Remove support for .packages files.

Simplify API which no longer needs to support two files.
(Replaces two existing functions with different ones.
The old methods are retained as deprecated, and will be
removed in a future release.)

Adds `@sealed` to model classes in anticipation of making
them `final` or `sealed` classes in the future.

Add tool to query the package configuration for a file or directory:
`bin/package_config_of.dart PATH`.

Author: lrhn

pkgs/package_config/CHANGELOG.md

@@ -1,24 +1,31 @@
-## 3.0.0-wip
+## 2.3.0-wip
 
 - Removes support for the `.packages` file.
   The Dart SDK no longer supports that file, and no new `.packages` files
   will be generated.
+  Since the SDK requirement for this package is above 3.0.0,
+  no supporting SDK can use or generate `.packages`.
 
-- **Breaking change**
-  Simplifies API that no longer needs to support two separate files.
+- Simplifies API that no longer needs to support two separate files.
   - Renamed `readAnyConfigFile` to `readConfigFile`, and removed
     the `preferNewest` parameter.
   - Same for `readAnyConfigFileUri` which becomes `readConfigFileUri`.
+  - Old functions still exists as deprecated, forwarding to the new
+    functions without the `preferNewest` argument.
 
-  Also makes `PackageConfig`, `Package` and `LanguageVersion` final classes.
+  Also makes `PackageConfig`, `Package` and `LanguageVersion` `@sealed` classes,
+  in preparation for making them `final` in a future update.
 
 - Adds `PackageConfig.minVersion` to complement `.maxVersion`.
   Currently both are `2`.
 
-- Adds relational operators to `LanguageVersion`.
+## 2.2.0
 
-- Includes correct parameter names in errors when validating
-  the `major` and `minor` versions in the `LanguageVersion()` constructor.
+- Add relational operators to `LanguageVersion` with extension methods
+  exported under `LanguageVersionRelationalOperators`.
+
+- Include correct parameter names in errors when validating
+  the `major` and `minor` versions in the `LanguageVersion.new` constructor.
 
 ## 2.1.1
 

pkgs/package_config/lib/package_config.dart

@@ -41,7 +41,7 @@ Future<PackageConfig> loadAnyPackageConfig(File file,
 /// Reads a specific package configuration URI.
 ///
 /// The file of the URI must exist, be readable,
-/// and be  a valid `package_config.json` file.
+/// and be a valid `package_config.json` file.
 ///
 /// If [loader] is provided, URIs are loaded using that function.
 /// The future returned by the loader must complete with a [Uint8List]
@@ -54,7 +54,7 @@ Future<PackageConfig> loadAnyPackageConfig(File file,
 /// As such, it may throw any error that [loader] throws.
 ///
 /// If no [loader] is supplied, a default loader is used which
-/// only accepts `file:`,  `http:` and `https:` URIs,
+/// only accepts `file:`, `http:` and `https:` URIs,
 /// and which uses the platform file system and HTTP requests to
 /// fetch file content. The default loader never throws because
 /// of an I/O issue, as long as the location URIs are valid.

pkgs/package_config/lib/package_config_types.dart

@@ -17,5 +17,6 @@ export 'src/package_config.dart'
     show
         InvalidLanguageVersion,
         LanguageVersion,
+        LanguageVersionRelationalOperators,
         Package,
         PackageConfig;

pkgs/package_config/lib/src/package_config.dart

@@ -4,6 +4,8 @@
 
 import 'dart:typed_data';
 
+import 'package:meta/meta.dart' show sealed;
+
 import 'errors.dart';
 import 'package_config_json.dart';
 import 'util.dart';
@@ -15,7 +17,8 @@ import 'util.dart';
 /// More members may be added to this class in the future,
 /// so classes outside of this package must not implement [PackageConfig]
 /// or any subclass of it.
-abstract final class PackageConfig {
+@sealed
+abstract class PackageConfig {
   /// The lowest configuration version currently supported.
   static const int minVersion = 2;
 
