eslint-parser: ES2020 features (#11815)

* chore: update espree test on nullish coalescing

* feat: add optional chaining support

* fix: adapt to estree AST shape

* chore: update lockfile

* add estree optional-chaining test fixtures

* address review comments

* chore: simplify smoke test

* export * support

Co-authored-by: Brian Ng <bng412@gmail.com>

packages/babel-parser/src/plugins/estree.js

@@ -388,8 +388,6 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         delete node.arguments;
         // $FlowIgnore - callee isn't optional in the type definition
         delete node.callee;
-      } else if (node.type === "CallExpression") {
-        (node: N.Node).optional = false;
       }
 
       return node;
@@ -431,10 +429,38 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       return node;
     }
 
-    parseSubscript(...args) {
-      const node = super.parseSubscript(...args);
+    parseSubscript(
+      base: N.Expression,
+      startPos: number,
+      startLoc: Position,
+      noCalls: ?boolean,
+      state: N.ParseSubscriptState,
+    ) {
+      const node = super.parseSubscript(
+        base,
+        startPos,
+        startLoc,
+        noCalls,
+        state,
+      );
 
-      if (node.type === "MemberExpression") {
+      if (state.optionalChainMember) {
+        // https://github.com/estree/estree/blob/master/es2020.md#chainexpression
+        if (
+          node.type === "OptionalMemberExpression" ||
+          node.type === "OptionalCallExpression"
+        ) {
+          node.type = node.type.substring(8); // strip Optional prefix
+        }
+        if (state.stop) {
+          const chain = this.startNodeAtNode(node);
+          chain.expression = node;
+          return this.finishNode(chain, "ChainExpression");
+        }
+      } else if (
+        node.type === "MemberExpression" ||
+        node.type === "CallExpression"
+      ) {
         node.optional = false;
       }