fix: do not attempt substitution if the loader failed

Author: Jacques Germishuys

lib/loader/file-loader.ts

@@ -100,8 +100,11 @@ export const fileLoader = (
       searchPlaces,
       ...options,
       loaders,
-      transform: (result: Record<string, any>) => {
-        if (options.ignoreEnvironmentVariableSubstitution ?? true) {
+      transform: (result: Record<string, any> | null) => {
+        if (
+          !result ||
+          (options.ignoreEnvironmentVariableSubstitution ?? true)
+        ) {
           return result;
         }
 

tests/e2e/yaml-file-substitutions.spec.ts

@@ -225,6 +225,18 @@ describe('Environment variable substitutions error cases', () => {
     );
   });
 
+  it('should not attempt substitution if the loader failed', async () => {
+    expect(() =>
+      AppModule.withYamlSubstitution(
+        {
+          ignoreEnvironmentVariableSubstitution: true,
+        },
+        ConfigWithAlias,
+        ['.env-missing.yaml'],
+      ),
+    ).toThrowError(`Failed to find configuration file.`);
+  });
+
   it('array primitives substitution', async () => {
     expect(() =>
       AppModule.withYamlSubstitution(

tests/src/app.module.ts

@@ -49,7 +49,8 @@ export type TestYamlFile =
   | '.env-reference-object.sub.yaml'
   | '.env-reference-array-of-primitives.sub.yaml'
   | '.env-advanced-backward-reference.sub.yaml'
-  | '.env-with-default.sub.yaml';
+  | '.env-with-default.sub.yaml'
+  | '.env-missing.yaml';
 
 @Module({})
 export class AppModule {