serverless/lib/configuration/variables/sources/env.js

'use strict';

const ensureString = require('type/string/ensure');
const ServerlessError = require('../../../serverless-error');

// Used to track env variable dependencies in specific resolution phases
// This collection is cleared on demand externally
const missingEnvVariables = new Set();

module.exports = {
  resolve: ({ address, isSourceFulfilled }) => {
    if (!address) {
      throw new ServerlessError(
        'Missing address argument in variable "env" source',
        'MISSING_ENV_SOURCE_ADDRESS'
      );
    }
    address = ensureString(address, {
      Error: ServerlessError,
      errorMessage: 'Non-string address argument in variable "env" source: %v',
      errorCode: 'INVALID_ENV_SOURCE_ADDRESS',
    });

    if (!process.env[address]) missingEnvVariables.add(address);
    return { value: process.env[address] || null, isPending: !isSourceFulfilled };
  },
  missingEnvVariables,
};