optimize: don't memoise non-root right when there is only one destruc…

…turing in the left

packages/babel-plugin-proposal-destructuring-private/src/index.ts

@@ -125,6 +125,7 @@ export default declare(function ({
           declarator.init,
           scope,
           /* isAssignment */ false,
+          /* shouldPreserveCompletion */ false,
           name => state.addHelper(name),
           objectRestNoSymbols,
           /* useBuiltIns */ true,
@@ -140,38 +141,42 @@ export default declare(function ({
       const { node, scope, parent } = path;
       if (!hasPrivateKeys(node.left)) return;
       const assignments = [];
+      const shouldPreserveCompletion =
+        (!isExpressionStatement(parent) && !isSequenceExpression(parent)) ||
+        path.isCompletionRecord();
       for (const { left, right } of transformPrivateKeyDestructuring(
         // @ts-expect-error The left of an assignment expression must not be a RestElement
         node.left,
         node.right,
         scope,
         /* isAssignment */ true,
+        shouldPreserveCompletion,
         name => state.addHelper(name),
         objectRestNoSymbols,
         /* useBuiltIns */ true,
       )) {
         assignments.push(assignmentExpression("=", left, right));
       }
       // preserve completion record
-      if (
-        (!isExpressionStatement(parent) && !isSequenceExpression(parent)) ||
-        path.isCompletionRecord()
-      ) {
-        const { left } = assignments[0];
-        if (scope.isStatic(node.right)) {
+      if (shouldPreserveCompletion) {
+        const { left, right } = assignments[0];
+        // If node.right is right and left is an identifier, then the left is an effectively-constant memoised id
+        if (isIdentifier(left) && right === node.right) {
+          if (
+            !isIdentifier(assignments[assignments.length - 1].right, {
+              name: left.name,
+            })
+          ) {
+            // If the last assignment does not end with left, then we push `left` as the completion value
+            assignments.push(cloneNode(left));
+          }
+          // do nothing as `left` is already at the end of assignments
+        } else {
           const tempId = scope.generateDeclaredUidIdentifier("m");
           assignments.unshift(
             assignmentExpression("=", tempId, cloneNode(node.right)),
           );
           assignments.push(cloneNode(tempId));
-        } else if (
-          !isIdentifier(assignments[assignments.length - 1].right, {
-            name: left.name,
-          })
-        ) {
-          // If node.right is non-static and then the left is an effectively-constant memoised id
-          // If the last assignment does not end with left, that we can safely reuse `left` as the completion value
-          assignments.push(cloneNode(left));
         }
       }
 

packages/babel-plugin-proposal-destructuring-private/src/util.ts

@@ -281,6 +281,8 @@ function rightWillBeReferencedOnce(left: LHS) {
     case "Identifier":
     case "ArrayPattern":
       return true;
+    case "ObjectPattern":
+      return left.properties.length === 1;
     default:
       return false;
   }
@@ -302,11 +304,13 @@ export function* transformPrivateKeyDestructuring(
   right: t.Expression,
   scope: Scope,
   isAssignment: boolean,
+  shouldPreserveCompletion: boolean,
   addHelper: File["addHelper"],
   objectRestNoSymbols: boolean,
   useBuiltIns: boolean,
 ): Generator<Transformed, void, void> {
   const stack: Item[] = [];
+  const rootRight = right;
   // The stack holds patterns that we don't known whether they contain private key
   stack.push({
     left,
@@ -353,7 +357,14 @@ export function* transformPrivateKeyDestructuring(
         (index = indexPath.shift()) !== undefined ||
         left.type === "AssignmentPattern"
       ) {
-        if (!rightWillBeReferencedOnce(left) && !scope.isStatic(right)) {
+        const isRightSafeToReuse =
+          // If we should preserve completion and the right is the rootRight, then the
+          // right is NOT safe to reuse because we will insert a new memoising statement
+          // in the AssignmentExpression visitor, which causes right to be referenced more
+          // than once
+          !(shouldPreserveCompletion && right === rootRight) &&
+          (rightWillBeReferencedOnce(left) || scope.isStatic(right));
+        if (!isRightSafeToReuse) {
           const tempId = scope.generateUidIdentifier("m");
           if (isAssignment) {
             scope.push({ id: cloneNode(tempId) });

packages/babel-plugin-proposal-destructuring-private/test/fixtures/assignment--es2015/array-rest-only/output.js

