dedupe environment variables in amplify env type generator (#2153)

Author: ykethan

.changeset/silver-rocks-return.md

@@ -0,0 +1,6 @@
+---
+'@aws-amplify/backend-function': patch
+'@aws-amplify/backend': patch
+---
+
+dedupe environment variables in amplify env type generator

packages/backend-function/src/function_env_type_generator.test.ts

@@ -69,4 +69,36 @@ void describe('FunctionEnvironmentTypeGenerator', () => {
 
     await fsp.rm(targetDirectory, { recursive: true, force: true });
   });
+
+  void it('does not generate duplicate environment variables', () => {
+    const fsOpenSyncMock = mock.method(fs, 'openSync');
+    const fsWriteFileSyncMock = mock.method(fs, 'writeFileSync', () => null);
+    fsOpenSyncMock.mock.mockImplementation(() => 0);
+    const functionEnvironmentTypeGenerator =
+      new FunctionEnvironmentTypeGenerator('testFunction');
+
+    functionEnvironmentTypeGenerator.generateTypedProcessEnvShim([
+      'TEST_ENV',
+      'TEST_ENV',
+      'ANOTHER_ENV',
+    ]);
+
+    const generatedContent =
+      fsWriteFileSyncMock.mock.calls[0].arguments[1]?.toString() ?? '';
+
+    // Check TEST_ENV appears only once
+    assert.equal(
+      (generatedContent.match(/TEST_ENV: string;/g) || []).length,
+      1,
+      'TEST_ENV should appear only once'
+    );
+
+    // Check ANOTHER_ENV also appears
+    assert.ok(
+      generatedContent.includes('ANOTHER_ENV: string;'),
+      'ANOTHER_ENV should be included'
+    );
+
+    mock.restoreAll();
+  });
 });

packages/backend-function/src/function_env_type_generator.ts

@@ -57,7 +57,11 @@ export class FunctionEnvironmentTypeGenerator {
       `/** Amplify backend environment variables available at runtime, this includes environment variables defined in \`defineFunction\` and by cross resource mechanisms */`
     );
     declarations.push(`type ${amplifyBackendEnvVarTypeName} = {`);
-    amplifyBackendEnvVars.forEach((envName) => {
+
+    // Use a Set to remove duplicates
+    const uniqueEnvVars = new Set(amplifyBackendEnvVars);
+
+    uniqueEnvVars.forEach((envName) => {
       const declaration = `${this.indentation}${envName}: string;`;
 
       declarations.push(declaration);