handle undefined input value with spread

[tanhauhau]

Fixes #5270

this caused by the difference between setAttribute vs setting the property using propertyName.

not really sure is this the right way of handling it? if so, should we also handle all the other attribute that has a custom propertyName in

svelte/src/compiler/compile/render_dom/wrappers/Element/Attribute.ts

Line 291 in 4021063

const attribute_lookup = {

?

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Tests

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[Conduitry]

The CI failure here seems to be legit. I'm seeing spread-element-input-bind-group-with-value-attr fail locally.

[tanhauhau]

i've fixed the failed test case.

i start to feel that special logic for DOM elements that has special case is dispersed at various places, eg: attribute, bindings, and spread, and we are slowly copying from each other as someone found more edge cases...

I'm thinking of consolidating them into a new class, such as TextInput, RadioInput, CheckboxInput that keeps logic for rendering attributes like value, checked, which can be composed within Attribute, Binding and Spread.

what do you think?

[Conduitry]

I'd be worried about changing the type fields in the AST, but if we could do this with regular class inheritance (without changing the AST shape), that sounds reasonable to me.