Make hasMultipleVersions a property of the description

lib/src/command/upgrade.dart

@@ -249,7 +249,7 @@ be direct 'dependencies' or 'dev_dependencies', following packages are not:
       final declaredUpgradableDependencies = [
         ...package.dependencies.values,
         ...package.devDependencies.values,
-      ].where((dep) => dep.source.hasMultipleVersions);
+      ].where((dep) => dep.description.hasMultipleVersions);
       for (final dep in declaredUpgradableDependencies) {
         final resolvedPackage = resolvedPackages[dep.name]!;
         if (!toUpgrade.contains(dep.name)) {

lib/src/package_name.dart

@@ -174,7 +174,7 @@ class PackageRange {
   bool get _showVersionConstraint {
     if (isRoot) return false;
     if (!constraint.isAny) return true;
-    return description.source.hasMultipleVersions;
+    return description.hasMultipleVersions;
   }
 
   /// Returns a copy of `this` with the same semantics, but with a `^`-style

lib/src/solver/version_solver.dart

@@ -578,7 +578,10 @@ class VersionSolver {
     // can't be downgraded.
     if (_type == SolveType.downgrade) {
       final locked = _lockFile.packages[package];
-      if (locked != null && !locked.source.hasMultipleVersions) return locked;
+      if (locked != null &&
+          !locked.description.description.hasMultipleVersions) {
+        return locked;
+      }
     }
 
     if (_unlock.isEmpty || _unlock.contains(package)) return null;

lib/src/source.dart

@@ -51,12 +51,6 @@ abstract class Source {
   /// all sources.
   String get name;
 
-  /// Whether this source can choose between multiple versions of the same
-  /// package during version solving.
-  ///
-  /// Defaults to `false`.
-  bool get hasMultipleVersions => false;
-
   /// Parses a [PackageRef] from a name and a user-provided [description].
   ///
   /// When a [Pubspec] is parsed, it reads in the description for each
@@ -190,6 +184,11 @@ abstract class Source {
 /// with a version constraint.
 abstract class Description {
   Source get source;
+
+  /// Whether the source can choose between multiple versions of this
+  /// package during version solving.
+  bool get hasMultipleVersions;
+
   Object? serializeForPubspec({
     required String? containingDir,
     required LanguageVersion languageVersion,

lib/src/source/git.dart

@@ -32,8 +32,6 @@ class GitSource extends CachedSource {
 
   @override
   final name = 'git';
-  @override
-  final hasMultipleVersions = true;
 
   @override
   PackageRef parseRef(
@@ -343,42 +341,56 @@ class GitSource extends CachedSource {
     return await _pool.withResource(() async {
       await _ensureRepoCache(description, cache);
       final path = _repoCachePath(description, cache);
-      final List<String> revisions;
+      final result = <PackageId>[];
       if (description.tagPattern case final String tagPattern) {
-        revisions = await _listRevisionsWithTagPattern(path, tagPattern);
+        final revisions = await _listRevisionsWithTagPattern(path, tagPattern);
+        final seenVersions = <Version, String>{};
+        for (final revision in revisions) {
+          final Pubspec pubspec;
+          try {
+            pubspec = await _describeUncached(ref, revision, cache);
+            result.add(
+              PackageId(
+                ref.name,
+                pubspec.version,
+                ResolvedGitDescription(description, revision),
+              ),
+            );
+          } on Exception catch (e) {
+            log.fine('No mathcing pubspec at $revision, $e');
+            continue;
+          }
+          final prev = seenVersions[pubspec.version];
+
+          if (prev != null) {
+            log.fine(
+              'Repeated version ${pubspec.version} of ${ref.name} '
+              'at $revision and $prev',
+            );
+          }
+          seenVersions[pubspec.version] = revision;
+        }
+        return result;
       } else {
-        revisions = [await _firstRevision(path, description.ref)];
-      }
+        final revision = await _firstRevision(path, description.ref);
 
-      final result = <PackageId>[];
-      final seenVersions = <Version, String>{};
-      for (final revision in revisions) {
         final Pubspec pubspec;
-        try {
-          pubspec = await _describeUncached(ref, revision, cache);
-        } on Exception {
-          log.fine(
-            'Found no valid pubspec of ${ref.name} at $revision, ignoring,',
-          );
-          continue;
-        }
-        final prev = seenVersions[pubspec.version];
-        if (prev != null) {
-          log.fine(
-            'Repeated version ${pubspec.version} of ${ref.name} '
-            'at $revision and $prev',
-          );
-        }
-        seenVersions[pubspec.version] = revision;
+        pubspec = await _describeUncached(ref, revision, cache);
         result.add(
           PackageId(
             ref.name,
             pubspec.version,
             ResolvedGitDescription(description, revision),
           ),
         );
+        return [
+          PackageId(
+            ref.name,
+            pubspec.version,
+            ResolvedGitDescription(description, revision),
+          ),
+        ];
       }
-      return result;
     });
   }
 
@@ -950,6 +962,9 @@ class GitDescription extends Description {
     }
     return p.prettyUri(url);
   }
+
+  @override
+  bool get hasMultipleVersions => tagPattern != null;
 }
 
 class ResolvedGitDescription extends ResolvedDescription {
@@ -979,7 +994,7 @@ class ResolvedGitDescription extends ResolvedDescription {
     return {
       'url': url,
       'ref': description.ref,
-      'tag_pattern': description.tagPattern,
+      if (description.tagPattern != null) 'tag_pattern': description.tagPattern,
       'resolved-ref': resolvedRef,
       'path': description.path,
     };

lib/src/source/hosted.dart

@@ -127,8 +127,6 @@ class HostedSource extends CachedSource {
 
   @override
   final name = 'hosted';
-  @override
-  final hasMultipleVersions = true;
 
   static String pubDevUrl = 'https://pub.dev';
   static String pubDartlangUrl = 'https://pub.dartlang.org';
@@ -1820,6 +1818,9 @@ class HostedDescription extends Description {
 
   @override
   HostedSource get source => HostedSource.instance;
+
+  @override
+  bool get hasMultipleVersions => true;
 }
 
 class ResolvedHostedDescription extends ResolvedDescription {

lib/src/source/path.dart

@@ -300,6 +300,9 @@ class PathDescription extends Description {
 
   @override
   int get hashCode => canonicalize(path).hashCode;
+
+  @override
+  bool get hasMultipleVersions => false;
 }
 
 class ResolvedPathDescription extends ResolvedDescription {

lib/src/source/root.dart

@@ -121,4 +121,7 @@ class RootDescription extends Description {
 
   @override
   int get hashCode => 'root'.hashCode;
+
+  @override
+  bool get hasMultipleVersions => false;
 }

lib/src/source/sdk.dart

@@ -188,6 +188,9 @@ class SdkDescription extends Description {
   bool operator ==(Object other) {
     return other is SdkDescription && other.sdk == sdk;
   }
+
+  @override
+  bool get hasMultipleVersions => false;
 }
 
 class ResolvedSdkDescription extends ResolvedDescription {

lib/src/source/unknown.dart

@@ -113,6 +113,9 @@ class UnknownDescription extends Description {
 
   @override
   int get hashCode => Object.hash(source.name, json.encode(description));
+
+  @override
+  bool get hasMultipleVersions => false;
 }
 
 class ResolvedUnknownDescription extends ResolvedDescription {