JS: Allow await/yield as property names

javascript/extractor/src/com/semmle/jcorn/Parser.java

@@ -2296,9 +2296,11 @@ protected Identifier parseIdent(boolean liberal) {
           && (this.options.ecmaVersion() >= 6
               || inputSubstring(this.start, this.end).indexOf("\\") == -1))
         this.raiseRecoverable(this.start, "The keyword '" + this.value + "' is reserved");
-      if (!isPrivateField && this.inGenerator && this.value.equals("yield"))
+      // `yield` and `await` are only restricted as bindings and references. `liberal` means we
+      // are parsing a property name, where they are ordinary identifiers.
+      if (!liberal && this.inGenerator && this.value.equals("yield"))
         this.raiseRecoverable(this.start, "Can not use 'yield' as identifier inside a generator");
-      if (!isPrivateField && this.inAsync && this.value.equals("await"))
+      if (!liberal && this.inAsync && this.value.equals("await"))
         this.raiseRecoverable(
             this.start, "Can not use 'await' as identifier inside an async function");
       name = String.valueOf(this.value);

javascript/extractor/test/com/semmle/js/extractor/test/AllTests.java

@@ -27,7 +27,8 @@
   ExportExtensionsTests.class,
   AutoBuildTests.class,
   RobustnessTests.class,
-  NumericSeparatorTests.class
+  NumericSeparatorTests.class,
+  AwaitYieldIdentifierTests.class
 })
 public class AllTests {
 

javascript/extractor/test/com/semmle/js/extractor/test/AwaitYieldIdentifierTests.java

@@ -0,0 +1,62 @@
+package com.semmle.js.extractor.test;
+
+import com.semmle.jcorn.CustomParser;
+import com.semmle.jcorn.Options;
+import com.semmle.jcorn.SyntaxError;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Tests for using <code>await</code> and <code>yield</code> as property names inside async
+ * functions and generators, where they are only restricted as bindings and references.
+ */
+public class AwaitYieldIdentifierTests {
+  private void testSucceed(String input) {
+    new CustomParser(new Options().esnext(true), input, 0).parse();
+  }
+
+  private void testFail(String input, String msg) {
+    try {
+      new CustomParser(new Options().esnext(true), input, 0).parse();
+      Assert.fail("Expected syntax error, but parsing succeeded.");
+    } catch (SyntaxError e) {
+      Assert.assertEquals(msg, e.getMessage());
+    }
+  }
+
+  @Test
+  public void awaitAsPropertyName() {
+    testSucceed("async function f(pool) { return await pool.await(); }");
+    testSucceed("async function f(o) { return o?.await; }");
+    testSucceed("async function f() { return { await: 42 }; }");
+    testSucceed("async function f() { class C { await() {} } }");
+    testSucceed("async function f(o) { o.await = 42; }");
+  }
+
+  @Test
+  public void yieldAsPropertyName() {
+    testSucceed("function* g(o) { yield o.yield(); }");
+    testSucceed("function* g() { return { yield: 42 }; }");
+    testSucceed("function* g() { class C { yield() {} } }");
+  }
+
+  @Test
+  public void awaitAsIdentifier() {
+    testFail(
+        "async function f() { var await = 42; }",
+        "Can not use 'await' as identifier inside an async function (1:25)");
+    testFail(
+        "async function f() { return { await }; }",
+        "'await' can not be used as shorthand property (1:30)");
+  }
+
+  @Test
+  public void yieldAsIdentifier() {
+    testFail(
+        "function* g() { var yield = 42; }",
+        "Can not use 'yield' as identifier inside a generator (1:20)");
+    testFail(
+        "function* g() { return { yield }; }",
+        "'yield' can not be used as shorthand property (1:25)");
+  }
+}

javascript/extractor/tests/es2017/input/await-yield-property.js

@@ -0,0 +1,17 @@
+const o = { await: 42, yield: 43 };
+
+async function f(pool) {
+  console.log(o.await);
+  o.await = 1;
+  return await pool.await();
+}
+
+function* g() {
+  yield o.yield;
+  yield o?.yield;
+}
+
+class C {
+  async await() {}
+  *yield() {}
+}