Fix unresolved P2P references losing Configuration in solution builds

documentation/wiki/ChangeWaves.md

@@ -34,6 +34,7 @@ Change wave checks around features will be removed in the release that accompani
 - [TaskHostTask forwards request-level global properties (e.g. MSBuildRestoreSessionId) to out-of-proc TaskHost in -mt mode](https://github.com/dotnet/msbuild/pull/13443)
 - [Fix ShouldTreatWarningAsError in OOP TaskHost checking wrong collection (WarningsAsMessages instead of WarningsAsErrors)](https://github.com/dotnet/msbuild/issues/11952)
 - [Fix ToolTask hang when tool spawns grandchild processes that inherit stdout/stderr pipe handles](https://github.com/dotnet/msbuild/issues/2981)
+- [Unresolved project references in solution builds inherit parent Configuration and Platform instead of stripping them via GlobalPropertiesToRemove](https://github.com/dotnet/msbuild/issues/13453)
 
 ### 18.5
 - [FindUnderPath and AssignTargetPath tasks no longer throw on invalid path characters when using TaskEnvironment.GetAbsolutePath](https://github.com/dotnet/msbuild/pull/13069)

src/Tasks.UnitTests/AssignProjectConfigurationChangeWave_Tests.cs

@@ -0,0 +1,207 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Shared;
+using Microsoft.Build.Tasks;
+using Microsoft.Build.Utilities;
+using Shouldly;
+using Xunit;
+using Xunit.Abstractions;
+
+#nullable disable
+
+namespace Microsoft.Build.UnitTests
+{
+    /// <summary>
+    /// Tests for the ChangeWave 18.6 behavior change in AssignProjectConfiguration:
+    /// When project references are not found in the solution configuration blob,
+    /// they should inherit the parent's Configuration and Platform rather than
+    /// having them stripped via GlobalPropertiesToRemove.
+    /// </summary>
+    public sealed class AssignProjectConfigurationChangeWave_Tests
+    {
+        private readonly ITestOutputHelper _output;
+
+        public AssignProjectConfigurationChangeWave_Tests(ITestOutputHelper output)
+        {
+            _output = output;
+        }
+
+        /// <summary>
+        /// Verifies that when ShouldUnsetParentConfigurationAndPlatform is true,
+        /// unresolved project references do NOT get GlobalPropertiesToRemove=Configuration;Platform
+        /// set on them. This ensures child projects inherit the parent's Configuration and Platform
+        /// rather than falling back to their defaults (which breaks non-standard configuration names
+        /// like "Debug Unicode").
+        /// </summary>
+        [Fact]
+        public void UnresolvedReferencesDoNotStripConfigurationUnderChangeWave()
+        {
+            using TestEnvironment env = TestEnvironment.Create(_output);
+
+            var projectRefs = new ArrayList();
+            // This reference is NOT in the solution config → will be unresolved
+            var unresolvedRef = ResolveNonMSBuildProjectOutput_Tests.CreateReferenceItem(
+                "Utility.vcxproj",
+                "{AAAAAAAA-AAAA-AAAA-AAAA-AAAAAAAAAAAA}",
+                "{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}",
+                "Utility");
+            projectRefs.Add(unresolvedRef);
+
+            // Solution config only contains a DIFFERENT project
+            var projectConfigurations = new Hashtable();
+            projectConfigurations.Add("{BBBBBBBB-BBBB-BBBB-BBBB-BBBBBBBBBBBB}", @"Debug Unicode|x64");
+
+            string xmlString = ResolveNonMSBuildProjectOutput_Tests.CreatePregeneratedPathDoc(projectConfigurations);
+
+            MockEngine engine = new MockEngine(_output);
+            AssignProjectConfiguration task = new AssignProjectConfiguration();
+            task.BuildEngine = engine;
+            task.SolutionConfigurationContents = xmlString;
+            task.ProjectReferences = (ITaskItem[])projectRefs.ToArray(typeof(ITaskItem));
+            task.ShouldUnsetParentConfigurationAndPlatform = true;
