Add the darc vmr diff --name-only option (#4880)

Adds a new option that only lists the differing file names

dotnet/source-build#5201

Author: premun

src/Microsoft.DotNet.Darc/Darc/Operations/VirtualMonoRepo/VmrDiffOperation.cs

@@ -46,7 +46,7 @@ await PrepareReposAsync(repo2, repo1, tmpPath) :
                 await PrepareReposAsync(repo1, repo2, tmpPath);
 
             IReadOnlyCollection<string> exclusionFilters = await GetDiffFilters(tmpVmrProductRepo / ".." / "..", repo1.IsVmr ? repo1.Ref : repo2.Ref, mapping);
-            await AddRemoteAndGenerateDiffAsync(tmpProductRepo, tmpVmrProductRepo, repo2.Ref, exclusionFilters);
+            await GenerateDiff(tmpProductRepo, tmpVmrProductRepo, repo2.Ref, exclusionFilters);
         }
         finally
         {
@@ -242,7 +242,7 @@ private async Task VerifyInput(Repo repo1, Repo repo2)
     private async Task<bool> IsRepoVmrAsync(string uri, string branch)
         => await gitRepoFactory.CreateClient(uri).IsRepoVmrAsync(uri, branch);
 
-    private async Task AddRemoteAndGenerateDiffAsync(string repo1, string repo2, string repo2Branch, IReadOnlyCollection<string> filters)
+    private async Task GenerateDiff(string repo1, string repo2, string repo2Branch, IReadOnlyCollection<string> filters)
     {
         string remoteName = Guid.NewGuid().ToString();
 
@@ -285,10 +285,52 @@ await processManager.ExecuteGit(repo1, [
             includeAdditionalMappings: false,
             CancellationToken.None);
 
-        // If tmpDirectory is not null, it means the output path was not provided, so we just want to
-        // print out the whole diff
-        if (!string.IsNullOrEmpty(tmpDirectory))
+        try
+        {
+            await OutputDiff(patches);
+        }
+        finally
+        {
+            if (!string.IsNullOrEmpty(tmpDirectory))
+            {
+                fileSystem.DeleteDirectory(tmpDirectory, true);
+            }
+        }
+    }
+
+    private async Task OutputDiff(List<VmrIngestionPatch> patches)
+    {
+        if (options.NameOnly)
+        {
+            var files = new List<UnixPath>();
+
+            // For name-only mode, we'll print the filenames directly from the git patch summary lines
+            foreach (var patch in patches)
+            {
+                files.AddRange(await patchHandler.GetPatchedFiles(patch.Path, CancellationToken.None));
+            }
+
+            var list = files
+                .Select(f => f.Path)
+                .OrderBy(f => f);
+
+            // If the output path was provided, the list will be stored there
+            // Otherwise we want to print it
+            if (string.IsNullOrEmpty(options.OutputPath))
+            {
+                foreach (var file in list)
+                {
+                    Console.WriteLine(file);
+                }
+            }
+            else
+            {
+                await File.WriteAllLinesAsync(options.OutputPath, list);
+            }
+        }
+        else
         {
+            // For regular diff mode, we print the full diff content
             foreach (var patch in patches)
             {
                 using FileStream fs = new(patch.Path, FileMode.Open, FileAccess.Read);
@@ -299,7 +341,6 @@ await processManager.ExecuteGit(repo1, [
                     Console.WriteLine(line);
                 }
             }
-            fileSystem.DeleteDirectory(tmpDirectory, true);
         }
     }
 

src/Microsoft.DotNet.Darc/Darc/Options/VirtualMonoRepo/VmrDiffOptions.cs

@@ -5,6 +5,7 @@
 using Microsoft.DotNet.Darc.Operations.VirtualMonoRepo;
 
 namespace Microsoft.DotNet.Darc.Options.VirtualMonoRepo;
+
 [Verb("diff", HelpText = "Diffs the VMR and the product repositories. Outputs the diff to stdout, "
     + "or saves it to a patch file (or multiple if patch > 1 GB), if --output-path is provided")]
 internal class VmrDiffOptions : VmrCommandLineOptions<VmrDiffOperation>
@@ -17,4 +18,7 @@ internal class VmrDiffOptions : VmrCommandLineOptions<VmrDiffOperation>
         "where remote can be a local path or remote URI. Alternatively, only one target can be provided in " +
         "which case current directory will be used as the source for the diff")]
     public string Repositories { get; set; }
+
+    [Option("name-only", Required = false, HelpText = "Only list differing files without the diffs")]
+    public bool NameOnly { get; set; }
 }

src/Microsoft.DotNet.Darc/DarcLib/VirtualMonoRepo/VmrPatchHandler.cs

@@ -293,7 +293,6 @@ public async Task ApplyPatch(
     /// <summary>
     /// Resolves a list of all files that are part of a given patch diff.
     /// </summary>
-    /// <param name="repoPath">Path (to the repo) the patch applies onto</param>
     /// <param name="patchPath">Path to the patch file</param>
     /// <returns>List of all files (paths relative to repo's root) that are part of a given patch diff</returns>
     public async Task<IReadOnlyCollection<UnixPath>> GetPatchedFiles(string patchPath, CancellationToken cancellationToken)
@@ -305,7 +304,7 @@ public async Task<IReadOnlyCollection<UnixPath>> GetPatchedFiles(string patchPat
             return files;
         }
 
-        var result = await _processManager.ExecuteGit(_vmrInfo.VmrPath, ["apply", "--numstat", patchPath], cancellationToken: cancellationToken);
+        var result = await _processManager.ExecuteGit(_vmrInfo.TmpPath, ["apply", "--numstat", patchPath], cancellationToken: cancellationToken);
         result.ThrowIfFailed($"Failed to enumerate files from a patch at `{patchPath}`");
 
         foreach (var line in result.StandardOutput.Split(Environment.NewLine))