Fix Default/OEM encoding behavior PowerShell Core (#3467)

Based on the conclusion in discussion #3248, this PR fix "OEM" and "Default" encoding in powershell.
1. OEM -- We need an internal fix because .Net Core has no "OEM" encoding.
The fix gives the following PowerShell Core behavior on "OEM" encoding:
   - on Windows - as Windows PowerShell based on GetOEMCP() and legacy encodings (System.Text.Encoding.CodePages)
   - on Unix - the same as default encoding in PowerShell Core

2. Default -- We need internal fix because CoreFX `Encoding.default` for all platforms is UTF8.
Until we complete the `Encoding RFC` we should restore behavior as in Windows PowerShell.
The fix gives the following PowerShell Core behavior on "Default" encoding:
   - on Windows - as Windows PowerShell based on GetACP() and legacy encodings (System.Text.Encoding.CodePages)
   - on Unix - UTF-8 without BOM (We are expecting that the same will be [in CoreFX](https://github.com/dotnet/coreclr/issues/10643))

src/Microsoft.PowerShell.SDK/Microsoft.PowerShell.SDK.csproj

@@ -85,7 +85,6 @@
     <PackageReference Include="System.ServiceModel.Primitives" Version="4.3.0" />
     <PackageReference Include="System.ServiceModel.Security" Version="4.3.0" />
     <PackageReference Include="System.ServiceProcess.ServiceController" Version="4.3.0" />
-    <PackageReference Include="System.Text.Encoding.CodePages" Version="4.3.0" />
     <PackageReference Include="System.Text.Encodings.Web" Version="4.3.0" />
     <PackageReference Include="System.Threading.AccessControl" Version="4.3.0" />
     <PackageReference Include="System.Threading.Overlapped" Version="4.3.0" />

src/System.Management.Automation/System.Management.Automation.csproj

@@ -47,6 +47,7 @@
     <PackageReference Include="System.Security.Cryptography.Algorithms" Version="4.3.0" />
     <PackageReference Include="System.Security.Cryptography.Pkcs" Version="4.3.0" />
     <PackageReference Include="System.Security.Cryptography.X509Certificates" Version="4.3.0" />
+    <PackageReference Include="System.Text.Encoding.CodePages" Version="4.3.0" />
     <PackageReference Include="System.Threading.Thread" Version="4.3.0" />
     <PackageReference Include="System.Threading.Tasks.Parallel" Version="4.3.0" />
     <PackageReference Include="System.Xml.XPath.XmlDocument" Version="4.3.0" />

src/System.Management.Automation/namespaces/FileSystemProvider.cs

@@ -7569,8 +7569,7 @@ private static Encoding GetEncodingFromEnum(FileSystemCmdletProviderEncoding typ
 
                 case FileSystemCmdletProviderEncoding.Oem:
                     {
-                        uint oemCP = NativeMethods.GetOEMCP();
-                        encoding = System.Text.Encoding.GetEncoding((int)oemCP);
+                        encoding = ClrFacade.GetOEMEncoding();
                     }
                     break;
 
@@ -7607,11 +7606,6 @@ public bool WasStreamTypeSpecified
             } // get
         } // WasStreamTypeSpecified
 
-        private static class NativeMethods
-        {
-            [DllImport(PinvokeDllNames.GetOEMCPDllName, SetLastError = false, CharSet = CharSet.Unicode)]
-            internal static extern uint GetOEMCP();
-        }
     } // class FileSystemContentDynamicParametersBase
 
     /// <summary>

src/System.Management.Automation/utils/ClrFacade.cs

@@ -530,22 +530,26 @@ internal static object[] GetCustomAttributes<T>(Assembly assembly)
         #region Encoding
 
