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[2.0] `createContext(undefined)` throws ContextNotFoundError, even when a provider passes `undefined`

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Valutazione

Difficoltà
4/5
Tempo stimato
3-5 giorni
Idoneità per principianti
56/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Attiva
Stack tecnologico
javascript, typescript
Ambito
api, backend

Direzione di ricerca

Start in packages/signals/src/core/context.ts and read getContext alongside the reported examples. Reproduce the cases for an explicit undefined default and provider value, then check how context errors affect computations. Done means the chosen behavior matches the expected cases and the error or docs explain the undefined behavior; the issue does not name a test file.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Describe the bug

getContext (packages/signals/src/core/context.ts) treats undefined as "not found":

let value = owner._context[context.id];
if (value === undefined) value = context.defaultValue;
if (value === undefined) throw new ContextNotFoundError();

So createContext<T | undefined>(undefined), the most common optional-context idiom in React and Solid 1 (where useContext returned undefined), throws when read outside a provider. It also throws when a provider explicitly passes undefined. Inside a computation, the throw halts reactivity for the whole app (#4178).

The message, "Context must either be created with a default value or a value must be provided before accessing it", sounds wrong when the caller did pass a default.

Your Example Website or App

Minimal repro inline below (signals-only).

Steps to Reproduce the Bug or Issue
import { createContext, getContext, setContext, createRoot, createSignal, createRenderEffect, flush } from "@solidjs/signals";

const Opt = createContext<string | undefined>(undefined);
const OptNull = createContext<string | null>(null);

createRoot(() => getContext(Opt));                              // throws ContextNotFoundError
createRoot(() => { setContext(Opt, "x"); getContext(Opt); });   // "x"
createRoot(() => { setContext(Opt, undefined); getContext(Opt); }); // throws ContextNotFoundError
createRoot(() => getContext(OptNull));                          // null

// Inside a computation:
const [show, setShow] = createSignal(false);
const [b, setB] = createSignal(0);
createRoot(() => createRenderEffect(b, v => console.log("b", v)));
createRoot(() => createRenderEffect(() => (show() ? getContext(Opt) : null), () => {}));
flush();
setShow(true); flush(); // StatusError (ContextNotFoundError) + [REACTIVITY_HALTED]
setB(1); flush();       // "b 1" never logs
Expected behavior
  • Distinguish "no default argument" from an explicit undefined default (arguments.length or a sentinel), and throw only for the former.
  • Treat a provider's explicit value={undefined} as a provided value.
  • If that's not wanted, at minimum say in the error message and the docs/cheatsheet that undefined counts as missing, and that null is the way to make a context optional.
Screenshots or Videos

No response

Platform
  • OS: macOS (Darwin 25.5)
  • Browser: n/a (reproduced in Node v24.18.0 with vitest, importing source)
  • Version: solid next @ b0ad1df50 (2026-10-20, after 2.0.0-rc.16)
Additional context

This came up while verifying examples for the From React docs additions (solidjs/solid-docs#1664). It's also a silent migration break from 1.x, where useContext returned undefined.

Lingua principale
TypeScript
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