Detect cycle between root project and transitive dependency in new dependency resolver

src/NuGet.Core/NuGet.Commands/RestoreCommand/DependencyGraphResolver.DependencyGraphItemIndexer.cs

@@ -86,6 +86,16 @@ public sealed class DependencyGraphItemIndexer
             /// </summary>
             private LibraryRangeIndex _nextLibraryRangeIndex = LibraryRangeIndex.Project + 1;
 
+            /// <summary>
+            /// Initializes a new instance of the <see cref="DependencyGraphItemIndexer" /> class.
+            /// </summary>
+            /// <param name="libraryDependency">A <see cref="LibraryDependency" /> representing the root project.</param>
+            public DependencyGraphItemIndexer(LibraryDependency libraryDependency)
+            {
+                _libraryDependencyTable.TryAdd(libraryDependency.Name, LibraryDependencyIndex.Project);
+                _libraryRangeTable.TryAdd(libraryDependency.LibraryRange, LibraryRangeIndex.Project);
+            }
+
             /// <summary>
             /// Indexes a <see cref="LibraryDependency" /> and returns a <see cref="LibraryDependencyIndex" /> associated with the its name.
             /// </summary>

src/NuGet.Core/NuGet.Commands/RestoreCommand/DependencyGraphResolver.cs

@@ -45,7 +45,7 @@ internal sealed partial class DependencyGraphResolver
         /// <summary>
         /// A <see cref="DependencyGraphItemIndexer" /> used to index dependency graph items.
         /// </summary>
-        private readonly DependencyGraphItemIndexer _indexingTable = new();
+        private readonly DependencyGraphItemIndexer _indexingTable;
 
         /// <summary>
         /// A <see cref="RestoreCollectorLogger" /> used for logging.
@@ -67,6 +67,11 @@ internal sealed partial class DependencyGraphResolver
         /// </summary>
         private readonly TelemetryActivity _telemetryActivity;
 
+        /// <summary>
+        /// Represents the root project as a <see cref="LibraryDependency" />.
+        /// </summary>
+        private readonly LibraryDependency _rootProjectLibraryDependency;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="DependencyGraphResolver" /> class.
         /// </summary>
@@ -78,6 +83,16 @@ public DependencyGraphResolver(RestoreCollectorLogger logger, RestoreRequest res
             _logger = logger;
             _request = restoreRequest;
             _telemetryActivity = telemetryActivity;
+
+            _rootProjectLibraryDependency = new LibraryDependency(
+                new LibraryRange()
+                {
+                    Name = _request.Project.Name,
+                    VersionRange = new VersionRange(_request.Project.Version),
+                    TypeConstraint = LibraryDependencyTarget.Project | LibraryDependencyTarget.ExternalProject
+                });
+
+            _indexingTable = new DependencyGraphItemIndexer(_rootProjectLibraryDependency);
         }
 
         /// <summary>
@@ -133,15 +148,6 @@ public async Task<ValueTuple<bool, List<RestoreTargetGraph>, RuntimeGraph>> Reso
             // Stores the list of download results which contribute to the overall success of the graph resolution
             DownloadDependencyResolutionResult[]? downloadDependencyResolutionResults = default;
 
-            // A LibraryDependency representing the root of the graph which is the project itself
-            LibraryDependency mainProjectDependency = new(
-                new LibraryRange()
-                {
-                    Name = _request.Project.Name,
-                    VersionRange = new VersionRange(_request.Project.Version),
-                    TypeConstraint = LibraryDependencyTarget.Project | LibraryDependencyTarget.ExternalProject
-                });
-
             // Create the list of framework/runtime pairs to resolve graphs for.  This method returns the pairs in order with the target framework pairs without runtime identifiers come first
             List<FrameworkRuntimePair> projectFrameworkRuntimePairs = RestoreCommand.CreateFrameworkRuntimePairs(_request.Project, runtimeIds: RequestRuntimeUtility.GetRestoreRuntimes(_request));
 
