Add input caching for glob change detection

src/dotnet/commands/dotnet-build/CompilerIO.cs

@@ -2,18 +2,43 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.Collections.Generic;
+using System.Linq;
 
 namespace Microsoft.DotNet.Tools.Build
 {
-    internal struct CompilerIO
+    internal class CompilerIO
     {
-        public readonly List<string> Inputs;
-        public readonly List<string> Outputs;
+        public readonly IEnumerable<string> Inputs;
+        public readonly IEnumerable<string> Outputs;
 
-        public CompilerIO(List<string> inputs, List<string> outputs)
+        public CompilerIO(IEnumerable<string> inputs, IEnumerable<string> outputs)
         {
             Inputs = inputs;
             Outputs = outputs;
         }
+
+        public DiffResult DiffInputs(CompilerIO other)
+        {
+            var myInputSet = new HashSet<string>(Inputs);
+            var otherInputSet = new HashSet<string>(other.Inputs);
+
+            var additions = myInputSet.Except(otherInputSet);
+            var deletions = otherInputSet.Except(myInputSet);
+
+            return new DiffResult(additions, deletions);
+        }
+
+        internal class DiffResult
+        {
+            public IEnumerable<string> Additions { get; private set; }
+            public IEnumerable<string> Deletions { get; private set; }
+
+            public DiffResult(IEnumerable<string> additions, IEnumerable<string> deletions)
+            {
+                Additions = additions;
+                Deletions = deletions;
+            }
+        }
+
     }
 }