Wrong Path returned by DirectoryInfo.FullName

[Unknown6656]

Description

I have an application which contains the following code line:

string foo = new DirectoryInfo("c:").FullName;

The string "c:" is user-provided and may be a longer path. If the user passes a path consisting only of the drive label and the colon (while omitting the finishing forward or backward slash) and the drive is the one matching the drive of the current execution directory, then the execution directory is returned instead of the root drive.

Reproduction Steps

1. Use a machine with multiple drives (if you do not have any explorer-mapped devices/drives, you may use the subst cmd command.
2. Create the following program:

using System.IO;
using System;


Console.WriteLine("current dir: " + Directory.GetCurrentDirectory());

foreach (string path in new[] {
    "d:",
    "d:/",
    "d:\\",
    "c:",
    "c:/",
    "c:\\",
})
    Console.WriteLine($"    {path,5}  --->  {new DirectoryInfo(path).FullName}");

4. compile it with net6.0-windows. I use the following version:

C:\> dotnet --list-sdks
3.1.416 [C:\Program Files\dotnet\sdk]
6.0.200-preview.21617.4 [C:\Program Files\dotnet\sdk]

3. Run it on the main system drive (i.e. c:/).

Expected output

current dir: C:\Users\xxxxx\Documents\TestProject1\bin
       d:  --->  D:\
      d:/  --->  d:\
      d:\  --->  d:\
       c:  --->  C:\
      c:/  --->  c:\
      c:\  --->  c:\

Actual output

current dir: C:\Users\xxxxx\Documents\TestProject1\bin
       d:  --->  D:\
      d:/  --->  d:\
      d:\  --->  d:\
       c:  --->  C:\Users\xxxxx\Documents\TestProject1\bin
      c:/  --->  c:\
      c:\  --->  c:\

Regression?

I do not think that this bug occured in a previous version.

Known Workarounds

I could check whether the path exactly matches ^[a-z]:$ and append a / if that is the case.

Configuration

I am using .NET 6.0.200-preview.21617.4 on Windows 11 Pro 64Bit:

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Issue Details

---

Description

I have an application which contains the following code line:

string foo = new DirectoryInfo("c:").FullName;

The string "c:" is user-provided and may be a longer path. If the user passes a path consisting only of the drive label and the colon (while omitting the finishing forward or backward slash) and the drive is the one matching the drive of the current execution directory, then the execution directory is returned instead of the root drive.

Reproduction Steps

1. Use a machine with multiple drives (if you do not have any explorer-mapped devices/drives, you may use the subst cmd command.
2. Create the following program:

using System.IO;
using System;


Console.WriteLine("current dir: " + Directory.GetCurrentDirectory());

foreach (string path in new[] {
    "d:",
    "d:/",
    "d:\\",
    "c:",
    "c:/",
    "c:\\",
})
    Console.WriteLine($"    {path,5}  --->  {new DirectoryInfo(path).FullName}");

4. compile it with net6.0-windows. I use the following version:

C:\> dotnet --list-sdks
3.1.416 [C:\Program Files\dotnet\sdk]
6.0.200-preview.21617.4 [C:\Program Files\dotnet\sdk]

3. Run it on the main system drive (i.e. c:/).

Expected behavior

Expected output:

current dir: C:\Users\xxxxx\Documents\TestProject1\bin
       d:  --->  D:\
      d:/  --->  d:\
      d:\  --->  d:\
       c:  ---> C:\
      c:/  --->  c:\
      c:\  --->  c:\

Actual behavior

Actual output:

current dir: C:\Users\xxxxx\Documents\TestProject1\bin
       d:  --->  D:\
      d:/  --->  d:\
      d:\  --->  d:\
       c:  ---> C:\Users\xxxxx\Documents\TestProject1\bin
      c:/  --->  c:\
      c:\  --->  c:\

Regression?

I do not think that this bug occured in a previous version.

Known Workarounds

I could check whether the path exactly matches ^[a-z]:$ and append a / if that is the case.

Configuration

I am using .NET 6.0.200-preview.21617.4 on Windows 11 Pro 64Bit:

Other information

No response

Author:	Unknown6656
Assignees:	-
Labels:	area-System.IO, untriaged
Milestone:	-

[danmoseley]

Hello @Unknown6656 this seems to be original behavior:

C:\proj\9>dotnet run -f net6.0
current dir: C:\proj\9
       d:  --->  D:\
      d:/  --->  d:\
      d:\  --->  d:\
       c:  --->  C:\proj\9
      c:/  --->  c:\
      c:\  --->  c:\

C:\proj\9>dotnet run -f net48
current dir: C:\proj\9
       d:  --->  D:\
      d:/  --->  d:\
      d:\  --->  d:\
       c:  --->  C:\proj\9
      c:/  --->  c:\
      c:\  --->  c:\

On Windows, "X:" means "current directory on the X drive". Our implementation ultimately calls GetFullPathName which gives the example "If you specify "U:" the path returned is the current directory on the "U:" drive".

If you want the behavior you describe, your workaround sounds like a good one.

thanks for opening the issue!

[Unknown6656]

Hello @danmoseley,
Thank you for replying so quickly. I was not aware that this behaviour was intended. Thanks for taking your time in order to clear up the issue. I must admit that the behaviour of resolving "x:" to the current path is a bit off-putting, but thanks anyways!