Get rid of unclear isBuiltin check Get elements number for tuples if callType is PyUnionType

python/src/com/jetbrains/python/inspections/PyStringFormatInspection.java

@@ -605,19 +605,27 @@ public class PyStringFormatInspection extends PyInspection {
         .collect(
           Collectors.summarizingInt(
             callType -> {
-              if (callType instanceof PyTupleType) {
-                return ((PyTupleType)callType).getElementCount();
-              }
-              else if (callType instanceof PyNoneType) {
+              if (callType instanceof PyNoneType) {
                 return 1;
               }
               else if (callType instanceof PyClassType) {
-                if (PyBuiltinCache.getInstance(callExpression).isBuiltin(((PyClassType)callType).getPyClass())) {
-                  return 1;
-                }
+                return countElements(evalContext, (PyClassType)callType);
               }
               else if (callType instanceof PyUnionType) {
-                if (((PyUnionType)callType).getMembers().stream().allMatch(PyType::isBuiltin)) return 1;
+                int maxNumber = 1;
+                boolean allForSure = true;
+                for (PyType member : ((PyUnionType)callType).getMembers()) {
+                  PyClassType classType = as(member, PyClassType.class);
+                  if (classType != null) {
+                    int elementsCount = countElements(evalContext, classType);
+                    allForSure = allForSure && elementsCount != -1;
+                    maxNumber = Math.max(maxNumber, elementsCount);
+                  }
+                  else {
+                    allForSure = false;
+                  }
+                }
+                return allForSure ? maxNumber : -1;
               }
 
               return -1;
@@ -633,6 +641,16 @@ public class PyStringFormatInspection extends PyInspection {
       }
     }
 
+    private static int countElements(@NotNull TypeEvalContext evalContext, PyClassType callType) {
+      if (!callType.getPyClass().isSubclass(PyNames.TUPLE, evalContext)) {
+        return 1;
+      }
+      else if (callType instanceof PyTupleType) {
+        return ((PyTupleType)callType).getElementCount();
+      }
+      return -1;
+    }
+
     public Visitor(final ProblemsHolder holder, LocalInspectionToolSession session) {
       super(holder, session);
     }

python/testData/inspections/PyStringFormatInspection/UnionCallType.py

@@ -0,0 +1,54 @@
+from collections import namedtuple
+
+def simple_func(cond):
+    if cond:
+        return 1
+    else:
+        return 1, 2
+
+Point = namedtuple('Point', ['x', 'y'])
+def named_tuple_func(cond):
+    if cond:
+        return 1
+    else:
+        return Point(1, 1)
+
+def primitive_types_func(cond):
+    if cond:
+        return 1
+    else:
+        return 2
+
+def collection_func(cond):
+    if cond:
+        return [1, 2]
+    else:
+        return {1, 2}
+
+def list_tuple(cond):
+    if cond:
+        return [1, 2]
+    else:
+        return 1, 2
+
+"%s %s" % simple_func(True)
+"%s %s" % simple_func(False)
+"%s %s %s" % <warning descr="Too few arguments for format string">simple_func(False)</warning>
+
+"%s %s" % named_tuple_func(True)
+"%s %s" % named_tuple_func(False)
+"%s %s %s" % named_tuple_func(False)
+
+"%s" % primitive_types_func(True)
+"%s %s" % <warning descr="Too few arguments for format string">primitive_types_func(True)</warning>
+"%s %s" % <warning descr="Too few arguments for format string">primitive_types_func(False)</warning>
+"%s %s %s" % <warning descr="Too few arguments for format string">primitive_types_func(False)</warning>
+
+"%s %s" % <warning descr="Too few arguments for format string">collection_func(True)</warning>
+"%s %s" % <warning descr="Too few arguments for format string">collection_func(False)</warning>
+"%s %s %s" % <warning descr="Too few arguments for format string">collection_func(False)</warning>
+
+"%s %s" % list_tuple(True)
+"%s %s" % list_tuple(True)
+"%s %s %s" % <warning descr="Too few arguments for format string">list_tuple(True)</warning>
+

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

@@ -208,6 +208,10 @@ public class PyStringFormatInspectionTest extends PyTestCase {
     doTest();
   }
 
+  public void testUnionCallType() {
+    doTest();
+  }
+
   private void doTest() {
     myFixture.configureByFile(TEST_DIRECTORY + getTestName(false) + ".py");
     myFixture.enableInspections(PyStringFormatInspection.class);