Ensure running powershell within PowerShell starts instance of currently running PowerShell (#4481)

Modify PATH env var at startup so that $PSHOME is in front

src/Microsoft.PowerShell.ConsoleHost/host/msh/ConsoleHost.cs

@@ -134,6 +134,14 @@ namespace Microsoft.PowerShell
             }
 #endif
 
+            // put PSHOME in front of PATH so that calling `powershell` within `powershell` always starts the same running version
+            string path = Environment.GetEnvironmentVariable("PATH");
+            string pshome = Utils.DefaultPowerShellAppBase;
+            if (!path.Contains(pshome))
+            {
+                Environment.SetEnvironmentVariable("PATH", pshome + Path.PathSeparator + path);
+            }
+
             try
             {
                 string profileDir;

test/powershell/Host/ConsoleHost.Tests.ps1

@@ -486,6 +486,12 @@ foo
             bash -c "unset HOME;$powershell -c '1+1'" | Should BeExactly 2
         }
     }
+
+    Context "PATH environment variable" {
+        It "`$PSHOME should be in front so that powershell.exe starts current running PowerShell" {
+            powershell -v | Should Match $psversiontable.GitCommitId
+        }
+    }
 }
 
 Describe "Console host api tests" -Tag CI {