From c74ba00219fb6d06bc3da08d98102da7ab7bce96 Mon Sep 17 00:00:00 2001
From: Alex Waygood <Alex.Waygood@Gmail.com>
Date: Tue, 1 Apr 2025 19:03:42 +0100
Subject: [PATCH] [red-knot] Fix more `redundant-cast` false positives (#17119)

## Summary

There are quite a few places we infer `Todo` types currently, and some
of them are nested somewhat deeply in type expressions. These can cause
spurious issues for the new `redundant-cast` diagnostics. We fixed all
the false positives we saw in the mypy_primer report before merging
https://github.com/astral-sh/ruff/pull/17100, but I think there are
still lots of places where we'd emit false positives due to this check
-- we currently don't run on that many projects at all in our
mypy_primer check:


https://github.com/astral-sh/ruff/blob/d0c8eaa0923352ccc4ec30c9fac1f573f20998b3/.github/workflows/mypy_primer.yaml#L71

This PR fixes some more false positives from this diagnostic by making
the `Type::contains_todo()` method more expansive.

## Test Plan

I added a regression test which causes us to emit a spurious diagnostic
on `main`, but does not with this PR.
---
 .../resources/mdtest/directives/cast.md       | 11 ++++
 crates/red_knot_python_semantic/src/types.rs  | 56 ++++++++++++++++++-
 2 files changed, 65 insertions(+), 2 deletions(-)

diff --git a/crates/red_knot_python_semantic/resources/mdtest/directives/cast.md b/crates/red_knot_python_semantic/resources/mdtest/directives/cast.md
index e991849f3e..81712cff8b 100644
--- a/crates/red_knot_python_semantic/resources/mdtest/directives/cast.md
+++ b/crates/red_knot_python_semantic/resources/mdtest/directives/cast.md
@@ -38,3 +38,14 @@ def function_returning_any() -> Any:
 # error: [redundant-cast] "Value is already of type `Any`"
 cast(Any, function_returning_any())
 ```
+
+Complex type expressions (which may be unsupported) do not lead to spurious `[redundant-cast]`
+diagnostics.
+
+```py
+from typing import Callable
+
+def f(x: Callable[[dict[str, int]], None], y: tuple[dict[str, int]]):
+    a = cast(Callable[[list[bytes]], None], x)
+    b = cast(tuple[list[bytes]], y)
+```
diff --git a/crates/red_knot_python_semantic/src/types.rs b/crates/red_knot_python_semantic/src/types.rs
index 923884d268..774f6fd0ce 100644
--- a/crates/red_knot_python_semantic/src/types.rs
+++ b/crates/red_knot_python_semantic/src/types.rs
@@ -321,8 +321,60 @@ impl<'db> Type<'db> {
     }
 
     pub fn contains_todo(&self, db: &'db dyn Db) -> bool {
-        self.is_todo()
-            || matches!(self, Type::Union(union) if union.elements(db).iter().any(Type::is_todo))
+        match self {
+            Self::Dynamic(DynamicType::Todo(_) | DynamicType::TodoProtocol) => true,
+
+            Self::AlwaysFalsy
+            | Self::AlwaysTruthy
+            | Self::Never
+            | Self::BooleanLiteral(_)
+            | Self::BytesLiteral(_)
+            | Self::FunctionLiteral(_)
+            | Self::Instance(_)
+            | Self::ModuleLiteral(_)
+            | Self::ClassLiteral(_)
+            | Self::KnownInstance(_)
+            | Self::StringLiteral(_)
+            | Self::IntLiteral(_)
+            | Self::LiteralString
+            | Self::SliceLiteral(_)
+            | Self::Dynamic(DynamicType::Unknown | DynamicType::Any)
+            | Self::Callable(
+                CallableType::BoundMethod(_)
+                | CallableType::WrapperDescriptorDunderGet
+                | CallableType::MethodWrapperDunderGet(_),
+            ) => false,
+
+            Self::Callable(CallableType::General(callable)) => {
+                let signature = callable.signature(db);
+                signature.parameters().iter().any(|param| {
+                    param
+                        .annotated_type()
+                        .is_some_and(|ty| ty.contains_todo(db))
+                }) || signature.return_ty.is_some_and(|ty| ty.contains_todo(db))
+            }
+
+            Self::SubclassOf(subclass_of) => match subclass_of.subclass_of() {
+                ClassBase::Dynamic(DynamicType::Todo(_) | DynamicType::TodoProtocol) => true,
+                ClassBase::Dynamic(DynamicType::Unknown | DynamicType::Any) => false,
+                ClassBase::Class(_) => false,
+            },
+
+            Self::Tuple(tuple) => tuple.elements(db).iter().any(|ty| ty.contains_todo(db)),
+
+            Self::Union(union) => union.elements(db).iter().any(|ty| ty.contains_todo(db)),
+
+            Self::Intersection(intersection) => {
+                intersection
+                    .positive(db)
+                    .iter()
+                    .any(|ty| ty.contains_todo(db))
+                    || intersection
+                        .negative(db)
+                        .iter()
+                        .any(|ty| ty.contains_todo(db))
+            }
+        }
     }
 
     pub const fn class_literal(class: Class<'db>) -> Self {