feat: support listing cycles in dependencies (#491)

docs/commands/list.mdx

@@ -69,3 +69,11 @@ Show dependency graph in Graphviz DOT language. Defaults to `false`.
 ```bash
 melos list --gviz
 ```
+
+## --cycles
+
+Find cycles in package dependencies in the workspace.
+
+```bash
+melos list --cycles
+```

packages/melos/lib/src/command_runner/list.dart

@@ -56,6 +56,11 @@ class ListCommand extends MelosCommand {
       negatable: false,
       help: 'Show dependency graph in Graphviz DOT language.',
     );
+    argParser.addFlag(
+      'cycles',
+      negatable: false,
+      help: 'Find cycles in package dependencies in the workspace.',
+    );
   }
 
   @override
@@ -80,6 +85,7 @@ class ListCommand extends MelosCommand {
     final relative = argResults!['relative'] as bool;
     final graph = argResults!['graph'] as bool;
     final gviz = argResults!['gviz'] as bool;
+    final cycles = argResults!['cycles'] as bool;
 
     final melos = Melos(logger: logger, config: config);
 
@@ -89,6 +95,7 @@ class ListCommand extends MelosCommand {
     if (json) kind = ListOutputKind.json;
     if (graph) kind = ListOutputKind.graph;
     if (gviz) kind = ListOutputKind.gviz;
+    if (cycles) kind = ListOutputKind.cycles;
 
     return melos.list(
       long: long,

packages/melos/lib/src/commands/exec.dart

@@ -112,7 +112,9 @@ mixin _ExecMixin on _Melos {
     final sortedPackages = packages.toList(growable: false);
 
     if (orderDependents) {
-      sortPackagesTopologically(sortedPackages);
+      // TODO: This is not really the right way to do this. Cyclic dependencies
+      // are handled in a way that is specific for publishing.
+      sortPackagesForPublishing(sortedPackages);
     }
 
     final packageResults = Map.fromEntries(

packages/melos/lib/src/commands/list.dart

@@ -1,7 +1,7 @@
 part of 'runner.dart';
 
 // TODO find better names
-enum ListOutputKind { json, parsable, graph, gviz, column }
+enum ListOutputKind { json, parsable, graph, gviz, column, cycles }
 
 mixin _ListMixin on _Melos {
   Future<void> list({
@@ -36,6 +36,8 @@ mixin _ListMixin on _Melos {
         );
       case ListOutputKind.gviz:
         return _listGviz(workspace);
+      case ListOutputKind.cycles:
+        return _listCyclesInDependencies(workspace);
     }
   }
 
@@ -256,4 +258,20 @@ mixin _ListMixin on _Melos {
 
     logger.stdout(buffer.join('\n'));
   }
+
+  Future<void> _listCyclesInDependencies(MelosWorkspace workspace) async {
+    final cycles = findCyclicDependenciesInWorkspace(
+      workspace.filteredPackages.values.toList(),
+    );
+
+    if (cycles.isEmpty) {
+      logger.stdout('🎉 No cycles in dependencies found.');
+    } else {
+      logger.stdout('🚨 ${cycles.length} cycles in dependencies found:');
+      for (final cycle in cycles) {
+        logger
+            .stdout('[ ${cycle.map((package) => package.name).join(' -> ')} ]');
+      }
+    }
+  }
 }

packages/melos/lib/src/commands/publish.dart

@@ -48,7 +48,7 @@ mixin _PublishMixin on _ExecMixin {
       return;
     }
 
-    sortPackagesTopologically(unpublishedPackages);
+    sortPackagesForPublishing(unpublishedPackages);
 
     logger
       ..newLine()

packages/melos/lib/src/common/utils.dart

@@ -22,6 +22,7 @@ import 'dart:isolate';
 
 import 'package:ansi_styles/ansi_styles.dart';
 import 'package:args/args.dart';
+import 'package:collection/collection.dart' hide stronglyConnectedComponents;
 import 'package:graphs/graphs.dart';
 import 'package:path/path.dart' as p;
 import 'package:prompts/prompts.dart' as prompts;
@@ -577,26 +578,56 @@ bool isPubSubcommand({required MelosWorkspace workspace}) {
   }
 }
 
