implement Logical Assignment proposal

src/engine.mjs

@@ -37,6 +37,10 @@ export const FEATURES = Object.freeze([
     name: 'WeakRefs',
     url: 'https://github.com/tc39/proposal-weakrefs',
   },
+  {
+    name: 'LogicalAssignment',
+    url: 'https://github.com/tc39/proposal-logical-assignment',
+  },
 ].map(Object.freeze));
 
 // #sec-agents

src/parse.mjs

@@ -76,25 +76,50 @@ const Parser = acorn.Parser.extend((P) => (class Parse262 extends P {
   }
 
   getTokenFromCode(code) {
-    if (code === 63) {
+    if (code === 63) { // ?
       this.pos += 1;
       const next = this.input.charCodeAt(this.pos);
-      if (next === 46) {
+      if (next === 46) { // .
         const nextNext = this.input.charCodeAt(this.pos + 1);
         if (nextNext < 48 || nextNext > 57) {
           this.pos += 1;
           return this.finishToken(optionalChainToken);
         }
       }
-      if (next === 63) {
+      if (next === 63) { // ??
         this.pos += 1;
+        const nextNext = this.input.charCodeAt(this.pos);
+        if (nextNext === 61 && surroundingAgent.feature('LogicalAssignment')) { // ??=
+          this.pos -= 2;
+          return this.finishOp(acorn.tokTypes.assign, 3);
+        }
         return this.finishToken(nullishCoalescingToken, nullishCoalescingToken.label);
       }
       return this.finishToken(acorn.tokTypes.question);
     }
     return super.getTokenFromCode(code);
   }
 
+  readToken_pipe_amp(code) {
+    const next = this.input.charCodeAt(this.pos + 1);
+    if (next === code) { // || or &&
+      const nextNext = this.input.charCodeAt(this.pos + 2);
+      // https://tc39.es/proposal-logical-assignment/#sec-assignment-operators
+      if (nextNext === 61 && surroundingAgent.feature('LogicalAssignment')) { // ||= or &&=
+        return this.finishOp(acorn.tokTypes.assign, 3);
+      }
+      return this.finishOp(code === 124
+        ? acorn.tokTypes.logicalOR
+        : acorn.tokTypes.logicalAND, 2);
+    }
+    if (next === 61) { // |= or &=
+      return this.finishOp(acorn.tokTypes.assign, 2);
+    }
+    return this.finishOp(code === 124
+      ? acorn.tokTypes.bitwiseOR
+      : acorn.tokTypes.bitwiseAND, 1);
+  }
+
   parseStatement(context, topLevel, exports) {
     if (this.type === acorn.tokTypes._import && surroundingAgent.feature('import.meta')) { // eslint-disable-line no-underscore-dangle
       skipWhiteSpace.lastIndex = this.pos;
@@ -156,7 +181,7 @@ const Parser = acorn.Parser.extend((P) => (class Parse262 extends P {
      *
      *  a.b?.c.d.e
      *  @=>
-     *  OptionalExpressoin a.b?.c.d.e
+     *  OptionalExpression a.b?.c.d.e
      *      MemberExpression a.b
      *      OptionalChain ?.c.d.e
      *          OptionalChain ?.c.d

src/runtime-semantics/AssignmentExpression.mjs

@@ -1,8 +1,10 @@
-import { Q, ReturnIfAbrupt } from '../completion.mjs';
+import { Value } from '../value.mjs';
+import { Q, X, ReturnIfAbrupt } from '../completion.mjs';
 import {
   GetReferencedName,
   GetValue,
   PutValue,
+  ToBoolean,
 } from '../abstract-ops/all.mjs';
 import {
   IsAnonymousFunctionDefinition,
@@ -19,6 +21,10 @@ import {
 //   AssignmentExpression :
 //     LeftHandSideExpression `=` AssignmentExpression
 //     LeftHandSideExpression AssignmentOperator AssignmentExpression
+// https://tc39.es/proposal-logical-assignment/#sec-assignment-operators-runtime-semantics-evaluation
+//     LeftHandSideExpression `&&=` AssignmentExpression
+//     LeftHandSideExpression `||=` AssignmentExpression
+//     LeftHandSideExpression `??=` AssignmentExpression
 export function* Evaluate_AssignmentExpression(node) {
   const LeftHandSideExpression = node.left;
   const AssignmentExpression = node.right;
@@ -41,6 +47,61 @@ export function* Evaluate_AssignmentExpression(node) {
     const rval = Q(GetValue(rref));
     Q(yield* DestructuringAssignmentEvaluation_AssignmentPattern(assignmentPattern, rval));
     return rval;
+  } else if (node.operator === '&&=') {
+    // 1. Let lref be the result of evaluating LeftHandSideExpression.
+    const lref = yield* Evaluate(LeftHandSideExpression);
+    // 2. Let lval be ? GetValue(lref).
+    const lval = Q(GetValue(lval));
+    // 3. Let lbool be ! ToBoolean(lval).
+    const lbool = X(ToBoolean(lval));
+    // 4. If lbool is false, return lval.
+    if (lbool === Value.false) {
+      return lval;
+    }
+    // 5. Let rref be the result of evaluating AssignmentExpression.
+    const rref = yield* Evaluate(AssignmentExpression);
+    // 6. Let rval be ? GetValue(rref).
+    const rval = Q(GetValue(rref));
+    // 7. Perform ? PutValue(lref, rval).
+    Q(PutValue(lref, rval));
+    // 8. Return rval.
+    return rval;
+  } else if (node.operator === '||=') {
+    // 1. Let lref be the result of evaluating LeftHandSideExpression.
+    const lref = yield* Evaluate(LeftHandSideExpression);
+    // 2. Let lval be ? GetValue(lref).
+    const lval = Q(GetValue(lref));
+    // 3. Let lbool be ! ToBoolean(lval).
+    const lbool = X(ToBoolean(lval));
+    // 4. If lbool is true, return lval.
+    if (lbool === Value.true) {
+      return lval;
+    }
+    // 5. Let rref be the result of evaluating AssignmentExpression.
+    const rref = yield* Evaluate(AssignmentExpression);
+    // 6. Let rval be ? GetValue(rref).
+    const rval = Q(GetValue(rref));
+    // 7. Perform ? PutValue(lref, rval).
+    Q(PutValue(lref, rval));
+    // 8. Return rval.
+    return rval;
+  } else if (node.operator === '??=') {
+    // 1.Let lref be the result of evaluating LeftHandSideExpression.
+    const lref = yield* Evaluate(LeftHandSideExpression);
+    // 2. Let lval be ? GetValue(lref).
+    const lval = Q(GetValue(lref));
+    // 3. If lval is not undefined nor null, return lval.
+    if (lval !== Value.undefined && lval !== Value.null) {
+      return lval;
+    }
+    // 4. Let rref be the result of evaluating AssignmentExpression.
+    const rref = yield* Evaluate(AssignmentExpression);
+    // 5. Let rval be ? GetValue(rref).
+    const rval = Q(GetValue(rref));
+    // 6. Perform ? PutValue(lref, rval).
+    Q(PutValue(lref, rval));
+    // 7. Return rval.
+    return rval;
   } else {
     const AssignmentOperator = node.operator;