Fixes #380 but on 3.0 branch

Author: Johannes Egger

GitVersionCore.Tests/VersionCalculation/Strategies/MergeMessageBaseVersionStrategyTests.cs

@@ -34,6 +34,7 @@ public void ShouldNotAllowIncrementOfVersion()
         [TestCase("Merge branch '4.0.3'", true, "4.0.3")] //TODO: possible make it a config option to support this
         [TestCase("Merge branch 'release-10.10.50'", true, "10.10.50")]
         [TestCase("Merge branch 's'", true, null)] // Must start with a number
+        [TestCase("Merge tag '10.10.50'", true, "10.10.50")]
         [TestCase("Merge branch 'release-0.2.0'", true, "0.2.0")]
         [TestCase("Merge branch 'Release-0.2.0'", true, "0.2.0")]
         [TestCase("Merge branch 'Release/0.2.0'", true, "0.2.0")]

GitVersionCore/VersionCalculation/BaseVersionCalculators/MergeMessageBaseVersionStrategy.cs

@@ -55,6 +55,17 @@ static bool Inner(Commit mergeCommit, out string versionPart)
             foreach (var prefix in knownMergePrefixes)
             {
                 if (message.StartsWith(prefix))
+            if (message.StartsWith("Merge tag '"))
+            {
+                var suffix = message.Replace("Merge tag '", "");
+
+                if (suffix.Contains("-"))
+                {
+                    suffix = suffix.Split('-')[1];
+                }
+                return TryGetPrefix(suffix, out versionPart, "'");
+            }
+
                 {
                     var suffix = message.Substring(prefix.Length);
                     return TryGetPrefix(suffix, out versionPart, "'");