Typescript: Context.Provider value should not be assignable to undefined in the default case

Author: David Emanuel Luksic

packages/solid/src/reactive/signal.ts

@@ -1130,10 +1130,10 @@ export function registerGraph(value: SourceMapValue): void {
 export type ContextProviderComponent<T> = FlowComponent<{ value: T }>;
 
 // Context API
-export interface Context<T> {
+export interface Context<T, D = T> {
   id: symbol;
   Provider: ContextProviderComponent<T>;
-  defaultValue: T;
+  defaultValue: D;
 }
 
 /**
@@ -1158,7 +1158,7 @@ export interface Context<T> {
 export function createContext<T>(
   defaultValue?: undefined,
   options?: EffectOptions
-): Context<T | undefined>;
+): Context<T, undefined>;
 export function createContext<T>(defaultValue: T, options?: EffectOptions): Context<T>;
 export function createContext<T>(
   defaultValue?: T,
@@ -1176,7 +1176,7 @@ export function createContext<T>(
  *
  * @description https://www.solidjs.com/docs/latest/api#usecontext
  */
-export function useContext<T>(context: Context<T>): T {
+export function useContext<T, D>(context: Context<T, D>): D extends undefined ? T | undefined : T {
   return Owner && Owner.context && Owner.context[context.id] !== undefined
     ? Owner.context[context.id]
     : context.defaultValue;
@@ -1215,7 +1215,7 @@ export type SuspenseContextType = {
   resolved?: boolean;
 };
 
-type SuspenseContext = Context<SuspenseContextType | undefined> & {
+type SuspenseContext = Context<SuspenseContextType, undefined> & {
   active?(): boolean;
   increment?(): void;
   decrement?(): void;
@@ -1224,7 +1224,7 @@ type SuspenseContext = Context<SuspenseContextType | undefined> & {
 let SuspenseContext: SuspenseContext;
 
 export function getSuspenseContext() {
-  return SuspenseContext || (SuspenseContext = createContext<SuspenseContextType | undefined>());
+  return SuspenseContext || (SuspenseContext = createContext<SuspenseContextType>());
 }
 
 // Interop

packages/solid/web/test/context.spec.tsx

@@ -20,13 +20,14 @@ describe("Testing Context", () => {
       </Show>
     );
   };
-  const div = document.createElement("div");
+
   it("should create context properly", () => {
     expect(ThemeContext.id).toBeDefined();
     expect(ThemeContext.defaultValue).toBe("light");
   });
 
   it("should work with single provider child", () => {
+    const div = document.createElement("div");
     render(
       () => (
         <ThemeContext.Provider value="dark">
@@ -35,11 +36,11 @@ describe("Testing Context", () => {
       ),
       div
     );
-    expect((div.firstChild as HTMLDivElement).innerHTML).toBe("dark");
-    div.innerHTML = "";
+    expect(div.children[0].innerHTML).toBe("dark");
   });
 
   it("should work with single conditional provider child", () => {
+    const div = document.createElement("div");
     render(
       () => (
         <ThemeContext.Provider value="dark">
@@ -48,11 +49,11 @@ describe("Testing Context", () => {
       ),
       div
     );
-    expect((div.firstChild as HTMLDivElement).innerHTML).toBe("dark");
-    div.innerHTML = "";
+    expect(div.children[0].innerHTML).toBe("dark");
   });
 
   it("should work with multi provider child", () => {
+    const div = document.createElement("div");
     render(
       () => (
         <ThemeContext.Provider value="dark">
@@ -62,11 +63,11 @@ describe("Testing Context", () => {
       ),
       div
     );
-    expect((div.firstChild!.nextSibling! as HTMLDivElement).innerHTML).toBe("dark");
-    div.innerHTML = "";
+    expect(div.children[1].innerHTML).toBe("dark");
   });
 
   it("should work with multi conditional provider child", () => {
+    const div = document.createElement("div");
     render(
       () => (
         <ThemeContext.Provider value="dark">
@@ -76,11 +77,11 @@ describe("Testing Context", () => {
       ),
       div
     );
-    expect((div.firstChild!.nextSibling! as HTMLDivElement).innerHTML).toBe("dark");
-    div.innerHTML = "";
+    expect(div.children[1].innerHTML).toBe("dark");
   });
 
   it("should work with dynamic multi provider child", () => {
+    const div = document.createElement("div");
     const child = () => <Component />;
     render(
       () => (
@@ -91,11 +92,11 @@ describe("Testing Context", () => {
       ),
       div
     );
-    expect((div.firstChild!.nextSibling! as HTMLDivElement).innerHTML).toBe("dark");
-    div.innerHTML = "";
+    expect(div.children[1].innerHTML).toBe("dark");
   });
 
   it("should work with dynamic multi conditional provider child", () => {
+    const div = document.createElement("div");
     const child = () => <CondComponent />;
     render(
       () => (
@@ -106,7 +107,29 @@ describe("Testing Context", () => {
       ),
       div
     );
-    expect((div.firstChild!.nextSibling! as HTMLDivElement).innerHTML).toBe("dark");
-    div.innerHTML = "";
+    expect(div.children[1].innerHTML).toBe("dark");
+  });
+
+  const ThemeContextWithoutDefault = createContext<string>();
+  const ComponentWithoutDefault = () => {
+    const theme = useContext(ThemeContextWithoutDefault);
+    return <div>{theme ?? 'no-default'}</div>;
+  };
+
+  it("should work with no default provided", () => {
+    const div = document.createElement("div");
+    render(
+      () => (
+        <>
+          <ComponentWithoutDefault />
+          <ThemeContextWithoutDefault.Provider value="dark">
+            <ComponentWithoutDefault />
+          </ThemeContextWithoutDefault.Provider>
+        </>
+      ),
+      div
+    );
+    expect(div.children[0].innerHTML!).toBe("no-default");
+    expect(div.children[1].innerHTML!).toBe("dark");
   });
 });