Consolidate GetUserName code

Once .NET Core 1.1 becomes available, we can likely remove the entirety
of CorePsExtensions.cs.

src/System.Management.Automation/CoreCLR/CorePsExtensions.cs

@@ -1026,25 +1026,8 @@ namespace System.Management.Automation
                 {
                     return Platform.NonWindowsGetDomainName();
                 }
-            }
-        }
 
-        internal static string WinGetUserName()
-        {
-            StringBuilder domainName = new StringBuilder(1024);
-            uint domainNameLen = (uint)domainName.Capacity;
-
-            byte ret = Win32Native.GetUserNameEx(Win32Native.NameSamCompatible, domainName, ref domainNameLen);
-            if (ret == 1)
-            {
-                string samName = domainName.ToString();
-                int index = samName.IndexOf('\\');
-                if (index != -1)
-                {
-                    return samName.Substring(index + 1);
-                }
             }
-            return string.Empty;
         }
 
         /// <summary>
@@ -1054,14 +1037,24 @@ namespace System.Management.Automation
         {
             get
             {
-                if (Platform.IsWindows)
+                #if UNIX
+                return Platform.Unix.UserName;
+                #else
+                StringBuilder domainName = new StringBuilder(1024);
+                uint domainNameLen = (uint)domainName.Capacity;
+
+                byte ret = Win32Native.GetUserNameEx(Win32Native.NameSamCompatible, domainName, ref domainNameLen);
+                if (ret == 1)
                 {
-                    return WinGetUserName();
-                }
-                else
-                {
-                    return Platform.NonWindowsGetUserName();
+                    string samName = domainName.ToString();
+                    int index = samName.IndexOf('\\');
+                    if (index != -1)
+                    {
+                        return samName.Substring(index + 1);
+                    }
                 }
+                return string.Empty;
+                #endif
             }
         }
 

src/System.Management.Automation/CoreCLR/CorePsPlatform.cs

@@ -314,11 +314,6 @@ namespace System.Management.Automation
             return string.Empty;
         }
 
-        internal static string NonWindowsGetUserName()
-        {
-            return Unix.UserName;
-        }
-
         // Hostname in this context seems to be the FQDN
         internal static string NonWindowsGetHostName()
         {

src/System.Management.Automation/engine/InformationRecord.cs

@@ -6,6 +6,10 @@ using Dbg = System.Management.Automation.Diagnostics;
 using System.Runtime.Serialization;
 using System.Collections.Generic;
 
+#if CORECLR
+using Environment = System.Management.Automation.Environment;
+#endif
+
 namespace System.Management.Automation
 {
     /// <summary>
@@ -38,15 +42,12 @@ namespace System.Management.Automation
 
             this.TimeGenerated = DateTime.Now;
             this.Tags = new List<string>();
-            if (Platform.IsWindows)
-            {
-                this.User = System.Security.Principal.WindowsIdentity.GetCurrent().Name;
-            }
-            else
-            {
-                this.User = Platform.NonWindowsGetUserName();
-            }
-            // Porting note: PsUtils.GetHostName() already handles platform specifics
+            // domain\user on Windows, just user on Unix
+            #if UNIX
+            this.User = Platform.Unix.UserName;
+            #else
+            this.User = System.Security.Principal.WindowsIdentity.GetCurrent().Name;
+            #endif
             this.Computer = PsUtils.GetHostName();
             this.ProcessId = (uint)System.Diagnostics.Process.GetCurrentProcess().Id;
             this.NativeThreadId = PsUtils.GetNativeThreadId();

src/System.Management.Automation/engine/InitialSessionState.cs

@@ -3148,7 +3148,13 @@ namespace System.Management.Automation.Runspaces
             // otherwise use the current user name.
             var userName = (!string.IsNullOrEmpty(this.UserDriveUserName)) ?
                 this.UserDriveUserName :
-                System.Security.Principal.WindowsIdentity.GetCurrent().Name;
+                // domain\user on Windows, just user on Unix
+                #if UNIX
+                Platform.Unix.UserName
+                #else
+                System.Security.Principal.WindowsIdentity.GetCurrent().Name
+                #endif
+                ;
 
             // Ensure that user name contains no invalid path characters.
             // MSDN indicates that logon names cannot contain any of these invalid characters,

test/csharp/test_CorePsPlatform.cs

@@ -34,7 +34,7 @@ namespace PSTests
                 // The process should return an exit code of 0 on success
                 Assert.Equal(0, process.ExitCode);
                 // It should be the same as what our platform code returns
-                Assert.Equal(username, Platform.NonWindowsGetUserName());
+                Assert.Equal(username, Platform.Unix.UserName());
             }
         }