Enable the creation of dummy encodings from C extensions.

Author: aardvark179

lib/truffle/truffle/cext.rb

@@ -733,6 +733,11 @@ def rb_enc_to_index(enc)
     Truffle.invoke_primitive :encoding_get_encoding_index, enc
   end
 
+  def rb_define_dummy_encoding(name)
+    enc, idx = Truffle::EncodingOperations.dummy_encoding(name)
+    idx
+  end
+
   def rb_str_new_frozen(value)
     if value.frozen?
       value
@@ -899,7 +904,7 @@ def rb_str_encode(str, to, ecflags, ecopts)
   end
 
   def rb_str_conv_enc_opts(str, from, to, ecflags, ecopts)
-    if (to.ascii_compatible? && str.ascii_only?) || to == Encoding::ASCII_8BIT
+    if (to.ascii_compatible? && str.ascii_only?) || to == Encoding::ASCII_8BIT || to.dummy?
       if str.encoding != to
         str = str.dup
         str.force_encoding(to)

src/main/c/cext/ruby.c

@@ -3099,7 +3099,7 @@ int rb_enc_replicate(const char *name, rb_encoding *encoding) {
 }
 
 int rb_define_dummy_encoding(const char *name) {
-  rb_tr_error("rb_define_dummy_encoding not implemented");
+  return polyglot_as_i32(RUBY_CEXT_INVOKE_NO_WRAP("rb_define_dummy_encoding", rb_str_new_cstr(name)));
 }
 
 #undef rb_enc_str_new_cstr

src/main/java/org/truffleruby/core/CoreLibrary.java

@@ -1424,6 +1424,7 @@ public DynamicObject getWarningModule() {
             "/core/truffle/boot.rb",
             "/core/truffle/debug.rb",
             "/core/truffle/warnings.rb",
+            "/core/truffle/encoding_operations.rb",
             "/core/truffle/exception_operations.rb",
             "/core/truffle/hash_operations.rb",
             "/core/truffle/numeric_operations.rb",

src/main/java/org/truffleruby/core/encoding/EncodingManager.java

@@ -260,6 +260,18 @@ public DynamicObject defineAlias(Encoding encoding, String name) {
         return rubyEncoding;
     }
 
+    @TruffleBoundary
+    public synchronized DynamicObject dummyEncoding(String name) {
+        if (getRubyEncoding(name) != null) {
+            return null;
+        }
+
+        EncodingDB.dummy(name);
+        byte[] nameBytes = name.getBytes();
+        final Entry entry = EncodingDB.getEncodings().get(nameBytes);
+        return defineEncoding(entry, nameBytes, 0, nameBytes.length);
+    }
+
     @TruffleBoundary
     public synchronized DynamicObject replicateEncoding(Encoding encoding, String name) {
         if (getRubyEncoding(name) != null) {

src/main/java/org/truffleruby/core/encoding/EncodingNodes.java

@@ -676,6 +676,29 @@ private DynamicObject replicate(String name, Encoding encoding) {
 
     }
 
+    @Primitive(name = "dummy_encoding", needsSelf = false)
+    public static abstract class DummyEncodingeNode extends PrimitiveArrayArgumentsNode {
+
+        @Specialization(guards = "isRubyString(nameObject)")
+        public DynamicObject dummyEncoding(DynamicObject nameObject) {
+            final String name = StringOperations.getString(nameObject);
+
+            final DynamicObject newEncoding = dummy(name);
+            if (newEncoding == null) {
+                throw new RaiseException(getContext(), coreExceptions().argumentErrorEncodingAlreadyRegistered(name, this));
+            }
+
+            final int index = Layouts.ENCODING.getEncoding(newEncoding).getIndex();
+            return createArray(new Object[]{ newEncoding, index }, 2);
+        }
+
+        @TruffleBoundary
+        private DynamicObject dummy(String name) {
+            return getContext().getEncodingManager().dummyEncoding(name);
+        }
+
+    }
+
     @Primitive(name = "encoding_get_encoding_by_index", needsSelf = false, lowerFixnum = 1)
     public static abstract class GetEncodingObjectByIndexNode extends PrimitiveArrayArgumentsNode {
 

src/main/ruby/core/truffle/encoding_operations.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+# Copyright (c) 2018 Oracle and/or its affiliates. All rights reserved. This
+# code is released under a tri EPL/GPL/LGPL license. You can use it,
+# redistribute it and/or modify it under the terms of the:
+#
+# Eclipse Public License version 1.0, or
+# GNU General Public License version 2, or
+# GNU Lesser General Public License version 2.1.
+
+module Truffle
+  module EncodingOperations
+    def self.dummy_encoding(name)
+      new_encoding, index = Truffle.invoke_primitive :dummy_encoding, name
+      ::Encoding::EncodingMap[name.upcase.to_sym] = [nil, index]
+      [new_encoding, index]
+    end
+  end
+end