[GR-15297] Reintroduce Truffle::MAIN for interop code.

PullRequest: truffleruby/808

Author: chrisseaton

spec/truffle/interop/import_spec.rb

@@ -0,0 +1,27 @@
+# Copyright (c) 2019 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.
+
+require_relative '../../ruby/spec_helper'
+
+guard -> { Truffle::Interop.polyglot_access? } do
+  describe "Truffle::Interop.import" do
+
+    it "imports an object" do
+      object = Object.new
+      Truffle::Interop.export :imports_an_object, object
+      Truffle::Interop.import(:imports_an_object).should == object
+    end
+
+    it "raises NameError if not found" do
+      -> {
+        Truffle::Interop.import(:not_registered_export_test)
+      }.should raise_error(NameError, "import 'not_registered_export_test' not found")
+    end
+
+  end
+end

src/main/java/org/truffleruby/RubyLanguage.java

@@ -145,7 +145,12 @@ protected Object findExportedSymbol(RubyContext context, String symbolName, bool
             return null;
         }
 
-        return context.send(context.getCoreLibrary().getTruffleInteropModule(), "lookup_symbol", context.getSymbolTable().getSymbol(symbolName));
+        Object implicit = context.send(context.getCoreLibrary().getTruffleInteropModule(), "lookup_symbol", context.getSymbolTable().getSymbol(symbolName));
+        if (implicit == NotProvided.INSTANCE) {
+            return null;
+        } else {
+            return implicit;
+        }
     }
 
     @SuppressWarnings("deprecation")

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

@@ -8,8 +8,10 @@
 # GNU General Public License version 2, or
 # GNU Lesser General Public License version 2.1.
 
-module Truffle
+# Used by Truffle::Interop.lookup_symbol
+Truffle::Interop::MAIN = self
 
+module Truffle
   module Interop
 
     def self.import_method(name)
@@ -111,7 +113,7 @@ def self.lookup_symbol(name)
       elsif Truffle::SymbolOperations.is_constant?(name) && Object.const_defined?(name)
         Object.const_get(name)
       else
-        nil
+        undefined
       end
     end