Function resolve

src/esm.ts:153–225

(
    specifier: string,
    context: { parentURL: string },
    defaultResolve: typeof resolve
  )

  const rememberResolvedViaCommonjsFallback = new Set();

  async function resolve(
    specifier: string,
    context: { parentURL: string },
    defaultResolve: typeof resolve
  ): Promise<{ url: string; format?: NodeLoaderHooksFormat }> {
    const defer = async () => {
      const r = await defaultResolve(specifier, context, defaultResolve);
      return r;
    };
    // See: https://github.com/nodejs/node/discussions/41711
    // nodejs will likely implement a similar fallback.  Till then, we can do our users a favor and fallback today.
    async function entrypointFallback(
      cb: () => ReturnType<typeof resolve> | Awaited<ReturnType<typeof resolve>>
    ): ReturnType<typeof resolve> {
      try {
        const resolution = await cb();
        if (
          resolution?.url &&
          isProbablyEntrypoint(specifier, context.parentURL)
        )
          rememberIsProbablyEntrypoint.add(resolution.url);
        return resolution;
      } catch (esmResolverError) {
        if (!isProbablyEntrypoint(specifier, context.parentURL))
          throw esmResolverError;
        try {
          let cjsSpecifier = specifier;
          // Attempt to convert from ESM file:// to CommonJS path
          try {
            if (specifier.startsWith('file://'))
              cjsSpecifier = fileURLToPath(specifier);
          } catch {}
          const resolution = pathToFileURL(
            createRequire(process.cwd()).resolve(cjsSpecifier)
          ).toString();
          rememberIsProbablyEntrypoint.add(resolution);
          rememberResolvedViaCommonjsFallback.add(resolution);
          return { url: resolution, format: 'commonjs' };
        } catch (commonjsResolverError) {
          throw esmResolverError;
        }
      }
    }

    return addShortCircuitFlag(async () => {
      const parsed = parseUrl(specifier);
      const { pathname, protocol, hostname } = parsed;

      if (!isFileUrlOrNodeStyleSpecifier(parsed)) {
        return entrypointFallback(defer);
      }

      if (protocol !== null && protocol !== 'file:') {
        return entrypointFallback(defer);
      }

      // Malformed file:// URL?  We should always see `null` or `''`
      if (hostname) {