feat(config): Support multiple configuration sources for an option

packages/config/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.9.1
+
+ - **FEAT**(config): Support multiple configuration sources for an option (#127).
+
 ## 0.9.0
 
  - Bumped minimum Dart SDK version to 3.6

packages/config/README.md

@@ -200,7 +200,8 @@ The configuration library resolves each option value in a specific order, with e
 
 3. **Configuration files**
    - Values from configuration files (e.g. YAML/JSON)
-   - Lookup key is specified using `configKey`
+   - Lookup key is specified using `configKey` or `configKeys`
+     (multiple keys are tried in order of precedence)
 
 4. **Custom value providers**
    - Values from custom callbacks
@@ -349,14 +350,28 @@ YAML file and the JSON pointer syntax is used.
   ));
 ```
 
+An option can look up values from multiple configuration sources by specifying
+`configKeys` in order of precedence. The first key that yields a value is used:
+
+```dart
+  dir(DirOption(
+    argName: 'dir',
+    configKeys: ['local:/dir', 'settings:/my_dir'],
+    helpText: 'the local directory',
+  )),
+```
+
+`configKey` can still be used for a single source. If both are specified,
+`configKey` is tried first, then each key in `configKeys`.
+
 See the full example in [example/config_file_example.dart](example/config_file_example.dart).
 
 ### Multiple configuration sources
 
 By using the `MultiDomainConfigBroker`, configuration sources
 from multiple providers can be used, called configuration *domains*.
 
-They are distinguished by the format used in the configKey,
+They are distinguished by the format used in the config key,
 which needs to specify a so-called *qualified key* -
 qualifying the key with the domain it is found in.
 

packages/config/lib/src/config/config_parser.dart

@@ -57,6 +57,7 @@ class ConfigParser implements ArgParser {
     final List<String> aliases = const [],
     final String? envName,
     final String? configKey,
+    final List<String>? configKeys,
     final bool? Function(Configuration cfg)? fromCustom,
     final bool Function()? fromDefault,
     final String? valueHelp,
@@ -71,6 +72,7 @@ class ConfigParser implements ArgParser {
         argAbbrev: abbr,
         envName: envName,
         configKey: configKey,
+        configKeys: configKeys,
         fromCustom: fromCustom,
         fromDefault: fromDefault,
         defaultsTo: defaultsTo,
@@ -106,6 +108,7 @@ class ConfigParser implements ArgParser {
     final int? argPos,
     final String? envName,
     final String? configKey,
+    final List<String>? configKeys,
     final String? Function(Configuration cfg)? fromCustom,
     final String Function()? fromDefault,
     final OptionGroup? group,
@@ -119,6 +122,7 @@ class ConfigParser implements ArgParser {
         argPos: argPos,
         envName: envName,
         configKey: configKey,
+        configKeys: configKeys,
         fromCustom: fromCustom,
         fromDefault: fromDefault,
         defaultsTo: defaultsTo,
@@ -153,6 +157,7 @@ class ConfigParser implements ArgParser {
     final List<String> aliases = const [],
     final String? envName,
     final String? configKey,
+    final List<String>? configKeys,
     final List<String>? Function(Configuration cfg)? fromCustom,
     final List<String> Function()? fromDefault,
     final OptionGroup? group,
@@ -167,6 +172,7 @@ class ConfigParser implements ArgParser {
           argAbbrev: abbr,
           envName: envName,
           configKey: configKey,
+          configKeys: configKeys,
           fromCustom: fromCustom,
           fromDefault: fromDefault,
           defaultsTo: defaultsTo?.toList(),
@@ -188,6 +194,7 @@ class ConfigParser implements ArgParser {
           argAbbrev: abbr,
           envName: envName,
           configKey: configKey,
+          configKeys: configKeys,
           fromCustom: fromCustom,
           fromDefault: fromDefault,
           defaultsTo: defaultsTo?.toList(),

packages/config/lib/src/config/configuration.dart

@@ -194,7 +194,7 @@ class Configuration<O extends OptionDefinition> {
           (argName != null && o.option.argName == argName) ||
           (argPos != null && o.option.argPos == argPos) ||
           (envName != null && o.option.envName == envName) ||
-          (configKey != null && o.option.configKey == configKey);
+          (configKey != null && o.option.allConfigKeys.contains(configKey));
     });
   }
 

packages/config/lib/src/config/file_system_options.dart

@@ -40,6 +40,7 @@ class DirOption extends ConfigOptionBase<Directory> {
     super.argPos,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,
@@ -109,6 +110,7 @@ class FileOption extends ConfigOptionBase<File> {
     super.argPos,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,

packages/config/lib/src/config/option_types.dart

@@ -21,6 +21,7 @@ class StringOption extends ConfigOptionBase<String> {
     super.argPos,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,
