Parenthesized expressions (#8025)

* Add parser createParenthesizedExpressions option  …

When set to `true` we create `ParenthesizedExpression` nodes instead of
setting `extra.parenthesized`.

* Also update babel-parser.d.ts

packages/babel-parser/src/options.js

@@ -19,6 +19,7 @@ export type Options = {
   strictMode: ?boolean,
   ranges: boolean,
   tokens: boolean,
+  createParenthesizedExpressions: boolean,
 };
 
 export const defaultOptions: Options = {
@@ -55,6 +56,9 @@ export const defaultOptions: Options = {
   ranges: false,
   // Adds all parsed tokens to a `tokens` property on the `File` node
   tokens: false,
+  // Whether to create ParenthesizedExpression AST nodes (if false
+  // the parser sets extra.parenthesized on the expression nodes instead).
+  createParenthesizedExpressions: false,
 };
 
 // Interpret and default an options object

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

@@ -185,17 +185,28 @@ export default class ExpressionParser extends LValParser {
 
       let patternErrorMsg;
       let elementName;
-      if (left.type === "ObjectPattern") {
+
+      const unwrap = node => {
+        return node.type === "ParenthesizedExpression"
+          ? unwrap(node.expression)
+          : node;
+      };
+      const maybePattern = unwrap(left);
+      if (maybePattern.type === "ObjectPattern") {
         patternErrorMsg = "`({a}) = 0` use `({a} = 0)`";
         elementName = "property";
-      } else if (left.type === "ArrayPattern") {
+      } else if (maybePattern.type === "ArrayPattern") {
         patternErrorMsg = "`([a]) = 0` use `([a] = 0)`";
         elementName = "element";
       }
 
-      if (patternErrorMsg && left.extra && left.extra.parenthesized) {
+      if (
+        patternErrorMsg &&
+        ((left.extra && left.extra.parenthesized) ||
+          left.type === "ParenthesizedExpression")
+      ) {
         this.raise(
-          left.start,
+          maybePattern.start,
           `You're trying to assign to a parenthesized expression, eg. instead of ${patternErrorMsg}`,
         );
       }
@@ -309,7 +320,8 @@ export default class ExpressionParser extends LValParser {
         if (
           operator === "**" &&
           left.type === "UnaryExpression" &&
-          !(left.extra && left.extra.parenthesized)
+          (this.options.createParenthesizedExpressions ||
+            !(left.extra && left.extra.parenthesized))
         ) {
           this.raise(
             left.argument.start,
@@ -1155,13 +1167,6 @@ export default class ExpressionParser extends LValParser {
     return this.finishNode(node, type);
   }
 
-  parseParenExpression(): N.Expression {
-    this.expect(tt.parenL);
-    const val = this.parseExpression();
-    this.expect(tt.parenR);
-    return val;
-  }
-
   parseParenAndDistinguishExpression(canBeArrow: boolean): N.Expression {
     const startPos = this.state.start;
     const startLoc = this.state.startLoc;
@@ -1272,10 +1277,16 @@ export default class ExpressionParser extends LValParser {
       val = exprList[0];
     }
 
-    this.addExtra(val, "parenthesized", true);
-    this.addExtra(val, "parenStart", startPos);
+    if (!this.options.createParenthesizedExpressions) {
+      this.addExtra(val, "parenthesized", true);
+      this.addExtra(val, "parenStart", startPos);
+      return val;
+    }
 
-    return val;
+    const parenExpression = this.startNodeAt(startPos, startLoc);
+    parenExpression.expression = val;
+    this.finishNode(parenExpression, "ParenthesizedExpression");
+    return parenExpression;
   }
 
   shouldParseArrow(): boolean {

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

@@ -92,6 +92,14 @@ export default class LValParser extends NodeUtils {
           }
           break;
 
+        case "ParenthesizedExpression":
+          node.expression = this.toAssignable(
+            node.expression,
+            isBinding,
+            contextDescription,
+          );
+          break;
+
         case "MemberExpression":
           if (!isBinding) break;
 
@@ -407,6 +415,15 @@ export default class LValParser extends NodeUtils {
         this.checkLVal(expr.argument, isBinding, checkClashes, "rest element");
         break;
 
+      case "ParenthesizedExpression":
+        this.checkLVal(
+          expr.expression,
+          isBinding,
+          checkClashes,
+          "parenthesized expression",
+        );
+        break;
+
       default: {
         const message =
           (isBinding

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

@@ -426,6 +426,13 @@ export default class StatementParser extends ExpressionParser {
     return this.finishNode(node, "DebuggerStatement");
   }
 
+  parseHeaderExpression(): N.Expression {
+    this.expect(tt.parenL);
+    const val = this.parseExpression();
+    this.expect(tt.parenR);
+    return val;
+  }
+
   parseDoStatement(node: N.DoWhileStatement): N.DoWhileStatement {
     this.next();
     this.state.labels.push(loopLabel);
@@ -442,7 +449,7 @@ export default class StatementParser extends ExpressionParser {
     this.state.labels.pop();
 
     this.expect(tt._while);
-    node.test = this.parseParenExpression();
+    node.test = this.parseHeaderExpression();
     this.eat(tt.semi);
     return this.finishNode(node, "DoWhileStatement");
   }
@@ -531,7 +538,7 @@ export default class StatementParser extends ExpressionParser {
 
   parseIfStatement(node: N.IfStatement): N.IfStatement {
     this.next();
-    node.test = this.parseParenExpression();
+    node.test = this.parseHeaderExpression();
     node.consequent = this.parseStatement("if");
     node.alternate = this.eat(tt._else) ? this.parseStatement("if") : null;
     return this.finishNode(node, "IfStatement");
@@ -560,7 +567,7 @@ export default class StatementParser extends ExpressionParser {
 
   parseSwitchStatement(node: N.SwitchStatement): N.SwitchStatement {
     this.next();
-    node.discriminant = this.parseParenExpression();
+    node.discriminant = this.parseHeaderExpression();
     const cases = (node.cases = []);
     this.expect(tt.braceL);
     this.state.labels.push(switchLabel);
@@ -669,7 +676,7 @@ export default class StatementParser extends ExpressionParser {
 
   parseWhileStatement(node: N.WhileStatement): N.WhileStatement {
     this.next();
-    node.test = this.parseParenExpression();
+    node.test = this.parseHeaderExpression();
     this.state.labels.push(loopLabel);
 
     node.body =
@@ -691,7 +698,7 @@ export default class StatementParser extends ExpressionParser {
       this.raise(this.state.start, "'with' in strict mode");
     }
     this.next();
-    node.object = this.parseParenExpression();
+    node.object = this.parseHeaderExpression();
 
     node.body =
       // For the smartPipelines plugin:

packages/babel-parser/src/types.js

@@ -566,6 +566,11 @@ export type SequenceExpression = NodeBase & {
   expressions: $ReadOnlyArray<Expression>,
 };
 
+export type ParenthesizedExpression = NodeBase & {
+  type: "ParenthesizedExpression",
+  expression: Expression,
+};
+
 // Pipelines
 
 export type PipelineBody = NodeBase & {