Factor out Guard.ArgumentIsGitPath

Author: jcansdale

src/GitHub.Exports/Services/GitService.cs

@@ -239,7 +239,7 @@ public Task<Patch> Compare(
             Guard.ArgumentNotNull(repository, nameof(repository));
             Guard.ArgumentNotEmptyString(sha1, nameof(sha1));
             Guard.ArgumentNotEmptyString(sha2, nameof(sha2));
-            Guard.ArgumentNotEmptyString(path, nameof(path));
+            Guard.ArgumentIsGitPath(path, nameof(path));
 
             return Task.Run(() =>
             {
@@ -266,11 +266,7 @@ public Task<ContentChanges> CompareWith(IRepository repository, string sha1, str
             Guard.ArgumentNotNull(repository, nameof(repository));
             Guard.ArgumentNotEmptyString(sha1, nameof(sha1));
             Guard.ArgumentNotEmptyString(sha2, nameof(sha1));
-            Guard.ArgumentNotEmptyString(path, nameof(path));
-            if (path.Contains('\\'))
-            {
-                throw new ArgumentException($"The value for '{nameof(path)}' must use '/' not '\\' as directory separator", nameof(path));
-            }
+            Guard.ArgumentIsGitPath(path, nameof(path));
 
             return Task.Run(() =>
             {

src/GitHub.Extensions/Guard.cs

@@ -1,13 +1,27 @@
 using System;
-using System.Collections.Generic;
-using System.Diagnostics;
+using System.IO;
 using System.Globalization;
 using System.Linq;
 
 namespace GitHub.Extensions
 {
     public static class Guard
     {
+        public static void ArgumentIsGitPath(string value, string name)
+        {
+            ArgumentNotNull(value, name);
+
+            if (value.Contains('\\'))
+            {
+                throw new ArgumentException($"The value '{value}' must use '/' not '\\' as directory separator", name);
+            }
+
+            if (Path.IsPathRooted(value))
+            {
+                throw new ArgumentException($"The value '{value}' must not be rooted", name);
+            }
+        }
+
         public static void ArgumentNotNull(object value, string name)
         {
             if (value != null) return;

test/GitHub.Exports.UnitTests/GitServiceIntegrationTests.cs

@@ -58,6 +58,24 @@ public async Task One_File_Is_Modified(string content1, string content2)
                 Assert.That(treeChanges.Modified.FirstOrDefault()?.Path, Is.EqualTo(path));
             }
         }
+
+
+        [Test]
+        public void Path_Must_Not_Use_Windows_Directory_Separator()
+        {
+            using (var temp = new TempRepository())
+            {
+                var path = @"dir\foo.txt";
+                var oldContent = "oldContent";
+                var newContent = "newContent";
+                var commit1 = AddCommit(temp.Repository, path, oldContent);
+                var commit2 = AddCommit(temp.Repository, path, newContent);
+                var target = new GitService(new RepositoryFacade());
+
+                Assert.ThrowsAsync<ArgumentException>(() =>
+                    target.Compare(temp.Repository, commit1.Sha, commit2.Sha, path));
+            }
+        }
     }
 
     public class TheCompareWithMethod