@@ -9,10 +9,10 @@ var _x = {
 };
 
 (() => {
-  var _p, _m, _m2;
+  var _p, _m;
 
   var x, z;
-  [..._p] = [C], _m = _p[0], _m2 = babelHelpers.classStaticPrivateFieldSpecGet(_m, C, _x), x = _m2 === void 0 ? 1 : _m2, z = babelHelpers.objectWithoutProperties(_p, _excluded);
+  [..._p] = [C], _m = babelHelpers.classStaticPrivateFieldSpecGet(_p[0], C, _x), x = _m === void 0 ? 1 : _m, z = babelHelpers.objectWithoutProperties(_p, _excluded);
   result = {
     x,
     z

packages/babel-plugin-proposal-destructuring-private/test/fixtures/assignment--es2015/nested-under-array-pattern/output.js

@@ -19,8 +19,8 @@ var _z = {
 babelHelpers.defineProperty(C, "self", C);
 
 (() => {
-  var _p, _p2, _p3, _m, _p4, _m2, _m3;
+  var _p, _p2, _p3, _p4, _m;
 
   let x, y, z;
-  [_p, _p2,, _p3] = [C, C], _m = _p === void 0 ? C.self : _p, x = babelHelpers.classStaticPrivateFieldSpecGet(_m, C, _x), [, _p4] = babelHelpers.classStaticPrivateFieldSpecGet(_p2, C, _y), _m2 = _p4 === void 0 ? C.self : _p4, _m3 = babelHelpers.classStaticPrivateFieldSpecGet(_m2, C, _z), y = _m3 === void 0 ? babelHelpers.classStaticPrivateMethodGet(C, C, _self).call(C) : _m3, z = _p3 === void 0 ? babelHelpers.classStaticPrivateFieldSpecGet(y, C, _y) : _p3;
+  [_p, _p2,, _p3] = [C, C], x = babelHelpers.classStaticPrivateFieldSpecGet(_p === void 0 ? C.self : _p, C, _x), [, _p4] = babelHelpers.classStaticPrivateFieldSpecGet(_p2, C, _y), _m = babelHelpers.classStaticPrivateFieldSpecGet(_p4 === void 0 ? C.self : _p4, C, _z), y = _m === void 0 ? babelHelpers.classStaticPrivateMethodGet(C, C, _self).call(C) : _m, z = _p3 === void 0 ? babelHelpers.classStaticPrivateFieldSpecGet(y, C, _y) : _p3;
 })();

packages/babel-plugin-proposal-destructuring-private/test/fixtures/assignment--es2015/under-param-initializer/output.js

@@ -5,7 +5,7 @@ let a;
 class C {
   static m(r = (_m2 = C, ({
     a
-  } = babelHelpers.classStaticPrivateFieldSpecGet(C, C, _x)), _m2)) {}
+  } = babelHelpers.classStaticPrivateFieldSpecGet(_m2, C, _x)), _m2)) {}
 
 }
 
@@ -24,7 +24,7 @@ var _x = {
 
   (function f(r = (_m = C, ({
     b
-  } = babelHelpers.classStaticPrivateFieldSpecGet(C, C, _x)), _m)) {})();
+  } = babelHelpers.classStaticPrivateFieldSpecGet(_m, C, _x)), _m)) {})();
 })();
 
 C.m();

packages/babel-plugin-proposal-destructuring-private/test/fixtures/assignment/array-rest-only/output.js

@@ -4,10 +4,10 @@ let result;
 class C {
   static #x;
   static {
-    var _p, _m, _m2;
+    var _p, _m;
 
     var x, z;
-    [..._p] = [C], _m = _p[0], _m2 = _m.#x, x = _m2 === void 0 ? 1 : _m2, z = babelHelpers.objectWithoutProperties(_p, _excluded);
+    [..._p] = [C], _m = _p[0].#x, x = _m === void 0 ? 1 : _m, z = babelHelpers.objectWithoutProperties(_p, _excluded);
     result = {
       x,
       z

packages/babel-plugin-proposal-destructuring-private/test/fixtures/assignment/nested-under-array-pattern/output.js

