Use Array#findLastIndex (#16384)

scripts/build/shims/array-find-last-index.js

@@ -0,0 +1,20 @@
+const arrayFindLastIndex = (isOptionalObject, array, callback) => {
+  if (isOptionalObject && (array === undefined || array === null)) {
+    return;
+  }
+
+  if (array.findLastIndex) {
+    return array.findLastIndex(callback);
+  }
+
+  for (let index = array.length - 1; index >= 0; index--) {
+    const element = array[index];
+    if (callback(element, index, array)) {
+      return index;
+    }
+  }
+
+  return -1;
+};
+
+export default arrayFindLastIndex;

scripts/build/transform/transforms/index.js

@@ -1,11 +1,13 @@
 import transformArrayFindLast from "./transform-array-find-last.js";
+import transformArrayFindLastIndex from "./transform-array-find-last-index.js";
 import transformObjectHasOwnCall from "./transform-object-has-own.js";
 import transformRelativeIndexing from "./transform-relative-indexing.js";
 import transformStringReplaceAll from "./transform-string-replace-all.js";
 
 export default [
+  transformArrayFindLast,
+  transformArrayFindLastIndex,
   transformObjectHasOwnCall,
   transformRelativeIndexing,
   transformStringReplaceAll,
-  transformArrayFindLast,
 ];

scripts/build/transform/transforms/transform-array-find-last-index.js

@@ -0,0 +1,13 @@
+import createMethodCallTransform from "./create-method-call-transform.js";
+
+const transformArrayFindLastIndex = createMethodCallTransform({
+  methodName: "findLastIndex",
+  argumentsLength: 1,
+  functionName: "__arrayFindLastIndex",
+  functionImplementationUrl: new URL(
+    "../../shims/array-find-last-index.js",
+    import.meta.url,
+  ),
+});
+
+export default transformArrayFindLastIndex;

src/main/range-util.js

@@ -24,16 +24,15 @@ function findCommonAncestor(startNodeAndParents, endNodeAndParents) {
 }
 
 function dropRootParents(parents) {
-  let lastParentIndex = parents.length - 1;
-  while (true) {
-    const parent = parents[lastParentIndex];
-    if (parent?.type === "Program" || parent?.type === "File") {
-      lastParentIndex--;
-    } else {
-      break;
-    }
+  const index = parents.findLastIndex(
+    (node) => node.type !== "Program" && node.type !== "File",
+  );
+
+  if (index === -1) {
+    return parents;
   }
-  return parents.slice(0, lastParentIndex + 1);
+
+  return parents.slice(0, index + 1);
 }
 
 function findSiblingAncestors(

tests/unit/syntax-transform.js

@@ -75,3 +75,21 @@ test("Array#findLast", () => {
     transform("foo.findLast(callback, thisArgument)"),
   ).toMatchInlineSnapshot(`"foo.findLast(callback, thisArgument)"`);
 });
+
+test("Array#findLastIndex", () => {
+  expect(transform("foo.findLastIndex(callback)")).toMatchInlineSnapshot(`
+    "import __arrayFindLastIndex from "<SHIMS>/array-find-last-index.js";
+
+    __arrayFindLastIndex( /* isOptionalObject */false, foo, callback);"
+  `);
+  expect(transform("foo?.findLastIndex(callback)")).toMatchInlineSnapshot(`
+    "import __arrayFindLastIndex from "<SHIMS>/array-find-last-index.js";
+
+    __arrayFindLastIndex( /* isOptionalObject */true, foo, callback);"
+  `);
+
+  // Don't support
+  expect(
+    transform("foo.findLastIndex(callback, thisArgument)"),
+  ).toMatchInlineSnapshot(`"foo.findLastIndex(callback, thisArgument)"`);
+});