Predict Fakes outputs based on FakesOutputPath MSBuild property

src/BuildPrediction/Predictors/FakesOutputPathPredictor.cs

@@ -0,0 +1,27 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using Microsoft.Build.Execution;
+
+namespace Microsoft.Build.Prediction.Predictors
+{
+    /// <summary>
+    /// Predicts the output directory for Microsoft Fakes assemblies based on the FakesOutputPath property.
+    /// </summary>
+    public sealed class FakesOutputPathPredictor : IProjectPredictor
+    {
+        internal const string FakesOutputPathPropertyName = "FakesOutputPath";
+
+        /// <inheritdoc/>
+        public void PredictInputsAndOutputs(
+            ProjectInstance projectInstance,
+            ProjectPredictionReporter predictionReporter)
+        {
+            string fakesOutputPath = projectInstance.GetPropertyValue(FakesOutputPathPropertyName);
+            if (!string.IsNullOrWhiteSpace(fakesOutputPath))
+            {
+                predictionReporter.ReportOutputDirectory(fakesOutputPath);
+            }
+        }
+    }
+}

src/BuildPrediction/ProjectPredictors.cs

@@ -64,6 +64,7 @@ public static class ProjectPredictors
         /// <item><see cref="GenerateBuildDependencyFilePredictor"/></item>
         /// <item><see cref="GeneratePublishDependencyFilePredictor"/></item>
         /// <item><see cref="GenerateRuntimeConfigurationFilesPredictor"/></item>
+        /// <item><see cref="FakesOutputPathPredictor"/></item>
         /// </list>
         /// </remarks>
         /// <returns>A collection of <see cref="IProjectPredictor"/>.</returns>
@@ -114,6 +115,7 @@ public static class ProjectPredictors
             new GenerateBuildDependencyFilePredictor(),
             new GeneratePublishDependencyFilePredictor(),
             new GenerateRuntimeConfigurationFilesPredictor(),
+            new FakesOutputPathPredictor(),
             //// NOTE! When adding a new predictor here, be sure to update the doc comment above.
         };
 

src/BuildPredictionTests/Predictors/FakesOutputPathPredictorTests.cs

@@ -0,0 +1,96 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using Microsoft.Build.Construction;
+using Microsoft.Build.Execution;
+using Microsoft.Build.Prediction.Predictors;
+using Xunit;
+
+namespace Microsoft.Build.Prediction.Tests.Predictors
+{
+    public class FakesOutputPathPredictorTests
+    {
+        [Fact]
+        public void FakesOutputPathFoundAsOutputDir()
+        {
+            const string FakesOutputPath = @"C:\repo\FakesAssemblies";
+            ProjectInstance projectInstance = CreateTestProjectInstance(FakesOutputPath);
+            new FakesOutputPathPredictor()
+                .GetProjectPredictions(projectInstance)
+                .AssertPredictions(
+                    projectInstance,
+                    null,
+                    null,
+                    null,
+                    new[] { new PredictedItem(FakesOutputPath, nameof(FakesOutputPathPredictor)) });
+        }
+
+        [Fact]
+        public void RelativeFakesOutputPathFoundAsOutputDir()
+        {
+            const string FakesOutputPath = @"bin\FakesAssemblies";
+            ProjectInstance projectInstance = CreateTestProjectInstance(FakesOutputPath);
+            new FakesOutputPathPredictor()
+                .GetProjectPredictions(projectInstance)
+                .AssertPredictions(
+                    projectInstance,
+                    null,
+                    null,
+                    null,
+                    new[] { new PredictedItem(FakesOutputPath, nameof(FakesOutputPathPredictor)) });
+        }
+
+        [Fact]
+        public void DefaultFakesAssembliesDirectoryFoundAsOutputDir()
+        {
+            const string FakesOutputPath = @"FakesAssemblies";
+            ProjectInstance projectInstance = CreateTestProjectInstance(FakesOutputPath);
+            new FakesOutputPathPredictor()
+                .GetProjectPredictions(projectInstance)
+                .AssertPredictions(
+                    projectInstance,
+                    null,
+                    null,
+                    null,
+                    new[] { new PredictedItem(FakesOutputPath, nameof(FakesOutputPathPredictor)) });
+        }
+
+        [Fact]
+        public void NoOutputsReportedIfNoFakesOutputPath()
+        {
+            ProjectInstance projectInstance = CreateTestProjectInstance(null);
+            new FakesOutputPathPredictor()
+                .GetProjectPredictions(projectInstance)
+                .AssertNoPredictions();
+        }
+
+        [Fact]
+        public void NoOutputsReportedIfEmptyFakesOutputPath()
+        {
+            ProjectInstance projectInstance = CreateTestProjectInstance(string.Empty);
+            new FakesOutputPathPredictor()
+                .GetProjectPredictions(projectInstance)
+                .AssertNoPredictions();
+        }
+
+        [Fact]
+        public void NoOutputsReportedIfWhitespaceFakesOutputPath()
+        {
+            ProjectInstance projectInstance = CreateTestProjectInstance("   ");
+            new FakesOutputPathPredictor()
+                .GetProjectPredictions(projectInstance)
+                .AssertNoPredictions();
+        }
+
+        private static ProjectInstance CreateTestProjectInstance(string fakesOutputPath)
+        {
+            ProjectRootElement projectRootElement = ProjectRootElement.Create();
+            if (fakesOutputPath != null)
+            {
+                projectRootElement.AddProperty(FakesOutputPathPredictor.FakesOutputPathPropertyName, fakesOutputPath);
+            }
+
+            return TestHelpers.CreateProjectInstanceFromRootElement(projectRootElement);
+        }
+    }
+}