fix(types): accept an explicit undefined wherever a consumer writes an optional member

src/__tests__/native/styled.test.ios.tsx

@@ -163,6 +163,25 @@ test.each(["nativeStyleMapping", "nativeStyleToProp"] as const)(
   },
 );
 
+test("a mapping entry set to undefined maps nothing", () => {
+  registerCSS(`.subject { color: blue; background-color: red; }`);
+  const StyledView = styled(View, {
+    className: {
+      target: "style",
+      nativeStyleMapping: {
+        color: "accessibilityLabel",
+        backgroundColor: undefined,
+      },
+    },
+  });
+
+  render(<StyledView testID={testID} className="subject" />);
+
+  const props = screen.getByTestId(testID).props;
+  expect(props.accessibilityLabel).toBe("#00f");
+  expect(props.style).toEqual({ backgroundColor: "#f00" });
+});
+
 test.each([false, true])(
   "current mapping wins over deprecated alias (empty: %s)",
   (empty) => {

src/__tests__/types/_program.ts

@@ -0,0 +1,69 @@
+import { join } from "node:path";
+
+import ts from "typescript";
+
+export const root = join(__dirname, "../../..").replaceAll("\\", "/");
+
+// The repository's own compiler options with exactOptionalPropertyTypes on, and a fixture's unused names allowed
+export function compilerOptions(): ts.CompilerOptions {
+  const { config } = ts.readConfigFile(`${root}/tsconfig.json`, (path) =>
+    ts.sys.readFile(path),
+  );
+  const { options } = ts.parseJsonConfigFileContent(config, ts.sys, root);
+  return {
+    ...options,
+    exactOptionalPropertyTypes: true,
+    noUnusedLocals: false,
+    noUnusedParameters: false,
+  };
+}
+
+export function createProgram(
+  rootNames: readonly string[],
+  virtualFiles: Readonly<Record<string, string>> = {},
+): ts.Program {
+  const options = compilerOptions();
+  const host = ts.createCompilerHost(options, true);
+
+  return ts.createProgram(rootNames, options, {
+    ...host,
+    getCurrentDirectory: () => root,
+    fileExists: (name) => name in virtualFiles || host.fileExists(name),
+    readFile: (name) => virtualFiles[name] ?? host.readFile(name),
+    getSourceFile: (name, languageVersion, ...rest) => {
+      const text = virtualFiles[name];
+      return text === undefined
+        ? host.getSourceFile(name, languageVersion, ...rest)
+        : ts.createSourceFile(name, text, languageVersion, true);
+    },
+  });
+}
+
+export function createLanguageService(
+  virtualFiles: Readonly<Record<string, string>>,
+): ts.LanguageService {
+  const options = compilerOptions();
+
+  return ts.createLanguageService(
+    {
+      getScriptFileNames: () => Object.keys(virtualFiles),
+      getScriptVersion: () => "1",
+      getScriptSnapshot: (name) => {
+        const text = virtualFiles[name] ?? ts.sys.readFile(name);
+        return text === undefined
+          ? undefined
+          : ts.ScriptSnapshot.fromString(text);
+      },
+      getCurrentDirectory: () => root,
+      getCompilationSettings: () => options,
+      getDefaultLibFileName: ts.getDefaultLibFilePath,
+      fileExists: (name) => name in virtualFiles || ts.sys.fileExists(name),
+      readFile: (name) => virtualFiles[name] ?? ts.sys.readFile(name),
+      readDirectory: (path, extensions, excludes, includes, depth) =>
+        ts.sys.readDirectory(path, extensions, excludes, includes, depth),
+      directoryExists: (name) => ts.sys.directoryExists(name),
+      getDirectories: (name) => ts.sys.getDirectories(name),
+    },
+    ts.createDocumentRegistry(),
+  );
+}