Pin diff --submodule=short so Patch reports a moved submodule as its gitlink

GitIntegration.Test/Builders/GitPatchBuilderTests.cs

@@ -28,6 +28,7 @@ public void BuildsTheDefaultPatchVector()
 			"--no-color",
 			"--src-prefix=a/",
 			"--dst-prefix=b/",
+			"--submodule=short",
 			"-U3",
 			"--no-renames",
 		];

GitIntegration.Test/Integration/GitSubmoduleTests.cs

@@ -3,6 +3,7 @@
 namespace ktsu.GitIntegration.Test;
 
 using System.Collections.Generic;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -164,6 +165,53 @@
 		Assert.AreNotEqual(after[0].Sha, after[0].CheckedOutSha);
 	}
 
+	[TestMethod]
+	[DataRow("log")]
+	[DataRow("diff")]
+	public async Task PatchReportsAMovedSubmoduleAsItsGitlinkWhateverDiffSubmoduleSaysAsync(string format)
+	{
+		CancellationToken cancellationToken = TestContext.CancellationTokenSource.Token;
+		await IntegrationGitFixture.RequireGitAsync(cancellationToken).ConfigureAwait(false);
+
+		using TemporaryRepository subDirectory = new();
+		using TemporaryRepository superDirectory = new();
+
+		GitRepository sub = await CreateRepositoryAsync(subDirectory, "s.txt", cancellationToken).ConfigureAwait(false);
+		GitRepository super = await CreateRepositoryAsync(superDirectory, "m.txt", cancellationToken).ConfigureAwait(false);
+
+		await AddSubmoduleAsync(super, sub.LocalPath!, "libs/sub", cancellationToken).ConfigureAwait(false);
+
+		// Move the submodule's checkout on by a commit, so the superproject sees its gitlink change.
+		GitRepository checkout = new()
+		{
+			LocalPath = System.IO.Path.Join(superDirectory.RootPath, "libs", "sub").As<AbsoluteDirectoryPath>(),
+			ProcessRunner = super.ProcessRunner,
+		};
+
+		await IntegrationGitFixture.ConfigureIdentityAsync(checkout, AuthorName, AuthorEmail, cancellationToken)
+			.ConfigureAwait(false);
+
+		superDirectory.WriteFile("libs/sub/s.txt", "two\n");
+		_ = await checkout.Add().All().ExecuteAsync(cancellationToken).ConfigureAwait(false);
+		_ = await checkout.Commit("c2".As<GitCommitMessage>()).ExecuteAsync(cancellationToken).ConfigureAwait(false);
+
+		// Written into the superproject's own config, which is the nearest scope git reads it from.
+		_ = await new GitTextBuilder(super.ProcessRunner!, super.LocalPath, "config", "diff.submodule", format)
+			.ExecuteAsync(cancellationToken).ConfigureAwait(false);
+
+		GitPatch patch = await super.Patch().ExecuteAsync(cancellationToken).ConfigureAwait(false);
+
+		// "log" left the change out entirely, and "diff" reported libs/sub/s.txt in its place
+		// (ktsu-dev/GitIntegration#124).
+		GitFilePatch file = patch.Files.Single();
+		Assert.AreEqual("libs/sub".As<RelativeFilePath>(), file.Path);
+
+		_ = await super.Apply(file.PatchFor(file.Hunks)).ToIndex().ExecuteAsync(cancellationToken).ConfigureAwait(false);
+
+		GitPatch staged = await super.Patch().Staged().ExecuteAsync(cancellationToken).ConfigureAwait(false);
+		Assert.AreEqual("libs/sub".As<RelativeFilePath>(), staged.Files.Single().Path);
+	}
+
 	[TestMethod]
 	public async Task ReportsAnUninitializedSubmoduleAndThenUpdatesItAsync()
 	{

GitIntegration/Builders/GitPatchBuilder.cs

@@ -178,6 +178,12 @@ protected override void AppendVerbArguments(ICollection<string> arguments)
 		arguments.Add("--src-prefix=a/");
 		arguments.Add("--dst-prefix=b/");
 
+		// diff.submodule=log prints a moved submodule as a "Submodule sub a..b:" summary with no
+		// diff --git block, so the change is missing from the patch, and =diff prints the
+		// submodule's own files as if they were the superproject's, which apply then refuses.
+		// Only the short form is a gitlink patch that stages (ktsu-dev/GitIntegration#124).
+		arguments.Add("--submodule=short");
+
 		if (_staged)
 		{
 			arguments.Add("--cached");