Match commits based on versions that used either endian to calculate

Author: AArnott

src/NerdBank.GitVersioning.Tests/LibGit2GitExtensionsTests.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Buffers.Binary;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
@@ -368,6 +369,19 @@ public void GetIdAsVersion_Roundtrip_UnstableOffset(int startingOffset, int offs
         }
     }
 
+    [Fact]
+    public void GetCommitsFromVersion_MatchesOnEitherEndian()
+    {
+        this.InitializeSourceControl();
+        Commit commit = this.WriteVersionFile(new VersionOptions { Version = SemanticVersion.Parse("1.2"), GitCommitIdShortAutoMinimum = 4 });
+
+        Version originalVersion = new VersionOracle(this.Context).Version;
+        Version swappedEndian = new Version(originalVersion.Major, originalVersion.Minor, originalVersion.Build, BinaryPrimitives.ReverseEndianness((ushort)originalVersion.Revision));
+        ushort twoBytesFromCommitId = checked((ushort)originalVersion.Revision);
+        Assert.Contains(commit, LibGit2GitExtensions.GetCommitsFromVersion(this.Context, originalVersion));
+        Assert.Contains(commit, LibGit2GitExtensions.GetCommitsFromVersion(this.Context, swappedEndian));
+    }
+
     [Fact]
     public void GetIdAsVersion_Roundtrip_WithSubdirectoryVersionFiles()
     {

src/NerdBank.GitVersioning.Tests/TestUtilities.cs

@@ -79,6 +79,10 @@ internal static ExpandedRepo ExtractRepoArchive(string repoArchiveName)
         }
     }
 
+    internal static string ToHex(ushort number) => number.ToString("X");
+
+    internal static ushort FromHex(string hex) => ushort.Parse(hex, System.Globalization.NumberStyles.HexNumber);
+
     internal class ExpandedRepo : IDisposable
     {
         internal ExpandedRepo(string repoPath)

src/NerdBank.GitVersioning.Tests/VersionOracleTests.cs

@@ -854,15 +854,12 @@ public void GitCommidIdLeading16BitsDecodedWithBigEndian()
         var oracle = new VersionOracle(this.Context);
 
         string leadingFourChars = this.Context.GitCommitId.Substring(0, 4);
-        ushort expectedNumber = FromHex(leadingFourChars);
+        ushort expectedNumber = TestUtilities.FromHex(leadingFourChars);
         ushort actualNumber = checked((ushort)oracle.Version.Revision);
         this.Logger.WriteLine("First two characters from commit ID in hex is {0}", leadingFourChars);
         this.Logger.WriteLine("First two characters, converted to a number is {0}", expectedNumber);
-        this.Logger.WriteLine("Generated 16-bit ushort from commit ID is {0}, whose hex representation is {1}", actualNumber, ToHex(actualNumber));
+        this.Logger.WriteLine("Generated 16-bit ushort from commit ID is {0}, whose hex representation is {1}", actualNumber, TestUtilities.ToHex(actualNumber));
         Assert.Equal(expectedNumber, actualNumber);
-
-        static string ToHex(ushort number) => number.ToString("X");
-        static ushort FromHex(string hex) => ushort.Parse(hex, System.Globalization.NumberStyles.HexNumber);
     }
 
     [Fact(Skip = "Slow test")]

src/NerdBank.GitVersioning/LibGit2/LibGit2GitExtensions.cs

@@ -284,7 +284,11 @@ private static bool IsCommitIdMismatch(Version version, VersionOptions versionOp
                     ushort objectIdLeadingValue = (ushort)expectedCommitIdLeadingValue;
                     ushort objectIdMask = (ushort)(objectIdLeadingValue == MaximumBuildNumberOrRevisionComponent ? 0xfffe : 0xffff);
 
-                    return !commit.Id.StartsWith(objectIdLeadingValue, objectIdMask);
+                    // Accept a big endian match or a little endian match.
+                    // Nerdbank.GitVersioning up to v3.4 would produce versions based on the endianness of the CPU it ran on (typically little endian).
+                    // Starting with v3.5, it deterministically used big endian. In order for `nbgv get-commits` to match on versions computed before and after the change,
+                    // we match on either endian setting.
+                    return !(commit.Id.StartsWith(objectIdLeadingValue, bigEndian: true, objectIdMask) || commit.Id.StartsWith(objectIdLeadingValue, bigEndian: false, objectIdMask));
                 }
             }
 
@@ -298,10 +302,11 @@ private static bool IsCommitIdMismatch(Version version, VersionOptions versionOp
         /// <param name="object">The object whose ID is to be tested.</param>
         /// <param name="leadingBytes">The leading 16-bits to be tested.</param>
         /// <param name="bitMask">The mask that indicates which bits should be compared.</param>
+        /// <param name="bigEndian"><see langword="true"/> to read the first two bytes as big endian (v3.5+ behavior); <see langword="false"/> to use little endian (v3.4 and earlier behavior).</param>
         /// <returns><c>True</c> if the object's ID starts with <paramref name="leadingBytes"/> after applying the <paramref name="bitMask"/>.</returns>
-        private static bool StartsWith(this ObjectId @object, ushort leadingBytes, ushort bitMask = 0xffff)
+        private static bool StartsWith(this ObjectId @object, ushort leadingBytes, bool bigEndian, ushort bitMask = 0xffff)
         {
-            ushort truncatedObjectId = BinaryPrimitives.ReadUInt16BigEndian(@object.RawId);
+            ushort truncatedObjectId = bigEndian ? BinaryPrimitives.ReadUInt16BigEndian(@object.RawId) : BinaryPrimitives.ReadUInt16LittleEndian(@object.RawId);
             return (truncatedObjectId & bitMask) == leadingBytes;
         }