Yarn Dedup & rename hasMoreThanOneBinding to shouldStoreRHSInTemporar…

…yVariable
babel · Sep 7, 2021 · 4be2624 · 4be2624
1 parent 317065d
commit 4be2624
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Showing 6 changed files with 38 additions and 30 deletions.
diff --git a/packages/babel-plugin-proposal-object-rest-spread/package.json b/packages/babel-plugin-proposal-object-rest-spread/package.json
@@ -28,8 +28,8 @@
   },
   "devDependencies": {
     "@babel/core": "workspace:*",
-    "@babel/parser": "workspace:*",
-    "@babel/helper-plugin-test-runner": "workspace:*"
+    "@babel/helper-plugin-test-runner": "workspace:*",
+    "@babel/parser": "workspace:*"
   },
   "engines": {
     "node": ">=6.9.0"

diff --git a/packages/babel-plugin-proposal-object-rest-spread/src/hasMoreThanOneBinding.js b/packages/babel-plugin-proposal-object-rest-spread/src/hasMoreThanOneBinding.js
diff --git a/packages/babel-plugin-proposal-object-rest-spread/src/index.js b/packages/babel-plugin-proposal-object-rest-spread/src/index.js
@@ -4,7 +4,7 @@ import { types as t } from "@babel/core";
 import { convertFunctionParams } from "@babel/plugin-transform-parameters";
 import { isRequired } from "@babel/helper-compilation-targets";
 import compatData from "@babel/compat-data/corejs2-built-ins";
-import hasMoreThanOneBinding from "./hasMoreThanOneBinding";
+import shouldStoreRHSInTemporaryVariable from "./shouldStoreRHSInTemporaryVariable";
 
 // TODO: Remove in Babel 8
 // @babel/types <=7.3.3 counts FOO as referenced in var { x: FOO }.
@@ -336,7 +336,7 @@ export default declare((api, opts) => {
             // skip single-property case, e.g.
             // const { ...x } = foo();
             // since the RHS will not be duplicated
-            hasMoreThanOneBinding(originalPath.node.id) &&
+            shouldStoreRHSInTemporaryVariable(originalPath.node.id) &&
             !t.isIdentifier(originalPath.node.init)
           ) {
             // const { a, ...b } = foo();

diff --git a/packages/babel-plugin-proposal-object-rest-spread/src/shouldStoreRHSInTemporaryVariable.js b/packages/babel-plugin-proposal-object-rest-spread/src/shouldStoreRHSInTemporaryVariable.js
@@ -0,0 +1,30 @@
+import { types as t } from "@babel/core";
+
+/**
+ * This is a helper function to determine if we should create an intermediate variable
+ * such that the RHS of an assignment is not duplicated.
+ *
+ * See https://github.com/babel/babel/pull/13711#issuecomment-914388382 for discussion
+ * on further optimizations.
+ */
+export default function shouldStoreRHSInTemporaryVariable(node) {
+  if (t.isArrayPattern(node)) {
+    const nonNullElements = node.elements.filter(element => element !== null);
+    if (nonNullElements.length > 1) return true;
+    else return shouldStoreRHSInTemporaryVariable(nonNullElements[0]);
+  } else if (t.isObjectPattern(node)) {
+    if (node.properties.length > 1) return true;
+    else if (node.properties.length === 0) return false;
+    else return shouldStoreRHSInTemporaryVariable(node.properties[0]);
+  } else if (t.isObjectProperty(node)) {
+    return shouldStoreRHSInTemporaryVariable(node.value);
+  } else if (t.isAssignmentPattern(node)) {
+    return shouldStoreRHSInTemporaryVariable(node.left);
+  } else if (t.isRestElement(node)) {
+    if (t.isIdentifier(node.argument)) return true;
+    return shouldStoreRHSInTemporaryVariable(node.argument);
+  } else {
+    // node is Identifier or MemberExpression
+    return false;
+  }
+}
diff --git a/packages/babel-plugin-proposal-object-rest-spread/test/hasMoreThanOneBinding.test.js b/packages/babel-plugin-proposal-object-rest-spread/test/hasMoreThanOneBinding.test.js
@@ -1,11 +1,11 @@
 import { parse } from "@babel/parser";
-import hasMoreThanOneBinding from "../lib/hasMoreThanOneBinding";
+import shouldStoreRHSInTemporaryVariable from "../lib/shouldStoreRHSInTemporaryVariable";
 
 function getFistObjectPattern(program) {
   return parse(program, { sourceType: "module" }).program.body[0]
     .declarations[0].id;
 }
-describe("hasMoreThanOneBinding", function () {
+describe("shouldStoreRHSInTemporaryVariable", function () {
   it.each([
     ["const { x: { ...y } } = z();", true],
     ["let { x4: { ...y4 } } = z();", true],
@@ -40,7 +40,7 @@ describe("hasMoreThanOneBinding", function () {
     ["const [,,x27] = z();", false],
   ])("%s", (code, expectedResult) => {
     const ast = getFistObjectPattern(code);
-    const result = hasMoreThanOneBinding(ast);
+    const result = shouldStoreRHSInTemporaryVariable(ast);
     expect(result).toEqual(expectedResult);
   });
 });
diff --git a/yarn.lock b/yarn.lock
@@ -1412,6 +1412,7 @@ __metadata:
     "@babel/helper-compilation-targets": "workspace:^7.14.5"
     "@babel/helper-plugin-test-runner": "workspace:*"
     "@babel/helper-plugin-utils": "workspace:^7.14.5"
+    "@babel/parser": "workspace:*"
     "@babel/plugin-syntax-object-rest-spread": ^7.8.3
     "@babel/plugin-transform-parameters": "workspace:^7.14.5"
   peerDependencies: