Accept SHA256 hashes (64 characters) in addition to SHA1 hashes (40 characters)

Co-authored-by: tmat <41759+tmat@users.noreply.github.com>

Author: Copilot

src/Microsoft.Build.Tasks.Git.UnitTests/GitReferenceResolverTests.cs

@@ -40,6 +40,32 @@ public void ResolveReference()
             Assert.Null(resolver.ResolveReference("ref: refs/heads/none" + string.Join("/", Path.GetInvalidPathChars())));
         }
 
+        [Fact]
+        public void ResolveReference_SHA256()
+        {
+            using var temp = new TempRoot();
+
+            var gitDir = temp.CreateDirectory();
+
+            var commonDir = temp.CreateDirectory();
+            var refsHeadsDir = commonDir.CreateDirectory("refs").CreateDirectory("heads");
+
+            // SHA256 hash (64 characters)
+            refsHeadsDir.CreateFile("master").WriteAllText("0000000000000000000000000000000000000000000000000000000000000000");
+            refsHeadsDir.CreateFile("br1").WriteAllText("ref: refs/heads/br2");
+            refsHeadsDir.CreateFile("br2").WriteAllText("ref: refs/heads/master");
+
+            var resolver = new GitReferenceResolver(gitDir.Path, commonDir.Path);
+
+            // Verify SHA256 hash is accepted directly
+            Assert.Equal("0123456789ABCDEFabcdef00000000000000000000000000000000000000000000", 
+                         resolver.ResolveReference("0123456789ABCDEFabcdef00000000000000000000000000000000000000000000"));
+
+            Assert.Equal("0000000000000000000000000000000000000000000000000000000000000000", resolver.ResolveReference("ref: refs/heads/master"));
+            Assert.Equal("0000000000000000000000000000000000000000000000000000000000000000", resolver.ResolveReference("ref: refs/heads/br1"));
+            Assert.Equal("0000000000000000000000000000000000000000000000000000000000000000", resolver.ResolveReference("ref: refs/heads/br2"));
+        }
+
         [Fact]
         public void ResolveReference_Errors()
         {
@@ -59,8 +85,12 @@ public void ResolveReference_Errors()
             Assert.Throws<InvalidDataException>(() => resolver.ResolveReference("ref: xyz/heads/rec1"));
             Assert.Throws<InvalidDataException>(() => resolver.ResolveReference("ref:refs/heads/rec1"));
             Assert.Throws<InvalidDataException>(() => resolver.ResolveReference("refs/heads/rec1"));
+            // Invalid SHA1 hash lengths
             Assert.Throws<InvalidDataException>(() => resolver.ResolveReference(new string('0', 39)));
             Assert.Throws<InvalidDataException>(() => resolver.ResolveReference(new string('0', 41)));
+            // Invalid SHA256 hash lengths
+            Assert.Throws<InvalidDataException>(() => resolver.ResolveReference(new string('0', 63)));
+            Assert.Throws<InvalidDataException>(() => resolver.ResolveReference(new string('0', 65)));
         }
 
         [Fact]
@@ -87,6 +117,31 @@ 2222222222222222222222222222222222222222 refs/heads/br2
             Assert.Equal("2222222222222222222222222222222222222222", resolver.ResolveReference("ref: refs/heads/br2"));
         }
 
+        [Fact]
+        public void ResolveReference_Packed_SHA256()
+        {
+            using var temp = new TempRoot();
+
+            var gitDir = temp.CreateDirectory();
+
+            // Packed refs with SHA256 hashes (64 characters)
+            gitDir.CreateFile("packed-refs").WriteAllText(
+@"# pack-refs with: peeled fully-peeled sorted
+1111111111111111111111111111111111111111111111111111111111111111 refs/heads/master
+2222222222222222222222222222222222222222222222222222222222222222 refs/heads/br2
+");
+            var commonDir = temp.CreateDirectory();
+            var refsHeadsDir = commonDir.CreateDirectory("refs").CreateDirectory("heads");
+
+            refsHeadsDir.CreateFile("br1").WriteAllText("ref: refs/heads/br2");
+
+            var resolver = new GitReferenceResolver(gitDir.Path, commonDir.Path);
+
+            Assert.Equal("1111111111111111111111111111111111111111111111111111111111111111", resolver.ResolveReference("ref: refs/heads/master"));
+            Assert.Equal("2222222222222222222222222222222222222222222222222222222222222222", resolver.ResolveReference("ref: refs/heads/br1"));
+            Assert.Equal("2222222222222222222222222222222222222222222222222222222222222222", resolver.ResolveReference("ref: refs/heads/br2"));
+        }
+
         [Fact]
         public void ReadPackedReferences()
         {
@@ -110,6 +165,29 @@ 7777777777777777777777777777777777777777 refs/heads/br
             }, actual.Select(e => $"{e.Key}:{e.Value}"));
         }
 
+        [Fact]
+        public void ReadPackedReferences_SHA256()
+        {
+            var packedRefs =
+@"# pack-refs with:
+1111111111111111111111111111111111111111111111111111111111111111 refs/heads/master
+2222222222222222222222222222222222222222222222222222222222222222 refs/heads/br
+^3333333333333333333333333333333333333333333333333333333333333333
+4444444444444444444444444444444444444444444444444444444444444444 x
+5555555555555555555555555555555555555555555555555555555555555555 y 
+6666666666666666666666666666666666666666666666666666666666666666 y z
+7777777777777777777777777777777777777777777777777777777777777777 refs/heads/br
+";
+
+            var actual = GitReferenceResolver.ReadPackedReferences(new StringReader(packedRefs), "<path>");
+
+            AssertEx.SetEqual(new[]
+            {
+                "refs/heads/br:2222222222222222222222222222222222222222222222222222222222222222",
+                "refs/heads/master:1111111111111111111111111111111111111111111111111111111111111111"
+            }, actual.Select(e => $"{e.Key}:{e.Value}"));
+        }
+
         [Theory]
         [InlineData("# pack-refs with:")]
         [InlineData("# pack-refs with:xyz")]

src/Microsoft.Build.Tasks.Git/GitDataReader/GitReferenceResolver.cs

@@ -255,6 +255,6 @@ internal static string ReadReferenceFromFile(string path)
             => _lazyPackedReferences.Value.TryGetValue(reference, out var objectId) ? objectId : null;
 
         private static bool IsObjectId(string reference)
-            => reference.Length == 40 && reference.All(CharUtils.IsHexadecimalDigit);
+            => (reference.Length == 40 || reference.Length == 64) && reference.All(CharUtils.IsHexadecimalDigit);
     }
 }