Describe the bug

First, remember that a function like showCount(label: string) can be called with the Tagged Template syntax of javascript as

showCount`Count:`

If such a function is declared with $derived as

let count = $state(0);
let showCount = $derived((s)=> s   ' '   this.count);

calling showCount from a .svelte file such as {showCount`Count:`} becomes reactive and is re-evaluated when count is updated.

When count and showCount are members of a class object, it is also reactive as expected, so that {obj.showCount`Count:`} is re-evaluated when obj.count is updated.

class TObj {
	count = $state(0);
	showCount = $derived((s: string)=>s   ' '   this.count);
};
	
let obj = new TObj();

An issue is observed when obj.showCount is stored in a variable.

const { showCount } = obj;

In this case, {showCount('Count:')} is still reactive but {showCount`Count:`} is no more.

Svelte 5 compiler fails to apply $.template_effect to $derive member function calls in Tagged Template syntax without object name.

Reproduction

Here is a demonstration code. Try it online at svelte-5-preview.vercel.app.

<script lang='ts'>
  class TObj {
    count = $state(0);
    showCount = $derived((s: string)=>s   ' '   this.count);
  };
	
  let obj = new TObj();

  const { showCount } = obj;

  let showCount2 = $derived((s: string)=>s   ' '   obj.count);

  function increment() {
    obj.count  = 1;
  }
</script>

<div>{showCount`Called by tagged template syntax without object name:`}</div>
<div>{showCount('Called by normal function syntax without object name:')}</div>
<div>{obj.showCount`Called by tagged template syntax with object name:`}</div>
<div>{obj.showCount('Called by normal function syntax with object name:')}</div>
<div>{showCount2`Called by tagged template syntax as an independent function:`}</div>

<button onclick={increment}>Click</button>

After clicking the button four times, the result was as follows:

Called by tagged template syntax without object name: 0
Called by normal function syntax without object name: 4
Called by tagged template syntax with object name: 4
Called by normal function syntax with object name: 4
Called by tagged template syntax as an independent function: 4
[Click]

Only the member function call in the tagged template syntax without object name is missing reactivity.

Logs

No response

System Info

This issue was locally tested under the following environment:

  System:
    OS: Windows 10 10.0.19045
    CPU: (12) x64 AMD Ryzen 5 5600U with Radeon Graphics
    Memory: 1.98 GB / 14.83 GB
  Binaries:
    Node: 22.4.1 - C:\Programs\nodejs\node.EXE
    npm: 10.8.1 - C:\Programs\nodejs\npm.CMD
    pnpm: 9.5.0 - C:\Programs\nodejs\pnpm.CMD
  Browsers:
    Edge: Chromium (127.0.2651.74)
    Internet Explorer: 11.0.19041.4355
  npmPackages:
    svelte: 5.0.0-next.175 => 5.0.0-next.175

### Severity

annoyance