Add parser support for optional chain in assignments

packages/babel-parser/data/schema.json

@@ -182,6 +182,7 @@
               "objectRestSpread",
               "optionalCatchBinding",
               "optionalChaining",
+              "optionalChainingAssign",
               "partialApplication",
               "pipelineOperator",
               "placeholders",

packages/babel-parser/src/parse-error/standard-errors.ts

@@ -146,6 +146,10 @@ export default {
     `Invalid left-hand side in ${toNodeDescription(ancestor)}.`,
   InvalidLhsBinding: ({ ancestor }: { ancestor: LValAncestor }) =>
     `Binding invalid left-hand side in ${toNodeDescription(ancestor)}.`,
+  InvalidLhsOptionalChaining: ({ ancestor }: { ancestor: LValAncestor }) =>
+    `Invalid optional chaining in the left-hand side of ${toNodeDescription(
+      ancestor,
+    )}.`,
   InvalidNumber: "Invalid number.",
   InvalidOrMissingExponent:
     "Floating-point numbers require a valid exponent after the 'e'.",

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

@@ -117,7 +117,10 @@ export default abstract class LValParser extends NodeUtils {
             Errors.InvalidParenthesizedAssignment,
             { at: node },
           );
-        } else if (parenthesized.type !== "MemberExpression") {
+        } else if (
+          parenthesized.type !== "MemberExpression" &&
+          !this.isOptionalMemberExpression(parenthesized)
+        ) {
           // A parenthesized member expression can be in LHS but not in pattern.
           // If the LHS is later interpreted as a pattern, `checkLVal` will throw for member expression binding
           // i.e. `([(a.b) = []] = []) => {}`
@@ -556,6 +559,11 @@ export default abstract class LValParser extends NodeUtils {
     );
   }
 
+  // Overridden by the estree plugin
+  isOptionalMemberExpression(expression: Node) {
+    return expression.type === "OptionalMemberExpression";
+  }
+
   /**
    * Verify that a target expression is an lval (something that can be assigned to).
    *
@@ -604,7 +612,19 @@ export default abstract class LValParser extends NodeUtils {
     // toAssignable already reported this error with a nicer message.
     if (this.isObjectMethod(expression)) return;
 
-    if (type === "MemberExpression") {
+    const isOptionalMemberExpression =
+      this.isOptionalMemberExpression(expression);
+
+    if (isOptionalMemberExpression || type === "MemberExpression") {
+      if (isOptionalMemberExpression) {
+        this.expectPlugin("optionalChainingAssign", expression.loc.start);
+        if (ancestor.type !== "AssignmentExpression") {
+          this.raise(Errors.InvalidLhsOptionalChaining, {
+            at: expression,
+            ancestor,
+          });
+        }
+      }
       if (binding !== BIND_NONE) {
         this.raise(Errors.InvalidPropertyBindingPattern, { at: expression });
       }
@@ -651,9 +671,7 @@ export default abstract class LValParser extends NodeUtils {
       ? validity
       : [validity, type === "ParenthesizedExpression"];
     const nextAncestor =
-      type === "ArrayPattern" ||
-      type === "ObjectPattern" ||
-      type === "ParenthesizedExpression"
+      type === "ArrayPattern" || type === "ObjectPattern"
         ? ({ type } as const)
         : ancestor;
 

packages/babel-parser/src/plugins/estree.ts

@@ -535,6 +535,13 @@ export default (superClass: typeof Parser) =>
       return node;
     }
 
+    isOptionalMemberExpression(node: N.Node) {
+      if (node.type === "ChainExpression") {
+        return node.expression.type === "MemberExpression";
+      }
+      return super.isOptionalMemberExpression(node);
+    }
+
     hasPropertyAsPrivateName(node: N.Node): boolean {
       if (node.type === "ChainExpression") {
         node = node.expression;

packages/babel-parser/src/typings.d.ts

@@ -32,6 +32,7 @@ export type Plugin =
   | "objectRestSpread"
   | "optionalCatchBinding"
   | "optionalChaining"
+  | "optionalChainingAssign"
   | "partialApplication"
   | "placeholders"
   | "privateIn" // Enabled by default

packages/babel-parser/test/fixtures/core/create-parenthesized-expressions/invalid-parenthesized-left-hand-side/output.json

@@ -2,7 +2,7 @@
   "type": "File",
   "start":0,"end":9,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":9,"index":9}},
   "errors": [
-    "SyntaxError: Invalid left-hand side in parenthesized expression. (1:1)"
+    "SyntaxError: Invalid left-hand side in assignment expression. (1:1)"
   ],
   "program": {
     "type": "Program",

packages/babel-parser/test/fixtures/experimental/_no-plugin/optional-chaining-assign/input.js

