provide type, and therefore completion, for function decorated with @property (PY-5951)

python/src/com/jetbrains/python/psi/impl/PyReferenceExpressionImpl.java

@@ -306,14 +306,18 @@ public class PyReferenceExpressionImpl extends PyElementImpl implements PyRefere
       PsiFile file = ((PsiDirectory)target).findFile(PyNames.INIT_DOT_PY);
       if (file != null) return getTypeFromTarget(file, context, anchor);
     }
+    if (target instanceof PyFunction) {
+      final PyDecoratorList decoratorList = ((PyFunction)target).getDecoratorList();
+      if (decoratorList != null) {
+        final PyDecorator decorator = decoratorList.findDecorator(PyNames.PROPERTY);
+        if (decorator != null) {
+          return PyBuiltinCache.getInstance(target).getObjectType(PyNames.PROPERTY);
+        }
+      }
+    }
     return null;
   }
 
-  @Nullable
-  private static PyType getTypeIfExpr(PyElement def, TypeEvalContext context) {
-    return def instanceof PyExpression ? context.getType((PyExpression)def) : null;
-  }
-
   @Nullable
   public static PyType getReferenceTypeFromProviders(@NotNull final PsiElement target,
                                                      TypeEvalContext context,

python/src/com/jetbrains/python/psi/resolve/CompletionVariantsProcessor.java

@@ -8,9 +8,11 @@ import com.intellij.psi.PsiElement;
 import com.intellij.psi.util.PsiTreeUtil;
 import com.intellij.util.Function;
 import com.intellij.util.PlatformIcons;
+import com.jetbrains.python.PyNames;
 import com.jetbrains.python.codeInsight.completion.PyClassInsertHandler;
 import com.jetbrains.python.codeInsight.completion.PyFunctionInsertHandler;
 import com.jetbrains.python.psi.*;
+import com.jetbrains.python.psi.impl.PyBuiltinCache;
 import com.jetbrains.python.psi.types.PyType;
 import com.jetbrains.python.psi.types.TypeEvalContext;
 import org.jetbrains.annotations.Nullable;
@@ -65,6 +67,13 @@ public class CompletionVariantsProcessor extends VariantsProcessor {
   }
 
   private static boolean isSingleArgDecoratorCall(PsiElement elementInCall, PyFunction callee) {
+    // special case hack to avoid the need of patching generator3.py
+    PyClass containingClass = callee.getContainingClass();
+    if (containingClass != null && PyNames.PROPERTY.equals(containingClass.getName()) &&
+        PyBuiltinCache.getInstance(elementInCall).hasInBuiltins(containingClass)) {
+      return true;
+    }
+
     if (callee.getParameterList().getParameters().length > 1) {
       return false;
     }

python/testData/completion/propertyDecorator.after.py

@@ -0,0 +1,9 @@
+class C(object):
+    def __init__(self):
+        self._x = None
+
+    @property
+    def x(self):
+        return self._x
+
+    @x.setter

python/testData/completion/propertyDecorator.py

@@ -0,0 +1,9 @@
+class C(object):
+    def __init__(self):
+        self._x = None
+
+    @property
+    def x(self):
+        return self._x
+
+    @x.set<caret>

python/testSrc/com/jetbrains/python/Py3CompletionTest.java

@@ -0,0 +1,25 @@
+package com.jetbrains.python;
+
+import com.intellij.testFramework.LightProjectDescriptor;
+import com.jetbrains.python.fixtures.PyTestCase;
+
+/**
+ * @author yole
+ */
+public class Py3CompletionTest extends PyTestCase {
+  @Override
+  protected LightProjectDescriptor getProjectDescriptor() {
+    return ourPy3Descriptor;
+  }
+
+  public void testPropertyDecorator() {
+    doTest();
+  }
+
+  private void doTest() {
+    final String testName = "completion/" + getTestName(true);
+    myFixture.configureByFile(testName + ".py");
+    myFixture.completeBasic();
+    myFixture.checkResultByFile(testName + ".after.py");
+  }
+}

python/testSrc/com/jetbrains/python/PythonAllTestsSuite.java

@@ -39,6 +39,7 @@ public class PythonAllTestsSuite {
     CythonResolveTest.class,
     PyAssignmentMappingTest.class,
     PythonCompletionTest.class,
+    Py3CompletionTest.class,
     PyInheritorsSearchTest.class,
     PyParameterInfoTest.class,
     PyDecoratorTest.class,