Add support for Symbol member expression in class method definition (#1602)

Summary:


## Summary:
This diff introduces support for [Symbol.iterator] and [Symbol.asyncIterator] as a method definition in flow defs generation. It can be confirmed in the flow lexer that these are the only two tokens prefixed with `@@`. Previously, that type of code wasn't supported and caused an exception:

```js
export default {
  [Symbol.iterator]() {};
  [Symbol.asyncIterator]() {};
}
```

The generated output if the type is not specified should be:

```js
declare export default {
  @iterator(): void;
  @asyncIterator(): void;
}
```

There are a few places in react-native source that will benefit from this, like: DOMRectList, URLSeachParams, NodeList and HTMLCollection.

Changelog:
[flow-api-translator] - Added support for Symbol member expression in class method definition

Reviewed By: pieterv

Differential Revision: D68766740

Author: coado

tools/hermes-parser/js/flow-api-translator/__tests__/flowToFlowDef-test.js

@@ -444,6 +444,16 @@ describe('flowToFlowDef', () => {
            static 2(): void;
          }`,
       );
+      await expectTranslate(
+        `export class A {
+           [Symbol.iterator]() {}
+           static get [Symbol.asyncIterator]() {}
+         }`,
+        `declare export class A {
+           @@iterator(): void;
+           static get @@asyncIterator(): void;
+         }`,
+      );
     });
   });
   describe('InterfaceDeclaration', () => {

tools/hermes-parser/js/flow-api-translator/src/flowToFlowDef.js

@@ -85,6 +85,7 @@ import {
   isStringLiteral,
   isNumericLiteral,
   isIdentifier,
+  isMemberExpressionWithNonComputedProperty,
 } from 'hermes-estree';
 
 const EMPTY_TRANSLATION_RESULT = [null, []];
@@ -1218,7 +1219,13 @@ function convertClassMember(
       if (
         !isIdentifier(member.key) &&
         !isStringLiteral(member.key) &&
-        !isNumericLiteral(member.key)
+        !isNumericLiteral(member.key) &&
+        !(
+          isMemberExpressionWithNonComputedProperty(member.key) &&
+          member.key.object.type === 'Identifier' &&
+          member.key.object.name === 'Symbol' &&
+          ['iterator', 'asyncIterator'].includes(member.key.property.name)
+        )
       ) {
         throw translationError(
           member.key,
@@ -1229,15 +1236,23 @@ function convertClassMember(
 
       const [resultValue, deps] = convertAFunction(member.value, context);
 
+      const newKey =
+        isMemberExpressionWithNonComputedProperty(member.key) &&
+        member.key.object.type === 'Identifier' &&
+        member.key.object.name === 'Symbol'
+          ? t.Identifier({name: `@@${member.key.property.name}`})
+          : member.key;
+
       if (member.kind === 'get' || member.kind === 'set') {
         // accessors are methods - but flow accessor signatures are properties
         const kind = member.kind;
+
         return [
           t.ObjectTypeAccessorSignature({
             // $FlowFixMe[incompatible-call]
             key: asDetachedNode<
               ClassPropertyNameComputed | ClassPropertyNameNonComputed,
-            >(member.key),
+            >(newKey),
             value: resultValue,
             static: member.static,
             kind,
@@ -1251,7 +1266,7 @@ function convertClassMember(
           // $FlowFixMe[incompatible-call]
           key: asDetachedNode<
             ClassPropertyNameComputed | ClassPropertyNameNonComputed,
-          >(member.key),
+          >(newKey),
           value: resultValue,
           static: member.static,
         }),