Fix calculating arguments for __setitem__ (PY-27949)

python/psi-api/src/com/jetbrains/python/psi/PySubscriptionExpression.java

@@ -15,9 +15,11 @@
  */
 package com.jetbrains.python.psi;
 
+import com.intellij.psi.PsiElement;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
@@ -35,6 +37,12 @@ public interface PySubscriptionExpression extends PyQualifiedExpression, PyCallS
   @NotNull
   @Override
   default List<PyExpression> getArguments(@Nullable PyCallable resolvedCallee) {
+    if (AccessDirection.of(this) == AccessDirection.WRITE) {
+      final PsiElement parent = getParent();
+      if (parent instanceof PyAssignmentStatement) {
+        return Arrays.asList(getIndexExpression(), ((PyAssignmentStatement)parent).getAssignedValue());
+      }
+    }
     return Collections.singletonList(getIndexExpression());
   }
 

python/testData/inspections/PyTypeCheckerInspection/AssigningToDictEntry.py

@@ -0,0 +1,5 @@
+from typing import Dict
+
+data = {}  # type: Dict[int, str]
+data[<weak_warning descr="Expected type 'int' (matched generic type '_KT'), got 'str' instead">'test'</weak_warning>] = <weak_warning descr="Expected type 'str' (matched generic type '_VT'), got 'int' instead">12</weak_warning>
+data[12] = 'test'

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

@@ -530,4 +530,9 @@ public class PyTypeCheckerInspectionTest extends PyInspectionTestCase {
   public void testOverloadedFunctionAssignedToTargetInStub() {
     doMultiFileTest();
   }
+
+  // PY-27949
+  public void testAssigningToDictEntry() {
+    doTest();
+  }
 }