Expose the assume-unchanged flag to IndexEntry

Fix #928

Author: zpete

LibGit2Sharp.Tests/IndexFixture.cs

@@ -466,6 +466,20 @@ public void CanMimicGitAddAll()
             }
         }
 
+        [Fact]
+        public void RetrievingAssumedUnchangedMarkedIndexEntries()
+        {
+            var path = SandboxAssumeUnchangedTestRepo();
+            using (var repo = new Repository(path))
+            {             
+                var regularFile = repo.Index["hello.txt"];
+                Assert.False(regularFile.AssumeUnchanged);
+
+                var assumeUnchangedFile = repo.Index["world.txt"];
+                Assert.True(assumeUnchangedFile.AssumeUnchanged);                
+            }
+        }
+
         private static void AddSomeCornerCases(Repository repo)
         {
             // Turn 1.txt into a directory in the Index

LibGit2Sharp/Core/GitIndexEntry.cs

@@ -6,6 +6,8 @@ namespace LibGit2Sharp.Core
     [StructLayout(LayoutKind.Sequential)]
     internal class GitIndexEntry
     {
+        internal const ushort GIT_IDXENTRY_VALID = 0x8000;
+
         public GitIndexTime CTime;
         public GitIndexTime MTime;
         public uint Dev;

LibGit2Sharp/IndexEntry.cs

@@ -30,6 +30,11 @@ public class IndexEntry : IEquatable<IndexEntry>
         /// </summary>
         public virtual StageLevel StageLevel { get; private set; }
 
+        /// <summary>
+        /// Whether the file is marked as assume-unchanged
+        /// </summary>
+        public virtual bool AssumeUnchanged { get; private set; }
+
         /// <summary>
         /// Gets the id of the <see cref="Blob"/> pointed at by this index entry.
         /// </summary>
@@ -51,7 +56,8 @@ internal static IndexEntry BuildFromPtr(IndexEntrySafeHandle handle)
                            Path = path.Native,
                            Id = entry.Id,
                            StageLevel = Proxy.git_index_entry_stage(handle),
-                           Mode = (Mode)entry.Mode
+                           Mode = (Mode)entry.Mode,
+                           AssumeUnchanged = (GitIndexEntry.GIT_IDXENTRY_VALID & entry.Flags) == GitIndexEntry.GIT_IDXENTRY_VALID
                        };
         }