Add specs for Truffle::Interop.languages and other_languages?

Author: eregon

spec/tags/truffle/interop/languages_tags.txt

@@ -0,0 +1,3 @@
+fails(GR-24618):Truffle::Interop.other_languages? returns true with --polyglot
+slow:Truffle::Interop.languages returns only ruby from the RubyLauncher
+slow:Truffle::Interop.other_languages? returns false without --polyglot

spec/truffle/interop/languages_spec.rb

@@ -0,0 +1,35 @@
+# Copyright (c) 2020 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 2.0, or
+# GNU General Public License version 2, or
+# GNU Lesser General Public License version 2.1.
+
+require_relative '../../ruby/spec_helper'
+
+describe "Truffle::Interop.languages" do
+  it "returns the public languages" do
+    Truffle::Interop.languages.should.include?('ruby')
+  end
+
+  guard_not -> { TruffleRuby.native? and Truffle::Boot.was_preinitialized? } do # GR-24618
+    it "returns only ruby from the RubyLauncher" do
+      # Use RbConfig.ruby to remove a potential --polyglot option
+      `#{RbConfig.ruby} -e 'p Truffle::Interop.languages'`.should == "[\"ruby\"]\n"
+    end
+  end
+end
+
+describe "Truffle::Interop.other_languages?" do
+  guard_not -> { TruffleRuby.native? } do
+    it "returns true with --polyglot" do
+      ruby_exe('p Truffle::Interop.other_languages?', options: '--polyglot').should == "true\n"
+    end
+  end
+
+  it "returns false without --polyglot" do
+    # Use RbConfig.ruby to remove a potential --polyglot option
+    `#{RbConfig.ruby} -e 'p Truffle::Interop.other_languages?'`.should == "false\n"
+  end
+end

src/main/java/org/truffleruby/interop/InteropNodes.java

@@ -1056,6 +1056,16 @@ protected DynamicObject languages() {
 
     }
 
+    @CoreMethod(names = "other_languages?", onSingleton = true, required = 0)
+    public abstract static class HasOtherLanguagesNode extends CoreMethodArrayArgumentsNode {
+
+        @Specialization
+        protected boolean hasOtherlanguages() {
+            return getContext().hasOtherPublicLanguages();
+        }
+
+    }
+
     @CoreMethod(names = "eval", onSingleton = true, required = 2)
     @ImportStatic({ StringCachingGuards.class, StringOperations.class })
     @ReportPolymorphism