+
+            bool result = task.Execute();
+            result.ShouldBeTrue();
+
+            // The reference should be unresolved (not in solution config)
+            task.UnassignedProjects.Length.ShouldBe(1);
+            task.AssignedProjects.Length.ShouldBe(0);
+
+            // Under ChangeWave 18.6, GlobalPropertiesToRemove should NOT include Configuration;Platform
+            ITaskItem unresolved = task.UnassignedProjects[0];
+            string globalPropertiesToRemove = unresolved.GetMetadata("GlobalPropertiesToRemove");
+            globalPropertiesToRemove.ShouldNotContain("Configuration");
+            globalPropertiesToRemove.ShouldNotContain("Platform");
+        }
+
+        /// <summary>
+        /// Verifies that when ShouldUnsetParentConfigurationAndPlatform is false,
+        /// unresolved references never had GlobalPropertiesToRemove set (this behavior
+        /// is unchanged by the ChangeWave).
+        /// </summary>
+        [Fact]
+        public void UnresolvedReferencesWithoutShouldUnsetDoNotStripConfiguration()
+        {
+            using TestEnvironment env = TestEnvironment.Create(_output);
+
+            var projectRefs = new ArrayList();
+            var unresolvedRef = ResolveNonMSBuildProjectOutput_Tests.CreateReferenceItem(
+                "Utility.vcxproj",
+                "{AAAAAAAA-AAAA-AAAA-AAAA-AAAAAAAAAAAA}",
+                "{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}",
+                "Utility");
+            projectRefs.Add(unresolvedRef);
+
+            var projectConfigurations = new Hashtable();
+            projectConfigurations.Add("{BBBBBBBB-BBBB-BBBB-BBBB-BBBBBBBBBBBB}", @"Debug Unicode|x64");
+
+            string xmlString = ResolveNonMSBuildProjectOutput_Tests.CreatePregeneratedPathDoc(projectConfigurations);
+
+            MockEngine engine = new MockEngine(_output);
+            AssignProjectConfiguration task = new AssignProjectConfiguration();
+            task.BuildEngine = engine;
+            task.SolutionConfigurationContents = xmlString;
+            task.ProjectReferences = (ITaskItem[])projectRefs.ToArray(typeof(ITaskItem));
+            task.ShouldUnsetParentConfigurationAndPlatform = false; // default for non-solution builds
+
+            bool result = task.Execute();
+            result.ShouldBeTrue();
+
+            task.UnassignedProjects.Length.ShouldBe(1);
+            ITaskItem unresolved = task.UnassignedProjects[0];
+            string globalPropertiesToRemove = unresolved.GetMetadata("GlobalPropertiesToRemove");
+            globalPropertiesToRemove.ShouldBeEmpty();
+        }
+
+        /// <summary>
+        /// Verifies that resolved references still get correct SetConfiguration and SetPlatform
+        /// metadata with configurations containing spaces.
+        /// </summary>
+        [Fact]
+        public void ResolvedReferencesPreserveSpacesInConfigurationName()
+        {
+            using TestEnvironment env = TestEnvironment.Create(_output);
+
+            var projectRefs = new ArrayList();
+            var resolvedRef = ResolveNonMSBuildProjectOutput_Tests.CreateReferenceItem(
+                "Main.vcxproj",
+                "{CCCCCCCC-CCCC-CCCC-CCCC-CCCCCCCCCCCC}",
+                "{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}",
+                "Main");
+            projectRefs.Add(resolvedRef);
+
+            // Solution config contains this project with a space in config name
+            var projectConfigurations = new Hashtable();
+            projectConfigurations.Add("{CCCCCCCC-CCCC-CCCC-CCCC-CCCCCCCCCCCC}", @"Debug Unicode|x64");
+
+            string xmlString = ResolveNonMSBuildProjectOutput_Tests.CreatePregeneratedPathDoc(projectConfigurations);
+
+            MockEngine engine = new MockEngine(_output);
+            AssignProjectConfiguration task = new AssignProjectConfiguration();
