Optional Chaining: Stage 1 plugin

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
 

src/parser/expression.js

@@ -301,6 +301,24 @@ 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.eat(tt.questionDot)) {
+        if (this.eat(tt.bracketL)) {
+          const node = this.startNodeAt(startPos, startLoc);
+          node.object = base;
+          node.optional = true;
+          node.property = this.parseExpression();
+          node.computed = true;
+          this.expect(tt.bracketR);
+          base = this.finishNode(node, "MemberExpression");
+        } else {
+          const node = this.startNodeAt(startPos, startLoc);
+          node.object = base;
+          node.property = this.parseIdentifier(true);
+          node.optional = true;
+          node.computed = false;
+          base = this.finishNode(node, "MemberExpression");
+        }
       } else if (this.eat(tt.dot)) {
         const node = this.startNodeAt(startPos, startLoc);
         node.object = base;

src/tokenizer/index.js

@@ -420,6 +420,18 @@ 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);
+    if (next === 46) { // 46 = question '.'
+      this.state.pos += 2;
+      return this.finishToken(tt.questionDot);
+    }
+    else {
+      ++this.state.pos;
+      return this.finishToken(tt.question);
+    }
+  }
+
   getTokenFromCode(code: number): void {
     switch (code) {
 
@@ -463,7 +475,7 @@ 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: // '`'
@@ -908,7 +920,7 @@ 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 @@
+new C?.()

test/fixtures/experimental/optional-chaining/function-call/actual.js

@@ -0,0 +1 @@
+func?.()

test/fixtures/experimental/optional-chaining/member-access-bracket/actual.js

@@ -0,0 +1 @@
+obj?.[expr]

test/fixtures/experimental/optional-chaining/member-access-bracket/expected.json

@@ -0,0 +1,100 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 11,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 11
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 11,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 11
+      }
+    },
+    "sourceType": "script",
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 11,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 11
+          }
+        },
+        "expression": {
+          "type": "MemberExpression",
+          "start": 0,
+          "end": 11,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 11
+            }
+          },
+          "object": {
+            "type": "Identifier",
+            "start": 0,
+            "end": 3,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 0
+              },
+              "end": {
+                "line": 1,
+                "column": 3
+              },
+              "identifierName": "obj"
+            },
+            "name": "obj"
+          },
+          "optional": true,
+          "property": {
+            "type": "Identifier",
+            "start": 6,
+            "end": 10,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 6
+              },
+              "end": {
+                "line": 1,
+                "column": 10
+              },
+              "identifierName": "expr"
+            },
+            "name": "expr"
+          },
+          "computed": true
+        }
+      }
+    ],
+    "directives": []
+  }
+}

test/fixtures/experimental/optional-chaining/member-access/actual.js

@@ -0,0 +1 @@
+foo?.bar

test/fixtures/experimental/optional-chaining/member-access/expected.json

@@ -0,0 +1,100 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 8,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 8
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 8,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 8
+      }
+    },
+    "sourceType": "script",
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 8,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 8
+          }
+        },
+        "expression": {
+          "type": "MemberExpression",
+          "start": 0,
+          "end": 8,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 8
+            }
+          },
+          "object": {
+            "type": "Identifier",
+            "start": 0,
+            "end": 3,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 0
+              },
+              "end": {
+                "line": 1,
+                "column": 3
+              },
+              "identifierName": "foo"
+            },
+            "name": "foo"
+          },
+          "property": {
+            "type": "Identifier",
+            "start": 5,
+            "end": 8,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 5
+              },
+              "end": {
+                "line": 1,
+                "column": 8
+              },
+              "identifierName": "bar"
+            },
+            "name": "bar"
+          },
+          "optional": true,
+          "computed": false
+        }
+      }
+    ],
+    "directives": []
+  }
+}