Function call passed as props in #if tag runs even if #if condition is false #16583
Description
Describe the bug
If I have an {#if} block where the condition is false, any props passed to a component in the {#if} tag which are calculated by a function will still call the function, resulting in potentially unexpected behavior.
See repl: https://svelte.dev/playground/f1a27ae8e85f478f93e6718dcbe6d4d4?version=5.38.0
Here App displays a Component, which takes in a prop, which is initially defined. Then it's made undefined by the button click, so I would expect anything inside the #if (eg. the rendering of Component2) not to run. But it still triggers modifyProp which is called from inside #if, which attempts to modify a property of an undefined parameter, even though it seems like that would be protected by the {#if} clause guarding against undefined.
modifyProp is not run when not passed as a prop to another component.
Reproduction
https://svelte.dev/playground/f1a27ae8e85f478f93e6718dcbe6d4d4?version=5.38.0
Logs
TypeError
TypeError: Cannot read properties of undefined (reading 'property')
at modifyProp (playground:output:5179:72)
at eval (playground:output:5193:34)
at update_reaction (playground:output:3938:57)
at execute_derived (playground:output:1684:13)
at update_derived (playground:output:1700:15)
at is_dirty (playground:output:3857:7)
at flush_inspect_effects (playground:output:2543:8)
at internal_set (playground:output:2524:5)
at set (playground:output:2448:10)
at HTMLButtonElement.on_click (playground:output:5234:3)
System Info
System:
OS: macOS 15.6
CPU: (10) arm64 Apple M1 Pro
Memory: 79.20 MB / 32.00 GB
Shell: 5.9 - /bin/zsh
Binaries:
Node: 20.13.1 - /usr/local/bin/node
npm: 10.5.2 - /usr/local/bin/npm
Browsers:
Chrome: 138.0.7204.184
Safari: 18.6
npmPackages:
rollup: ^4.18.0 => 4.45.1
svelte: ^5.36.13 => 5.36.13Severity
annoyance