[Rich-Harris]

Fixed in 1.6.3, thanks (the answer was that the names need to be globally unique — it just so happened that in that case using the parent fragment's name maker had the same effect)