feat(CLI): Automatically expand loaded env variables

docs/environment-variables.md

@@ -12,6 +12,19 @@ With `useDotenv: true` set in your `serverless.yml` file, framework automaticall
 
 The framework looks for `.env` and `.env.{stage}` files in service directory and then tries to load them using `dotenv`. If `.env.{stage}` is found, `.env` will not be loaded. If stage is not explicitly defined, it defaults to `dev`.
 
+### Variable expansion
+
+It is possible to define environment variables as a combination of existing ones:
+
+```env
+BASE_URL=my.api.com
+PROTOCOL=https
+
+URL=$PROTOCOL/$BASE_URL
+```
+
+> This is supported through [dotenv-expand](https://github.com/motdotla/dotenv-expand)
+
 ### Differences against `serverless-dotenv-plugin`
 
 There are a few differences between above functionality and [serverless-dotenv-plugin](https://github.com/colynb/serverless-dotenv-plugin):

lib/cli/load-dotenv.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const dotenv = require('dotenv');
+const dotenvExpand = require('dotenv-expand');
 const path = require('path');
 const ServerlessError = require('../serverless-error');
 
@@ -11,19 +12,25 @@ const throwDotenvError = (error, filePath) => {
   throw new ServerlessError(errorMessage, 'DOTENV_LOAD_ERROR');
 };
 
+const loadDotenvFrom = (envFilePath) => {
+  const config = dotenv.config({ path: envFilePath });
+  return dotenvExpand(config);
+};
+
 module.exports = (stage) => {
   const defaultEnvFilePath = path.join(process.cwd(), '.env');
   const stageEnvFilePath = path.join(process.cwd(), `.env.${stage}`);
 
-  const { error: stageEnvResultError } = dotenv.config({ path: stageEnvFilePath });
+  const { error: stageEnvResultError } = loadDotenvFrom(stageEnvFilePath);
 
   if (!stageEnvResultError) return;
 
   if (!isMissingFileError(stageEnvResultError)) {
     throwDotenvError(stageEnvResultError, stageEnvFilePath);
   }
 
-  const { error: defaultEnvResultError } = dotenv.config({ path: defaultEnvFilePath });
+  const { error: defaultEnvResultError } = loadDotenvFrom(defaultEnvFilePath);
+
   if (defaultEnvResultError && !isMissingFileError(defaultEnvResultError)) {
     throwDotenvError(defaultEnvResultError, defaultEnvFilePath);
   }

package.json

@@ -41,6 +41,7 @@
     "dayjs": "^1.10.6",
     "decompress": "^4.2.1",
     "dotenv": "^10.0.0",
+    "dotenv-expand": "^5.1.0",
     "essentials": "^1.1.1",
     "fastest-levenshtein": "^1.0.12",
     "filesize": "^7.0.0",

test/unit/lib/Serverless.test.js

@@ -329,12 +329,16 @@ describe('test/unit/lib/Serverless.test.js', () => {
             custom: {
               fromDefaultEnv: '${env:DEFAULT_ENV_VARIABLE}',
               fromStageEnv: "${env:STAGE_ENV_VARIABLE, 'not-found'}",
+              fromDefaultExpandedEnv: '${env:DEFAULT_ENV_VARIABLE_EXPANDED}',
             },
           },
         })
       ).servicePath;
 
-      const defaultFileContent = 'DEFAULT_ENV_VARIABLE=valuefromdefault';
+      const defaultFileContent = `
+        DEFAULT_ENV_VARIABLE=valuefromdefault
+        DEFAULT_ENV_VARIABLE_EXPANDED=$DEFAULT_ENV_VARIABLE/expanded
+      `;
       await fs.promises.writeFile(path.join(serviceDir, '.env'), defaultFileContent);
       conditionallyLoadDotenv.clear();
     });
@@ -347,6 +351,9 @@ describe('test/unit/lib/Serverless.test.js', () => {
       });
 
       expect(result.serverless.service.custom.fromDefaultEnv).to.equal('valuefromdefault');
+      expect(result.serverless.service.custom.fromDefaultExpandedEnv).to.equal(
+        'valuefromdefault/expanded'
+      );
       expect(result.serverless.service.custom.fromStageEnv).to.equal('not-found');
     });
   });