Coverage: async arrow in ClassHeritage. Fixes gh-1736

src/class-elements/class-heritage-array-literal-arrow-heritage.case

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+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+desc: It's a SyntaxError if an array literal evaluated on ClassHeritage uses a private name.
+info: |
+    ClassTail : ClassHeritage { ClassBody }
+
+    ClassHeritage :
+        extends LeftHandSideExpression
+
+template: syntax/invalid
+---*/
+
+//- heritage
+extends () => {} 

src/class-elements/class-heritage-array-literal-async-arrow-heritage.case

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+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+desc: It's a SyntaxError if an array literal evaluated on ClassHeritage uses a private name.
+info: |
+    ClassTail : ClassHeritage { ClassBody }
+
+    ClassHeritage :
+        extends LeftHandSideExpression
+
+template: syntax/invalid
+---*/
+
+//- heritage
+extends async () => {} 

test/language/expressions/class/heritage-arrow-function.js

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+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-runtime-semantics-classdefinitionevaluation
+description: >
+  Throw a TypeError exception if IsConstructor(superclass) is false (async arrow)
+info: |
+  Runtime Semantics: ClassDefinitionEvaluation
+
+  ClassTail : ClassHeritage { ClassBody }
+      ...
+
+  5. Else,
+      Set the running execution context's LexicalEnvironment to classScope.
+      Let superclassRef be the result of evaluating ClassHeritage.
+      Set the running execution context's LexicalEnvironment to env.
+      Let superclass be ? GetValue(superclassRef).
+      If superclass is null, then
+          Let protoParent be null.
+          Let constructorParent be %Function.prototype%.
+      Else if IsConstructor(superclass) is false, throw a TypeError exception.
+      ...
+features: [class]
+---*/
+
+
+assert.throws(TypeError, () => {
+  var C = class extends (async () => {}) {};
+});
+

test/language/expressions/class/heritage-async-arrow-function.js

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+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-runtime-semantics-classdefinitionevaluation
+description: >
+  Throw a TypeError exception if IsConstructor(superclass) is false (async arrow)
+info: |
+  Runtime Semantics: ClassDefinitionEvaluation
+
+  ClassTail : ClassHeritage { ClassBody }
+      ...
+
+  5. Else,
+      Set the running execution context's LexicalEnvironment to classScope.
+      Let superclassRef be the result of evaluating ClassHeritage.
+      Set the running execution context's LexicalEnvironment to env.
+      Let superclass be ? GetValue(superclassRef).
+      If superclass is null, then
+          Let protoParent be null.
+          Let constructorParent be %Function.prototype%.
+      Else if IsConstructor(superclass) is false, throw a TypeError exception.
+      ...
+features: [class]
+---*/
+
+
+assert.throws(TypeError, () => {
+  var C = class extends (async () => {}) {};
+});
+