Support #dup and #clone on foreign strings

Author: eregon

CHANGELOG.md

@@ -24,6 +24,7 @@ Compatibility:
 * Fix `IO.pipe` - allow overriding `IO.new` that is used to create new pipes (#2692, @andykonchin).
 * Fix exception message when there are missing or extra keyword arguments - it contains all the missing/extra keywords now (#1522, @andrykonchin).
 * Always terminate native strings with enough `\0` bytes (#2704, @eregon).
+* Support `#dup` and `#clone` on foreign strings (@eregon).
 
 Performance:
 

spec/truffle/interop/polyglot/foreign_string_spec.rb

@@ -14,6 +14,7 @@
     @java_string = Truffle::Interop.as_string("abc")
     @truffle_string = Truffle::Interop.as_truffle_string("abc")
     @foreign_string = Truffle::Debug.foreign_string("abc")
+    @all = [@java_character, @java_string, @truffle_string, @foreign_string]
   end
 
   it "are of the expected Java class" do
@@ -99,6 +100,33 @@
     @foreign_string.should == "abc"
   end
 
+  it "supports #+@ and then mutation" do
+    @all.each do |foreign_string|
+      copy = +foreign_string
+      copy << "."
+      copy.should == "#{foreign_string}."
+    end
+  end
+
+  it "supports #dup and then mutation" do
+    @all.each do |foreign_string|
+      copy = foreign_string.dup
+      copy << "."
+      copy.should == "#{foreign_string}."
+    end
+  end
+
+  it "supports #clone and then mutation" do
+    @all.each do |foreign_string|
+      foreign_string.clone.should.frozen?
+      foreign_string.clone(freeze: true).should.frozen?
+
+      copy = foreign_string.clone(freeze: false)
+      copy << "."
+      copy.should == "#{foreign_string}."
+    end
+  end
+
   it "has all Ruby String methods" do
     @java_character.should == "C"
     @java_string.capitalize.should == "Abc"

src/main/ruby/truffleruby/core/truffle/polyglot_methods.rb

@@ -128,6 +128,10 @@ def clear(...)
       to_s.clear(...)
     end
 
+    def clone(...)
+      to_s.clone(...)
+    end
+
     def codepoints(...)
       to_s.codepoints(...)
     end
@@ -180,6 +184,10 @@ def dump(...)
       to_s.dump(...)
     end
 
+    def dup(...)
+      to_s.dup(...)
+    end
+
     def each_byte(...)
       to_s.each_byte(...)
     end

tool/generate-polyglot-methods.rb

@@ -17,11 +17,13 @@ module Polyglot
   module StringTrait
 RUBY
 
-string_methods = String.public_instance_methods(false).sort
+string_methods = String.public_instance_methods(false)
 # Already implemented
 string_methods -= %i[to_s to_str freeze frozen?]
+# Kernel methods which we want to handle by converting to a Ruby String first
+string_methods += %i[clone dup]
 
-string_methods.each do |name|
+string_methods.sort.each do |name|
   code << <<-RUBY
     def #{name}(...)
       to_s.#{name}(...)