PY-21048 Fixed: Strange inspection in return values of async function

Unwrap __coroutine in PyTypeCheckerInspection when matching expected and actual return types

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

@@ -91,7 +91,7 @@ public class PyTypeCheckerInspection extends PyInspection {
         if (annotation != null || typeCommentAnnotation != null) {
           final PyExpression returnExpr = node.getExpression();
           final PyType actual = returnExpr != null ? myTypeEvalContext.getType(returnExpr) : PyNoneType.INSTANCE;
-          final PyType expected = myTypeEvalContext.getReturnType(function);
+          final PyType expected = getExpectedReturnType(function);
           if (!PyTypeChecker.match(expected, actual, myTypeEvalContext)) {
             final String expectedName = PythonDocumentationProvider.getTypeName(expected, myTypeEvalContext);
             final String actualName = PythonDocumentationProvider.getTypeName(actual, myTypeEvalContext);
@@ -105,6 +105,17 @@ public class PyTypeCheckerInspection extends PyInspection {
       }
     }
 
+    @Nullable
+    private PyType getExpectedReturnType(@NotNull PyFunction function) {
+      final PyType returnType = myTypeEvalContext.getReturnType(function);
+
+      if (returnType instanceof PyCollectionType && PyNames.FAKE_COROUTINE.equals(returnType.getName())) {
+        return ((PyCollectionType)returnType).getElementTypes(myTypeEvalContext).get(0);
+      }
+
+      return returnType;
+    }
+
     @Override
     public void visitPyFunction(PyFunction node) {
       final PyAnnotation annotation = node.getAnnotation();

python/testData/inspections/PyTypeCheckerInspection/AsyncFunctionReturnType.py

@@ -0,0 +1,2 @@
+async def test(self, a) -> int:
+    return 123

python/testSrc/com/jetbrains/python/inspections/Py3TypeCheckerInspectionTest.java

@@ -158,4 +158,9 @@ public class Py3TypeCheckerInspectionTest extends PyTestCase {
   public void testComprehensionsOverAsyncGenerator() {
     doTest();
   }
+
+  // PY-21048
+  public void testAsyncFunctionReturnType() {
+    doTest();
+  }
 }