Allow to query the commit history of an empty repository

Fix issue #30.

LibGit2Sharp.Tests/CommitFixture.cs

@@ -77,7 +77,7 @@ public void CanEnumerateCommitsFromSha()
         }
 
         [Test]
-        public void BuildingACommitCollectionFromUnknownShaOrInvalidReferenceThrows()
+        public void QueryingTheCommitHistoryWithUnknownShaOrInvalidReferenceThrows()
         {
             using (var repo = new Repository(Constants.TestRepoPath))
             {
@@ -88,6 +88,17 @@ public void BuildingACommitCollectionFromUnknownShaOrInvalidReferenceThrows()
             }
         }
 
+        [Test]
+        public void QueryingTheCommitHistoryWithBadParamsThrows()
+        {
+            using (var repo = new Repository(Constants.TestRepoPath))
+            {
+                Assert.Throws<ArgumentException>(() => repo.Commits.QueryBy(new Filter { Since = string.Empty }));
+                Assert.Throws<ArgumentNullException>(() => repo.Commits.QueryBy(new Filter { Since = null }));
+                Assert.Throws<ArgumentNullException>(() => repo.Commits.QueryBy(null));
+            }
+        }
+
         [Test]
         public void CanEnumerateCommitsWithReverseTimeSorting()
         {
@@ -208,23 +219,5 @@ public void CanReadCommitWithMultipleParents()
                 commit.Parents.Count().ShouldEqual(2);
             }
         }
-
-        [Test]
-        public void PushingEmptyShaThrows()
-        {
-            using (var repo = new Repository(Constants.TestRepoPath))
-            {
-                Assert.Throws<ArgumentException>(() => repo.Commits.QueryBy(new Filter{Since = string.Empty}));
-            }
-        }
-
-        [Test]
-        public void PushingNullShaThrows()
-        {
-            using (var repo = new Repository(Constants.TestRepoPath))
-            {
-                Assert.Throws<ArgumentNullException>(() => repo.Commits.QueryBy(new Filter { Since = null }));
-            }
-        }
     }
 }

LibGit2Sharp.Tests/RepositoryFixture.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Linq;
 using LibGit2Sharp.Tests.TestHelpers;
 using NUnit.Framework;
 
@@ -57,7 +58,11 @@ private static void AssertInitializedRepository(Repository repo)
             repo.Info.IsHeadDetached.ShouldBeFalse();
             repo.Head.TargetIdentifier.ShouldEqual("refs/heads/master");
             repo.Head.ResolveToDirectReference().ShouldBeNull();
-            Assert.Throws<InvalidOperationException>(() => { var c = repo.Commits; });
+
+            repo.Commits.Count().ShouldEqual(0);
+            repo.Commits.QueryBy(new Filter { Since = repo.Head }).Count().ShouldEqual(0);
+            repo.Commits.QueryBy(new Filter { Since = "HEAD" }).Count().ShouldEqual(0);
+            repo.Commits.QueryBy(new Filter { Since = "refs/heads/master" }).Count().ShouldEqual(0);
         }
 
         [Test]

LibGit2Sharp/CommitCollection.cs

@@ -9,7 +9,7 @@ namespace LibGit2Sharp
     /// <summary>
     ///   A collection of commits in a <see cref = "Repository" />
     /// </summary>
-    public class CommitCollection : ICommitCollection
+    public class CommitCollection : IQueryableCommitCollection
     {
         private readonly Repository repo;
         private ObjectId pushedObjectId;
@@ -80,7 +80,14 @@ public ICommitCollection QueryBy(Filter filter)
             Ensure.ArgumentNotNull(filter, "filter");
             Ensure.ArgumentNotNull(filter.Since, "filter.Since");
 
-            GitObject gitObj = repo.Lookup(filter.Since.ToString());
+            string shaOrRefName = filter.Since.ToString();
+
+            if ((repo.Info.IsEmpty) && PointsAtTheHead(shaOrRefName))
+            {
+                return new EmptyCommitCollection(filter.SortBy);
+            }            
+
+            GitObject gitObj = repo.Lookup(shaOrRefName);
 
             if (gitObj == null) // TODO: Should we check the type? Git-log allows TagAnnotation oid as parameter. But what about Blobs and Trees?
             {
@@ -90,6 +97,11 @@ public ICommitCollection QueryBy(Filter filter)
             return new CommitCollection(repo, filter.SortBy) { pushedObjectId = gitObj.Id };
         }
 
