Plugin source map still not properly chained

Describe the bug

I am referring to my previous issue #18491, which was closed by #18518. The problem is still there in the latest version (5.57.0). I tried to follow the explanation of the PR and played with adding source and file in various forms and I couldn't get it working. I tried to inspect the variables in node_modules/svelte/src/compiler/utils/mapped_code.js inside the function combine_sourcemaps and checking conditions, reversing orders, etc. but I couldn't find the root cause.

Reproduction

Since the reproduction can't work in the REPL, and since it is fairly small, I'll provide the files here.

Start from the svelte template in npm create vite@latest, install magic-string, and edit only these two files:

vite.config.js

import { defineConfig } from 'vite'
import { svelte } from '@sveltejs/vite-plugin-svelte'
import MagicString from 'magic-string'

// https://vite.dev/config/
export default defineConfig({
    plugins: [
        {
            name: "tst",
            transform(code, id) {
                if (!id.includes('App.svelte')) {
                    return
                }
                const m = new MagicString(code)
                m.appendRight(10, 'let leben = 42\n\n')
                return {
                    code: m.toString(),
                    map: m.generateMap(/* add {file: id}, {source: id}, {file: 'App.svelte'}, etc */),
                }
            },
        },
        svelte()
    ],
})

App.svelte

<script>

console.error('helo')

</script>

Hello, see devtools

Then run it, go to devtools, and look at the location of the console.error message, it will be at the beginning of the script block, not at the actual location.

Logs

Not relevant

System Info

System:
    OS: Linux 7.0 Ubuntu 26.04 LTS 26.04 LTS (Resolute Raccoon)
    CPU: (8) x64 11th Gen Intel(R) Core(TM) i7-1195G7 @ 2.90GHz
    Memory: 10.74 GB / 15.27 GB
    Container: Yes
    Shell: 5.3.9 - /bin/bash
  Binaries:
    Node: 24.19.0 - /home/k1dv5/.local/bin/node
    npm: 11.17.0 - /home/k1dv5/.local/bin/npm
  Browsers:
    Firefox: 154.0.1
    Firefox Developer Edition: 154.0.1
  npmPackages:
    svelte: ^5.57.0 => 5.57.0

Severity

annoyance