-/// Sorts packages in topological order so they may be published in the order
-/// they're sorted.
+/// Sorts [packages] in topological order so they can be published without
+/// errors.
 ///
 /// Packages with inter-dependencies cannot be topologically sorted and will
-/// remain unchanged.
-void sortPackagesTopologically(List<Package> packages) {
-  final packageNames = packages.map((el) => el.name).toList();
+/// be sorted by name length. This is a heuristic to better handle cyclic
+/// dependencies in federated plugins.
+void sortPackagesForPublishing(List<Package> packages) {
+  final packageNames = packages.map((package) => package.name).toList();
   final graph = <String, Iterable<String>>{
     for (var package in packages)
-      package.name: package.dependencies.where(packageNames.contains),
+      package.name: [
+        ...package.dependencies.where(packageNames.contains),
+        ...package.devDependencies.where(packageNames.contains)
+      ],
   };
-  try {
-    final ordered = topologicalSort(graph.keys, (key) => graph[key]!);
-    packages.sort((a, b) {
-      // `ordered` is in reverse ordering to our desired publish precedence.
-      return ordered.indexOf(b.name).compareTo(ordered.indexOf(a.name));
-    });
-  } on CycleException<String> {
-    // Cannot sort packages with inter-dependencies. Leave as-is.
-  }
+  final ordered =
+      stronglyConnectedComponents(graph.keys, (package) => graph[package]!)
+          .expand(
+            (component) => component.sortedByCompare(
+              (package) => package.length,
+              (a, b) => b - a,
+            ),
+          )
+          .toList();
+
+  packages.sort((a, b) {
+    return ordered.indexOf(a.name).compareTo(ordered.indexOf(b.name));
+  });
+}
+
+/// Returns a list of dependency cycles between [packages], taking into
+/// account only workspace dependencies.
+///
+/// All dependencies between packages in the workspace are considered, including
+/// `dev_dependencies` and `dependency_overrides`.
+List<List<Package>> findCyclicDependenciesInWorkspace(List<Package> packages) {
+  return stronglyConnectedComponents(
+    packages,
+    (package) => package.allDependenciesInWorkspace.values,
+  ).where((component) => component.length > 1).map((component) {
+    try {
+      topologicalSort(
+        component,
+        (package) => package.allDependenciesInWorkspace.values,
+      );
+    } on CycleException<Package> catch (error) {
+      return error.cycle;
+    }
+    throw StateError('Expected a cycle to be found.');
+  }).toList();
 }
 
 /// Given a workspace and package, this assembles the correct command to run pub

packages/melos/lib/src/workspace_configs.dart

@@ -602,7 +602,7 @@ class VersionCommandConfigs {
 
     if (changelogsYaml != null) {
       for (var i = 0; i < changelogsYaml.length; i++) {
-        final entry = changelogsYaml[i]! as Map<String, Object?>;
+        final entry = changelogsYaml[i]! as Map<Object?, Object?>;
 
         final path = assertKeyIsA<String>(
           map: entry,

packages/melos/test/commands/publish_test.dart

@@ -8,7 +8,7 @@ import 'package:test/scaffolding.dart';
 void main() {
   group('publish', () {
     group('sort packages', () {
-      test('', () {
+      test('wo/ cyclic dependencies', () {
         //     b
         //   /   \
         // a       d
@@ -24,7 +24,7 @@ void main() {
           _dummyPackage('e', deps: ['f']),
         ]..shuffle();
         final packageNames = packages.map((el) => el.name).toList();
-        sortPackagesTopologically(packages);
+        sortPackagesForPublishing(packages);
 
         final published = <String>{};
         for (final package in packages) {
@@ -44,7 +44,7 @@ void main() {
           _dummyPackage('b', deps: ['a']),
         ];
         expect(
-          () => sortPackagesTopologically(packages),
+          () => sortPackagesForPublishing(packages),
           returnsNormally,
         );
       });