+            task.BuildEngine = engine;
+            task.SolutionConfigurationContents = xmlString;
+            task.ProjectReferences = (ITaskItem[])projectRefs.ToArray(typeof(ITaskItem));
+            task.ShouldUnsetParentConfigurationAndPlatform = true;
+
+            bool result = task.Execute();
+            result.ShouldBeTrue();
+
+            task.AssignedProjects.Length.ShouldBe(1);
+            task.UnassignedProjects.Length.ShouldBe(0);
+
+            ITaskItem resolved = task.AssignedProjects[0];
+            resolved.GetMetadata("SetConfiguration").ShouldBe("Configuration=Debug Unicode");
+            resolved.GetMetadata("SetPlatform").ShouldBe("Platform=x64");
+            resolved.GetMetadata("Configuration").ShouldBe("Debug Unicode");
+            resolved.GetMetadata("Platform").ShouldBe("x64");
+        }
+
+        /// <summary>
+        /// Verifies that existing GlobalPropertiesToRemove metadata on an unresolved reference
+        /// is preserved (not appended to) under ChangeWave 18.6.
+        /// </summary>
+        [Fact]
+        public void ExistingGlobalPropertiesToRemovePreservedForUnresolvedReferences()
+        {
+            using TestEnvironment env = TestEnvironment.Create(_output);
+
+            var projectRefs = new ArrayList();
+            var unresolvedRef = ResolveNonMSBuildProjectOutput_Tests.CreateReferenceItem(
+                "Utility.vcxproj",
+                "{AAAAAAAA-AAAA-AAAA-AAAA-AAAAAAAAAAAA}",
+                "{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}",
+                "Utility");
+            // Set some pre-existing GlobalPropertiesToRemove
+            unresolvedRef.SetMetadata("GlobalPropertiesToRemove", "TargetFramework");
+            projectRefs.Add(unresolvedRef);
+
+            var projectConfigurations = new Hashtable();
+            projectConfigurations.Add("{BBBBBBBB-BBBB-BBBB-BBBB-BBBBBBBBBBBB}", @"Debug|x64");
+
+            string xmlString = ResolveNonMSBuildProjectOutput_Tests.CreatePregeneratedPathDoc(projectConfigurations);
+
+            MockEngine engine = new MockEngine(_output);
+            AssignProjectConfiguration task = new AssignProjectConfiguration();
+            task.BuildEngine = engine;
+            task.SolutionConfigurationContents = xmlString;
+            task.ProjectReferences = (ITaskItem[])projectRefs.ToArray(typeof(ITaskItem));
+            task.ShouldUnsetParentConfigurationAndPlatform = true;
+
+            bool result = task.Execute();
+            result.ShouldBeTrue();
+
+            task.UnassignedProjects.Length.ShouldBe(1);
+            ITaskItem unresolved = task.UnassignedProjects[0];
+            string globalPropertiesToRemove = unresolved.GetMetadata("GlobalPropertiesToRemove");
+
+            // The pre-existing TargetFramework should still be there
+            globalPropertiesToRemove.ShouldContain("TargetFramework");
+            // But Configuration;Platform should NOT be appended
+            globalPropertiesToRemove.ShouldNotContain("Configuration");
+            globalPropertiesToRemove.ShouldNotContain("Platform");
+        }
+    }
+}

src/Tasks/AssignProjectConfiguration.cs

@@ -208,7 +208,8 @@ public override bool Execute()
                         // If the reference was unresolved, we want to undefine the Configuration and Platform
                         // global properties, so that the project will build using its default Configuration and
                         // Platform rather than that of its parent.
-                        if (ShouldUnsetParentConfigurationAndPlatform)
+                        if (ShouldUnsetParentConfigurationAndPlatform
+                            && !ChangeWaves.AreFeaturesEnabled(ChangeWaves.Wave18_6))
                         {
                             string globalPropertiesToRemove = projectRef.GetMetadata("GlobalPropertiesToRemove");