Match pre release tag formatting to parsing

Pre release tag parsing correctly identifies when there is no name, but there is a number, this changes the formatting method and tag verification so that a single pre release number is also considered

Author: carlos-vicente

src/GitVersionCore.Tests/VersionCalculation/SemanticVersionTests.cs

@@ -20,6 +20,7 @@ public class SemanticVersionTests : TestBase
         [TestCase("1.2-alpha4", 1, 2, 0, "alpha", 4, null, null, null, null, "1.2.0-alpha.4", null)]
         [TestCase("1.2.3-rc", 1, 2, 3, "rc", null, null, null, null, null, null, null)]
         [TestCase("1.2.3-rc3", 1, 2, 3, "rc", 3, null, null, null, null, "1.2.3-rc.3", null)]
+        [TestCase("1.2.3-3", 1, 2, 3, "", 3, null, null, null, null, "1.2.3-3", null)]
         [TestCase("1.2.3-RC3", 1, 2, 3, "RC", 3, null, null, null, null, "1.2.3-RC.3", null)]
         [TestCase("1.2.3-rc3.1", 1, 2, 3, "rc3", 1, null, null, null, null, "1.2.3-rc3.1", null)]
         [TestCase("01.02.03-rc03", 1, 2, 3, "rc", 3, null, null, null, null, "1.2.3-rc.3", null)]
@@ -119,6 +120,21 @@ public void ToStringSTests()
                 }
             };
             Assert.AreEqual("1.2.3-beta.4", fullSemVer.ToString("s"));
+            var fullSemVerNoPreReleaseName = new SemanticVersion
+            {
+                Major = 1,
+                Minor = 2,
+                Patch = 3,
+                PreReleaseTag = new SemanticVersionPreReleaseTag("", 4),
+                BuildMetaData = new SemanticVersionBuildMetaData
+                {
+                    Sha = "theSha",
+                    Branch = "TheBranch",
+                    CommitsSinceTag = 5,
+                    OtherMetaData = "TheOtherMetaData"
+                }
+            };
+            Assert.AreEqual("1.2.3-4", fullSemVerNoPreReleaseName.ToString("s"));
         }
         [Test]
         public void ToStringLTests()
@@ -183,6 +199,21 @@ public void ToStringTests()
                 }
             };
             Assert.AreEqual("1.2.3-beta.4", fullSemVer.ToString());
+            var fullSemVerNoPreReleaseName = new SemanticVersion
+            {
+                Major = 1,
+                Minor = 2,
+                Patch = 3,
+                PreReleaseTag = new SemanticVersionPreReleaseTag("", 4),
+                BuildMetaData = new SemanticVersionBuildMetaData
+                {
+                    Sha = "theSha",
+                    Branch = "TheBranch",
+                    CommitsSinceTag = 5,
+                    OtherMetaData = "TheOtherMetaData"
+                }
+            };
+            Assert.AreEqual("1.2.3-4", fullSemVerNoPreReleaseName.ToString());
         }
         [Test]
         public void ToStringFTests()

src/GitVersionCore/VersionCalculation/SemanticVersioning/SemanticVersionPreReleaseTag.cs

@@ -168,15 +168,15 @@ public string ToString(string format, IFormatProvider formatProvider = null)
 
             return format switch
             {
-                "t" => (Number.HasValue ? $"{Name}.{Number}" : Name),
+                "t" => (Number.HasValue ? string.IsNullOrEmpty(Name) ? $"{Number}" : $"{Name}.{Number}" : Name),
                 "l" => (Number.HasValue ? FormatLegacy(GetLegacyName(), Number.Value.ToString()) : FormatLegacy(GetLegacyName())),
                 _ => throw new ArgumentException("Unknown format", nameof(format))
             };
         }
 
         private string FormatLegacy(string tag, string number = "")
         {
-            var tagEndsWithANumber = char.IsNumber(tag.Last());
+            var tagEndsWithANumber = char.IsNumber(tag.LastOrDefault());
             if (tagEndsWithANumber && number.Length > 0)
                 number = "-" + number;
 
@@ -194,7 +194,7 @@ private string GetLegacyName()
 
         public bool HasTag()
         {
-            return !string.IsNullOrEmpty(Name);
+            return !string.IsNullOrEmpty(Name) || Number.HasValue;
         }
     }
 }