+        private static bool PointsAtTheHead(string shaOrRefName)
+        {
+            return ("HEAD".Equals(shaOrRefName, StringComparison.Ordinal) || "refs/heads/master".Equals(shaOrRefName, StringComparison.Ordinal));
+        }
+
         #region Nested type: CommitEnumerator
 
         private class CommitEnumerator : IEnumerator<Commit>

LibGit2Sharp/EmptyCommitCollection.cs

@@ -0,0 +1,53 @@
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace LibGit2Sharp
+{
+    internal class EmptyCommitCollection : IQueryableCommitCollection
+    {
+        internal EmptyCommitCollection(GitSortOptions sortedBy)
+        {
+            SortedBy = sortedBy;
+        }
+
+        /// <summary>
+        /// Returns an enumerator that iterates through the collection.
+        /// </summary>
+        /// <returns>
+        /// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
+        /// </returns>
+        /// <filterpriority>1</filterpriority>
+        public IEnumerator<Commit> GetEnumerator()
+        {
+            return Enumerable.Empty<Commit>().GetEnumerator();
+        }
+
+        /// <summary>
+        ///  Returns the list of commits of the repository matching the specified <paramref name="filter"/>.
+        /// </summary>
+        /// <param name="filter">The options used to control which commits will be returned.</param>
+        /// <returns>A collection of commits, ready to be enumerated.</returns>
+        public ICommitCollection QueryBy(Filter filter)
+        {
+            return new EmptyCommitCollection(filter.SortBy);
+        }
+
+        /// <summary>
+        /// Returns an enumerator that iterates through a collection.
+        /// </summary>
+        /// <returns>
+        /// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
+        /// </returns>
+        /// <filterpriority>2</filterpriority>
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+
+        /// <summary>
+        /// Gets the current sorting strategy applied when enumerating the collection.
+        /// </summary>
+        public GitSortOptions SortedBy { get; private set; }
+    }
+}

LibGit2Sharp/ICommitCollection.cs

@@ -5,7 +5,7 @@ namespace LibGit2Sharp
     public interface ICommitCollection : IEnumerable<Commit>
     {
         /// <summary>
-        /// Gets the current sorting strategy applied when enumerating the collection
+        /// Gets the current sorting strategy applied when enumerating the collection.
         /// </summary>
         GitSortOptions SortedBy { get; }
     }

LibGit2Sharp/IQueryableCommitCollection.cs

@@ -0,0 +1,12 @@
+namespace LibGit2Sharp
+{
+    public interface IQueryableCommitCollection : ICommitCollection
+    {
+        /// <summary>
+        ///  Returns the list of commits of the repository matching the specified <paramref name="filter"/>.
+        /// </summary>
+        /// <param name="filter">The options used to control which commits will be returned.</param>
+        /// <returns>A collection of commits, ready to be enumerated.</returns>
+        ICommitCollection QueryBy(Filter filter);
+    }
+}

LibGit2Sharp/LibGit2Sharp.csproj

@@ -71,6 +71,7 @@
     <Compile Include="DirectReference.cs" />
     <Compile Include="Core\GitIndexTime.cs" />
     <Compile Include="Core\GitIndexEntry.cs" />
+    <Compile Include="EmptyCommitCollection.cs" />
     <Compile Include="GitObject.cs" />
     <Compile Include="GitObjectType.cs" />
     <Compile Include="GitSortOptions.cs" />
@@ -82,6 +83,7 @@
     <Compile Include="Core\IndexSafeHandle.cs" />
     <Compile Include="IndexEntryState.cs" />
     <Compile Include="Filter.cs" />
+    <Compile Include="IQueryableCommitCollection.cs" />
     <Compile Include="ObjectId.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="Reference.cs" />

LibGit2Sharp/Repository.cs

@@ -49,7 +49,7 @@ internal RepositorySafeHandle Handle
         ///   Shortcut to return the reference to HEAD
         /// </summary>
         /// <returns></returns>
-        
+
         public Reference Head
         {
             get { return Refs["HEAD"]; }
@@ -75,9 +75,9 @@ public ReferenceCollection Refs
         ///   Lookup and enumerate commits in the repository. 
         ///   Iterating this collection directly starts walking from the HEAD.
         /// </summary>
-        public CommitCollection Commits
+        public IQueryableCommitCollection Commits
         {
-            get { return (CommitCollection)commits.QueryBy(new Filter{Since = Head}); }
+            get { return (IQueryableCommitCollection)commits.QueryBy(new Filter { Since = Head }); }
         }
 
         /// <summary>
@@ -219,7 +219,7 @@ public GitObject Lookup(string shaOrReferenceName, GitObjectType type = GitObjec
 
         private static bool IsReferencePeelable(Reference reference)
         {
-            return reference != null && ((reference is DirectReference) ||(reference is SymbolicReference && ((SymbolicReference)reference).Target != null));
+            return reference != null && ((reference is DirectReference) || (reference is SymbolicReference && ((SymbolicReference)reference).Target != null));
         }
     }
 }