Fix git tag pruning when fetching with specific refspecs

src/Agent.Plugins/GitCliManager.cs

@@ -235,6 +235,19 @@ public async Task<int> GitFetch(AgentTaskPluginExecutionContext context, string
 
             //define options for fetch
             string options = $"{forceTag} {tags} --prune {pruneTags} {progress} --no-recurse-submodules {remoteName} {depth} {string.Join(" ", filters.Select(filter => "--filter=" + filter))} {string.Join(" ", refSpec)}";
+
+            // When fetching with specific refspecs and tags enabled, git doesn't prune conflicting tag refs properly
+            // even with --prune-tags. Run git remote prune to clean up conflicting tag refs before fetch.
+            if (refSpec != null && refSpec.Count > 0 && fetchTags && !string.IsNullOrEmpty(pruneTags))
+            {
+                context.Debug("Running git remote prune before fetch to clean up conflicting tag refs.");
+                int pruneExitCode = await GitRemotePrune(context, repositoryPath, remoteName);
+                if (pruneExitCode != 0)
+                {
+                    context.Debug($"Git remote prune completed with exit code {pruneExitCode}. Continuing with fetch.");
+                }
+            }
+
             int retryCount = 0;
             int fetchExitCode = 0;
             while (retryCount < 3)
@@ -602,6 +615,13 @@ public async Task<int> GitPrune(AgentTaskPluginExecutionContext context, string
             return await ExecuteGitCommandAsync(context, repositoryPath, "prune", "-v");
         }
 
+        // git remote prune <remote>
+        public async Task<int> GitRemotePrune(AgentTaskPluginExecutionContext context, string repositoryPath, string remoteName)
+        {
+            context.Debug($"Prune remote tracking branches for remote: {remoteName}.");
+            return await ExecuteGitCommandAsync(context, repositoryPath, "remote", $"prune {remoteName}");
+        }
+
         // git lfs prune
         public async Task<int> GitLFSPrune(AgentTaskPluginExecutionContext context, string repositoryPath)
         {

src/Agent.Worker/Build/GitCommandManager.cs

@@ -54,6 +54,9 @@ public interface IGitCommandManager : IAgentService
         // get remote set-url --push <origin> <url>
         Task<int> GitRemoteSetPushUrl(IExecutionContext context, string repositoryPath, string remoteName, string remoteUrl);
 
+        // git remote prune <remote>
+        Task<int> GitRemotePrune(IExecutionContext context, string repositoryPath, string remoteName);
+
         // git submodule foreach --recursive "git clean -ffdx"
         Task<int> GitSubmoduleClean(IExecutionContext context, string repositoryPath);
 
@@ -295,6 +298,18 @@ public async Task<int> GitFetch(IExecutionContext context, string repositoryPath
             //define options for fetch
             string options = $"{tags} --prune {pruneTags} --progress --no-recurse-submodules {remoteName} {depth} {string.Join(" ", refSpec)}";
 
+            // When fetching with specific refspecs and tags enabled, git doesn't prune conflicting tag refs properly
+            // even with --prune-tags. Run git remote prune to clean up conflicting tag refs before fetch.
+            if (refSpec != null && refSpec.Count > 0 && fetchTags && !string.IsNullOrEmpty(pruneTags))
+            {
+                context.Debug("Running git remote prune before fetch to clean up conflicting tag refs.");
+                int pruneExitCode = await GitRemotePrune(context, repositoryPath, remoteName);
+                if (pruneExitCode != 0)
+                {
+                    context.Debug($"Git remote prune completed with exit code {pruneExitCode}. Continuing with fetch.");
+                }
+            }
+
             return await ExecuteGitCommandAsync(context, repositoryPath, "fetch", options, additionalCommandLine, cancellationToken);
         }
 
@@ -408,6 +423,15 @@ public async Task<int> GitRemoteSetPushUrl(IExecutionContext context, string rep
             return await ExecuteGitCommandAsync(context, repositoryPath, "remote", StringUtil.Format($"set-url --push {remoteName} {remoteUrl}"));
         }
 
