[GR-55302] Support properties magically calling Java getters/setters in Jython emulation mode

Author: timfel

CHANGELOG.md

@@ -10,8 +10,7 @@ language runtime. The main focus is on user-observable behavior of the engine.
 * Update to Python 3.11.7
 * We now provide intrinsified `_pickle` module also in the community version.
 * `polyglot.eval` now raises more meaningful exceptions. Unavaliable languages raise `ValueError`. Exceptions from the polyglot language are raised directly as interop objects (typed as `polyglot.ForeignException`). The shortcut for executing python files without specifying language has been removed, use regular `eval` for executing Python code.
-* Update to Python 3.11.7.
-* We now provide intrinsified `_pickle` and `_struct` modules also in the community version. This means more packages will no work without allowing native access.
+* In Jython emulation mode we now magically fall back to calling Java getters or setters when using Python attribute access for non-visible properties. This can help migrating away from Jython if you relied on this behavior. 
 
 ## Version 24.0.0
 * We now provide a collection of recipes in the form of GitHub Actions to build popular native extensions on GraalPy. These provide a reproducible way for the community to build native extensions for GraalPy with the correct dependencies. See scripts/wheelbuilder/README.md for details.

graalpython/com.oracle.graal.python.test/src/tests/test_interop.py

@@ -639,6 +639,16 @@ def test_jython_star_import():
             exec('from java.lang.Byte import *', g)
             assert type(g['MAX_VALUE']) is int
 
+    def test_jython_accessors():
+        if __graalpython__.jython_emulation_enabled:
+            from java.util.logging import LogRecord
+            from java.util.logging import Level
+            lr = LogRecord(Level.ALL, "message")
+
+            assert lr.message == "message"
+            lr.message = "new message"
+            assert lr.message == "new message"
+
     @skipUnless(test_polyglot_languages, "tests other language access")
     def test_doctest():
         import doctest

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/foreign/ForeignObjectBuiltins.java

@@ -1020,6 +1020,11 @@ static Object doIt(VirtualFrame frame, Object self, Object name,
         }
     }
 
+    @TruffleBoundary(allowInlining = true)
+    private static String asJavaPrefixedMethod(String prefix, String member) {
+        return prefix + member.substring(0, 1).toUpperCase() + member.substring(1);
+    }
+
     @GenerateInline
     @GenerateCached(false)
     @ImportStatic(PythonOptions.class)
@@ -1038,10 +1043,22 @@ static Object doIt(Node inliningTarget, Object object, Object memberObj,
                 String member = castToString.execute(memberObj);
                 if (read.isMemberReadable(object, member)) {
                     return toPythonNode.executeConvert(read.readMember(object, member));
+                } else if (PythonLanguage.get(inliningTarget).getEngineOption(PythonOptions.EmulateJython)) {
+                    // no profile, above condition should fold to false when EmulateJython is off
+                    if (PythonContext.get(inliningTarget).getEnv().isHostObject(object)) {
+                        String getter = asJavaPrefixedMethod("get", member);
+                        if (read.isMemberInvocable(object, getter)) {
+                            try {
+                                return toPythonNode.executeConvert(read.invokeMember(object, getter));
+                            } catch (UnsupportedTypeException ignored) {
+                                // fall through to AttributeError
+                            }
+                        }
+                    }
                 }
             } catch (CannotCastException e) {
                 throw raiseNode.get(inliningTarget).raise(PythonBuiltinClassType.TypeError, ErrorMessages.ATTR_NAME_MUST_BE_STRING, memberObj);
-            } catch (UnknownIdentifierException | UnsupportedMessageException ignore) {
+            } catch (UnknownIdentifierException | UnsupportedMessageException | ArityException ignore) {
             } finally {
                 gil.acquire();
             }
@@ -1061,15 +1078,38 @@ static void doSet(Object object, Object key, Object value,
                         @Shared @Cached GilNode gil,
                         @Shared @Cached PRaiseNode.Lazy raiseNode) {
             gil.release(true);
+            String member;
             try {
-                lib.writeMember(object, castToString.execute(key), value);
+                member = castToString.execute(key);
             } catch (CannotCastException e) {
                 throw raiseNode.get(inliningTarget).raise(PythonBuiltinClassType.TypeError, ErrorMessages.ATTR_NAME_MUST_BE_STRING, key);
-            } catch (UnknownIdentifierException | UnsupportedMessageException | UnsupportedTypeException e) {
-                throw raiseNode.get(inliningTarget).raise(PythonErrorType.AttributeError, ErrorMessages.FOREIGN_OBJ_HAS_NO_ATTR_S, key);
+            }
+            try {
+                try {
+                    lib.writeMember(object, member, value);
+                    return;
+                } catch (UnknownIdentifierException | UnsupportedMessageException e) {
+                    if (PythonLanguage.get(inliningTarget).getEngineOption(PythonOptions.EmulateJython)) {
+                        // no profile, above condition folds to false when EmulateJython is off
+                        try {
+                            if (PythonContext.get(inliningTarget).getEnv().isHostObject(object)) {
+                                String setter = asJavaPrefixedMethod("set", member);
+                                if (lib.isMemberInvocable(object, setter)) {
+                                    lib.invokeMember(object, setter, value);
+                                    return;
+                                }
+                            }
+                        } catch (ArityException | UnsupportedMessageException | UnknownIdentifierException ignore) {
+                            // fall through to AttributeError
+                        }
+                    }
+                }
+            } catch (UnsupportedTypeException e) {
+                throw raiseNode.get(inliningTarget).raise(PythonErrorType.TypeError, ErrorMessages.INVALID_TYPE_FOR_S, key);
             } finally {
                 gil.acquire();
             }
+            throw raiseNode.get(inliningTarget).raise(PythonErrorType.AttributeError, ErrorMessages.FOREIGN_OBJ_HAS_NO_ATTR_S, key);
         }
 
         @Specialization(guards = "isNoValue(value)")