feat: add custom esbuild entrypoint in function definitions (#546)

* feat: add custom esbuild entrypoint in function definitions

* docs: change quotes

README.md

@@ -282,6 +282,16 @@ module.exports = (serverless) => {
 
 As long as the plugin is properly installed, all regular Serverless operations `sls package`, `sls deploy`, `sls deploy function`, `sls invoke local`, `sls offline` will automatically compile using `serverless-esbuild`.
 
+### Specify a custom entrypoint for a function
+
+You can specify a custom entrypoint for ESBuild by specifying the `esbuildEntrypoint` field in your function definition.
+```typescript
+export const myLambdaFunction = {
+  handler: '/opt/nodejs/node_modules/my_custom_extension/handler.handler',
+  esbuildEntrypoint: './handler.main',
+};
+```
+
 ### Serverless Offline
 
 The plugin integrates very well with [serverless-offline](https://github.com/dherault/serverless-offline) to

src/helper.ts

@@ -62,14 +62,16 @@ export function extractFunctionEntries(
       return !(functions[functionAlias] as EsbuildFunctionDefinitionHandler).skipEsbuild;
     })
     .map((functionAlias) => {
-      const func = functions[functionAlias];
+      const func = functions[functionAlias] as EsbuildFunctionDefinitionHandler;
       assert(func, `${functionAlias} not found in functions`);
 
-      const { handler } = func;
-      const fnName = path.extname(handler);
-      const fnNameLastAppearanceIndex = handler.lastIndexOf(fnName);
+      const { handler, esbuildEntrypoint } = func;
+      const entrypoint = esbuildEntrypoint || handler;
+
+      const fnName = path.extname(entrypoint);
+      const fnNameLastAppearanceIndex = entrypoint.lastIndexOf(fnName);
       // replace only last instance to allow the same name for file and handler
-      const fileName = handler.substring(0, fnNameLastAppearanceIndex);
+      const fileName = entrypoint.substring(0, fnNameLastAppearanceIndex);
 
       const extensions = resolveExtensions ?? DEFAULT_EXTENSIONS;
 

src/tests/helper.test.ts

@@ -211,6 +211,27 @@ describe('extractFunctionEntries', () => {
       ]);
     });
 
+    it('should use esbuildEntrypoint in priority', () => {
+      jest.mocked(fs.existsSync).mockReturnValue(true);
+      const functionDefinitions = {
+        function1: {
+          events: [],
+          handler: '/opt/extension/my_custom_handler',
+          esbuildEntrypoint: 'file1.handler',
+        },
+      };
+
+      const fileNames = extractFunctionEntries(cwd, 'aws', functionDefinitions);
+
+      expect(fileNames).toStrictEqual([
+        {
+          entry: 'file1.ts',
+          func: functionDefinitions.function1,
+          functionAlias: 'function1',
+        },
+      ]);
+    });
+
     it('should throw an error if the handlers reference a file which does not exist', () => {
       jest.mocked(fs.existsSync).mockReturnValue(false);
       const functionDefinitions = {

src/types.ts

@@ -55,6 +55,7 @@ export interface Configuration extends EsbuildOptions {
 export interface EsbuildFunctionDefinitionHandler extends Serverless.FunctionDefinitionHandler {
   disposeContext?: boolean;
   skipEsbuild: boolean;
+  esbuildEntrypoint?: string;
 }
 
 export interface FunctionEntry {