Expose an API to check if a helper is available in a given version range.

lib/third-party-libs.js.flow

@@ -32,6 +32,20 @@ declare module "lodash/merge" {
   declare export default <T: Object>(T, Object) => T;
 }
 
+declare module "semver" {
+  declare module.exports: {
+    valid(v: string): boolean;
+    gt(v1: string, v2: string): boolean;
+    lt(v1: string, v2: string): boolean;
+    major(v: string): number;
+    minor(v: string): number;
+    patch(v: string): number;
+    satisfies(v1: string, r1: string): boolean;
+
+    intersects(r1: string, r2: string): boolean;
+  }
+}
+
 declare module "source-map" {
   declare export type SourceMap = {
     version: 3,

packages/babel-core/src/transformation/file/file.js

@@ -5,6 +5,7 @@ import { NodePath, Hub, Scope } from "@babel/traverse";
 import { codeFrameColumns } from "@babel/code-frame";
 import traverse from "@babel/traverse";
 import * as t from "@babel/types";
+import semver from "semver";
 
 import type { NormalizedFile } from "../normalize-file";
 
@@ -136,6 +137,30 @@ export default class File {
     );
   }
 
+  /**
+   * Check if a given helper is available in @babel/core's helper list.
+   *
+   * This _also_ allows you to pass a Babel version specifically. If the
+   * helper exists, but was not available for the full given range, it will be
+   * considered unavailable.
+   */
+  availableHelper(name: string, versionRange: ?string) {
+    let minVersion;
+    try {
+      minVersion = helpers.minVersion(name);
+    } catch (err) {
+      if (err.code !== "BABEL_HELPER_UNKNOWN") throw err;
+
+      return false;
+    }
+
+    return (
+      typeof versionRange !== "string" ||
+      (!semver.intersects(`<${minVersion}`, versionRange) &&
+        !semver.intersects(`>=8.0.0`, versionRange))
+    );
+  }
+
   addHelper(name: string): Object {
     const declar = this.declarations[name];
     if (declar) return t.cloneNode(declar);

packages/babel-core/src/transformation/plugin-pass.js

@@ -31,6 +31,10 @@ export default class PluginPass {
     return this._map.get(key);
   }
 
+  availableHelper(name: string, versionRange: ?string) {
+    return this.file.availableHelper(name, versionRange);
+  }
+
   addHelper(name: string) {
     return this.file.addHelper(name);
   }