@@ -0,0 +1 @@
+a?.b = c;

packages/babel-parser/test/fixtures/experimental/_no-plugin/optional-chaining-assign/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "This experimental syntax requires enabling the parser plugin: \"optionalChainingAssign\". (1:0)"
+}

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-destruturing-arr/input.js

@@ -0,0 +1 @@
+[a?.b] = [];

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-destruturing-arr/output.json

@@ -0,0 +1,52 @@
+{
+  "type": "File",
+  "start":0,"end":12,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":12,"index":12}},
+  "errors": [
+    "SyntaxError: Invalid optional chaining in the left-hand side of array destructuring pattern. (1:1)"
+  ],
+  "program": {
+    "type": "Program",
+    "start":0,"end":12,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":12,"index":12}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start":0,"end":12,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":12,"index":12}},
+        "expression": {
+          "type": "AssignmentExpression",
+          "start":0,"end":11,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":11,"index":11}},
+          "operator": "=",
+          "left": {
+            "type": "ArrayPattern",
+            "start":0,"end":6,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":6,"index":6}},
+            "elements": [
+              {
+                "type": "OptionalMemberExpression",
+                "start":1,"end":5,"loc":{"start":{"line":1,"column":1,"index":1},"end":{"line":1,"column":5,"index":5}},
+                "object": {
+                  "type": "Identifier",
+                  "start":1,"end":2,"loc":{"start":{"line":1,"column":1,"index":1},"end":{"line":1,"column":2,"index":2},"identifierName":"a"},
+                  "name": "a"
+                },
+                "computed": false,
+                "property": {
+                  "type": "Identifier",
+                  "start":4,"end":5,"loc":{"start":{"line":1,"column":4,"index":4},"end":{"line":1,"column":5,"index":5},"identifierName":"b"},
+                  "name": "b"
+                },
+                "optional": true
+              }
+            ]
+          },
+          "right": {
+            "type": "ArrayExpression",
+            "start":9,"end":11,"loc":{"start":{"line":1,"column":9,"index":9},"end":{"line":1,"column":11,"index":11}},
+            "elements": []
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-destruturing-obj/input.js

@@ -0,0 +1 @@
+({ prop: a?.b } = {});

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-destruturing-obj/output.json

@@ -0,0 +1,68 @@
+{
+  "type": "File",
+  "start":0,"end":22,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":22,"index":22}},
+  "errors": [
+    "SyntaxError: Invalid optional chaining in the left-hand side of object destructuring pattern. (1:9)"
+  ],
+  "program": {
+    "type": "Program",
+    "start":0,"end":22,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":22,"index":22}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start":0,"end":22,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":22,"index":22}},
+        "expression": {
+          "type": "AssignmentExpression",
+          "start":1,"end":20,"loc":{"start":{"line":1,"column":1,"index":1},"end":{"line":1,"column":20,"index":20}},
+          "operator": "=",
+          "left": {
+            "type": "ObjectPattern",
+            "start":1,"end":15,"loc":{"start":{"line":1,"column":1,"index":1},"end":{"line":1,"column":15,"index":15}},
+            "properties": [
+              {
+                "type": "ObjectProperty",
+                "start":3,"end":13,"loc":{"start":{"line":1,"column":3,"index":3},"end":{"line":1,"column":13,"index":13}},
+                "method": false,
+                "key": {
+                  "type": "Identifier",
+                  "start":3,"end":7,"loc":{"start":{"line":1,"column":3,"index":3},"end":{"line":1,"column":7,"index":7},"identifierName":"prop"},
+                  "name": "prop"
+                },
+                "computed": false,
+                "shorthand": false,
+                "value": {
+                  "type": "OptionalMemberExpression",
+                  "start":9,"end":13,"loc":{"start":{"line":1,"column":9,"index":9},"end":{"line":1,"column":13,"index":13}},
+                  "object": {
+                    "type": "Identifier",
+                    "start":9,"end":10,"loc":{"start":{"line":1,"column":9,"index":9},"end":{"line":1,"column":10,"index":10},"identifierName":"a"},
+                    "name": "a"
+                  },
+                  "computed": false,
+                  "property": {
+                    "type": "Identifier",
+                    "start":12,"end":13,"loc":{"start":{"line":1,"column":12,"index":12},"end":{"line":1,"column":13,"index":13},"identifierName":"b"},
+                    "name": "b"
+                  },
+                  "optional": true
+                }
+              }
+            ]
+          },
+          "right": {
+            "type": "ObjectExpression",
+            "start":18,"end":20,"loc":{"start":{"line":1,"column":18,"index":18},"end":{"line":1,"column":20,"index":20}},
+            "properties": []
+          },
+          "extra": {
+            "parenthesized": true,
+            "parenStart": 0
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-fn-param-arrow/input.js

