Merge pull request #545 from xtuc/feat-optional-chaining

Optional Chaining: Stage 1 plugin

src/parser/expression.js

@@ -301,6 +301,44 @@ export default class ExpressionParser extends LValParser {
         node.object = base;
         node.callee = this.parseNoCallExpr();
         return this.parseSubscripts(this.finishNode(node, "BindExpression"), startPos, startLoc, noCalls);
+
+      } else if (this.match(tt.questionDot)) {
+        if (!this.hasPlugin("optionalChaining")) {
+          this.raise(startPos, "You can only use optional-chaining when the 'optionalChaining' plugin is enabled.");
+        }
+
+        if (noCalls && this.lookahead().type == tt.parenL) {
+          return base;
+        }
+        this.next();
+
+        const node = this.startNodeAt(startPos, startLoc);
+
+        if (this.eat(tt.bracketL)) {
+          node.object = base;
+          node.property = this.parseExpression();
+          node.computed = true;
+          node.optional = true;
+          this.expect(tt.bracketR);
+          base = this.finishNode(node, "MemberExpression");
+        } else if (this.eat(tt.parenL)) {
+          const possibleAsync = this.state.potentialArrowAt === base.start &&
+            base.type === "Identifier" &&
+            base.name === "async" &&
+            !this.canInsertSemicolon();
+
+          node.callee = base;
+          node.arguments = this.parseCallExpressionArguments(tt.parenR, possibleAsync);
+          node.optional = true;
+
+          base = this.finishNode(node, "CallExpression");
+        } else {
+          node.object = base;
+          node.property = this.parseIdentifier(true);
+          node.computed = false;
+          node.optional = true;
+          base = this.finishNode(node, "MemberExpression");
+        }
       } else if (this.eat(tt.dot)) {
         const node = this.startNodeAt(startPos, startLoc);
         node.object = base;
@@ -736,6 +774,7 @@ export default class ExpressionParser extends LValParser {
     }
 
     node.callee = this.parseNoCallExpr();
+    const optional = this.eat(tt.questionDot);
 
     if (this.eat(tt.parenL)) {
       node.arguments = this.parseExprList(tt.parenR);
@@ -743,6 +782,9 @@ export default class ExpressionParser extends LValParser {
     } else {
       node.arguments = [];
     }
+    if (optional) {
+      node.optional = true;
+    }
 
     return this.finishNode(node, "NewExpression");
   }