fix(babel-preset): deprecate looseClassTransform (#3042)

.changeset/spotty-guests-explain.md

@@ -0,0 +1,5 @@
+---
+"@rnx-kit/babel-preset-metro-react-native": patch
+---
+
+Deprecate `looseClassTransform`

packages/babel-preset-metro-react-native/package.json

@@ -24,6 +24,7 @@
     "test": "NODE_OPTIONS=--experimental-vm-modules rnx-kit-scripts test"
   },
   "dependencies": {
+    "@rnx-kit/console": "^1.0.12",
     "babel-plugin-const-enum": "^1.0.0"
   },
   "peerDependencies": {

packages/babel-preset-metro-react-native/src/index.js

@@ -25,6 +25,25 @@
  * @typedef {MetroPresetOptions & RnxPresetOptions} PresetOptions
  */
 
+/**
+ * Converts version string to a number.
+ * @param {string} version
+ * @returns {number}
+ */
+function parseVersion(version) {
+  const [major, minor = 0] = version.split(".");
+  return Number(major) * 1000 + Number(minor);
+}
+
+/**
+ * Returns whether Babel implements compiler assumptions.
+ * @param {ConfigAPI | undefined} api
+ * @returns {boolean}
+ */
+function hasCompilerAssumptions(api) {
+  return Boolean(api?.version && parseVersion(api.version) >= 7013);
+}
+
 /**
  * Returns plugin for transforming `const enum` if necessary.
  *
@@ -36,8 +55,7 @@ function constEnumPlugin() {
     const {
       version,
     } = require("@babel/plugin-transform-typescript/package.json");
-    const { [0]: major, [1]: minor } = version.split(".");
-    if (Number(major) * 1000 + Number(minor) >= 7015) {
+    if (parseVersion(version) >= 7015) {
       return [];
     }
   } catch (_) {
@@ -136,7 +154,7 @@ function overridesFor(transformProfile, env) {
  * @type {(api?: ConfigAPI, opts?: PresetOptions) => TransformOptions}
  */
 module.exports = (
-  _,
+  api,
   {
     additionalPlugins,
     looseClassTransform,
@@ -164,6 +182,12 @@ module.exports = (
   });
 
   if (looseClassTransform) {
+    if (hasCompilerAssumptions(api)) {
+      const { warn } = require("@rnx-kit/console");
+      warn(
+        "`looseClassTransform` is deprecated — consider migrating to the top level assumptions for more granular control (see https://babeljs.io/docs/babel-plugin-transform-classes#loose)"
+      );
+    }
     const pluginClasses = require.resolve("@babel/plugin-transform-classes", {
       paths: [babelPreset],
     });

yarn.lock

@@ -3549,6 +3549,7 @@ __metadata:
     "@babel/core": "npm:^7.20.0"
     "@babel/plugin-transform-typescript": "npm:^7.20.0"
     "@rnx-kit/babel-plugin-import-path-remapper": "npm:*"
+    "@rnx-kit/console": "npm:^1.0.12"
     "@rnx-kit/eslint-config": "npm:*"
     "@rnx-kit/scripts": "npm:*"
     "@rnx-kit/tsconfig": "npm:*"