Add '-settingsfile' to 'pwsh' to support loading a custom powershell …

…config file. (PowerShell#5920)

Support loading a custom `powershell.config.json` file via the command-line for use in testing.
This change supports replacing the default `powershell.config.json` file that's usually loaded from the `PSHome` directory with a custom version file.

The primary use-cases for this command-line option are as follows:
1. Allow the CI system to disable settings that impact test run times; such as disabling syslog usage on Linux and MacOS
2. Support testing of syslog and os_log without interfering with normal PowerShell operations during test runs via launching an instance with custom log settings.

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

@@ -188,6 +188,7 @@ internal class CommandLineParameterParser
             "file",
             "executionpolicy",
             "command",
+            "settingsfile",
             "help"
         };
 
@@ -709,6 +710,36 @@ private void ParseHelper(string[] args)
                         break;
                     }
                 }
+
+                else if (MatchSwitch(switchKey, "settingsfile", "settings") )
+                {
+                    ++i;
+                    if (i >= args.Length)
+                    {
+                        WriteCommandLineError(
+                            CommandLineParameterParserStrings.MissingSettingsFileArgument);
+                        break;
+                    }
+                    string configFile = null;
+                    try
+                    {
+                        configFile = NormalizeFilePath(args[i]);
+                    }
+                    catch (Exception ex)
+                    {
+                        string error = string.Format(CultureInfo.CurrentCulture, CommandLineParameterParserStrings.InvalidSettingsFileArgument, args[i], ex.Message);
+                        WriteCommandLineError(error);
+                        break;
+                    }
+
+                    if (!System.IO.File.Exists(configFile))
+                    {
+                        string error = string.Format(CultureInfo.CurrentCulture, CommandLineParameterParserStrings.SettingsFileNotExists, configFile);
+                        WriteCommandLineError(error);
+                        break;
+                    }
+                    PowerShellConfig.Instance.SetSystemConfigFilePath(configFile);
+                }
 #if STAMODE
                 // explicit setting of the ApartmentState Not supported on NanoServer
                 else if (MatchSwitch(switchKey, "sta", "s"))
@@ -849,6 +880,15 @@ private void ParseExecutionPolicy(string[] args, ref int i, ref string execution
             executionPolicy = args[i];
         }
 
+        private static string NormalizeFilePath(string path)
+        {
+            // Normalize slashes
+            path = path.Replace(StringLiterals.AlternatePathSeparator,
+                                StringLiterals.DefaultPathSeparator);
+
+            return Path.GetFullPath(path);
+        }
+
         private bool ParseFile(string[] args, ref int i, bool noexitSeen)
         {
             // Process file execution. We don't need to worry about checking -command
@@ -906,10 +946,7 @@ bool TryGetBoolValue(string arg, out bool boolValue)
                 string exceptionMessage = null;
                 try
                 {
-                    // Normalize slashes
-                    _file = args[i].Replace(StringLiterals.AlternatePathSeparator,
-                                            StringLiterals.DefaultPathSeparator);
-                    _file = Path.GetFullPath(_file);
+                    _file = NormalizeFilePath(args[i]);
                 }
                 catch (Exception e)
                 {
@@ -986,11 +1023,11 @@ bool TryGetBoolValue(string arg, out bool boolValue)
                                 string argName = arg.Substring(0, offset);
                                 if (TryGetBoolValue(argValue, out bool boolValue))
                                 {
-                                        _collectedArgs.Add(new CommandParameter(argName, boolValue));
+                                    _collectedArgs.Add(new CommandParameter(argName, boolValue));
                                 }
                                 else
                                 {
-                                        _collectedArgs.Add(new CommandParameter(argName, argValue));
+                                    _collectedArgs.Add(new CommandParameter(argName, argValue));
                                 }
                             }
                         }

src/Microsoft.PowerShell.ConsoleHost/resources/CommandLineParameterParserStrings.resx

@@ -186,6 +186,15 @@
   <data name="MissingConfigurationNameArgument" xml:space="preserve">
     <value>Cannot process the command because -Configuration requires an argument that is a remote endpoint configuration name. Specify this argument and try again.</value>
   </data>
+  <data name="MissingSettingsFileArgument" xml:space="preserve">
+    <value>Cannot process the command because -SettingsFile requires a file path. Supply a path for the SettingsFile parameter and then try the command again.</value>
+  </data>
+  <data name="InvalidSettingsFileArgument" xml:space="preserve">
+    <value>Processing -SettingsFile '{0}' failed: {1}. Specify a valid path for the -SettingsFile parameter.</value>
+  </data>
+  <data name="SettingsFileNotExists" xml:space="preserve">
+    <value>The argument '{0}' passed to the -SettingsFile does not exist. Provide the path to an existing json file as an argument to the -SettingsFile parameter.</value>
+  </data>
   <data name="InvalidArgument" xml:space="preserve">
     <value>Invalid argument '{0}', did you mean:</value>
   </data>

src/Microsoft.PowerShell.ConsoleHost/resources/ManagedEntranceStrings.resx

@@ -239,6 +239,17 @@ All parameters are case-insensitive.</value>
 
 -WindowStyle | -w
     Sets the window style to Normal, Minimized, Maximized or Hidden.
+
+-SettingsFile | -settings
+    Overrides the system-wide powershell.config.json settings file for the session.
+    By default, system-wide settings are read from the powershell.config.json
+    in the $PSHOME directory.
+
+    Note that these settings are not used by the endpoint specified
+    by the -ConfigurationName argument.
+
+    Example: pwsh -SettingsFile c:\myproject\powershell.config.json
+
     </value>
   </data>
 </root>