[flake8-pyi] Implement PYI041 (#5722)

## Summary

Implements PYI041 from flake8-pyi. See [original
code](2a86db8271/pyi.py (L1283)).

This check only applies to function parameters in order to avoid issues
with mypy. See https://github.com/PyCQA/flake8-pyi/issues/299.

ref: #848

## Test Plan

Snapshots, manual runs of flake8.

crates/ruff/resources/test/fixtures/flake8_pyi/PYI041.py

@@ -0,0 +1,47 @@
+from typing import (
+    Union,
+)
+
+from typing_extensions import (
+    TypeAlias,
+)
+
+TA0: TypeAlias = int
+TA1: TypeAlias = int | float | bool
+TA2: TypeAlias = Union[int, float, bool]
+
+
+def good1(arg: int) -> int | bool:
+    ...
+
+
+def good2(arg: int, arg2: int | bool) -> None:
+    ...
+
+
+def f0(arg1: float | int) -> None:
+    ...
+
+
+def f1(arg1: float, *, arg2: float | list[str] | type[bool] | complex) -> None:
+    ...
+
+
+def f2(arg1: int, /, arg2: int | int | float) -> None:
+    ...
+
+
+def f3(arg1: int, *args: Union[int | int | float]) -> None:
+    ...
+
+
+async def f4(**kwargs: int | int | float) -> None:
+    ...
+
+
+class Foo:
+    def good(self, arg: int) -> None:
+        ...
+
+    def bad(self, arg: int | float | complex) -> None:
+        ...

crates/ruff/resources/test/fixtures/flake8_pyi/PYI041.pyi

@@ -0,0 +1,39 @@
+from typing import (
+    Union,
+)
+
+from typing_extensions import (
+    TypeAlias,
+)
+
+# Type aliases not flagged
+TA0: TypeAlias = int
+TA1: TypeAlias = int | float | bool
+TA2: TypeAlias = Union[int, float, bool]
+
+
+def good1(arg: int) -> int | bool: ...
+
+
+def good2(arg: int, arg2: int | bool) -> None: ...
+
+
+def f0(arg1: float | int) -> None: ...  # PYI041
+
+
+def f1(arg1: float, *, arg2: float | list[str] | type[bool] | complex) -> None: ...  # PYI041
+
+
+def f2(arg1: int, /, arg2: int | int | float) -> None: ...  # PYI041
+
+
+def f3(arg1: int, *args: Union[int | int | float]) -> None: ...  # PYI041
+
+
+async def f4(**kwargs: int | int | float) -> None: ...  # PYI041
+
+
+class Foo:
+    def good(self, arg: int) -> None: ...
+
+    def bad(self, arg: int | float | complex) -> None: ...  # PYI041

crates/ruff/src/checkers/ast/mod.rs

@@ -443,6 +443,9 @@ where
                             args,
                         );
                     }
+                    if self.enabled(Rule::RedundantNumericUnion) {
+                        flake8_pyi::rules::redundant_numeric_union(self, args);
+                    }
                 }
                 if self.enabled(Rule::DunderFunctionName) {
                     if let Some(diagnostic) = pep8_naming::rules::dunder_function_name(

crates/ruff/src/codes.rs

@@ -639,6 +639,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8Pyi, "034") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::NonSelfReturnType),
         (Flake8Pyi, "035") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::UnassignedSpecialVariableInStub),
         (Flake8Pyi, "036") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::BadExitAnnotation),
+        (Flake8Pyi, "041") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::RedundantNumericUnion),
         (Flake8Pyi, "042") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::SnakeCaseTypeAlias),
         (Flake8Pyi, "043") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::TSuffixedTypeAlias),
         (Flake8Pyi, "044") => (RuleGroup::Unspecified, rules::flake8_pyi::rules::FutureAnnotationsInStub),

crates/ruff/src/rules/flake8_pyi/mod.rs

@@ -49,6 +49,8 @@ mod tests {
     #[test_case(Rule::PassStatementStubBody, Path::new("PYI009.pyi"))]
     #[test_case(Rule::QuotedAnnotationInStub, Path::new("PYI020.py"))]
     #[test_case(Rule::QuotedAnnotationInStub, Path::new("PYI020.pyi"))]
+    #[test_case(Rule::RedundantNumericUnion, Path::new("PYI041.py"))]
+    #[test_case(Rule::RedundantNumericUnion, Path::new("PYI041.pyi"))]
     #[test_case(Rule::SnakeCaseTypeAlias, Path::new("PYI042.py"))]
     #[test_case(Rule::SnakeCaseTypeAlias, Path::new("PYI042.pyi"))]
     #[test_case(Rule::UnassignedSpecialVariableInStub, Path::new("PYI035.py"))]

