Add support for optional chain in assignments

packages/babel-helper-function-name/src/index.ts

@@ -224,7 +224,11 @@ export default function <N extends t.FunctionExpression | t.Class>(
     node: N;
     parent?: NodePath<N>["parent"];
     scope: Scope;
-    id?: t.LVal | t.StringLiteral | t.NumericLiteral | t.BigIntLiteral;
+    id?:
+      | t.AssignmentExpression["left"]
+      | t.StringLiteral
+      | t.NumericLiteral
+      | t.BigIntLiteral;
   },
   localBinding = false,
   supportUnicodeId = false,

packages/babel-helper-member-expression-to-functions/src/index.ts

@@ -169,12 +169,12 @@ const handle = {
       const willEndPathCastToBoolean = willPathCastToBoolean(endPath);
 
       const rootParentPath = endPath.parentPath;
-      if (
-        rootParentPath.isUpdateExpression({ argument: node }) ||
-        rootParentPath.isAssignmentExpression({ left: node })
-      ) {
-        throw member.buildCodeFrameError(`can't handle assignment`);
+      if (rootParentPath.isUpdateExpression({ argument: node })) {
+        throw member.buildCodeFrameError(`can't handle update expression`);
       }
+      const isAssignment = rootParentPath.isAssignmentExpression({
+        left: endPath.node,
+      });
       const isDeleteOperation = rootParentPath.isUnaryExpression({
         operator: "delete",
       });
@@ -252,6 +252,9 @@ const handle = {
         parentPath.isUnaryExpression({ operator: "delete" })
       ) {
         parentPath.replaceWith(this.delete(member));
+      } else if (parentPath.isAssignmentExpression()) {
+        // `a?.#b = c` to `(a == null ? void 0 : a.#b = c)`
+        handleAssignment(this, member, parentPath);
       } else {
         member.replaceWith(this.get(member));
       }
@@ -295,7 +298,7 @@ const handle = {
       }
 
       let replacementPath: NodePath = endPath;
-      if (isDeleteOperation) {
+      if (isDeleteOperation || isAssignment) {
         replacementPath = endParentPath;
         regular = endParentPath.node;
       }
@@ -432,44 +435,7 @@ const handle = {
     // MEMBER += VALUE   ->   _set(MEMBER, _get(MEMBER) + VALUE)
     // MEMBER ??= VALUE   ->   _get(MEMBER) ?? _set(MEMBER, VALUE)
     if (parentPath.isAssignmentExpression({ left: node })) {
-      if (this.simpleSet) {
-        member.replaceWith(this.simpleSet(member));
-        return;
-      }
-
-      const { operator, right: value } = parentPath.node;
-
-      if (operator === "=") {
-        parentPath.replaceWith(this.set(member, value));
-      } else {
-        const operatorTrunc = operator.slice(0, -1);
-        if (LOGICAL_OPERATORS.includes(operatorTrunc)) {
-          // Give the state handler a chance to memoise the member, since we'll
-          // reference it twice. The first access (the get) should do the memo
-          // assignment.
-          this.memoise(member, 1);
-          parentPath.replaceWith(
-            logicalExpression(
-              operatorTrunc as t.LogicalExpression["operator"],
-              this.get(member),
-              this.set(member, value),
-            ),
-          );
-        } else {
-          // Here, the second access (the set) is evaluated first.
-          this.memoise(member, 2);
-          parentPath.replaceWith(
-            this.set(
-              member,
-              binaryExpression(
-                operatorTrunc as t.BinaryExpression["operator"],
-                this.get(member),
-                value,
-              ),
-            ),
-          );
-        }
-      }
+      handleAssignment(this, member, parentPath);
       return;
     }
 
@@ -549,6 +515,51 @@ const handle = {
   },
 };
 
+function handleAssignment(
+  state: HandlerState,
+  member: NodePath<t.MemberExpression | t.OptionalMemberExpression>,
+  parentPath: NodePath<t.AssignmentExpression>,
+) {
+  if (state.simpleSet) {
+    member.replaceWith(state.simpleSet(member));
+    return;
+  }
+
+  const { operator, right: value } = parentPath.node;
+
+  if (operator === "=") {
+    parentPath.replaceWith(state.set(member, value));
+  } else {
+    const operatorTrunc = operator.slice(0, -1);
+    if (LOGICAL_OPERATORS.includes(operatorTrunc)) {
+      // Give the state handler a chance to memoise the member, since we'll
+      // reference it twice. The first access (the get) should do the memo
+      // assignment.
+      state.memoise(member, 1);
+      parentPath.replaceWith(
+        logicalExpression(
+          operatorTrunc as t.LogicalExpression["operator"],
+          state.get(member),
+          state.set(member, value),
+        ),
+      );
+    } else {
+      // Here, the second access (the set) is evaluated first.
+      state.memoise(member, 2);
+      parentPath.replaceWith(
+        state.set(
+          member,
+          binaryExpression(
+            operatorTrunc as t.BinaryExpression["operator"],
+            state.get(member),
+            value,
+          ),
+        ),
+      );
+    }
+  }
+}
+
 export interface Handler<State> {
   memoise?(
     this: HandlerState<State> & State,

packages/babel-helpers/src/helpers.ts

@@ -1884,3 +1884,9 @@ helpers.identity = helper("7.17.0")`
     return x;
   }
 `;
+
+helpers.nullishReceiverError = helper("7.22.6")`
+  export default function _nullishReceiverError(r) {
+    throw new TypeError("Cannot set property of null or undefined.");
+  }
+`;

packages/babel-parser/data/schema.json

@@ -145,6 +145,23 @@
             "additionalItems": false,
             "type": "array"
           },
+          {
+            "items": [
+              {
+                "type": "string",
+                "enum": ["optionalChainingAssign"]
+              },
+              {
+                "type": "object",
+                "properties": {
+                  "version": {
+                    "type": "string",
+                    "enum": ["2023-07"]
+                  }
+                }
+              }
+            ]
+          },
           {
             "enum": [
               "asyncDoExpressions",

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

@@ -147,6 +147,10 @@ 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

@@ -113,7 +113,10 @@ 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) = []] = []) => {}`
@@ -552,6 +555,11 @@ 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).
    *
@@ -600,7 +608,20 @@ 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 !== BindingFlag.TYPE_NONE) {
         this.raise(Errors.InvalidPropertyBindingPattern, { at: expression });
       }
@@ -649,9 +670,7 @@ 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/plugin-utils.ts

@@ -232,6 +232,17 @@ export function validatePlugins(plugins: PluginList) {
     error.missingPlugins = "doExpressions";
     throw error;
   }
+
+  if (
+    hasPlugin(plugins, "optionalChainingAssign") &&
+    getPluginOption(plugins, "optionalChainingAssign", "version") !== "2023-07"
+  ) {
+    throw new Error(
+      "The 'optionalChainingAssign' plugin requires a 'version' option," +
+        " representing the last proposal update. Currently, the" +
+        " only supported value is '2023-07'.",
+    );
+  }
 }
 
 // These plugins are defined using a mixin which extends the parser class.

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

@@ -47,6 +47,7 @@ export type ParserPluginWithOptions =
   | ["importAttributes", { deprecatedAssertSyntax: boolean }]
   // @deprecated
   | ["moduleAttributes", { version: "may-2020" }]
+  | ["optionalChainingAssign", { version: "2023-07" }]
   | ["pipelineOperator", PipelineOperatorPluginOptions]
   | ["recordAndTuple", RecordAndTuplePluginOptions]
   | ["flow", FlowPluginOptions]

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 } = {});