Solidjs V2 Migration

Migrate Solid 1.x → 2.0

Convert 1.x code to 2.0 in passes: mechanical first, then semantic, then diagnostics-driven cleanup. The full rename/removal table with before/after recipes is in references/migration-map.md — read it before starting; this file is the workflow.

Step 0 — establish the direction

• Source must be Solid 1.x (imports like solid-js/web, solid-js/store, createResource, Suspense). Target version: whatever solid-js@2.x / @solidjs/web prerelease the project declares (or the latest, if you're also bumping package.json).
• Prereleases drift. The installed typings (node_modules/solid-js/types, @solidjs/web) outrank docs and this skill's references when they disagree.
• Upgrade solid-js, @solidjs/web, and the Solid compiler integration together. babel-preset-solid is replaced by @solidjs/babel-plugin; Vite uses @solidjs/vite-plugin (native @solidjs/compiler by default).

Pass 1 — mechanical (grep-and-replace, low judgement)

1. Dependencies: solid-js@2.x, add @solidjs/web, and replace babel-preset-solid with matching @solidjs/babel-plugin (or use @solidjs/vite-plugin).
2. tsconfig.json: "jsxImportSource": "@solidjs/web".
3. Import paths and pure renames — tables at the top of references/migration-map.md. Greppable: solid-js/web, solid-js/store, Suspense, SuspenseList, ErrorBoundary, mergeProps, splitProps, unwrap, onMount, createSelector, Context.Provider, classList, equalFn, getListener.

Mind the non-1:1 renames: Errored's fallback gets an error accessor (err()), splitProps → omit inverts the result (rest-only), merge treats undefined as an override, onSettled is a leaf owner.

Pass 2 — semantic rewrites (per call site, by intent)

Work through references/migration-map.md sections in this order — each names the decision to make:

1. Effects: single-callback createEffect → split (compute, apply); on() → compute phase; initialValue → default parameter; onCleanup inside effects → returned cleanup.
2. createComputed → createMemo / split effect / createSignal(fn) — pick by intent (derivation / side effect / writable derived).
3. batch → delete; add flush() only where code reads its own writes synchronously.
4. createResource → async createMemo (or createProjection for keyed collections) + <Loading>; .loading/.error/refetch/mutate each map differently — see the table.
5. Mutations: ad-hoc flag flipping / startTransition → action() + optimistic primitives + awaitable refresh() or until() live-source acknowledgement.
6. Stores: produce wrappers → plain drafts; path setters → drafts (or storePath compat); reconcile moves inside the draft; createMutable → createStore.
7. Lists: <Index> → <For keyed={false}>; audit default <For> callbacks — item is now raw, index is an accessor.
8. DOM: use: → ref factories; on:/attr:/bool:/class:/style: namespaces → standard forms; /*@once*/ → reactive or defaultValue; camelCase attributes → lowercase.
9. Context: .Provider → context-as-component; delete useX-with-throw wrappers (useContext now returns T and throws without Provider).
10. Server functions: old .GET/.withOptions call sites → declaration wrappers, prepareRequest, or per-call invoke; audit module-level versus function-level wrapper trust boundaries.
11. from/observable → async iterables / push-out effects.

Pass 3 — run dev and fix diagnostics

2.0 ships structured dev diagnostics; the first dev run after migration is the real review. Typical wave, in order of volume:

• STRICT_READ_UNTRACKED — top-level/destructured prop reads the old code tolerated. Move reads into JSX/memos, or untrack deliberate one-shots.
• REACTIVE_WRITE_IN_OWNED_SCOPE (throws) — 1.x effects that write signals. Rewrite as derivations or move writes to handlers/actions. untrack() is not an exemption: it suppresses dependency tracking, not ownership.
• ASYNC_OUTSIDE_LOADING_BOUNDARY — async reads with no <Loading> ancestor; add boundaries where fallback UI is wanted.
• CLEANUP_IN_FORBIDDEN_SCOPE — onCleanup inside onSettled; return the cleanup instead.

Then run the test suite: assertions reading right after writes need flush(), and reactive setups in tests need createRoot.

Pass 4 — behavioral audit (no grep pattern)

The "Behavioral changes that need an audit" section of the map: synchronous read-after-write assumptions, undefined-as-override in merges, forever-roots needing runWithOwner(null, ...).

Failure modes

• A 1.x API has no entry in the map → check the installed typings before inventing a replacement; some conveniences (e.g. observable, createDeferred) intentionally have none — surface the gap rather than papering over it.
• App mounts blank after migration → pending async outside Loading defers the root mount (ASYNC_OUTSIDE_LOADING_BOUNDARY in console).
• Migration of one file pulls in half the app → migrate bottom-up (leaf components first), keep passes 1–2 per-file but expect pass 3 diagnostics to surface cross-file issues.