@@ -182,12 +188,12 @@ public async Task<ValueTuple<bool, List<RestoreTargetGraph>, RuntimeGraph>> Reso
                 // Create a DependencyGraphItem representing the root project to add to the queue for processing
                 DependencyGraphItem rootProjectDependencyGraphItem = new()
                 {
-                    LibraryDependency = mainProjectDependency,
+                    LibraryDependency = _rootProjectLibraryDependency,
                     LibraryDependencyIndex = LibraryDependencyIndex.Project,
                     LibraryRangeIndex = LibraryRangeIndex.Project,
                     Suppressions = new HashSet<LibraryDependencyIndex>(),
                     FindLibraryTask = ResolverUtility.FindLibraryCachedAsync(
-                        mainProjectDependency.LibraryRange,
+                        _rootProjectLibraryDependency.LibraryRange,
                         frameworkRuntimePair.Framework,
                         runtimeIdentifier: string.IsNullOrWhiteSpace(frameworkRuntimePair.RuntimeIdentifier) ? null : frameworkRuntimePair.RuntimeIdentifier,
                         context,
@@ -1289,6 +1295,12 @@ .. chosenResolvedItem.Suppressions
                     LibraryDependency childDependency = chosenResolvedItem.Item.Data.Dependencies[i];
                     LibraryDependencyIndex childLibraryDependencyIndex = chosenResolvedItem.GetDependencyIndexForDependencyAt(i);
 
+                    if (childLibraryDependencyIndex == LibraryDependencyIndex.Project)
+                    {
+                        // Skip any dependency with the same name as the project
+                        continue;
+                    }
+
                     HashSet<LibraryDependency>? runtimeDependencies = default;
 
                     // Evaluate the runtime dependencies if any

test/NuGet.Core.FuncTests/NuGet.Commands.FuncTest/RestoreCommand_AlgorithmEquivalencyTests.cs

@@ -52,6 +52,56 @@ public async Task RestoreCommand_HigherLevelSuppressionsWin_VerifiesEquivalency(
             result.LockFile.Targets[0].Libraries[2].Name.Should().Be("X");
         }
 
+        // LightGbm (project) -> Microsoft.ML.LightGbm -> LightGBM 2.0.0 (package)
+        // This should result in an error with the cycle
+        [Fact]
+        public async Task RestoreCommand_WithCycleContainingProject_FailsAndLogsMessage()
+        {
+            // Arrange
+            using var pathContext = new SimpleTestPathContext();
+            await SimpleTestPackageUtility.CreateFolderFeedV3Async(
+                pathContext.PackageSource,
+                PackageSaveMode.Defaultv3,
+                new SimpleTestPackageContext("Microsoft.ML.LightGbm", "4.0.1")
+                {
+                    Dependencies =
+                    [
+                        new SimpleTestPackageContext("LightGBM", "3.3.5"),
+                    ]
+                });
+
+            PackageSpec projectSpec = ProjectTestHelpers.GetPackageSpecWithProjectNameAndSpec(
+                "LightGbm",
+                pathContext.SolutionRoot,
+                @"
+                {
+                    ""frameworks"": {
+                    ""net472"": {
+                        ""dependencies"": {
+                                ""Microsoft.ML.LightGbm"": ""4.0.1""
+                        }
+                    }
+                    }
+                }");
+
+            // Act & Assert
+            (var result, _) = await ValidateRestoreAlgorithmEquivalency(pathContext, projectSpec);
+
+            // Additional assert
+            result.Success.Should().BeFalse();
+
+            result.LogMessages.Should().HaveCount(1);
+
+            IAssetsLogMessage logMessage = result.LogMessages.Single();
+            logMessage.Code.Should().Be(NuGetLogCode.NU1108);
+            logMessage.Message.Should().Contain("LightGbm -> Microsoft.ML.LightGbm 4.0.1 -> LightGBM (>= 3.3.5)");
+
+            result.LockFile.Targets.Should().HaveCount(1);
+            result.LockFile.Targets[0].Libraries.Should().HaveCount(1);
+            result.LockFile.Targets[0].Libraries[0].Name.Should().Be("Microsoft.ML.LightGbm");
+            result.LockFile.Targets[0].Libraries[0].Version.Should().Be(new NuGetVersion("4.0.1"));
+        }
+
         // Project 1 -> a 1.0.0 -> b 1.0.0
         //           -> b 2.0.0
         // Does not install b 1.0.0 since it is eclipsed by a direct package reference