Dynamic properties in transition "in" directive not working

[sidharthv96]

Describe the bug

When the params passed to "in" transition is changed dynamically, the value is not reflected.
The values passed to "out" work fine.

Reproduction

https://svelte.dev/repl/ca9e1328264c4f3395d72d786c9aa113?version=3.38.3

Logs

No response

System Info

REPL

Severity

annoyance

intro.bug.mov

[baseballyama]

@tanhauhau

Preface

I would like to contribute to Svelte because this project is really fun!👍
And I want to start with bug fixes.

Now I'm trying to solve this issue.
But before create PR, I want to confirm that my way is correct or not.

Explain About This Issue

When in transition event occurred,
below code runs.

bundle.js

add_render_callback(() => {
	if (div_outro) div_outro.end(1);
	if (!div_intro) div_intro = create_in_transition(div, foo, {});
	div_intro.start();
});

According to this code, create_in_transition runs only if div_intro is not initialized.
But according to this issue, programmers can manage in:fly params if they use state or local variable or something.
It means runtime can't judge that create_in_transition is necessary or not at all times.

So my opinion is that remove if (!div_intro) for calling create_in_transition.

How To Solve This Issue

And for fix this issue, I need to change the compiler like this.

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

Before Fix (Line 755)

@add_render_callback(() => {
	if (${outro_name}) ${outro_name}.end(1);
	if (!${intro_name}) ${intro_name} = @create_in_transition(${this.var}, ${fn}, ${snippet});
	${intro_name}.start();
});

After Fix (Line 755)

@add_render_callback(() => {
	if (${outro_name}) ${outro_name}.end(1);
	${intro_name} = @create_in_transition(${this.var}, ${fn}, ${snippet});
	${intro_name}.start();
});

Thank you for reading.
And I hope you will tell me what should I do next!🧐

[tanhauhau]

sounds about right,

1. usually i would searched through git blames on that line of code

if (!${intro_name}) ${intro_name} = @create_in_transition(${this.var}, ${fn}, ${snippet});

whether it was always there since beginning, or was it added later on with some reason

2. I would write a test that would fail before the fix, and passed after the fix

[baseballyama]

Thank you for the reply quickly and guide me!🙏

usually i would searched through git blames on that line of code

Sure! I will check that why the IF statement is there.

I would write a test that would fail before the fix, and passed after the fix

Sure! I will follow the contribution guide.

Then I will create PR if there was nothing special.

[Conduitry]

This should be working now in 3.40.3 - https://svelte.dev/repl/ca9e1328264c4f3395d72d786c9aa113?version=3.40.3