@@ -46,6 +47,7 @@ class MultiStringOption extends MultiOption<String> {
     super.argAbbrev,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,
@@ -68,6 +70,7 @@ class MultiStringOption extends MultiOption<String> {
     super.argAbbrev,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,
@@ -134,6 +137,7 @@ class EnumOption<E extends Enum> extends ConfigOptionBase<E> {
     super.argPos,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,
@@ -173,6 +177,7 @@ class ComparableValueOption<V extends Comparable> extends ConfigOptionBase<V> {
     super.argPos,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,
@@ -230,6 +235,7 @@ class IntOption extends ComparableValueOption<int> {
     super.argPos,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,
@@ -279,6 +285,7 @@ class DateTimeOption extends ComparableValueOption<DateTime> {
     super.argPos,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,
@@ -397,6 +404,7 @@ class DurationOption extends ComparableValueOption<Duration> {
     super.argPos,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,
@@ -422,6 +430,7 @@ class DurationOption extends ComparableValueOption<Duration> {
     super.argPos,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,

packages/config/lib/src/config/options.dart

@@ -108,7 +108,8 @@ abstract class ValueParser<V> {
 /// 1. Named command line argument
 /// 2. Positional command line argument
 /// 3. Environment variable
-/// 4. By lookup key in configuration sources (such as files)
+/// 4. By lookup key in configuration sources (such as files).
+///    If multiple keys are specified, they are tried in order.
 /// 5. A custom callback function
 /// 6. Default value
 ///
@@ -185,7 +186,19 @@ abstract class ConfigOptionBase<V> implements OptionDefinition<V> {
   final String? argAbbrev;
   final int? argPos;
   final String? envName;
+
+  /// A single configuration source lookup key.
+  ///
+  /// For multiple sources, use [configKeys] instead, or specify both:
+  /// [configKey] is tried first, then each key in [configKeys].
   final String? configKey;
+
+  /// Configuration source lookup keys, in order of precedence.
+  ///
+  /// Keys are tried in order until a value is found.
+  /// If [configKey] is also set, it is tried first.
+  final List<String>? configKeys;
+
   final V? Function(Configuration cfg)? fromCustom;
   final V Function()? fromDefault;
   final V? defaultsTo;
@@ -208,6 +221,7 @@ abstract class ConfigOptionBase<V> implements OptionDefinition<V> {
     this.argPos,
     this.envName,
     this.configKey,
+    this.configKeys,
     this.fromCustom,
     this.fromDefault,
     this.defaultsTo,
@@ -221,6 +235,15 @@ abstract class ConfigOptionBase<V> implements OptionDefinition<V> {
     this.hide = false,
   });
 
+  /// Configuration lookup keys in order of precedence.
+  ///
+  /// Includes [configKey] if set, followed by [configKeys] if set.
+  List<String> get allConfigKeys {
+    final key = configKey;
+    final keys = configKeys;
+    return [if (key != null) key, ...?keys];
+  }
+
   V? defaultValue() {
     final df = fromDefault;
     return (df != null ? df() : defaultsTo);
@@ -310,8 +333,12 @@ abstract class ConfigOptionBase<V> implements OptionDefinition<V> {
     if (argPos != null) {
       return 'positional argument $argPos';
     }
-    if (configKey != null) {
-      return 'configuration key `$configKey`';
+    final keys = allConfigKeys;
+    if (keys.isNotEmpty) {
+      if (keys.length == 1) {
+        return 'configuration key `${keys.single}`';
+      }
+      return 'configuration keys ${keys.map((final k) => '`$k`').join(', ')}';
     }
     return _unnamedOptionString;
   }
@@ -439,9 +466,15 @@ abstract class ConfigOptionBase<V> implements OptionDefinition<V> {
     final Configuration cfg,
     final ConfigurationBroker? configBroker,
   ) {
-    final key = configKey;
-    if (configBroker == null || key == null) return null;
-    final value = configBroker.valueOrNull(key, cfg);
+    if (configBroker == null) return null;
+    final keys = allConfigKeys;
+    if (keys.isEmpty) return null;
+
+    Object? value;
+    for (final key in keys) {
+      value = configBroker.valueOrNull(key, cfg);
+      if (value != null) break;
+    }
     if (value == null) return null;
     if (value is String) {
       return OptionResolutionImpl(
@@ -536,6 +569,7 @@ class FlagOption extends ConfigOptionBase<bool> {
     super.argAbbrev,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,
@@ -628,6 +662,7 @@ class MultiOption<T> extends ConfigOptionBase<List<T>> {
     super.argAbbrev,
     super.envName,
     super.configKey,
+    super.configKeys,
     super.fromCustom,
     super.fromDefault,
     super.defaultsTo,

packages/config/pubspec.yaml

@@ -1,5 +1,5 @@
 name: config
-version: 0.9.0
+version: 0.9.1
 description: A package for parsing command-line arguments and configuration files.
 repository: https://github.com/serverpod/cli_tools
 issue_tracker: https://github.com/serverpod/cli_tools/issues