@@ -213,7 +216,8 @@ abstract final class PackageConfig {
 }
 
 /// Configuration data for a single package.
-abstract final class Package {
+@sealed
+abstract class Package {
   /// Creates a package with the provided properties.
   ///
   /// The [name] must be a valid package name.
@@ -301,7 +305,8 @@ abstract final class Package {
 /// If errors during parsing are handled using an `onError` handler,
 /// then an *invalid* language version may be represented by an
 /// [InvalidLanguageVersion] object.
-abstract final class LanguageVersion implements Comparable<LanguageVersion> {
+@sealed
+abstract class LanguageVersion implements Comparable<LanguageVersion> {
   /// The maximal value allowed by [major] and [minor] values;
   static const int maxValue = 0x7FFFFFFF;
 
@@ -368,40 +373,6 @@ abstract final class LanguageVersion implements Comparable<LanguageVersion> {
   @override
   int compareTo(LanguageVersion other);
 
-  /// Whether this language version is less than [other].
-  ///
-  /// If either version being compared is an [InvalidLanguageVersion],
-  /// a [StateError] is thrown. Verify versions are valid before comparing them.
-  ///
-  /// For details on how valid language versions are compared,
-  /// check out [LanguageVersion.compareTo].
-  bool operator <(LanguageVersion other);
-
-  /// Whether this language version is less than or equal to [other].
-  ///
-  /// If either version being compared is an [InvalidLanguageVersion],
-  /// a [StateError] is thrown. Verify versions are valid before comparing them.
-  ///
-  /// For details on how valid language versions are compared,
-  /// check out [LanguageVersion.compareTo].
-  bool operator <=(LanguageVersion other);
-
-  /// Whether this language version is greater than [other].
-  ///
-  /// Neither version being compared must be  an [InvalidLanguageVersion].
-  ///
-  /// For details on how valid language versions are compared,
-  /// check out [LanguageVersion.compareTo].
-  bool operator >(LanguageVersion other);
-
-  /// Whether this language version is greater than or equal to [other].
-  ///
-  /// Neither version being compared must be  an [InvalidLanguageVersion].
-  ///
-  /// For details on how valid language versions are compared,
-  /// check out [LanguageVersion.compareTo].
-  bool operator >=(LanguageVersion other);
-
   /// Valid language versions with the same [major] and [minor] values are
   /// equal.
   ///
@@ -428,7 +399,8 @@ abstract final class LanguageVersion implements Comparable<LanguageVersion> {
 /// which did not throw on an error.
 /// The caller which provided the `onError` handler which was called
 /// should be prepared to encounter invalid values.
-abstract final class InvalidLanguageVersion implements LanguageVersion {
+@sealed
+abstract class InvalidLanguageVersion implements LanguageVersion {
   /// The value -1 for an invalid language version.
   @override
   int get major;
@@ -449,14 +421,83 @@ abstract final class InvalidLanguageVersion implements LanguageVersion {
   String toString();
 }
 