@@ -0,0 +1 @@
+(a?.b) => {}

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-fn-param-arrow/output.json

@@ -0,0 +1,52 @@
+{
+  "type": "File",
+  "start":0,"end":12,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":12,"index":12}},
+  "errors": [
+    "SyntaxError: Invalid optional chaining in the left-hand side of function parameter list. (1:1)",
+    "SyntaxError: Binding member expression. (1:1)"
+  ],
+  "program": {
+    "type": "Program",
+    "start":0,"end":12,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":12,"index":12}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start":0,"end":12,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":12,"index":12}},
+        "expression": {
+          "type": "ArrowFunctionExpression",
+          "start":0,"end":12,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":12,"index":12}},
+          "id": null,
+          "generator": false,
+          "async": false,
+          "params": [
+            {
+              "type": "OptionalMemberExpression",
+              "start":1,"end":5,"loc":{"start":{"line":1,"column":1,"index":1},"end":{"line":1,"column":5,"index":5}},
+              "object": {
+                "type": "Identifier",
+                "start":1,"end":2,"loc":{"start":{"line":1,"column":1,"index":1},"end":{"line":1,"column":2,"index":2},"identifierName":"a"},
+                "name": "a"
+              },
+              "computed": false,
+              "property": {
+                "type": "Identifier",
+                "start":4,"end":5,"loc":{"start":{"line":1,"column":4,"index":4},"end":{"line":1,"column":5,"index":5},"identifierName":"b"},
+                "name": "b"
+              },
+              "optional": true
+            }
+          ],
+          "body": {
+            "type": "BlockStatement",
+            "start":10,"end":12,"loc":{"start":{"line":1,"column":10,"index":10},"end":{"line":1,"column":12,"index":12}},
+            "body": [],
+            "directives": []
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-fn-param-assign/input.js

@@ -0,0 +1 @@
+function f(a?.b = c) {}

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-fn-param-assign/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Unexpected token, expected \",\" (1:12)"
+}

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-fn-param/input.js

@@ -0,0 +1 @@
+function f(a?.b) {}

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-fn-param/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Unexpected token, expected \",\" (1:12)"
+}

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-for-await-of/input.js

@@ -0,0 +1 @@
+for (a?.b of x);

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-for-await-of/output.json

@@ -0,0 +1,46 @@
+{
+  "type": "File",
+  "start":0,"end":16,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":16,"index":16}},
+  "errors": [
+    "SyntaxError: Invalid optional chaining in the left-hand side of for-of statement. (1:5)"
+  ],
+  "program": {
+    "type": "Program",
+    "start":0,"end":16,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":16,"index":16}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ForOfStatement",
+        "start":0,"end":16,"loc":{"start":{"line":1,"column":0,"index":0},"end":{"line":1,"column":16,"index":16}},
+        "await": false,
+        "left": {
+          "type": "OptionalMemberExpression",
+          "start":5,"end":9,"loc":{"start":{"line":1,"column":5,"index":5},"end":{"line":1,"column":9,"index":9}},
+          "object": {
+            "type": "Identifier",
+            "start":5,"end":6,"loc":{"start":{"line":1,"column":5,"index":5},"end":{"line":1,"column":6,"index":6},"identifierName":"a"},
+            "name": "a"
+          },
+          "computed": false,
+          "property": {
+            "type": "Identifier",
+            "start":8,"end":9,"loc":{"start":{"line":1,"column":8,"index":8},"end":{"line":1,"column":9,"index":9},"identifierName":"b"},
+            "name": "b"
+          },
+          "optional": true
+        },
+        "right": {
+          "type": "Identifier",
+          "start":13,"end":14,"loc":{"start":{"line":1,"column":13,"index":13},"end":{"line":1,"column":14,"index":14},"identifierName":"x"},
+          "name": "x"
+        },
+        "body": {
+          "type": "EmptyStatement",
+          "start":15,"end":16,"loc":{"start":{"line":1,"column":15,"index":15},"end":{"line":1,"column":16,"index":16}}
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/optional-chaining-assign/invalid-for-in/input.js

@@ -0,0 +1 @@
+for (a?.b in x);