PY-9342 Follow assignments chain to determine that method is bound

python/src/com/jetbrains/python/psi/types/PyFunctionType.java

@@ -18,10 +18,12 @@ package com.jetbrains.python.psi.types;
 import com.intellij.psi.PsiElement;
 import com.intellij.util.ArrayUtil;
 import com.intellij.util.ProcessingContext;
+import com.intellij.util.containers.ContainerUtil;
 import com.jetbrains.python.PyNames;
 import com.jetbrains.python.psi.*;
 import com.jetbrains.python.psi.impl.PyBuiltinCache;
 import com.jetbrains.python.psi.resolve.PyResolveContext;
+import com.jetbrains.python.psi.resolve.QualifiedResolveResult;
 import com.jetbrains.python.psi.resolve.RatedResolveResult;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -116,12 +118,23 @@ public class PyFunctionType implements PyCallableType {
     final PyFunction function = as(getCallable(), PyFunction.class);
     final boolean isNonStaticMethod = function != null && function.getContainingClass() != null && function.getModifier() != STATICMETHOD;
     if (isNonStaticMethod) {
+      // In Python 2 unbound methods have __method fake type
       if (LanguageLevel.forElement(location).isOlderThan(LanguageLevel.PYTHON30)) {
         return true;
       }
+      final PyExpression qualifier;
       if (location.isQualified()) {
+        qualifier = location.getQualifier();
+      }
+      else {
+        final PyResolveContext resolveContext = PyResolveContext.noImplicits().withTypeEvalContext(context);
+        final QualifiedResolveResult resolveResult = location.followAssignmentsChain(resolveContext);
+        final List<PyExpression> qualifiers = resolveResult.getQualifiers();
+        qualifier = ContainerUtil.isEmpty(qualifiers) ? null : qualifiers.get(qualifiers.size() - 1);
+      }
+      if (qualifier != null) {
         //noinspection ConstantConditions
-        final PyType qualifierType = PyTypeChecker.toNonWeakType(context.getType(location.getQualifier()), context);
+        final PyType qualifierType = PyTypeChecker.toNonWeakType(context.getType(qualifier), context);
         if (isInstanceType(qualifierType)) {
           return true;
         }

python/testData/completion/reassignedMethodSpecialAttributes.py

@@ -0,0 +1,6 @@
+class MyClass(object):
+    def method(self):
+        pass
+
+m = MyClass().method
+m.__<caret>

python/testData/inspections/PyUnresolvedReferencesInspection/methodSpecialAttributes.py

@@ -0,0 +1,25 @@
+class MyClass(object):
+    def method(self):
+        pass
+
+    @staticmethod
+    def static_method():
+        pass
+
+
+# Unbound method still treated as __method in Python 2
+MyClass.method.__func__
+MyClass.method.<warning descr="Cannot find reference '__defaults__' in 'function'">__defaults__</warning>
+
+# Bound method with qualifier
+inst = MyClass()
+inst.method.__func__
+inst.method.<warning descr="Cannot find reference '__defaults__' in 'function'">__defaults__</warning>
+
+# Reassigned bound method without qualifier
+m = inst.method
+
+# Static method
+# This reference should be marked as unresolved, but such warnings are suppressed for methods with decorators
+inst.static_method.__func__
+inst.static_method.__defaults__

python/testSrc/com/jetbrains/python/PythonCompletionTest.java

@@ -694,6 +694,11 @@ public class PythonCompletionTest extends PyTestCase {
     assertUnderscoredFunctionAttributesSuggested();
   }
 
+  // PY-9342
+  public void testReassignedMethodSpecialAttributes() {
+    assertUnderscoredMethodSpecialAttributesSuggested();
+  }
+
   private void assertUnderscoredFunctionAttributesSuggested() {
     myFixture.configureByFile("completion/" + getTestName(true) + ".py");
     myFixture.completeBasic();

python/testSrc/com/jetbrains/python/inspections/PyUnresolvedReferencesInspectionTest.java

@@ -371,6 +371,11 @@ public class PyUnresolvedReferencesInspectionTest extends PyInspectionTestCase {
     doMultiFileTest();
   }
 
+  // PY-9342
+  public void testMethodSpecialAttributes() {
+    doTest();
+  }
+
   // PY-11472
   public void testUnusedImportBeforeStarImport() {
     doMultiFileTest();