Say nothing to delete instead of asking to delete zero files [patch]

FileDeduplicator.Test/DeduplicateConfirmationTests.cs

@@ -166,4 +166,29 @@ public void ConfirmingDeletesExactlyTheCopiesTheListingNamed()
 		Assert.Contains("Deleted 1 file(s).", output);
 		Assert.Contains("Reclaimed 5 B of disk space.", output);
 	}
+
+	/// <summary>
+	/// Empty files are never deleted, so a tree whose only duplicates are empty marker files has
+	/// nothing to approve: the verb says so, reads no answer, and succeeds.
+	/// </summary>
+	[TestMethod]
+	public void OnlyEmptyDuplicatesSkipTheConfirmationAndSucceed()
+	{
+		// Arrange -- the routine Python/git case: two empty __init__.py files and one unique file
+		using TempTree tree = new();
+		AbsoluteFilePath first = tree.Write("a/__init__.py", string.Empty);
+		AbsoluteFilePath second = tree.Write("b/__init__.py", string.Empty);
+		_ = tree.Write("u.txt", "unique");
+
+		// Act -- stdin is empty, as it is for a script with nothing piped in
+		string output = ConsoleCapture.Normalize(ConsoleCapture.Run(new Deduplicate { PathString = tree.Root.WeakString }, string.Empty, out int exitCode));
+
+		// Assert
+		Assert.AreEqual(0, exitCode, $"A run with nothing to delete reported failure. Output was:\n{output}");
+		Assert.Contains("Nothing to delete", output);
+		Assert.DoesNotContain("Proceed with deletion?", output, $"The verb asked to approve deleting nothing. Output was:\n{output}");
+		Assert.DoesNotContain("Aborted.", output);
+		Assert.IsTrue(TempTree.Exists(first), $"{first} is empty and should never have been touched.");
+		Assert.IsTrue(TempTree.Exists(second), $"{second} is empty and should never have been touched.");
+	}
 }

FileDeduplicator.Test/VerbOutputTests.cs

@@ -439,4 +439,24 @@ private static (string Output, int ExitCode) RunWithExitCode(BaseVerb verb, stri
 		string output = ConsoleCapture.Run(verb, stdin, out int exitCode);
 		return (output, exitCode);
 	}
+
+	/// <summary>
+	/// When every duplicate is empty, and so kept, Scan does not point at a Deduplicate run that
+	/// would have nothing to do.
+	/// </summary>
+	[TestMethod]
+	public void ScanDoesNotSuggestDeduplicateWhenOnlyEmptyDuplicatesExist()
+	{
+		// Arrange
+		using TempTree tree = new();
+		AbsoluteFilePath first = tree.Write("a/.gitkeep", string.Empty);
+		_ = tree.Write("b/.gitkeep", string.Empty);
+
+		// Act
+		string output = ConsoleCapture.Normalize(ConsoleCapture.Run(new Scan { PathString = tree.Root.WeakString }));
+
+		// Assert
+		Assert.Contains($"{first} [KEEP, empty]", output);
+		Assert.DoesNotContain("Run the 'Deduplicate' command", output, $"Scan suggested a Deduplicate run with nothing to delete. Output was:\n{output}");
+	}
 }

FileDeduplicator/Verbs/Deduplicate.cs

@@ -52,6 +52,15 @@ internal override void Run(Deduplicate options)
 		// and DryRun already print this; the verb that actually deletes is the one that needs it.
 		DeletionPlan plan = DuplicateReport.PlanDeletions(duplicates);
 
+		// Empty files are never deleted, so a tree whose only duplicates are empty marker files
+		// (__init__.py, .gitkeep) has nothing to do. Asking to approve deleting zero files would
+		// read stdin for nothing, and declining it would report failure to a script.
+		if (plan.FileCount == 0)
+		{
+			Console.WriteLine("Nothing to delete (only empty-file duplicates found).");
+			return;
+		}
+
 		Console.WriteLine($"Found {duplicates.Count} group(s) of duplicate files.");
 		Console.WriteLine("Keeping the copy with the shortest filename in each group.");
 		Console.WriteLine();

FileDeduplicator/Verbs/Scan.cs

@@ -50,13 +50,15 @@ internal override void Run(Scan options)
 
 		// Step 4: Display results
 		long totalWastedBytes = 0;
+		bool anyDeletable = false;
 		Console.WriteLine($"Found {duplicates.Count} group(s) of duplicate files:");
 		Console.WriteLine();
 
 		foreach (DuplicateGroup group in duplicates)
 		{
 			AbsoluteFilePath keeper = Deduplicator.SelectFileToKeep(group.Files);
 			bool deletable = Deduplicator.IsDeletable(group);
+			anyDeletable |= deletable;
 			long wastedBytes = group.FileSize * (group.Files.Count - 1);
 			totalWastedBytes += wastedBytes;
 
@@ -78,7 +80,13 @@ internal override void Run(Scan options)
 
 		Console.WriteLine($"Total duplicate groups: {duplicates.Count}");
 		Console.WriteLine($"Total wasted space: {DuplicateReport.FormatBytes(totalWastedBytes)}");
-		Console.WriteLine();
-		Console.WriteLine("Run the 'Deduplicate' command to remove duplicates.");
+
+		// Empty duplicates are kept, so pointing at Deduplicate when they are all there is would
+		// send the user to a verb with nothing to do.
+		if (anyDeletable)
+		{
+			Console.WriteLine();
+			Console.WriteLine("Run the 'Deduplicate' command to remove duplicates.");
+		}
 	}
 }