@@ -9,9 +9,9 @@ class C {
   }
 
   static {
-    var _p, _p2, _p3, _m, _p4, _m2, _m3;
+    var _p, _p2, _p3, _p4, _m;
 
     let x, y, z;
-    [_p, _p2,, _p3] = [this, this], _m = _p === void 0 ? C.self : _p, x = _m.#x, [, _p4] = _p2.#y, _m2 = _p4 === void 0 ? C.self : _p4, _m3 = _m2.#z, y = _m3 === void 0 ? C.#self() : _m3, z = _p3 === void 0 ? y.#y : _p3;
+    [_p, _p2,, _p3] = [this, this], x = (_p === void 0 ? C.self : _p).#x, [, _p4] = _p2.#y, _m = (_p4 === void 0 ? C.self : _p4).#z, y = _m === void 0 ? C.#self() : _m, z = _p3 === void 0 ? y.#y : _p3;
   }
 }

packages/babel-plugin-proposal-destructuring-private/test/fixtures/assignment/under-param-initializer/output.js

@@ -14,13 +14,13 @@ class C {
 
     (function f(r = (_m = C, ({
       b
-    } = C.#x), _m)) {})();
+    } = _m.#x), _m)) {})();
 
   }
 
   static m(r = (_m2 = C, ({
     a
-  } = C.#x), _m2)) {}
+  } = _m2.#x), _m2)) {}
 
 }
 

packages/babel-plugin-proposal-destructuring-private/test/fixtures/for-init--es2015/lhs-with-assign/output.js

@@ -8,7 +8,7 @@ var _x = {
 (() => {
   let x, y;
 
-  for (_m = (_m2 = C, y = babelHelpers.classStaticPrivateFieldSpecGet(C, C, _x), _m2), x = babelHelpers.classStaticPrivateFieldSpecGet(_m, C, _x), _m;;) {
+  for (_m = (_m2 = C, y = babelHelpers.classStaticPrivateFieldSpecGet(_m2, C, _x), _m2), x = babelHelpers.classStaticPrivateFieldSpecGet(_m, C, _x), _m;;) {
     var _m, _m2;
 
     break;

packages/babel-plugin-proposal-destructuring-private/test/fixtures/for-init--es2015/lhs/output.js

@@ -11,7 +11,7 @@ class C {
 }
 
 (() => {
-  for (_m = C, x = babelHelpers.classPrivateFieldGet(C, _x), _m;;) {
+  for (_m = C, x = babelHelpers.classPrivateFieldGet(_m, _x), _m;;) {
     var _m;
 
     break;

packages/babel-plugin-proposal-destructuring-private/test/fixtures/for-init--es2015/variable-declaration-with-assign/output.js

@@ -8,8 +8,8 @@ var _x = {
 (() => {
   let y;
 
-  for (let _m = (_m2 = C, y = babelHelpers.classStaticPrivateFieldSpecGet(C, C, _x), _m2), x = babelHelpers.classStaticPrivateFieldSpecGet(_m, C, _x);;) {
-    var _m2;
+  for (let x = babelHelpers.classStaticPrivateFieldSpecGet((_m = C, y = babelHelpers.classStaticPrivateFieldSpecGet(_m, C, _x), _m), C, _x);;) {
+    var _m;
 
     break;
   }

packages/babel-plugin-proposal-destructuring-private/test/fixtures/for-init/lhs-with-assign/output.js

@@ -3,7 +3,7 @@ class C {
   static {
     let x, y;
 
-    for (_m = (_m2 = C, y = C.#x, _m2), x = _m.#x, _m;;) {
+    for (_m = (_m2 = C, y = _m2.#x, _m2), x = _m.#x, _m;;) {
       var _m, _m2;
 
       break;

packages/babel-plugin-proposal-destructuring-private/test/fixtures/for-init/lhs/output.js

@@ -1,7 +1,7 @@
 class C {
   #x;
   static {
-    for (_m = this, x = this.#x, _m;;) {
+    for (_m = this, x = _m.#x, _m;;) {
       var _m;
 
       break;

packages/babel-plugin-proposal-destructuring-private/test/fixtures/for-init/variable-declaration-with-assign/output.js

@@ -3,8 +3,8 @@ class C {
   static {
     let y;
 
-    for (let _m = (_m2 = C, y = C.#x, _m2), x = _m.#x;;) {
-      var _m2;
+    for (let x = (_m = C, y = _m.#x, _m).#x;;) {
+      var _m;
 
       break;
     }

packages/babel-plugin-proposal-destructuring-private/test/fixtures/variable-declaration--es2015/array-rest-only/output.js