         /// <summary>
-        /// Facade for Encoding.Default
+        /// Facade for getting default encoding
         /// </summary>
         internal static Encoding GetDefaultEncoding()
         {
             if (s_defaultEncoding == null)
             {
-#if CORECLR     // Encoding.Default is not in CoreCLR
-                // As suggested by CoreCLR team (tarekms), use latin1 (ISO-8859-1, CodePage 28591) as the default encoding.
-                // We will revisit this if it causes any failures when running tests on Core PS.
-                s_defaultEncoding = Encoding.GetEncoding(28591);
-#else
+#if UNIX        // PowerShell Core on Unix
+                s_defaultEncoding = new UTF8Encoding(false);
+#elif CORECLR   // PowerShell Core on Windows
+                EncodingRegisterProvider();
+
+                uint currentAnsiCp = NativeMethods.GetACP();
+                s_defaultEncoding = Encoding.GetEncoding((int)currentAnsiCp);
+#else           // Windows PowerShell
                 s_defaultEncoding = Encoding.Default;
 #endif
             }
             return s_defaultEncoding;
         }
+
         private static volatile Encoding s_defaultEncoding;
 
         /// <summary>
@@ -555,18 +559,34 @@ internal static Encoding GetOEMEncoding()
         {
             if (s_oemEncoding == null)
             {
-#if CORECLR     // The OEM code page '437' is not supported by CoreCLR.
-                // Use the default encoding (ISO-8859-1, CodePage 28591) as the OEM encoding in OneCore powershell.
+#if UNIX        // PowerShell Core on Unix
                 s_oemEncoding = GetDefaultEncoding();
-#else
+#elif CORECLR   // PowerShell Core on Windows
+                EncodingRegisterProvider();
+
+                uint oemCp = NativeMethods.GetOEMCP();
+                s_oemEncoding = Encoding.GetEncoding((int)oemCp);
+
+#else           // Windows PowerShell
                 uint oemCp = NativeMethods.GetOEMCP();
                 s_oemEncoding = Encoding.GetEncoding((int)oemCp);
 #endif
             }
             return s_oemEncoding;
         }
+
         private static volatile Encoding s_oemEncoding;
 
+#if CORECLR
+        private static void EncodingRegisterProvider()
+        {
+            if (s_defaultEncoding == null && s_oemEncoding == null)
+            {
+                Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
+            }
+        }
+#endif
+
         #endregion Encoding
 
         #region Security
@@ -1033,6 +1053,12 @@ private static class NativeMethods
             [DllImport(PinvokeDllNames.GetOEMCPDllName, SetLastError = false, CharSet = CharSet.Unicode)]
             internal static extern uint GetOEMCP();
 
+            /// <summary>
+            /// Pinvoke for GetACP to get the Windows operating system code page.
+            /// </summary>
+            [DllImport(PinvokeDllNames.GetACPDllName, SetLastError = false, CharSet = CharSet.Unicode)]
+            internal static extern uint GetACP();
+
             public const int S_OK = 0x00000000;
 
             /// <summary>

src/System.Management.Automation/utils/PInvokeDllNames.cs

@@ -135,6 +135,7 @@ internal static class PinvokeDllNames
         internal const string CreateToolhelp32SnapshotDllName = "api-ms-win-core-toolhelp-l1-1-0";           /*120*/
         internal const string Process32FirstDllName = "api-ms-win-core-toolhelp-l1-1-0";                     /*121*/
         internal const string Process32NextDllName = "api-ms-win-core-toolhelp-l1-1-0";                      /*122*/
+        internal const string GetACPDllName = "api-ms-win-core-localization-l1-2-0.dll";                     /*123*/
 #else
         internal const string QueryDosDeviceDllName = "kernel32.dll";                                        /*1*/
         internal const string CreateSymbolicLinkDllName = "kernel32.dll";                                    /*2*/
@@ -257,6 +258,7 @@ internal static class PinvokeDllNames
         internal const string CreateToolhelp32SnapshotDllName = "kernel32.dll";                              /*120*/
         internal const string Process32FirstDllName = "kernel32.dll";                                        /*121*/
         internal const string Process32NextDllName = "kernel32.dll";                                         /*122*/
+        internal const string GetACPDllName = "kernel32.dll";                                                /*123*/
 #endif
     }
 }