Add repo reference to CompileStart event

Closes #1356

src/Tgstation.Server.Host/Components/Deployment/DreamMaker.cs

@@ -571,6 +571,7 @@ namespace Tgstation.Server.Host.Components.Deployment
 				progressReporter.StageName = "Copying repository";
 				var resolvedOutputDirectory = ioManager.ResolvePath(outputDirectory);
 				var repoOrigin = repository.Origin;
+				var repoReference = repository.Reference;
 				using (repository)
 					await repository.CopyTo(resolvedOutputDirectory, cancellationToken);
 
@@ -585,6 +586,7 @@ namespace Tgstation.Server.Host.Components.Deployment
 						resolvedOutputDirectory,
 						repoOrigin.ToString(),
 						engineLock.Version.ToString(),
+						repoReference,
 					},
 					true,
 					cancellationToken);

src/Tgstation.Server.Host/Components/Events/EventType.cs

@@ -55,7 +55,7 @@
 		EngineActiveVersionChange,
 
 		/// <summary>
-		/// After the repo is copied, before CodeModifications are applied. Parameters: Game directory path, origin commit sha, engine version string.
+		/// After the repo is copied, before CodeModifications are applied. Parameters: Game directory path, origin commit sha, engine version string, repository reference (or "(no branch)" if there is no reference).
 		/// </summary>
 		[EventScript("PreCompile")]
 		CompileStart,

src/Tgstation.Server.Host/Components/Repository/Repository.cs

@@ -46,6 +46,11 @@ namespace Tgstation.Server.Host.Components.Repository
 		/// </summary>
 		public const string RemoteTemporaryBranchName = "___TGSTempBranch";
 
+		/// <summary>
+		/// The value of <see cref="Reference"/> when not on a reference.
+		/// </summary>
+		public const string NoReference = "(no branch)";
+
 		/// <summary>
 		/// Used when a reference cannot be determined.
 		/// </summary>

tests/Tgstation.Server.Tests/TestRepository.cs

@@ -46,6 +46,9 @@ namespace Tgstation.Server.Tests
 
 				const string StartSha = "af4da8beb9f9b374b04a3cc4d65acca662e8cc1a";
 				await repo.CheckoutObject(StartSha, null, null, true, new JobProgressReporter(Mock.Of<ILogger<JobProgressReporter>>(), null, (stage, progress) => { }), CancellationToken.None);
+
+				Assert.AreEqual(Host.Components.Repository.Repository.NoReference, repo.Reference);
+
 				var result = await repo.CommittishIsParent("2f8588a3ca0f6b027704a2a04381215619de3412", CancellationToken.None);
 				Assert.IsTrue(result);
 				Assert.AreEqual(StartSha, repo.Head);