async resolveId(importee, importer, resolveOptions) {
      const customOptions = resolveOptions.custom;
      // All logic below is specific to ES imports.
      // Also, if we do not skip this logic for requires that are resolved while
      // transforming a commonjs file, it can easily lead to deadlocks.
      if (customOptions?.['node-resolve']?.isRequire) {
        return null;
      }
      const currentlyResolvingForParent = currentlyResolving.get(importer);
      if (currentlyResolvingForParent && currentlyResolvingForParent.has(importee)) {
        this.warn({
          code: 'THIS_RESOLVE_WITHOUT_OPTIONS',
          message:
            'It appears a plugin has implemented a "resolveId" hook that uses "this.resolve" without forwarding the third "options" parameter of "resolveId". This is problematic as it can lead to wrong module resolutions especially for the node-resolve plugin and in certain cases cause early exit errors for the commonjs plugin.\nIn rare cases, this warning can appear if the same file is both imported and required from the same mixed ES/CommonJS module, in which case it can be ignored.',
          url: 'https://rollupjs.org/guide/en/#resolveid'
        });
        return null;
      }

      if (isWrappedId(importee, WRAPPED_SUFFIX)) {
        return unwrapId(importee, WRAPPED_SUFFIX);
      }

      if (
        importee.endsWith(ENTRY_SUFFIX) ||
        isWrappedId(importee, MODULE_SUFFIX) ||
        isWrappedId(importee, EXPORTS_SUFFIX) ||
        isWrappedId(importee, PROXY_SUFFIX) ||
        isWrappedId(importee, ES_IMPORT_SUFFIX) ||
        isWrappedId(importee, EXTERNAL_SUFFIX) ||
        importee.startsWith(HELPERS_ID) ||
        importee === DYNAMIC_MODULES_ID
      ) {
        return importee;
      }

      if (importer) {
        if (
          importer === DYNAMIC_MODULES_ID ||
          // Proxies are only importing resolved ids, no need to resolve again
          isWrappedId(importer, PROXY_SUFFIX) ||
          isWrappedId(importer, ES_IMPORT_SUFFIX) ||
          importer.endsWith(ENTRY_SUFFIX)
        ) {
          return importee;
        }
        if (isWrappedId(importer, EXTERNAL_SUFFIX)) {
          // We need to return null for unresolved imports so that the proper warning is shown
          if (
            !(await this.resolve(
              importee,
              importer,
              Object.assign({ skipSelf: true }, resolveOptions)
            ))
          ) {
            return null;
          }
          // For other external imports, we need to make sure they are handled as external
          return { id: importee, external: true };
        }
      }

      if (importee.startsWith('\0')) {
        return null;
      }

      // If this is an entry point or ESM import, we need to figure out if the importee is wrapped and
      // if that is the case, we need to add a proxy.
      const resolved =
        (await this.resolve(
          importee,
          importer,
          Object.assign({ skipSelf: true }, resolveOptions)
        )) || resolveExtensions(importee, importer, extensions);
      // Make sure that even if other plugins resolve again, we ignore our own proxies
      if (
        !resolved ||
        resolved.external ||
        resolved.id.endsWith(ENTRY_SUFFIX) ||
        isWrappedId(resolved.id, ES_IMPORT_SUFFIX) ||
        !isPossibleCjsId(resolved.id)
      ) {
        return resolved;
      }
      const moduleInfo = await this.load(resolved);
      const {
        meta: { commonjs: commonjsMeta }
      } = moduleInfo;
      if (commonjsMeta) {
        const { isCommonJS } = commonjsMeta;
        if (isCommonJS) {
          if (resolveOptions.isEntry) {
            moduleInfo.moduleSideEffects = true;
            // We must not precede entry proxies with a `\0` as that will mess up relative external resolution
            return resolved.id + ENTRY_SUFFIX;
          }
          if (isCommonJS === IS_WRAPPED_COMMONJS) {
            return { id: wrapId(resolved.id, ES_IMPORT_SUFFIX), meta: { commonjs: { resolved } } };
          }
        }
      }
      return resolved;
    }
This is a Maps of importers to Sets of require sources being resolved at
the moment by resolveRequireSourcesAndUpdateMeta