Implement hasLanguage interop message for all enso objects

[Akirathan]

Blocks #11468

Pull Request Description

This PR implements the Truffle contract that all the Enso objects must export hasLanguage and getLanguage messages. By refactoring EnsoObject from an interface to an abstract class.

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
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• Unit tests have been written where possible.
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  • If applicable, it is suggested to paste a link to a successful run of the Extra Tests.

[JaroslavTulach]

Quick note: I believe there are other ways to enforce the contract while keeping EnsoObject an interface.

[JaroslavTulach]

I assume the goal is to provide default implementation of hasLanguage and getLanguage message for all Enso interop objects - e.g. those who implement EnsoObject interface.

• I would hope there is a better pattern to achieve this than converting to abstract class
• I don't like the toDisplayString to be defined, but unimplemented

Let's see if Truffle API offers some better alternative to achieve such a default common implementation of some ExportLibrary messages?

[Akirathan]

Let's see if Truffle API offers some better alternative to achieve such a default common implementation of some ExportLibrary messages?

I tried to leave EnsoObject as an interface, annotate it with @ExportLibrary(InteropLibrary.class), and implement hasLanguage and getLanguage as default methods. But @ExportMessage on default method on interface does not work - the Truffle DSL processor fails with an error. Any ideas are welcome.

As for toDisplayString implementation - that is required by Truffle DSL, because if you export one of getLanguage or hasLanguage messages, then, toDisplayString is abstract and has to be implemented. However, I am still not sure what is the proper way to define it here, in EnsoObject.

[Akirathan]

An approach with leaving EnsoObject as interfce, and defining a separate class LanguageForEnsoObject with @ExportLibrary(value = InteropLibrary.class, receiverType = EnsoObject.class) does not work:

diff --git a/engine/runtime/src/main/java/org/enso/interpreter/runtime/data/EnsoObject.java b/engine/runtime/src/main/java/org/enso/interpreter/runtime/data/EnsoObject.java
index ce60158116..eb65b641b2 100644
--- a/engine/runtime/src/main/java/org/enso/interpreter/runtime/data/EnsoObject.java
+++ b/engine/runtime/src/main/java/org/enso/interpreter/runtime/data/EnsoObject.java
@@ -1,6 +1,15 @@
 package org.enso.interpreter.runtime.data;

 import com.oracle.truffle.api.interop.TruffleObject;
+import com.oracle.truffle.api.library.DynamicDispatchLibrary;
+import com.oracle.truffle.api.library.ExportLibrary;
+import com.oracle.truffle.api.library.ExportMessage;

 /** All non-primitive Enso types extends from {@code EnsoObject}. */
-public interface EnsoObject extends TruffleObject {}
+@ExportLibrary(DynamicDispatchLibrary.class)
+public interface EnsoObject extends TruffleObject {
+  @ExportMessage
+  Class<?> dispatch() {
+    return LanguageForEnsoObject.class;
+  }
+}
diff --git a/engine/runtime/src/main/java/org/enso/interpreter/runtime/data/LanguageForEnsoObject.java b/engine/runtime/src/main/java/org/enso/interpreter/runtime/data/LanguageForEnsoObject.java
index cfd3eda4c0..6114f01e0e 100644
--- a/engine/runtime/src/main/java/org/enso/interpreter/runtime/data/LanguageForEnsoObject.java
+++ b/engine/runtime/src/main/java/org/enso/interpreter/runtime/data/LanguageForEnsoObject.java
@@ -1,8 +1,10 @@
 package org.enso.interpreter.runtime.data;

+import com.oracle.truffle.api.interop.InteropLibrary;
+import com.oracle.truffle.api.interop.TruffleObject;
 import com.oracle.truffle.api.library.ExportLibrary;

-@ExportLibrary()
-public final class LanguageForEnsoObject {
-
+@ExportLibrary(value = InteropLibrary.class, receiverType = EnsoObject.class)
+public final class LanguageForEnsoObject implements TruffleObject {
+  // TODO: Export hasLanguage and getLanguage methods
 }

This patch fails to compile because Truffle DSL processor fails with errror: "@ExportLibrary is not supported for interfaces". And the receiver type must export DynamicDispatchLibrary.

TL;DR; EnsoObject cannot stay as an interface.