Cache the result of FindMergeBase().

Author: DanielRose

src/GitVersionCore/LibGitExtensions.cs

@@ -72,13 +72,22 @@ public static BranchCommit FindCommitBranchWasBranchedFrom([NotNull] this Branch
             }
         }
 
+        private static List<MergeBaseData> cachedMergeBase = new List<MergeBaseData>();
+
         /// <summary>
         /// Find the merge base of the two branches, i.e. the best common ancestor of the two branches' tips.
         /// </summary>
         public static Commit FindMergeBase(this Branch branch, Branch otherBranch, IRepository repository)
         {
             using (Logger.IndentLog(string.Format("Finding merge base between '{0}' and '{1}'.", branch.FriendlyName, otherBranch.FriendlyName)))
             {
+                // Check the cache.
+                var cachedData = cachedMergeBase.FirstOrDefault(data => IsSameBranch(branch, data.Branch) && IsSameBranch(otherBranch, data.OtherBranch) && repository == data.Repository);
+                if (cachedData != null)
+                {
+                    return cachedData.MergeBase;
+                }
+
                 // Otherbranch tip is a forward merge
                 var commitToFindCommonBase = otherBranch.Tip;
                 var commit = branch.Tip;
@@ -113,6 +122,10 @@ public static Commit FindMergeBase(this Branch branch, Branch otherBranch, IRepo
                         }
                     } while (mergeBaseWasForwardMerge);
                 }
+
+                // Store in cache.
+                cachedMergeBase.Add(new MergeBaseData(branch, otherBranch, repository, findMergeBase));
+
                 return findMergeBase;
             }
         }
@@ -275,5 +288,22 @@ public static void CheckoutFilesIfExist(this IRepository repository, params stri
                 }
             }
         }
+
+        private class MergeBaseData
+        {
+            public Branch Branch { get; private set; }
+            public Branch OtherBranch { get; private set; }
+            public IRepository Repository { get; private set; }
+
+            public Commit MergeBase { get; private set; }
+
+            public MergeBaseData(Branch branch, Branch otherBranch, IRepository repository, Commit mergeBase)
+            {
+                Branch = branch;
+                OtherBranch = otherBranch;
+                Repository = repository;
+                MergeBase = mergeBase;
+            }
+        }
     }
 }