fix: preserve non-nullable ref return types

packages/hooks/src/__tests__/refTypes.spec.ts

@@ -0,0 +1,56 @@
+import { fileURLToPath } from 'node:url';
+import ts from 'typescript';
+import { describe, expect, test } from 'vitest';
+
+const emitDeclaration = (sourceFile: string) => {
+  let declaration = '';
+  const program = ts.createProgram([sourceFile], {
+    declaration: true,
+    emitDeclarationOnly: true,
+    jsx: ts.JsxEmit.React,
+    module: ts.ModuleKind.ESNext,
+    moduleResolution: ts.ModuleResolutionKind.Bundler,
+    skipLibCheck: true,
+    strictNullChecks: true,
+    target: ts.ScriptTarget.ES2015,
+    types: [],
+  });
+
+  const diagnostics = ts.getPreEmitDiagnostics(program);
+  if (diagnostics.length > 0) {
+    throw new Error(
+      ts.formatDiagnosticsWithColorAndContext(diagnostics, {
+        getCanonicalFileName: (fileName) => fileName,
+        getCurrentDirectory: () => process.cwd(),
+        getNewLine: () => '\n',
+      }),
+    );
+  }
+
+  const emitResult = program.emit(undefined, (fileName, text) => {
+    if (fileName.endsWith('.d.ts')) {
+      declaration = text;
+    }
+  });
+
+  expect(emitResult.emitSkipped).toBe(false);
+  return declaration;
+};
+
+describe('ref return type declarations', () => {
+  test.each([
+    [
+      'useLatest',
+      '../useLatest/index.ts',
+      'declare function useLatest<T>(value: T): MutableRefObject<T>;',
+    ],
+    [
+      'useUnmountedRef',
+      '../useUnmountedRef/index.tsx',
+      'declare const useUnmountedRef: () => MutableRefObject<boolean>;',
+    ],
+  ])('%s should expose a non-nullable mutable ref', (_hook, sourcePath, expected) => {
+    const sourceFile = fileURLToPath(new URL(sourcePath, import.meta.url));
+    expect(emitDeclaration(sourceFile)).toContain(expected);
+  });
+});

packages/hooks/src/useLatest/index.ts

@@ -1,6 +1,7 @@
+import type { MutableRefObject } from 'react';
 import { useRef } from 'react';
 
-function useLatest<T>(value: T) {
+function useLatest<T>(value: T): MutableRefObject<T> {
   const ref = useRef(value);
   ref.current = value;
 

packages/hooks/src/useUnmountedRef/index.tsx

@@ -1,6 +1,7 @@
+import type { MutableRefObject } from 'react';
 import { useEffect, useRef } from 'react';
 
-const useUnmountedRef = () => {
+const useUnmountedRef = (): MutableRefObject<boolean> => {
   const unmountedRef = useRef(false);
   useEffect(() => {
     unmountedRef.current = false;