Cache results of GetPackagesToPrune

Author: dsplaisted

src/Tasks/Microsoft.NET.Build.Tasks/GetPackagesToPrune.cs

@@ -27,8 +27,59 @@ public class GetPackagesToPrune : TaskBase
         [Output]
         public ITaskItem[] PackagesToPrune { get; set; }
 
+        class CacheKey
+        {
+            public string TargetFrameworkIdentifier { get; set; }
+            public string TargetFrameworkVersion { get; set; }
+            public HashSet<string> FrameworkReferences { get; set; }
+
+            public override bool Equals(object? obj) => obj is CacheKey key &&
+                TargetFrameworkIdentifier == key.TargetFrameworkIdentifier &&
+                TargetFrameworkVersion == key.TargetFrameworkVersion &&
+                FrameworkReferences.SetEquals(key.FrameworkReferences);
+            public override int GetHashCode()
+            {
+#if NET
+                var hashCode = new HashCode();
+                hashCode.Add(TargetFrameworkIdentifier);
+                hashCode.Add(TargetFrameworkVersion);
+                foreach (var frameworkReference in FrameworkReferences)
+                {
+                    hashCode.Add(frameworkReference);
+                }
+                return hashCode.ToHashCode();
+#else
+                int hashCode = 1436330440;
+                hashCode = hashCode * -1521134295 + EqualityComparer<string>.Default.GetHashCode(TargetFrameworkIdentifier);
+                hashCode = hashCode * -1521134295 + EqualityComparer<string>.Default.GetHashCode(TargetFrameworkVersion);
+
+                foreach (var frameworkReference in FrameworkReferences)
+                {
+                    hashCode = hashCode * -1521134295 + EqualityComparer<string>.Default.GetHashCode(frameworkReference);
+                }
+                return hashCode;
+#endif
+            }
+        }
+
+
         protected override void ExecuteCore()
         {
+            CacheKey key = new()
+            {
+                TargetFrameworkIdentifier = TargetFrameworkIdentifier,
+                TargetFrameworkVersion = TargetFrameworkVersion,
+                FrameworkReferences = FrameworkReferences.Select(i => i.ItemSpec).ToHashSet()
+            };
+
+            //  Cache framework package values per build
+            var existingResult = BuildEngine4.GetRegisteredTaskObject(key, RegisteredTaskObjectLifetime.Build);
+            if (existingResult != null)
+            {
+                PackagesToPrune = (ITaskItem[])existingResult;
+                return;
+            }
+
             var nugetFramework = new NuGetFramework(TargetFrameworkIdentifier, Version.Parse(TargetFrameworkVersion));
 
             Dictionary<string, NuGetVersion> packagesToPrune = new();
@@ -57,6 +108,8 @@ protected override void ExecuteCore()
                 item.SetMetadata("Version", p.Value.ToString());
                 return item;
             }).ToArray();
+
+            BuildEngine4.RegisterTaskObject(key, PackagesToPrune, RegisteredTaskObjectLifetime.Build, true);
         }
     }
 }