+/// Relational operators for [LanguageVersion].
+///
+/// Compares valid versions with [LanguageVersion.compareTo],
+/// and rejects invalid versions.
+///
+/// Versions should be verified as valid before using them.
+extension LanguageVersionRelationalOperators on LanguageVersion {
+  /// Whether this language version is less than [other].
+  ///
+  /// Neither version being compared must be an [InvalidLanguageVersion].
+  ///
+  /// For details on how valid language versions are compared,
+  /// check out [LanguageVersion.compareTo].
+  bool operator <(LanguageVersion other) {
+    // Throw an error if comparing an invalid language version.
+    if (this is InvalidLanguageVersion) _throwThisInvalid();
+    if (other is InvalidLanguageVersion) _throwOtherInvalid();
+    return compareTo(other) < 0;
+  }
+
+  /// Whether this language version is less than or equal to [other].
+  ///
+  /// Neither version being compared must be an [InvalidLanguageVersion].
+  ///
+  /// For details on how valid language versions are compared,
+  /// check out [LanguageVersion.compareTo].
+  bool operator <=(LanguageVersion other) {
+    // Throw an error if comparing an invalid language version.
+    if (this is InvalidLanguageVersion) _throwThisInvalid();
+    if (other is InvalidLanguageVersion) _throwOtherInvalid();
+    return compareTo(other) <= 0;
+  }
+
+  /// Whether this language version is greater than [other].
+  ///
+  /// Neither version being compared must be an [InvalidLanguageVersion].
+  ///
+  /// For details on how valid language versions are compared,
+  /// check out [LanguageVersion.compareTo].
+  bool operator >(LanguageVersion other) {
+    // Throw an error if comparing an invalid language version.
+    if (this is InvalidLanguageVersion) _throwThisInvalid();
+    if (other is InvalidLanguageVersion) _throwOtherInvalid();
+    return compareTo(other) > 0;
+  }
+
+  /// Whether this language version is greater than or equal to [other].
+  ///
+  /// If either version being compared is an [InvalidLanguageVersion],
+  /// a [StateError] is thrown. Verify versions are valid before comparing them.
+  ///
+  /// For details on how valid language versions are compared,
+  /// check out [LanguageVersion.compareTo].
+  bool operator >=(LanguageVersion other) {
+    // Throw an error if comparing an invalid language version.
+    if (this is InvalidLanguageVersion) _throwThisInvalid();
+    if (other is InvalidLanguageVersion) _throwOtherInvalid();
+    return compareTo(other) >= 0;
+  }
+
+  static Never _throwThisInvalid() => throw UnsupportedError(
+      'Can\'t compare an invalid language version to another language version. '
+      'Verify language versions are valid before use.');
+  static Never _throwOtherInvalid() => throw UnsupportedError(
+      'Can\'t compare a language version to an invalid language version. '
+      'Verify language versions are valid before use.');
+}
+
 // --------------------------------------------------------------------
-// Implementation of interfaces.
+// Implementation of interfaces. Not exported by top-level libraries.
 
 const bool _disallowPackagesInsidePackageUriRoot = false;
 
 // Implementations of the main data types exposed by the API of this package.
 
-final class SimplePackageConfig implements PackageConfig {
+@sealed
+class SimplePackageConfig implements PackageConfig {
   @override
   final int version;
   final Map<String, Package> _packages;
@@ -620,7 +661,8 @@ final class SimplePackageConfig implements PackageConfig {
 }
 
 /// Configuration data for a single package.
-final class SimplePackage implements Package {
+@sealed
+class SimplePackage implements Package {
   @override
   final String name;
   @override
@@ -779,7 +821,8 @@ LanguageVersion parseLanguageVersion(
   return SimpleLanguageVersion(major, minor, source);
 }
 
-abstract final class _SimpleLanguageVersionBase implements LanguageVersion {
+@sealed
+abstract class _SimpleLanguageVersionBase implements LanguageVersion {
   @override
   int compareTo(LanguageVersion other) {
     var result = major - other.major;
@@ -788,7 +831,8 @@ abstract final class _SimpleLanguageVersionBase implements LanguageVersion {
   }
 }
 
-final class SimpleLanguageVersion extends _SimpleLanguageVersionBase {
+@sealed
+class SimpleLanguageVersion extends _SimpleLanguageVersionBase {
   @override
   final int major;
   @override
@@ -805,66 +849,10 @@ final class SimpleLanguageVersion extends _SimpleLanguageVersionBase {
 
