Fix: Allow CopyToAsync from readonly source to writable destination

src/Ramstack.FileSystem.Abstractions/VirtualFile.cs

@@ -143,7 +143,7 @@ public ValueTask CopyToAsync(string destinationPath, bool overwrite, Cancellatio
     /// </remarks>
     public ValueTask CopyToAsync(VirtualFile destination, bool overwrite, CancellationToken cancellationToken = default)
     {
-        EnsureWritable();
+        destination.EnsureWritable();
         destination.Refresh();
 
         if (destination.FileSystem != FileSystem)

tests/Ramstack.FileSystem.Specification.Tests/Ramstack.FileSystem.Specification.Tests.csproj

@@ -45,6 +45,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\src\Ramstack.FileSystem.Abstractions\Ramstack.FileSystem.Abstractions.csproj" />
+    <ProjectReference Include="..\..\src\Ramstack.FileSystem.Physical\Ramstack.FileSystem.Physical.csproj" />
   </ItemGroup>
 
   <ItemGroup>

tests/Ramstack.FileSystem.Specification.Tests/VirtualFileSystemSpecificationTests.cs

@@ -1,6 +1,8 @@
 using System.Security.Cryptography;
 using System.Text;
 
+using Ramstack.FileSystem.Physical;
+
 namespace Ramstack.FileSystem.Specification.Tests;
 
 /// <summary>
@@ -353,6 +355,38 @@ await Assert.ThatAsync(
             Throws.Exception);
     }
 
+    [Test]
+    public async Task File_Readonly_ReadonlyToWritable_Succeeds()
+    {
+        using var fs = GetFileSystem();
+        using var ds = new PhysicalFileSystem(
+            Path.Combine(
+                Path.GetTempPath(),
+                Path.GetRandomFileName()));
+
+        if (!fs.IsReadOnly)
+            return;
+
+        var src = fs.GetFile("/project/README.md");
+        var dst = ds.GetFile("/README.md");
+
+        await src.CopyToAsync(dst);
+
+        Assert.That(
+            await dst.ExistsAsync(),
+            Is.True);
+
+        Assert.That(
+            await ds.FileExistsAsync("/README.md"),
+            Is.True);
+
+        Assert.That(
+            await src.ReadAllTextAsync(),
+            Is.EqualTo(await src.ReadAllTextAsync()));
+
+        Directory.Delete(ds.Root, true);
+    }
+
     [Test]
     public async Task File_CopyTo_Path()
     {