GitRepository: Implement ShortenObjectId

Author: qmfrederik

src/NerdBank.GitVersioning.Tests/GitContextTests.cs

@@ -85,6 +85,12 @@ public void SelectCommitByPartialId(bool fromPack)
         Assert.Equal(this.LibGit2Repository.Head.Tip.Sha, this.Context.GitCommitId);
     }
 
+    [Fact]
+    public void GetShortUniqueCommitId()
+    {
+        Assert.Equal("51cd9ed3", this.Context.GetShortUniqueCommitId(8));
+    }
+
     [Theory, CombinatorialData]
     public void SelectCommitByTag(bool packedRefs, bool canonicalName)
     {

src/NerdBank.GitVersioning/GitContext.cs

@@ -174,7 +174,7 @@ public static GitContext Create(string path, string? committish = null, bool wri
         /// </summary>
         /// <param name="minLength">A minimum length.</param>
         /// <returns>A string that is at least <paramref name="minLength"/> in length but may be more as required to uniquely identify the git object identified by <see cref="GitCommitId"/>.</returns>
-        internal abstract string GetShortUniqueCommitId(int minLength);
+        public abstract string GetShortUniqueCommitId(int minLength);
 
         internal abstract int CalculateVersionHeight(VersionOptions? committedVersion, VersionOptions? workingVersion);
 

src/NerdBank.GitVersioning/LibGit2/LibGit2Context.cs

@@ -79,7 +79,8 @@ public override bool TrySelectCommit(string committish)
         /// <inheritdoc />
         public override void Stage(string path) => Commands.Stage(this.Repository, path);
 
-        internal override string GetShortUniqueCommitId(int minLength) => this.Repository.ObjectDatabase.ShortenObjectId(this.Commit, minLength);
+        /// <inheritdoc/>
+        public override string GetShortUniqueCommitId(int minLength) => this.Repository.ObjectDatabase.ShortenObjectId(this.Commit, minLength);
 
         internal override int CalculateVersionHeight(VersionOptions? committedVersion, VersionOptions? workingVersion)
         {

src/NerdBank.GitVersioning/Managed/ManagedGitContext.cs

@@ -112,7 +112,8 @@ internal override Version GetIdAsVersion(VersionOptions? committedVersion, Versi
             return this.GetIdAsVersionHelper(version, versionHeight);
         }
 
-        internal override string GetShortUniqueCommitId(int minLength)
+        /// <inheritdoc/>
+        public override string GetShortUniqueCommitId(int minLength)
         {
             Verify.Operation(this.Commit is object, "No commit is selected.");
             return this.Repository.ShortenObjectId(this.Commit.Value.Sha, minLength);

src/NerdBank.GitVersioning/ManagedGit/GitRepository.cs

@@ -224,8 +224,19 @@ public GitRepository(string workingDirectory, string gitDirectory, string common
         /// </returns>
         public string ShortenObjectId(GitObjectId objectId, int minimum)
         {
-            // TODO: implement this properly.
-            return objectId.ToString().Substring(0, Math.Max(minimum, 8));
+            var sha = objectId.ToString();
+
+            for (int length = minimum; length < sha.Length; length += 2)
+            {
+                var objectish = sha.Substring(0, length);
+
+                if (this.Lookup(objectish) != null)
+                {
+                    return objectish;
+                }
+            }
+
+            return sha;
         }
 
         /// <summary>
@@ -402,7 +413,16 @@ public GitCommit GetCommit(GitObjectId sha, bool readAuthor = false)
                     // or in multiple pack files.
                     if (objectId != null && !possibleObjectIds.Contains(objectId.Value))
                     {
-                        possibleObjectIds.Add(objectId.Value);
+                        if (possibleObjectIds.Count > 0)
+                        {
+                            // If objectish already resolved to at least one object which is different from the current
+                            // object id, objectish is not well-defined; so stop resolving and return null instead.
+                            return null;
+                        }
+                        else
+                        {
+                            possibleObjectIds.Add(objectId.Value);
+                        }
                     }
                 }
             }

src/NerdBank.GitVersioning/NoGit/NoGitContext.cs

@@ -30,9 +30,9 @@ public NoGitContext(string workingTreePath)
 
         public override void ApplyTag(string name) => throw new InvalidOperationException(NotAGitRepoMessage);
         public override void Stage(string path) => throw new InvalidOperationException(NotAGitRepoMessage);
+        public override string GetShortUniqueCommitId(int minLength) => throw new InvalidOperationException(NotAGitRepoMessage);
         public override bool TrySelectCommit(string committish) => throw new InvalidOperationException(NotAGitRepoMessage);
         internal override int CalculateVersionHeight(VersionOptions? committedVersion, VersionOptions? workingVersion) => 0;
         internal override Version GetIdAsVersion(VersionOptions? committedVersion, VersionOptions? workingVersion, int versionHeight) => throw new NotImplementedException();
-        internal override string GetShortUniqueCommitId(int minLength) => throw new InvalidOperationException(NotAGitRepoMessage);
     }
 }