refactor: add new overload to the type of defineConfig

[vinassefranche]

Description

Fixes #13950 (at least partially)
Using a generic type for defineConfig avoids having the result being typed with a union type, with both functions or objects.

Additional context

I've run the typecheck locally and everything passed.

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the PR Title Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

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Run & review this pull request in StackBlitz Codeflow.

[patak-dev]

/ecosystem-ci run

[vite-ecosystem-ci]

📝 Ran ecosystem CI: Open

suite	result
analogjs	❌ failure
astro	✅ success
histoire	❌ failure
iles	❌ failure
ladle	✅ success
laravel	✅ success
marko	✅ success
nuxt	✅ success
nx	✅ success
previewjs	✅ success
qwik	❌ failure
rakkas	✅ success
sveltekit	✅ success
unocss	✅ success
vite-plugin-pwa	✅ success
vite-plugin-ssr	✅ success
vite-plugin-react	✅ success
vite-plugin-react-pages	❌ failure
vite-plugin-react-swc	✅ success
vite-plugin-svelte	✅ success
vite-plugin-vue	✅ success
vite-setup-catalogue	✅ success
vitepress	✅ success
vitest	✅ success

[sodatea]

I've tried this approach before.

First, it breaks Qwik's types because of an as any casting in their code https://github.com/BuilderIO/qwik/blob/d886be703d19545b9c56ca136ad9d2d7e349f871/packages/qwik-worker/vite.config.ts#L42
The reason is: microsoft/TypeScript#54987 (comment)

Secondly, extends ends up too permissive. See this example: https://www.typescriptlang.org/play?#code/C4TwDgpgBAqgzhATgYQPYDsBmBLA5lAXigG8AoKKYAQ0VwmAC4oAiCOAVmagB8W2AmAAwBGTjz5x0EAB7BmAbnJQcAGwgA5KgFsITABSZUiLVUZQ4wRNnS4AlIQB85y9dyKAvotCQoaLHgBRdAA3QihUACMAKwgAY2BSUhkwI2BKcGh4JD8cXAAxdAB5aLi0oj0IEKYcwJD7AicslAxcpOkUxDTvTIRm-3z0AAVEVC1sBDCKqt8W2uD6p2HR8YgAHiaa3Ac2jq6M2F7NgsnK4OrZ3CD5xwPsi-ElsYR1w4vtndT0nw2LgPbPghKXg-fpAqCPFYvO79bYUYGvfoFYoxeJgkG5AoQhBohEY9CJAD0ACoieQiVAACr7AAWEBUkEQlFQUBMAGtoNg0hAqHBsEgmVAAK4TYKciAAOliF3FwDgZKgVFisQgYFlCqgABNsIhSiQAAIqays259XLucIleIAGnCjKoykF6Hi2AwlGppigOuAgsQ6DgUE54vlFNpDqdwBd6E9cQg2GCbHVxANRpm-Su5siKK67q5-wQ-uAAHdmWARgyI2wGPKAAZSrQmdAa6tQCqc2mM6sAcgiguwKg1nebRigXd68cHthtVEbI60qA1EGrQagRIJH06YedroXOCkmz0Uv6THReFsx9xeHXaUwjq3UZ31gg+8PuSYWLWJ62Z-BIyeH4vWxXpuEbbhAu5PhcB4XOe0K5H8uzfp+8GpEBN7hpGmpgY+z7QSamzIZ0iEAQRaRkBQXo+lGL6Xu4iRoXemHgZsADqbYAOKVEg2CxHAqwUlAMjAJUGr+kh-ydA4UFHpS378WR0ber6UDUW4pC0aQD57hcrHANSHFSFYPF6HoCwtvJ1C0PQTCsBwzBWkoqgaNougtoYximKZ1bWAu0jigAJMQbkmGUBBEDZXAAPwsFoURwFw1mxLFzDuNW9nuLYtiKKQBIEuY1KoIK-YCYgIyMhEcRUMK0CoJgbrQI6rLoKghZRqWqDliAGlYVp-Q6XpnGGXAejmTQdBmDZnD2RQjmaDo+hBR5NxeY2Mj+YFRjBYQoUSJF0VJVACVJSlU3mKMEAwOgjXNUMZZIKATDCGpmWJF1TGQSNlnjWwk0OX2Tlza5G2LQ0I7eatAULSFYVsLtzAxXFB0sIlcXHU9WU5XlBVFUgpVQOVsSVRMNV1UKl1NS1UBtR1r3Ye9SgWWN1nfXZv1qLNLkGEDwCeWDvkQ1zW3QwjUVw-th0o6lShwGdF1XS1SwdQ9aOkEAA

[sodatea]

Maybe adding more overloads can solve your original problem already?

[vinassefranche]

Maybe adding more overloads can solve your original problem already?

I agree that adding this overload should fix my issue:

export function defineConfig(config: UserConfigFnObject): UserConfigFnObject

I'll check that it's indeed the case and hope it won't break something else

[vinassefranche]

@sodatea I've tested with the new overload and it would indeed fix my use case (if the same change would be done in vitest too but that's another issue and I'll try to port it when this is resolved)
Let's see if everything works fine with only the overload

[patak-dev]

/ecosystem-ci run

[vite-ecosystem-ci]

📝 Ran ecosystem CI: Open

suite	result
analogjs	❌ failure
astro	✅ success
histoire	❌ failure
iles	❌ failure
ladle	✅ success
laravel	✅ success
marko	✅ success
nuxt	✅ success
nx	✅ success
previewjs	✅ success
qwik	✅ success
rakkas	✅ success
sveltekit	✅ success
unocss	✅ success
vite-plugin-pwa	✅ success
vite-plugin-ssr	✅ success
vite-plugin-react	✅ success
vite-plugin-react-pages	❌ failure
vite-plugin-react-swc	✅ success
vite-plugin-svelte	✅ success
vite-plugin-vue	✅ success
vite-setup-catalogue	✅ success
vitepress	✅ success
vitest	✅ success

[patak-dev]

Ecosystem CI looks good, same tests are failing in main