Propagate is_function_like through decorators

Author: sharkdp

crates/ty_python_semantic/resources/mdtest/call/callables_as_descriptors.md

@@ -130,8 +130,5 @@ class C:
 
 C().method(1)
 
-# TODO: We shouldn't issue any errors here
-# error: [missing-argument]
-# error: [invalid-argument-type]
 C().method_decorated(1)
 ```

crates/ty_python_semantic/src/types.rs

@@ -998,6 +998,13 @@ impl<'db> Type<'db> {
         }
     }
 
+    pub(crate) const fn unwrap_as_callable_type(self) -> Option<CallableType<'db>> {
+        match self {
+            Type::Callable(callable_type) => Some(callable_type),
+            _ => None,
+        }
+    }
+
     pub(crate) const fn expect_dynamic(self) -> DynamicType<'db> {
         self.into_dynamic()
             .expect("Expected a Type::Dynamic variant")

crates/ty_python_semantic/src/types/infer/builder.rs

@@ -2174,7 +2174,23 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                 .try_call(self.db(), &CallArguments::positional([inferred_ty]))
                 .map(|bindings| bindings.return_type(self.db()))
             {
-                Ok(return_ty) => return_ty,
+                Ok(return_ty) => {
+                    let is_input_function_like = inferred_ty.is_function_literal()
+                        || inferred_ty
+                            .unwrap_as_callable_type()
+                            .is_some_and(|callable| callable.is_function_like(self.db()));
+                    if is_input_function_like
+                        && let Some(callable_type) = return_ty.unwrap_as_callable_type()
+                    {
+                        Type::Callable(CallableType::new(
+                            self.db(),
+                            callable_type.signatures(self.db()),
+                            true,
+                        ))
+                    } else {
+                        return_ty
+                    }
+                }
                 Err(CallError(_, bindings)) => {
                     bindings.report_diagnostics(&self.context, (*decorator_node).into());
                     bindings.return_type(self.db())