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

@@ -1026,11 +1026,20 @@ namespace System.Management.Automation
                 {
                     return Platform.NonWindowsGetDomainName();
                 }
+
             }
         }
 
-        internal static string WinGetUserName()
+        /// <summary>
+        /// UserName
+        /// </summary>
+        public static string UserName
         {
+            get
+            {
+                #if UNIX
+                return Platform.Unix.UserName;
+                #else
                 StringBuilder domainName = new StringBuilder(1024);
                 uint domainNameLen = (uint)domainName.Capacity;
 
@@ -1045,23 +1054,7 @@ namespace System.Management.Automation
                     }
                 }
                 return string.Empty;
-        }
-
-        /// <summary>
-        /// UserName
-        /// </summary>
-        public static string UserName
-        {
-            get
-            {
-                if (Platform.IsWindows)
-                {
-                    return WinGetUserName();
-                }
-                else
-                {
-                    return Platform.NonWindowsGetUserName();
-                }
+                #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)
-            {
+            // domain\user on Windows, just user on Unix
+            #if UNIX
+            this.User = Platform.Unix.UserName;
+            #else
             this.User = System.Security.Principal.WindowsIdentity.GetCurrent().Name;
-            }
-            else
-            {
-                this.User = Platform.NonWindowsGetUserName();
-            }
-            // Porting note: PsUtils.GetHostName() already handles platform specifics
+            #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());
             }
         }