@@ -10,9 +10,8 @@ var _x = {
 
 (() => {
   var [..._p] = [C],
-      _m = _p[0],
-      _m2 = babelHelpers.classStaticPrivateFieldSpecGet(_m, C, _x),
-      x = _m2 === void 0 ? 1 : _m2,
+      _m = babelHelpers.classStaticPrivateFieldSpecGet(_p[0], C, _x),
+      x = _m === void 0 ? 1 : _m,
       z = babelHelpers.objectWithoutProperties(_p, _excluded);
 
   result = {

packages/babel-plugin-proposal-destructuring-private/test/fixtures/variable-declaration--es2015/nested-under-array-pattern/output.js

@@ -20,11 +20,9 @@ babelHelpers.defineProperty(C, "self", C);
 
 (() => {
   var [_p, _p2,, _p3] = [C, C],
-      _m = _p === void 0 ? C.self : _p,
-      x = babelHelpers.classStaticPrivateFieldSpecGet(_m, C, _x),
+      x = babelHelpers.classStaticPrivateFieldSpecGet(_p === void 0 ? C.self : _p, C, _x),
       [, _p4] = babelHelpers.classStaticPrivateFieldSpecGet(_p2, C, _y),
-      _m2 = _p4 === void 0 ? C.self : _p4,
-      _m3 = babelHelpers.classStaticPrivateFieldSpecGet(_m2, C, _z),
-      y = _m3 === void 0 ? babelHelpers.classStaticPrivateMethodGet(C, C, _self).call(C) : _m3,
+      _m = babelHelpers.classStaticPrivateFieldSpecGet(_p4 === void 0 ? C.self : _p4, C, _z),
+      y = _m === void 0 ? babelHelpers.classStaticPrivateMethodGet(C, C, _self).call(C) : _m,
       z = _p3 === void 0 ? babelHelpers.classStaticPrivateFieldSpecGet(y, C, _y) : _p3;
 })();

packages/babel-plugin-proposal-destructuring-private/test/fixtures/variable-declaration--es2015/non-identifier-keys/output.js

@@ -2,13 +2,9 @@ class C {
   static #x;
   static {
     var _m = [C, C, C, C],
-        _m2 = _m["0"],
-        w = _m2.#x,
-        _m3 = _m[1],
-        x = _m3.#x,
-        _m4 = _m[2n],
-        y = _m4.#x,
-        _m5 = _m[3m],
-        z = _m5.#x;
+        w = _m["0"].#x,
+        x = _m[1].#x,
+        y = _m[2n].#x,
+        z = _m[3m].#x;
   }
 }

packages/babel-plugin-proposal-destructuring-private/test/fixtures/variable-declaration/array-rest-only/output.js

@@ -5,9 +5,8 @@ class C {
   static #x;
   static {
     var [..._p] = [C],
-        _m = _p[0],
-        _m2 = _m.#x,
-        x = _m2 === void 0 ? 1 : _m2,
+        _m = _p[0].#x,
+        x = _m === void 0 ? 1 : _m,
         z = babelHelpers.objectWithoutProperties(_p, _excluded);
     result = {
       x,

packages/babel-plugin-proposal-destructuring-private/test/fixtures/variable-declaration/nested-under-array-pattern/output.js

@@ -10,13 +10,10 @@ class C {
 
   static {
     var [_p, _p2,, _p3] = [this, this],
-        _m = _p === void 0 ? C.self : _p,
-        x = _m.#x,
+        x = (_p === void 0 ? C.self : _p).#x,
         [, _p4] = _p2.#y,
-        _m2 = _p4 === void 0 ? C.self : _p4,
-        _m3 = _m2.#z,
-        y = _m3 === void 0 ? C.#self() : _m3,
+        _m = (_p4 === void 0 ? C.self : _p4).#z,
+        y = _m === void 0 ? C.#self() : _m,
         z = _p3 === void 0 ? y.#y : _p3;
-
   }
 }

packages/babel-plugin-proposal-destructuring-private/test/fixtures/variable-declaration/non-identifier-keys/output.js

@@ -2,13 +2,9 @@ class C {
   static #x;
   static {
     var _m = [C, C, C, C],
-        _m2 = _m["0"],
-        w = _m2.#x,
-        _m3 = _m[1],
-        x = _m3.#x,
-        _m4 = _m[2n],
-        y = _m4.#x,
-        _m5 = _m[3m],
-        z = _m5.#x;
+        w = _m["0"].#x,
+        x = _m[1].#x,
+        y = _m[2n].#x,
+        z = _m[3m].#x;
   }
 }