From 899a52390ba5e819f4a2cfcce3c696a8ffef89e2 Mon Sep 17 00:00:00 2001
From: Dhruv Manilawala <dhruvmanila@gmail.com>
Date: Tue, 13 Aug 2024 19:25:49 +0530
Subject: [PATCH] Evaluate default parameter value in enclosing scope (#12852)

## Summary

This PR fixes a bug in the semantic model where it would evaluate the
default parameter value in the type parameter scope. For example,

```py
def foo[T1: int](a = T1):
    pass
```

Here, the `T1` in `a = T1` is undefined but Ruff doesn't flag it
(https://play.ruff.rs/ba2f7c2f-4da6-417e-aa2a-104aa63e6d5e).

The fix here is to evaluate the default parameter value in the
_enclosing_ scope instead.

## Test Plan

Add a test case which includes the above code under `F821`
(`undefined-name`) and validate the snapshot.
---
 .../resources/test/fixtures/pyflakes/F821_17.py       |  4 ++++
 crates/ruff_linter/src/checkers/ast/mod.rs            | 11 ++++++++---
 ...nter__rules__pyflakes__tests__F821_F821_17.py.snap |  7 +++++++
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/crates/ruff_linter/resources/test/fixtures/pyflakes/F821_17.py b/crates/ruff_linter/resources/test/fixtures/pyflakes/F821_17.py
index b2a7b7b4dd..649f88a672 100644
--- a/crates/ruff_linter/resources/test/fixtures/pyflakes/F821_17.py
+++ b/crates/ruff_linter/resources/test/fixtures/pyflakes/F821_17.py
@@ -111,3 +111,7 @@ def can_access_inside_nested[T](t: T) -> T:  # OK
         return x
 
     bar(t)
+
+
+def cannot_access_in_default[T](t: T = T):  # F821
+    pass
diff --git a/crates/ruff_linter/src/checkers/ast/mod.rs b/crates/ruff_linter/src/checkers/ast/mod.rs
index 8e8a5f04f4..814f2d9f38 100644
--- a/crates/ruff_linter/src/checkers/ast/mod.rs
+++ b/crates/ruff_linter/src/checkers/ast/mod.rs
@@ -691,6 +691,14 @@ impl<'a> Visitor<'a> for Checker<'a> {
                         self.semantic(),
                     );
 
+                // The default values of the parameters needs to be evaluated in the enclosing
+                // scope.
+                for parameter in &**parameters {
+                    if let Some(expr) = parameter.default() {
+                        self.visit_expr(expr);
+                    }
+                }
+
                 self.semantic.push_scope(ScopeKind::Type);
 
                 if let Some(type_params) = type_params {
@@ -715,9 +723,6 @@ impl<'a> Visitor<'a> for Checker<'a> {
                             }
                         }
                     }
-                    if let Some(expr) = parameter.default() {
-                        self.visit_expr(expr);
-                    }
                 }
                 if let Some(expr) = returns {
                     match annotation {
diff --git a/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F821_F821_17.py.snap b/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F821_F821_17.py.snap
index bb12cf83ab..ad2011d46c 100644
--- a/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F821_F821_17.py.snap
+++ b/crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F821_F821_17.py.snap
@@ -258,3 +258,10 @@ F821_17.py:103:17: F821 Undefined name `t`
     |                 ^ F821
 104 |                 return x
     |
+
+F821_17.py:116:40: F821 Undefined name `T`
+    |
+116 | def cannot_access_in_default[T](t: T = T):  # F821
+    |                                        ^ F821
+117 |     pass
+    |