Introduce ObjectDatabase.CanMergeWithoutConflict()

Author: joshvera

LibGit2Sharp/Core/NativeMethods.cs

@@ -678,6 +678,15 @@ internal static extern int git_merge(
             ref GitMergeOpts merge_opts,
             ref GitCheckoutOpts checkout_opts);
 
+        [DllImport(libgit2)]
+        internal static extern int git_merge_trees(
+            out IndexSafeHandle index,
+            RepositorySafeHandle repo,
+            GitObjectSafeHandle ancestor_tree,
+            GitObjectSafeHandle our_tree,
+            GitObjectSafeHandle their_tree,
+            ref GitMergeOpts merge_opts);
+
         [DllImport(libgit2)]
         internal static extern int git_merge_analysis(
             out GitMergeAnalysis status_out,

LibGit2Sharp/Core/Proxy.cs

@@ -1074,6 +1074,22 @@ public static void git_index_clear(Index index)
 
         #region git_merge_
 
+        public static IndexSafeHandle git_merge_trees(RepositorySafeHandle repo, GitObjectSafeHandle ancestorTree, GitObjectSafeHandle ourTree, GitObjectSafeHandle theirTree)
+        {
+            using (ThreadAffinity())
+            {
+                IndexSafeHandle index;
+                GitMergeOpts opts = new GitMergeOpts { Version = 1 };
+                int res = NativeMethods.git_merge_trees(out index, repo, ancestorTree, ourTree, theirTree, ref opts);
+                if (res != (int) GitErrorCode.Ok || index == null)
+                {
+                    return null;
+                }
+
+                return index;
+            }
+        }
+
         public static ObjectId git_merge_base_many(RepositorySafeHandle repo, GitOid[] commitIds)
         {
             using (ThreadAffinity())

LibGit2Sharp/ObjectDatabase.cs

@@ -406,5 +406,34 @@ public virtual string ShortenObjectId(GitObject gitObject, int? minLength = null
 
             return gitObject.Sha.Substring(0, minLength.Value);
         }
+
+        /// <summary>
+        /// Returns whether merging <paramref name="one"/> into <paramref name="another"/>
+        /// would result in merge conflicts.
+        /// </summary>
+        /// <param name="one">The commit wrapping the base tree to merge into.</param>
+        /// <param name="another">The commit wrapping the tree to merge into <paramref name="one"/>.</param>
+        /// <returns>True if the merge does not result in a conflict, false otherwise.</returns>
+        public virtual bool CanMergeWithoutConflict(Commit one, Commit another)
+        {
+            Ensure.ArgumentNotNull(one, "one");
+            Ensure.ArgumentNotNull(another, "another");
+
+            using (var ourHandle = Proxy.git_object_peel(repo.Handle, one.Id, GitObjectType.Tree, true))
+            using (var theirHandle = Proxy.git_object_peel(repo.Handle, another.Id, GitObjectType.Tree, true))
+            {
+                var ancestorCommit = repo.Commits.FindMergeBase(one, another);
+
+                var ancestorHandle = ancestorCommit != null
+                    ? Proxy.git_object_peel(repo.Handle, ancestorCommit.Id, GitObjectType.Tree, false)
+                    : new NullGitObjectSafeHandle();
+
+                using (ancestorHandle)
+                using (var indexHandle = Proxy.git_merge_trees(repo.Handle, ancestorHandle, ourHandle, theirHandle))
+                {
+                    return !Proxy.git_index_has_conflicts(indexHandle);
+                }
+            }
+        }
     }
 }