+        // git remote prune <remote>
+        public async Task<int> GitRemotePrune(IExecutionContext context, string repositoryPath, string remoteName)
+        {
+            ArgUtil.NotNull(context, nameof(context));
+
+            context.Debug($"Prune remote tracking branches for remote: {remoteName}.");
+            return await ExecuteGitCommandAsync(context, repositoryPath, "remote", StringUtil.Format($"prune {remoteName}"));
+        }
+
         // git submodule foreach --recursive "git clean -ffdx"
         public async Task<int> GitSubmoduleClean(IExecutionContext context, string repositoryPath)
         {

src/Test/L0/Worker/Build/GitSourceProviderL0.cs

@@ -352,6 +352,54 @@ public void GetSourceGitFetchPR()
             }
         }
 
+        [Fact]
+        [Trait("Level", "L0")]
+        [Trait("Category", "Worker")]
+        public void GetSourceGitFetchPR_CallsGitRemotePrune()
+        {
+            using (TestHostContext tc = new TestHostContext(this))
+            {
+                var trace = tc.GetTrace();
+                // Arrange.
+                string dumySourceFolder = Path.Combine(tc.GetDirectory(WellKnownDirectory.Bin), "SourceProviderL0");
+                try
+                {
+                    Directory.CreateDirectory(dumySourceFolder);
+                    string dumyGitFolder = Path.Combine(dumySourceFolder, ".git");
+                    Directory.CreateDirectory(dumyGitFolder);
+                    string dumyGitConfig = Path.Combine(dumyGitFolder, "config");
+                    File.WriteAllText(dumyGitConfig, "test git confg file");
+
+                    var executionContext = GetTestExecutionContext(tc, dumySourceFolder, "refs/pull/12345/merge", "a596e13f5db8869f44574be0392fb8fe1e790ce4", false);
+                    var endpoint = GetTestSourceEndpoint("https://github.com/microsoft/azure-pipelines-agent", false, false);
+
+                    var _gitCommandManager = GetDefaultGitCommandMock();
+                    tc.SetSingleton<IGitCommandManager>(_gitCommandManager.Object);
+                    tc.SetSingleton<IVstsAgentWebProxy>(new VstsAgentWebProxy());
+                    var _configStore = new Mock<IConfigurationStore>();
+                    _configStore.Setup(x => x.GetSettings()).Returns(() => new AgentSettings() { ServerUrl = "http://localhost:8080/tfs" });
+                    tc.SetSingleton<IConfigurationStore>(_configStore.Object);
+                    tc.SetSingleton<IAgentCertificateManager>(new AgentCertificateManager());
+
+                    GitSourceProvider gitSourceProvider = new ExternalGitSourceProvider();
+                    gitSourceProvider.Initialize(tc);
+                    gitSourceProvider.SetVariablesInEndpoint(executionContext.Object, endpoint);
+
+                    // Act.
+                    gitSourceProvider.GetSourceAsync(executionContext.Object, endpoint, default(CancellationToken)).GetAwaiter().GetResult();
+
+                    // Assert.
+                    // Verify that GitRemotePrune is called before GitFetch when we have refspecs and fetchTags is true
+                    _gitCommandManager.Verify(x => x.GitRemotePrune(executionContext.Object, dumySourceFolder, "origin"), Times.Once);
+                    _gitCommandManager.Verify(x => x.GitFetch(executionContext.Object, dumySourceFolder, "origin", It.IsAny<int>(), It.IsAny<bool>(), new List<string>() { "+refs/heads/*:refs/remotes/origin/*", "+refs/pull/12345/merge:refs/remotes/pull/12345/merge" }, It.IsAny<string>(), It.IsAny<CancellationToken>()), Times.Once);
+                }
+                finally
+                {
+                    IOUtil.DeleteDirectory(dumySourceFolder, CancellationToken.None);
+                }
+            }
+        }
+
         [Fact]
         [Trait("Level", "L0")]
         [Trait("Category", "Worker")]