fix: default to first declaration for getWellKnownSymbolPropertyOfType properties

src/nodes/typeGuards/compound.ts

@@ -61,6 +61,16 @@ export function isJsxTagNamePropertyAccess(
 	);
 }
 
+/**
+ * @remarks This always returns true.
+ * @see /~https://github.com/JoshuaKGoldberg/ts-api-utils/pull/16#discussion_r1106579774
+ */
+export function isNamedDeclaration(
+	node: ts.Declaration
+): node is ts.NamedDeclaration {
+	return true;
+}
+
 export function isNamespaceDeclaration(
 	node: ts.Node
 ): node is ts.NamespaceDeclaration {

src/test/utils.ts

@@ -29,7 +29,7 @@ export function createSourceFileAndTypeChecker(
 	sourceText: string,
 	fileName = "file.ts"
 ): SourceFileAndTypeChecker {
-	const compilerOptions = {};
+	const compilerOptions = { target: ts.ScriptTarget.ES2018 };
 	const fsMap = tsvfs
 		.createDefaultMapFromNodeModules(compilerOptions)
 		.set(fileName, sourceText);

src/types/getters.test.ts

@@ -0,0 +1,27 @@
+import * as ts from "typescript";
+import { describe, expect, it } from "vitest";
+
+import { createSourceFileAndTypeChecker } from "../test/utils.js";
+import { getWellKnownSymbolPropertyOfType } from "./getters.js";
+
+describe("getWellKnownSymbolPropertyOfType", () => {
+	// /~https://github.com/JoshuaKGoldberg/ts-api-tools/issues/15
+	it("gets the property when it does not have a value declaration", () => {
+		const { sourceFile, typeChecker } = createSourceFileAndTypeChecker(`
+            declare const x: Omit<{
+                [Symbol.asyncIterator](): AsyncIterator<any>;
+            }, 'z'>
+        `);
+
+		const node = (sourceFile.statements[0] as ts.VariableStatement)
+			.declarationList.declarations[0].name;
+
+		const type = typeChecker.getTypeAtLocation(node);
+
+		expect(
+			getWellKnownSymbolPropertyOfType(type, "asyncIterator", typeChecker)
+		).toMatchObject({
+			name: /^__@asyncIterator/,
+		});
+	});
+});

src/types/getters.ts

@@ -3,6 +3,7 @@
 
 import * as ts from "typescript";
 
+import { isNamedDeclaration } from "../nodes/typeGuards/index.js";
 import {
 	isIntersectionType,
 	isUnionType,
@@ -50,15 +51,21 @@ export function getWellKnownSymbolPropertyOfType(
 	const prefix = "__@" + wellKnownSymbolName;
 
 	for (const prop of type.getProperties()) {
-		if (!prop.name.startsWith(prefix)) continue;
+		if (!prop.name.startsWith(prefix)) {
+			continue;
+		}
+
+		const declaration = prop.valueDeclaration ?? prop.getDeclarations()![0];
+		if (
+			!isNamedDeclaration(declaration) ||
+			declaration.name === undefined ||
+			!ts.isComputedPropertyName(declaration.name)
+		) {
+			continue;
+		}
 
 		const globalSymbol = typeChecker.getApparentType(
-			typeChecker.getTypeAtLocation(
-				(
-					(prop.valueDeclaration as ts.NamedDeclaration)
-						.name as ts.ComputedPropertyName
-				).expression
-			)
+			typeChecker.getTypeAtLocation(declaration.name.expression)
 		).symbol;
 
 		if (