Add coverage for `Yield` parameter in RHS of `in`

test/language/expressions/in/rhs-yield-absent-non-strict.js

@@ -0,0 +1,30 @@
+// Copyright 2021 the V8 project authors.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: Parsing observes the `Yield` production parameter when absent (without strict mode)
+info: |
+  Syntax
+    RelationalExpression[In, Yield, Await]:
+    [...]
+    [+In] RelationalExpression[+In, ?Yield, ?Await] in ShiftExpression[?Yield, ?Await]
+
+  [...]
+
+  1. Let lref be the result of evaluating RelationalExpression.
+  2. Let lval be ? GetValue(lref).
+  3. Let rref be the result of evaluating ShiftExpression.
+  4. Let rval be ? GetValue(rref).
+  5. If Type(rval) is not Object, throw a TypeError exception.
+  6. Return ? HasProperty(rval, ? ToPropertyKey(lval)).
+esid: sec-relational-operators
+flags: [noStrict]
+---*/
+
+var yield;
+
+yield = {'': 0};
+assert.sameValue('' in (yield), true);
+
+yield = {};
+assert.sameValue('' in (yield), false);

test/language/expressions/in/rhs-yield-absent-strict.js

@@ -0,0 +1,20 @@
+// Copyright 2021 the V8 project authors.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: Parsing observes the `Yield` production parameter when absent (within strict mode)
+info: |
+  Syntax
+    RelationalExpression[In, Yield, Await]:
+    [...]
+    [+In] RelationalExpression[+In, ?Yield, ?Await] in ShiftExpression[?Yield, ?Await]
+esid: sec-relational-operators
+negative:
+  phase: parse
+  type: SyntaxError
+flags: [onlyStrict]
+---*/
+
+$DONOTEVALUATE();
+
+'' in (yield);

test/language/expressions/in/rhs-yield-present.js

@@ -0,0 +1,33 @@
+// Copyright 2021 the V8 project authors.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: Parsing observes the `Yield` production parameter when present
+info: |
+  Syntax
+    RelationalExpression[In, Yield, Await]:
+    [...]
+    [+In] RelationalExpression[+In, ?Yield, ?Await] in ShiftExpression[?Yield, ?Await]
+
+  [...]
+
+  1. Let lref be the result of evaluating RelationalExpression.
+  2. Let lval be ? GetValue(lref).
+  3. Let rref be the result of evaluating ShiftExpression.
+  4. Let rval be ? GetValue(rref).
+  5. If Type(rval) is not Object, throw a TypeError exception.
+  6. Return ? HasProperty(rval, ? ToPropertyKey(lval)).
+esid: sec-relational-operators-runtime-semantics-evaluation
+---*/
+
+function * isNameIn() {
+  return '' in (yield);
+}
+
+let iter1 = isNameIn();
+iter1.next();
+assert.sameValue(iter1.next({'': 0}).value, true);
+
+let iter2 = isNameIn();
+iter2.next();
+assert.sameValue(iter2.next({}).value, false);