Fix encoding 866 crash: register CodePagesEncodingProvider + SharedIO fallback

[dronov-dmitry]

Problem

Python.CreateEngine() crashes with:

InvalidOperationException:
  Failed to load language 'IronPython 2.7.12':
    No data is available for encoding 866.

This happens in hosting environments like Dynamo (Autodesk Revit) or on .NET Core where cp866 encoding is not registered by default.

Root cause

SharedIO.InitializeInput() accesses Console.InputEncoding without error handling. On Russian Windows this returns cp866, but in certain hosting environments the codepage data is unavailable, causing ArgumentException.

Fix (2 parts)

Part 1: DLR — SharedIO fallback

File: Src/DLR/Src/Microsoft.Scripting/Runtime/SharedIO.cs

Added TryGetConsoleEncoding() helper that wraps console encoding access in try-catch with UTF-8 fallback:

private static Encoding TryGetConsoleEncoding(Func<Encoding> getter, Encoding fallback) {
    try { return getter(); } catch { return fallback; }
}

Applied to:

• InitializeInput() — Console.InputEncoding → fallback Encoding.UTF8
• InitializeOutput() — Console.Out → fallback TextWriter.Null
• InitializeErrorOutput() — Console.Error → fallback TextWriter.Null

Full diff for DLR submodule:

diff --git a/Src/Microsoft.Scripting/Runtime/SharedIO.cs b/Src/Microsoft.Scripting/Runtime/SharedIO.cs
index 4087314..8c4be89 100644
--- a/Src/Microsoft.Scripting/Runtime/SharedIO.cs
+++ b/Src/Microsoft.Scripting/Runtime/SharedIO.cs
@@ -87,16 +87,24 @@
         internal SharedIO() {
         }
 
+        private static Encoding TryGetConsoleEncoding(Func<Encoding> getter, Encoding fallback) {
+            try {
+                return getter();
+            } catch {
+                return fallback;
+            }
+        }
+
         private void InitializeInput() {
             if (_inputStream == null) {
                 lock (_mutex) {
                     if (_inputStream == null) {
 #if FEATURE_FULL_CONSOLE
                         _inputStream = ConsoleInputStream.Instance;
-                        _inputEncoding = Console.InputEncoding;
+                        _inputEncoding = TryGetConsoleEncoding(() => Console.InputEncoding, Encoding.UTF8);
                         _inputReader = Console.In;
 #elif FEATURE_BASIC_CONSOLE
-                        _inputEncoding = Encoding.Default;
+                        _inputEncoding = TryGetConsoleEncoding(() => Encoding.Default, Encoding.UTF8);
                         _inputStream = new TextStream(Console.In, _inputEncoding);
                         _inputReader = Console.In;
 #else
@@ -115,7 +123,11 @@
                     if (_outputStream == null) {
 #if FEATURE_FULL_CONSOLE
                         _outputStream = Console.OpenStandardOutput();
-                        _outputWriter = Console.Out;
+                        try {
+                            _outputWriter = Console.Out;
+                        } catch {
+                            _outputWriter = TextWriter.Null;
+                        }
 #elif FEATURE_BASIC_CONSOLE
                         _outputStream = new TextStream(Console.Out);
                         _outputWriter = Console.Out;
@@ -134,7 +146,11 @@
                     if (_errorStream == null) {
 #if FEATURE_FULL_CONSOLE
                         _errorStream = Console.OpenStandardError();
-                        _errorWriter = Console.Error;
+                        try {
+                            _errorWriter = Console.Error;
+                        } catch {
+                            _errorWriter = TextWriter.Null;
+                        }
 #elif FEATURE_BASIC_CONSOLE
                         _errorStream =  new TextStream(Console.Error);
                         _errorWriter = Console.Error;

Part 2: IronPython — RegisterProvider (this PR)

File: Src/IronPython/Runtime/PythonContext.cs

Added static constructor that registers CodePagesEncodingProvider for .NET Core/Standard:

static PythonContext() {
    try {
#if NETCOREAPP || NETSTANDARD
        Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
#endif
    } catch { }
}

File: Src/IronPython/IronPython.csproj

Added System.Text.Encoding.CodePages package for non-net45 targets:

<ItemGroup Condition=" '\$(TargetFramework)' != 'net45' ">
    <PackageReference Include="System.Text.Encoding.CodePages" Version="4.6.0" />
</ItemGroup>

Testing

All tests pass (C# host simulating Dynamo + IronPython scripts):

[PASS] Python.CreateEngine()
[PASS] Script execution: x = 2 + 2 -> 4
[PASS] Cyrillic: привет = 'мир'
[PASS] groupBy from Processing_List_eng -> [(1,2),(2,3),(3,4)]
[PASS] External .py file execution
[PASS] Roundtrip encode/decode: utf-8, cp1251, iso-8859-1

Compatibility

• .NET Framework 4.5+ (codepages built-in, SharedIO fallback as safety net)
• .NET Core 3.1+ (RegisterProvider + SharedIO fallback)
• .NET Standard 2.0 (RegisterProvider + SharedIO fallback)

[dronov-dmitry]

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