split_path regex is failing when a form input name has hyphens

[vipero07]

Describe the bug

utils.js:105  Uncaught (in promise) Error: Invalid path soMe-Name-with_hyphens
    at split_path (utils.js:105:9)
    at convert_formdata (utils.js:92:20)
    at handle_submit (form.svelte.js:58:17)
    at HTMLFormElement.<anonymous> (form.svelte.js:239:11)
split_path @ utils.js:105
convert_formdata @ utils.js:92
handle_submit @ form.svelte.js:58
(anonymous) @ form.svelte.js:239

kit/packages/kit/src/runtime/utils.js

Line 98 in b5000df

const path_regex = /^[a-zA-Z_$]\w*(\.[a-zA-Z_$]\w*|\[\d+\])*$/;

This regex would fix the issue (though may cause other issues, I haven't fully looked into what the library is doing).
const path_regex = /^[a-zA-Z_$][\w-]*(\.[a-zA-Z_$][\w-]*|\[\d+\])*$/;

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-1vs2zrhj?file=src%2Froutes%2F%2Bpage.svelte

Logs

System Info

System:
    OS: macOS 15.6.1
    CPU: (12) arm64 Apple M2 Max
    Memory: 123.25 MB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.20.0 - ~/.volta/tools/image/node/22.20.0/bin/node
    Yarn: 4.10.3 - ~/.volta/tools/image/yarn/4.10.3/bin/yarn
    npm: 11.6.1 - ~/.volta/tools/image/npm/11.6.1/bin/npm
    bun: 1.2.0 - ~/.volta/bin/bun
  Browsers:
    Brave Browser: 121.1.62.156
    Edge: 140.0.3485.94
    Safari: 26.0.1
  npmPackages:
    @sveltejs/adapter-node: ^5.3.2 => 5.3.2 
    @sveltejs/enhanced-img: ^0.8.2 => 0.8.2 
    @sveltejs/kit: 2.43.5 => 2.43.5 
    @sveltejs/vite-plugin-svelte: ^6.2.1 => 6.2.1 
    svelte: 5.39.6 => 5.39.6 
    vite: 7.1.7 => 7.1.7

Severity

serious, but I can work around it

Additional Information

Form fields with hyphens are valid HTML (I believe). Using regex to test and cause a runtime failue seems wrong, though may be a limitation within svelte. If it is a (somewhat intentional) svelte limitation though, it should be caught in the compiler or linter.

[dummdidumm]

This is intended, and with #14481 it'll become even more "important". Basically, a form name should be a valid identifier. Of course, technically form data are much more relaxed about the name, but for SvelteKit to provide a good experience we have to restrict it a bit. In practice this shouldn't matter because you don't lose anything by being restricted; on the plus side you'll have a nicer time using our APIs

[vipero07]

Ah okay, I closed the PR... Prob should add some compile time or lint validation then. It just means I need to make sure my fields are not hyphenated.