Highlight the case when default and default_factory are specified (PY-27398)

python/src/com/jetbrains/python/inspections/PyDataclassInspection.kt

@@ -16,6 +16,7 @@ import com.jetbrains.python.codeInsight.typing.PyTypingTypeProvider
 import com.jetbrains.python.psi.*
 import com.jetbrains.python.psi.impl.PyBuiltinCache
 import com.jetbrains.python.psi.impl.PyCallExpressionHelper
+import com.jetbrains.python.psi.impl.stubs.PyDataclassFieldStubImpl
 import com.jetbrains.python.psi.resolve.PyResolveContext
 import com.jetbrains.python.psi.types.*
 
@@ -55,8 +56,9 @@ class PyDataclassInspection : PyInspection() {
 
           node.processClassLevelDeclarations { element, _ ->
             if (element is PyTargetExpression && !PyTypingTypeProvider.isClassVar(element, myTypeEvalContext)) {
-                processDefaultFieldValue(element)
-                processAsInitVar(element, postInit)?.let { initVars.add(it) }
+              processDefaultFieldValue(element)
+              processAsInitVar(element, postInit)?.let { initVars.add(it) }
+              processFieldFunctionCall(element)
             }
 
             true
@@ -189,6 +191,15 @@ class PyDataclassInspection : PyInspection() {
       return null
     }
 
+    private fun processFieldFunctionCall(field: PyTargetExpression) {
+      val fieldStub = PyDataclassFieldStubImpl.create(field)
+      if (fieldStub != null && fieldStub.hasDefault() && fieldStub.hasDefaultFactory()) {
+        val call = field.findAssignedValue() as? PyCallExpression ?: return
+
+        registerProblem(call.argumentList, "cannot specify both default and default_factory", ProblemHighlightType.GENERIC_ERROR)
+      }
+    }
+
     private fun processPostInitDefinition(postInit: PyFunction,
                                           dataclassParameters: DataclassParameters,
                                           initVars: List<PyTargetExpression>) {

python/testData/inspections/PyDataclassInspection/fieldDefaultAndDefaultFactory.py

@@ -0,0 +1,7 @@
+import dataclasses
+
+@dataclasses.dataclass
+class E1:
+    a: int = dataclasses.field(default=1)
+    b: int = dataclasses.field(default_factory=int)
+    c: int = dataclasses.field<error descr="cannot specify both default and default_factory">(default=1, default_factory=int)</error>

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

@@ -71,6 +71,11 @@ public class PyDataclassInspectionTest extends PyInspectionTestCase {
     doTest();
   }
 
+  // PY-27398
+  public void testFieldDefaultAndDefaultFactory() {
+    doTest();
+  }
+
   @Override
   protected void doTest() {
     runWithLanguageLevel(