From cc736c3a51a83e47f5f89a9ccc8a20d196272634 Mon Sep 17 00:00:00 2001
From: GiGaGon <107241144+MeGaGiGaGon@users.noreply.github.com>
Date: Tue, 1 Jul 2025 07:26:41 -0700
Subject: [PATCH] [`refurb`] Fix false positive on empty tuples (`FURB168`)
 (#19058)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

This PR fixes #19047 / the [isinstance-type-none
(FURB168)](https://docs.astral.sh/ruff/rules/isinstance-type-none/#isinstance-type-none-furb168)
tuple false positive by adding a check if the tuple is empty to the
code. I also noticed there was another false positive with the other
tuple check in the same function, so I fixed it the same way.
`Union[()]` is invalid at runtime with `TypeError: Cannot take a Union
of no types.`, but it is accepted by `basedpyright`
[playground](https://basedpyright.com/?pythonVersion=3.8&typeCheckingMode=all&code=GYJw9gtgBALgngBwJYDsDmUkQWEMoCqKSYKAsAFAgCmAbtQIYA2A%2BvAtQBREkoDanAJQBdQUA)
and is equivalent to `Never`, so I fixed it anyways. I'm getting on a
side tangent here, but it looks like MyPy doesn't accept it, and ty
[playground](https://play.ty.dev/c2c468b6-38e4-4dd9-a9fa-0276e843e395)
gives `@Todo`.

## Test Plan

<!-- How was it tested? -->

Added two test cases for the two false positives.
[playground](https://play.ruff.rs/a53afc21-9a1d-4b9b-9346-abfbeabeb449)
---
 .../ruff_linter/resources/test/fixtures/refurb/FURB168.py  | 7 +++++++
 .../src/rules/refurb/rules/isinstance_type_none.rs         | 7 +++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/crates/ruff_linter/resources/test/fixtures/refurb/FURB168.py b/crates/ruff_linter/resources/test/fixtures/refurb/FURB168.py
index 17238d520c..a9f31e3a78 100644
--- a/crates/ruff_linter/resources/test/fixtures/refurb/FURB168.py
+++ b/crates/ruff_linter/resources/test/fixtures/refurb/FURB168.py
@@ -85,3 +85,10 @@ def _():
 
     if isinstance(foo, type(None)):
         ...
+
+# https://github.com/astral-sh/ruff/issues/19047
+if isinstance(foo, ()):
+    pass
+
+if isinstance(foo, Union[()]):
+    pass
diff --git a/crates/ruff_linter/src/rules/refurb/rules/isinstance_type_none.rs b/crates/ruff_linter/src/rules/refurb/rules/isinstance_type_none.rs
index 793e0968ad..4ff1f1c4af 100644
--- a/crates/ruff_linter/src/rules/refurb/rules/isinstance_type_none.rs
+++ b/crates/ruff_linter/src/rules/refurb/rules/isinstance_type_none.rs
@@ -100,7 +100,9 @@ fn is_none(expr: &Expr, semantic: &SemanticModel) -> bool {
             }
 
             // Ex) `(type(None),)`
-            Expr::Tuple(tuple) => tuple.iter().all(|element| inner(element, false, semantic)),
+            Expr::Tuple(tuple) => {
+                !tuple.is_empty() && tuple.iter().all(|element| inner(element, false, semantic))
+            }
 
             // Ex) `type(None) | type(None)`
             Expr::BinOp(ast::ExprBinOp {
@@ -125,7 +127,8 @@ fn is_none(expr: &Expr, semantic: &SemanticModel) -> bool {
 
                 match slice.as_ref() {
                     Expr::Tuple(ast::ExprTuple { elts, .. }) => {
-                        elts.iter().all(|element| inner(element, true, semantic))
+                        !elts.is_empty()
+                            && elts.iter().all(|element| inner(element, true, semantic))
                     }
                     slice => inner(slice, true, semantic),
                 }