Do not allow member expressions to start async arrows (#10332)

* Do not allow member expressions to start async arrows

* Boolean -> boolean

packages/babel-parser/src/parser/expression.js

@@ -578,21 +578,16 @@ export default class ExpressionParser extends LValParser {
     startLoc: Position,
     noCalls?: ?boolean,
   ): N.Expression {
-    const maybeAsyncArrow = this.atPossibleAsync(base);
-
     const state = {
       optionalChainMember: false,
+      maybeAsyncArrow: this.atPossibleAsync(base),
       stop: false,
     };
     do {
-      base = this.parseSubscript(
-        base,
-        startPos,
-        startLoc,
-        noCalls,
-        state,
-        maybeAsyncArrow,
-      );
+      base = this.parseSubscript(base, startPos, startLoc, noCalls, state);
+
+      // After parsing a subscript, this isn't "async" for sure.
+      state.maybeAsyncArrow = false;
     } while (!state.stop);
     return base;
   }
@@ -607,7 +602,6 @@ export default class ExpressionParser extends LValParser {
     startLoc: Position,
     noCalls: ?boolean,
     state: N.ParseSubscriptState,
-    maybeAsyncArrow: boolean,
   ): N.Expression {
     if (!noCalls && this.eat(tt.doubleColon)) {
       const node = this.startNodeAt(startPos, startLoc);
@@ -695,7 +689,7 @@ export default class ExpressionParser extends LValParser {
 
       node.arguments = this.parseCallExpressionArguments(
         tt.parenR,
-        maybeAsyncArrow,
+        state.maybeAsyncArrow,
         base.type === "Import",
         base.type !== "Super",
       );
@@ -705,7 +699,7 @@ export default class ExpressionParser extends LValParser {
         this.finishOptionalCallExpression(node);
       }
 
-      if (maybeAsyncArrow && this.shouldParseAsyncArrow()) {
+      if (state.maybeAsyncArrow && this.shouldParseAsyncArrow()) {
         state.stop = true;
 
         this.checkCommaAfterRestFromSpread();

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

@@ -2634,7 +2634,6 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       startLoc: Position,
       noCalls: ?boolean,
       subscriptState: N.ParseSubscriptState,
-      maybeAsyncArrow: boolean,
     ): N.Expression {
       if (this.match(tt.questionDot) && this.isLookaheadRelational("<")) {
         this.expectPlugin("optionalChaining");
@@ -2687,7 +2686,6 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         startLoc,
         noCalls,
         subscriptState,
-        maybeAsyncArrow,
       );
     }
 

packages/babel-parser/src/plugins/typescript/index.js

@@ -1568,7 +1568,6 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       startLoc: Position,
       noCalls: ?boolean,
       state: N.ParseSubscriptState,
-      maybeAsyncArrow: boolean,
     ): N.Expression {
       if (!this.hasPrecedingLineBreak() && this.match(tt.bang)) {
         this.state.exprAllowed = false;
@@ -1631,14 +1630,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         if (result) return result;
       }
 
-      return super.parseSubscript(
-        base,
-        startPos,
-        startLoc,
-        noCalls,
-        state,
-        maybeAsyncArrow,
-      );
+      return super.parseSubscript(base, startPos, startLoc, noCalls, state);
     }
 
     parseNewArguments(node: N.NewExpression): void {

packages/babel-parser/src/types.js

@@ -1447,5 +1447,6 @@ export type Placeholder<N: PlaceholderTypes> = NodeBase & {
 
 export type ParseSubscriptState = {
   optionalChainMember: boolean,
+  maybeAsyncArrow: boolean,
   stop: boolean,
 };