Unclear error message comes if const is already declared in <script> section

[baseballyama]

Describe the bug

If I declare const or function inside {@const} tag and it is already declared in <script> section, an error occurs in the rollup.

The compiler needs to check duplication or rename it automatically.
(I think it would be better to check for duplicates and give the appropriate error message to avoid confusion.)

Reproduction

https://svelte.dev/repl/10aee9db38db4ec5b5c4a3fac24045ae?version=3.46.4

Logs

rollup v2.60.0
bundles src/main.js → public/build/bundle.js...
[!] Error: Unexpected token (Note that you need plugins to import files that are not JavaScript)
src/App.svelte (9:19)
 7:   <p>{dummy_const(item)}</p>
 8:   {@const bar = array.map((item) => {
 9:     const dummy_const = (item) => item * 2;
                         ^
10:     return dummy_const(item);
11:   })}
Error: Unexpected token (Note that you need plugins to import files that are not JavaScript)
    at error (/Users/baseballyama/Desktop/git/svelte-contributes/svelte-general/my-app/node_modules/rollup/dist/shared/rollup.js:158:30)
    at Module.error (/Users/baseballyama/Desktop/git/svelte-contributes/svelte-general/my-app/node_modules/rollup/dist/shared/rollup.js:12382:16)
    at Module.tryParse (/Users/baseballyama/Desktop/git/svelte-contributes/svelte-general/my-app/node_modules/rollup/dist/shared/rollup.js:12785:25)
    at Module.setSource (/Users/baseballyama/Desktop/git/svelte-contributes/svelte-general/my-app/node_modules/rollup/dist/shared/rollup.js:12688:24)
    at ModuleLoader.addModuleSource (/Users/baseballyama/Desktop/git/svelte-contributes/svelte-general/my-app/node_modules/rollup/dist/shared/rollup.js:22152:20)

System Info

System:
    OS: macOS 12.1
    CPU: (10) arm64 Apple M1 Pro
    Memory: 324.19 MB / 32.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 17.0.1 - /opt/homebrew/bin/node
    npm: 8.3.0 - /opt/homebrew/bin/npm
  Browsers:
    Chrome: 98.0.4758.80
    Firefox: 96.0.3
    Safari: 15.2
  npmPackages:
    rollup: ^2.3.4 => 2.60.0 
    svelte: ^3.0.0 => 3.46.3

Severity

annoyance

[dummdidumm]

I think the code should compile in the given form, as it's OK to redeclare a variable in a new context.

const foo = '';
() => {
  const foo = 1; // valid
}