Optional Chaining: Stage 1 plugin

README.md

@@ -139,6 +139,7 @@ require("babylon").parse("code", {
  - `functionSent`
  - `dynamicImport` ([proposal](https://github.com/tc39/proposal-dynamic-import))
  - `numericSeparator` ([proposal](https://github.com/samuelgoto/proposal-numeric-separator))
+ - `optionalChaining` ([proposal](https://github.com/tc39/proposal-optional-chaining))
  - `importMeta` ([proposal](https://github.com/tc39/proposal-import-meta))
 
 ### FAQ

ast/spec.md

@@ -859,10 +859,11 @@ interface MemberExpression <: Expression, Pattern {
   object: Expression | Super;
   property: Expression;
   computed: boolean;
+  optional: boolean | null;
 }
 ```
 
-A member expression. If `computed` is `true`, the node corresponds to a computed (`a[b]`) member expression and `property` is an `Expression`. If `computed` is `false`, the node corresponds to a static (`a.b`) member expression and `property` is an `Identifier`.
+A member expression. If `computed` is `true`, the node corresponds to a computed (`a[b]`) member expression and `property` is an `Expression`. If `computed` is `false`, the node corresponds to a static (`a.b`) member expression and `property` is an `Identifier`. The `optional` flags indicates that the member expression can be called even if the object is null or undefined. If this is the object value (null/undefined) should be returned.
 
 ### BindExpression
 
@@ -896,6 +897,7 @@ interface CallExpression <: Expression {
   type: "CallExpression";
   callee: Expression | Super | Import;
   arguments: [ Expression | SpreadElement ];
+  optional: boolean | null;
 }
 ```
 
@@ -906,6 +908,7 @@ A function or method call expression.
 ```js
 interface NewExpression <: CallExpression {
   type: "NewExpression";
+  optional: boolean | null;
 }
 ```
 

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;
@@ -736,13 +774,17 @@ 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);
       this.toReferencedList(node.arguments);
     } else {
       node.arguments = [];
     }
+    if (optional) {
+      node.optional = true;
+    }
 
     return this.finishNode(node, "NewExpression");
   }

src/tokenizer/index.js

@@ -426,6 +426,18 @@ export default class Tokenizer extends LocationParser {
     return this.finishOp(code === 61 ? tt.eq : tt.prefix, 1);
   }
 
+  readToken_question() { // '?'
+    const next = this.input.charCodeAt(this.state.pos + 1);
+    const next2 = this.input.charCodeAt(this.state.pos + 2);
+    if (next === 46 && !(next2 >= 48 && next2 <= 57)) { // '.' not followed by a number
+      this.state.pos += 2;
+      return this.finishToken(tt.questionDot);
+    } else {
+      ++this.state.pos;
+      return this.finishToken(tt.question);
+    }
+  }
+
   getTokenFromCode(code: number): void {
     switch (code) {
 
@@ -469,7 +481,7 @@ export default class Tokenizer extends LocationParser {
           return this.finishToken(tt.colon);
         }
 
-      case 63: ++this.state.pos; return this.finishToken(tt.question);
+      case 63: return this.readToken_question();
       case 64: ++this.state.pos; return this.finishToken(tt.at);
 
       case 96: // '`'
@@ -917,7 +929,7 @@ export default class Tokenizer extends LocationParser {
     const type = this.state.type;
     let update;
 
-    if (type.keyword && prevType === tt.dot) {
+    if (type.keyword && (prevType === tt.dot || prevType === tt.questionDot)) {
       this.state.exprAllowed = false;
     } else if (update = type.updateContext) {
       update.call(this, prevType);

src/tokenizer/types.js

@@ -102,6 +102,7 @@ export const types: { [name: string]: TokenType } = {
   doubleColon: new TokenType("::", { beforeExpr }),
   dot: new TokenType("."),
   question: new TokenType("?", { beforeExpr }),
+  questionDot: new TokenType("?."),
   arrow: new TokenType("=>", { beforeExpr }),
   template: new TokenType("template"),
   ellipsis: new TokenType("...", { beforeExpr }),

test/fixtures/experimental/optional-chaining/class-contructor-call/actual.js

@@ -0,0 +1,9 @@
+new C?.()
+
+new C?.(a, b)
+
+new B?.C?.()
+
+new B?.C?.(a, b)
+
+new B?.C