   @override
   String toString() => _source ??= '$major.$minor';
-
-  /// Whether this language version is less than [other].
-  ///
-  /// Neither version being compared must be  an [InvalidLanguageVersion].
-  ///
-  /// For details on how valid language versions are compared,
-  /// check out [LanguageVersion.compareTo].
-  @override
-  bool operator <(LanguageVersion other) {
-    // Throw an error if comparing with an invalid language version.
-    if (other is InvalidLanguageVersion) _throwOtherInvalid();
-
-    return compareTo(other) < 0;
-  }
-
-  /// Whether this language version is less than or equal to [other].
-  ///
-  /// Neither version being compared must be  an [InvalidLanguageVersion].
-  ///
-  /// For details on how valid language versions are compared,
-  /// check out [LanguageVersion.compareTo].
-  @override
-  bool operator <=(LanguageVersion other) {
-    // Throw an error if comparing with an invalid language version.
-    if (other is InvalidLanguageVersion) _throwOtherInvalid();
-    return compareTo(other) <= 0;
-  }
-
-  /// Whether this language version is greater than [other].
-  ///
-  /// Neither version being compared must be  an [InvalidLanguageVersion].
-  ///
-  /// For details on how valid language versions are compared,
-  /// check out [LanguageVersion.compareTo].
-  @override
-  bool operator >(LanguageVersion other) {
-    if (other is InvalidLanguageVersion) _throwOtherInvalid();
-    return compareTo(other) > 0;
-  }
-
-  /// Whether this language version is greater than or equal to [other].
-  ///
-  /// If either version being compared is an [InvalidLanguageVersion],
-  /// a [StateError] is thrown. Verify versions are valid before comparing them.
-  ///
-  /// For details on how valid language versions are compared,
-  /// check out [LanguageVersion.compareTo].
-  @override
-  bool operator >=(LanguageVersion other) {
-    // Throw an error if comparing with an invalid language version.
-    if (other is InvalidLanguageVersion) _throwOtherInvalid();
-    return compareTo(other) >= 0;
-  }
-
-  static Never _throwOtherInvalid() => throw StateError(
-      'Can\'t compare a language version to an invalid language version. '
-      'Verify language versions are valid after parsing.');
 }
 
-final class SimpleInvalidLanguageVersion extends _SimpleLanguageVersionBase
+@sealed
+class SimpleInvalidLanguageVersion extends _SimpleLanguageVersionBase
     implements InvalidLanguageVersion {
   final String? _source;
   SimpleInvalidLanguageVersion(this._source);
@@ -873,32 +861,8 @@ final class SimpleInvalidLanguageVersion extends _SimpleLanguageVersionBase
   @override
   int get minor => -1;
 
-  @override
-  bool operator <(LanguageVersion other) {
-    _throwThisInvalid();
-  }
-
-  @override
-  bool operator <=(LanguageVersion other) {
-    _throwThisInvalid();
-  }
-
-  @override
-  bool operator >(LanguageVersion other) {
-    _throwThisInvalid();
-  }
-
-  @override
-  bool operator >=(LanguageVersion other) {
-    _throwThisInvalid();
-  }
-
   @override
   String toString() => _source!;
-
-  static Never _throwThisInvalid() => throw StateError(
-      'Can\'t compare an invalid language version to another language version. '
-      'Verify language versions are valid after parsing.');
 }
 
 abstract class PackageTree {

pkgs/package_config/pubspec.yaml

@@ -1,15 +1,16 @@
 name: package_config
-version: 3.0.0-wip
+version: 2.3.0-wip
 description: Support for reading and writing Dart Package Configuration files.
 repository: https://github.com/dart-lang/tools/tree/main/pkgs/package_config
 issue_tracker: https://github.com/dart-lang/tools/labels/package%3Apackage_config
 
 environment:
-  sdk: ^3.4.0
+  sdk: ^3.7.0
 
 dependencies:
+  meta: ^1.15.0
   path: ^1.8.0
 
 dev_dependencies:
-  dart_flutter_team_lints: ^3.1.0
+  dart_flutter_team_lints: ^3.4.0
   test: ^1.16.0