babel.config.js

module.exports = function (api) {
  // Keyed on the environment rather than cached forever, because the config is
  // no longer identical across environments — see the jest-only plugin below.
  // `api.env()` configures the cache itself, so the `api.cache(true)` that used
  // to be on the line above is gone rather than kept alongside it: calling
  // `api.cache(true)` FIRST and then `api.env()` throws "Caching has already
  // been configured with .never or .forever()". (The reverse order happens to
  // be tolerated, but relying on that is a trap not worth setting.)
  const isTest = api.env('test');

  return {
    presets: [
      [
        'babel-preset-expo',
        {
          unstable_transformImportMeta: true,
        },
      ],
    ],
    plugins: [
      // Makes `await import(...)` reachable under jest, where there is no Metro
      // to resolve it. Without this every such call site throws — 93 of them
      // across 40 files — and the 41 sitting inside a try/catch swallow it and
      // take their error branch while the suite still reports green. Full
      // rationale in the plugin file.
      //
      // Deleting this line is SILENT: measured 2026-08-17, it turns only 4 of
      // 1030 tests red and restores the blind spot everywhere else.
      // `__tests__/dynamicImportTransform.test.ts` exists to make it loud, and
      // asserts both that the transform is here and that it stays out of every
      // other environment.
      //
      // Required as a FUNCTION, not named by path. `dev/harness/babel.harness.js`
      // composes this config by calling it directly, and a relative plugin path
      // is then resolved against Babel's own internals rather than this file —
      // which broke every harness scenario with "Cannot find module". A function
      // reference has no such ambiguity. `require` here is relative to this
      // file, so it resolves correctly however the config is loaded.
      ...(isTest ? [require('./jest/babel-plugin-dynamic-import-to-require.js')] : []),
      // Reanimated plugin must remain last.
      'react-native-reanimated/plugin',
    ],
    // @polkadot/* ships untranspiled ES2022 class syntax that Hermes rejects.
    // babel-preset-expo doesn't lower it, so do it here, scoped to the
    // @polkadot packages only. (Applying to all of node_modules breaks
    // TS-source packages like expo-file-system, whose `declare` fields must
    // be transformed by the TypeScript plugin before these class plugins run.)
    overrides: [
      {
        test: /node_modules[\\/]@polkadot[\\/]/,
        plugins: [
          '@babel/plugin-transform-class-static-block',
          '@babel/plugin-transform-class-properties',
          '@babel/plugin-transform-private-methods',
          '@babel/plugin-transform-private-property-in-object',
        ],
      },
    ],
  };
};