feature: implemented ability to set default values for file loaders, with dotenv-expand syntax

Author: vsamofal

lib/loader/file-loader.ts

@@ -3,6 +3,8 @@ import { basename, dirname } from 'path';
 import { debug } from '../utils/debug.util';
 import { loadPackage } from '../utils/load-package.util';
 
+const DEFAULT_VALUE_SEPARATOR = ':-';
+
 let parseToml: any;
 let cosmiconfig: any;
 
@@ -165,7 +167,9 @@ function transformFileLoaderResult(
     const match = obj.match(/\$\{(.+?)\}/g);
     if (match) {
       for (const placeholder of match) {
-        const variable = placeholder.slice(2, -1);
+        const { variable, defaultValue } =
+          extractVariableNameAndDefaultValue(placeholder);
+
         let resolvedValue = resolveReference(variable, context);
 
         if (obj === resolvedValue) {
@@ -219,6 +223,8 @@ function transformFileLoaderResult(
                 .replace(placeholder, resolvedValue.toString());
             }
           }
+        } else if (defaultValue !== undefined) {
+          obj = defaultValue;
         } else if (disallowUndefinedEnvironmentVariables) {
           throw new Error(
             `Environment variable is not set for variable name: '${variable}'`,
@@ -263,3 +269,20 @@ function transformFileLoaderResult(
   }
   return obj;
 }
+
+function extractVariableNameAndDefaultValue(placeholder: string): {
+  variable: string;
+  defaultValue?: string;
+} {
+  const placeholderWithoutBrackets = placeholder.slice(2, -1);
+  const splitValues = placeholderWithoutBrackets.split(DEFAULT_VALUE_SEPARATOR);
+  const defaultValue =
+    splitValues.length === 1
+      ? undefined
+      : splitValues.slice(1).join(DEFAULT_VALUE_SEPARATOR);
+
+  return {
+    variable: splitValues[0],
+    defaultValue,
+  };
+}

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

@@ -1,8 +1,10 @@
 import { AppModule, TestYamlFile } from '../src/app.module';
 import {
   ConfigWithAlias,
+  ConfigWithDefaultValuesForEnvs,
   DatabaseConfig,
   DatabaseConfigAlias,
+  DatabaseConfigAliasCopy,
   DatabaseConfigWithAliasAndAuthCopy,
 } from '../src/config.model';
 import { INestApplication } from '@nestjs/common';
@@ -53,6 +55,25 @@ describe('Environment variable substitutions success cases', () => {
     expect(alias).toStrictEqual(instanceToPlain(databaseConfig));
   });
 
+  it(`should load yaml and fill default values successfully`, async () => {
+    await init(
+      { ignoreEnvironmentVariableSubstitution: false },
+      ['.env-with-default.sub.yaml'],
+      ConfigWithDefaultValuesForEnvs,
+    );
+    const config = app.get(ConfigWithDefaultValuesForEnvs);
+    const databaseConfig = app.get(DatabaseConfigAliasCopy);
+    const databaseConfigAlias = app.get(DatabaseConfigAlias);
+    const alias = instanceToPlain(databaseConfigAlias);
+
+    expect(alias).toStrictEqual(instanceToPlain(databaseConfig));
+    expect(alias.port).toBe(12345);
+    expect(alias.table.name).toBe(tableName);
+    expect(alias.host).toBe('my-default-host.com');
+    expect(config.isAuthEnabled).toBe(false);
+    expect(config.defaultEmptyString).toBe('');
+  });
+
   it(`self substitution advanced case`, async () => {
     await init({ ignoreEnvironmentVariableSubstitution: false }, [
       '.env-advanced-self-referencing-tricky.sub.yaml',

tests/src/.env-with-default.sub.yaml

@@ -1,9 +1,10 @@
-isAuthEnabled: ${AUTH_ENABLED:-true}
+isAuthEnabled: ${AUTH_ENABLED:-false}
+defaultEmptyString: ${EMPTY_STRING:-}
 database:
-  host: ${DATABASE_HOST:-127.0.0.1}
-  port: ${DATABASE_PORT:-3000}
+  host: ${DATABASE_HOST:-my-default-host.com}
+  port: ${DATABASE_PORT:-12345}
   table:
-    name: ${TABLE_NAME:-users}
+    name: ${TABLE_NAME:-custom-name}
 
 databaseAlias:
   host: ${database.host}

tests/src/config.model.ts

@@ -7,6 +7,7 @@ import {
   IsString,
   ValidateNested,
 } from 'class-validator';
+import { applyDecorators } from '@nestjs/common';
 
 export class TableConfig {
   @IsString()
@@ -26,7 +27,19 @@ export class DatabaseConfig {
   public readonly table!: TableConfig;
 }
 
-export class DatabaseConfigAlias extends DatabaseConfig {}
+export class DatabaseConfigAlias extends DatabaseConfig {
+  @IsInt()
+  @Type(() => Number)
+  public readonly port!: number;
+}
+
+export class DatabaseConfigAliasCopy extends DatabaseConfigAlias {}
+
+const ToBoolean = applyDecorators(
+  Transform(({ value }) =>
+    typeof value === 'boolean' ? value : value === 'true',
+  ),
+);
 
 export class Config {
   @Type(() => DatabaseConfig)
@@ -38,6 +51,25 @@ export class Config {
   public readonly isAuthEnabled!: boolean;
 }
 
+export class ConfigWithDefaultValuesForEnvs {
+  @IsBoolean()
+  @ToBoolean
+  public readonly isAuthEnabled!: boolean;
+
+  @IsString()
+  public readonly defaultEmptyString!: string;
+
+  @Type(() => DatabaseConfigAliasCopy)
+  @ValidateNested()
+  @IsDefined()
+  public readonly database!: DatabaseConfigAliasCopy;
+
+  @Type(() => DatabaseConfigAlias)
+  @ValidateNested()
+  @IsDefined()
+  public readonly databaseAlias!: DatabaseConfigAlias;
+}
+
 export class ConfigWithAlias extends Config {
   @Type(() => DatabaseConfigAlias)
   @ValidateNested()
@@ -46,9 +78,7 @@ export class ConfigWithAlias extends Config {
 }
 
 export class DatabaseConfigWithAliasAndAuthCopy extends ConfigWithAlias {
-  @Transform(({ value }) =>
-    typeof value === 'boolean' ? value : value === 'true',
-  )
+  @ToBoolean
   @IsBoolean()
   public readonly isAuthEnabledCopy!: boolean;
 }