fix(config): keep $ServerOnly templates in the client dev build

[lxsmnsyc]

Fixes #1930. The 1.x fix is #2341.

In dev, editing a component whose root element uses $ServerOnly throws TypeError: template is not a function on the first hot update, and the component's content disappears from the page.

Cause

In hydratable builds, the Solid compiler leaves the templates of $ServerOnly elements out of the client bundle. Hydration does not need them, since it reuses the server-rendered DOM. Hot module replacement re-runs the component on the client, though, and there is no template to create it from. birkskyum reduced this to a plain vite-plugin-solid reproduction in solidjs/solid-vite-plugin#308, which is still open.

Fix

babel-plugin-jsx-dom-expressions 0.40.10 added an omitServerOnlyTemplates option, and babel-preset-solid passes it through.

• New config/solid.ts exports solidPlugins. It hands vite-plugin-solid its own solid options object and sets omitServerOnlyTemplates: false from configResolved, using the same condition vite-plugin-solid uses to enable hot reloading (command === "serve", mode !== "production", hot !== false). vite-plugin-solid reads these options on every transform, so the value applies to the whole dev session. The option only affects client (DOM) output, so SSR output is unchanged.
• Production builds still leave the templates out. If the user sets omitServerOnlyTemplates themselves, their value is kept.
• Lockfile: babel-preset-solid 1.9.12 → 1.9.15, which brings babel-plugin-jsx-dom-expressions 0.40.7 → 0.40.11. I picked 1.9.15 rather than 1.9.16 because 1.9.16 requires solid-js ^1.9.16 and the repo is on 1.9.15. Those two packages are the only lockfile changes.
• Older compiler versions ignore the option, so nothing changes for them. Fresh installs already get 0.40.11.

Testing

• New solid.spec.ts runs the real vite-plugin-solid transform through solidPlugins on a $ServerOnly component. It checks that the client dev build keeps the template, the production build leaves it out, a user value of true is kept, and hot: false leaves it out. The dev-build case fails without the fix.
• basic fixture in a browser, route with a $ServerOnly root: before, the first edit threw template is not a function and the content disappeared. After, the edit applies with no errors. With the user setting omitServerOnlyTemplates: true, the error comes back, as expected.
• Production build: the $ServerOnly text is in the server output and in none of the 7 client JS files. As a control, forcing omitServerOnlyTemplates: false everywhere puts it in a client file, so the check does detect a leak.
• @solidjs/start: test:ci (217 tests), typecheck, validate-imports and build pass.
• apps/tests: unit tests, Playwright e2e (42) and bundled-dev e2e (42) pass.

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Latest commit: 6179bd6

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commit: 6179bd6

[brenelz]

I had a potential fix for this here. Is this a more complete one?

solidjs/solid-vite-plugin#362

[lxsmnsyc]

Closing in favor of solidjs/solid-vite-plugin#362, which makes the same fix in vite-plugin-solid itself and covers both SolidStart lines through their existing vite-plugin-solid ranges.

[lxsmnsyc]

@brenelz I wasn't aware of it. It supercedes.