System.Diagnostics.Process long paths issues #58492

Unhandled exception. System.ComponentModel.Win32Exception (206): The filename or extension is too long.
   at System.Diagnostics.Process.StartWithCreateProcess(ProcessStartInfo startInfo) in System.Diagnostics.Process.dll:token 0x600016a+0x37c
   at System.Diagnostics.Process.Start() in System.Diagnostics.Process.dll:token 0x600013f+0xab
   at System.Diagnostics.Process.Start(ProcessStartInfo startInfo) in System.Diagnostics.Process.dll:token 0x6000143+0x1b
   at ConsoleApp40.Program.Main(String[] args) in C:\Users\kwicher\source\repos\ConsoleApp40\x\ConsoleApp40\Program.cs:line 77
When using path directly:
Unhandled exception. System.ComponentModel.Win32Exception (2): The system cannot find the file specified.
   at System.Diagnostics.Process.StartWithCreateProcess(ProcessStartInfo startInfo) in System.Diagnostics.Process.dll:token 0x600016a+0x37c
   at System.Diagnostics.Process.Start() in System.Diagnostics.Process.dll:token 0x600013f+0xab
   at System.Diagnostics.Process.Start(ProcessStartInfo startInfo) in System.Diagnostics.Process.dll:token 0x6000143+0x1b
   at ConsoleApp40.Program.Main(String[] args) in C:\Users\kwicher\source\repos\ConsoleApp40\x\ConsoleApp40\Program.cs:line 77
It's possible to workaround this issue by using `GetShortPathName`, i.e. (in this example shorten the path by using `GetFileName` method):
Click to expand code
        [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
        private static unsafe extern int GetShortPathName(char* longPath, char* shortPath, int numChars);
        public static unsafe string GetFileName(string longPath)
            longPath = Path.GetFullPath(longPath);
            const int MAX_PATH = 260;
            if (longPath.Length < MAX_PATH)
                return longPath;
            if (!longPath.StartsWith(@"\\?\"))
                longPath = @"\\?\" + longPath;
            fixed (char* longPathBuff = longPath)
                int size = GetShortPathName(longPathBuff, null, 0);
                if (size == 0)
                    // error, best attempt is to at least try with that path:
                    return longPath;
                char[] buff = new char[size];
                fixed (char* shortPathBuff = buff)
                    if (GetShortPathName(longPathBuff, shortPathBuff, size) == 0)
                        // error, best attempt:
                        return longPath;
                return new string(buff);
When starting a process by passing just a file name (without directory) to FileName and directory to WorkingDirectory in the ProcessStructInfo this always throws an exception as well:
Click to see exception details
Regardless of using \\?\ prefix you get the same exception:
Unhandled exception. System.ComponentModel.Win32Exception (267): The directory name is invalid.
   at System.Diagnostics.Process.StartWithCreateProcess(ProcessStartInfo startInfo) in System.Diagnostics.Process.dll:token 0x600016a+0x37c
   at System.Diagnostics.Process.Start() in System.Diagnostics.Process.dll:token 0x600013f+0xab
   at System.Diagnostics.Process.Start(ProcessStartInfo startInfo) in System.Diagnostics.Process.dll:token 0x6000143+0x1b
   at ConsoleApp40.Program.Main(String[] args) in C:\Users\kwicher\source\repos\ConsoleApp40\x\ConsoleApp40\Program.cs:line 78
Possibly  same workaround as above could work to fix this although have not tried.
When using workaround from the first bullet point the arguments passed to ProcessStartInfo disappear, meaning that args in main has zero length even though arguments were passed - I have not digged into why this happens or where do they get lost
I've tried on netcoreapp3.1, net5.0 and net6.0 (preview) and seeing the same results.
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