crates/ruff/src/rules/flake8_pyi/rules/mod.rs

@@ -16,6 +16,7 @@ pub(crate) use pass_in_class_body::*;
 pub(crate) use pass_statement_stub_body::*;
 pub(crate) use prefix_type_params::*;
 pub(crate) use quoted_annotation_in_stub::*;
+pub(crate) use redundant_numeric_union::*;
 pub(crate) use simple_defaults::*;
 pub(crate) use str_or_repr_defined_in_stub::*;
 pub(crate) use string_or_bytes_too_long::*;
@@ -45,6 +46,7 @@ mod pass_in_class_body;
 mod pass_statement_stub_body;
 mod prefix_type_params;
 mod quoted_annotation_in_stub;
+mod redundant_numeric_union;
 mod simple_defaults;
 mod str_or_repr_defined_in_stub;
 mod string_or_bytes_too_long;

crates/ruff/src/rules/flake8_pyi/rules/redundant_numeric_union.rs

@@ -0,0 +1,133 @@
+use rustpython_parser::ast::{Arguments, Expr, Ranged};
+
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+
+use crate::checkers::ast::Checker;
+use crate::rules::flake8_pyi::helpers::traverse_union;
+
+/// ## What it does
+/// Checks for union annotations that contain redundant numeric types (e.g.,
+/// `int | float`).
+///
+/// ## Why is this bad?
+/// In Python, `int` is a subtype of `float`, and `float` is a subtype of
+/// `complex`. As such, a union that includes both `int` and `float` is
+/// redundant, as it is equivalent to a union that only includes `float`.
+///
+/// For more, see [PEP 3141], which defines Python's "numeric tower".
+///
+/// Unions with redundant elements are less readable than unions without them.
+///
+/// ## Example
+/// ```python
+/// def foo(x: float | int) -> None:
+///     ...
+/// ```
+///
+/// Use instead:
+/// ```python
+/// def foo(x: float) -> None:
+///     ...
+/// ```
+///
+/// ## References
+/// - [Python documentation: The numeric tower](https://docs.python.org/3/library/numbers.html#the-numeric-tower)
+///
+/// [PEP 3141]: https://peps.python.org/pep-3141/
+#[violation]
+pub struct RedundantNumericUnion {
+    redundancy: Redundancy,
+}
+
+impl Violation for RedundantNumericUnion {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let (subtype, supertype) = match self.redundancy {
+            Redundancy::FloatComplex => ("float", "complex"),
+            Redundancy::IntComplex => ("int", "complex"),
+            Redundancy::IntFloat => ("int", "float"),
+        };
+        format!("Use `{supertype}` instead of `{subtype} | {supertype}`")
+    }
+}
+
+/// PYI041
+pub(crate) fn redundant_numeric_union(checker: &mut Checker, args: &Arguments) {
+    for annotation in args
+        .args
+        .iter()
+        .chain(args.posonlyargs.iter())
+        .chain(args.kwonlyargs.iter())
+        .filter_map(|arg| arg.def.annotation.as_ref())
+    {
+        check_annotation(checker, annotation);
+    }
+
+    // If annotations on `args` or `kwargs` are flagged by this rule, the annotations themselves
+    // are not accurate, but check them anyway. It's possible that flagging them will help the user
+    // realize they're incorrect.
+    for annotation in args
+        .vararg
+        .iter()
+        .chain(args.kwarg.iter())
+        .filter_map(|arg| arg.annotation.as_ref())
+    {
+        check_annotation(checker, annotation);
+    }
+}
+
+#[derive(Debug, Clone, Copy, Eq, PartialEq)]
+enum Redundancy {
+    FloatComplex,
+    IntComplex,
+    IntFloat,
+}
+
+fn check_annotation(checker: &mut Checker, annotation: &Expr) {
+    let mut has_float = false;
+    let mut has_complex = false;
+    let mut has_int = false;
+
+    let mut func = |expr: &Expr, _parent: Option<&Expr>| {
+        let Some(call_path) = checker.semantic().resolve_call_path(expr) else {
+            return;
+        };
+
+        match call_path.as_slice() {
+            ["" | "builtins", "int"] => has_int = true,
+            ["" | "builtins", "float"] => has_float = true,
+            ["" | "builtins", "complex"] => has_complex = true,
+            _ => (),
+        }
+    };
+
+    traverse_union(&mut func, checker.semantic(), annotation, None);
+
+    if has_complex {
+        if has_float {
+            checker.diagnostics.push(Diagnostic::new(
+                RedundantNumericUnion {
+                    redundancy: Redundancy::FloatComplex,
+                },
+                annotation.range(),
+            ));
+        }
+
+        if has_int {
+            checker.diagnostics.push(Diagnostic::new(
+                RedundantNumericUnion {
+                    redundancy: Redundancy::IntComplex,
+                },
+                annotation.range(),
+            ));
+        }
+    } else if has_float && has_int {
+        checker.diagnostics.push(Diagnostic::new(
+            RedundantNumericUnion {
+                redundancy: Redundancy::IntFloat,
+            },
+            annotation.range(),
+        ));
+    }
+}

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI041_PYI041.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff/src/rules/flake8_pyi/mod.rs
+---
+

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI041_PYI041.pyi.snap

@@ -0,0 +1,44 @@
+---
+source: crates/ruff/src/rules/flake8_pyi/mod.rs
+---
+PYI041.pyi:21:14: PYI041 Use `float` instead of `int | float`
+   |
+21 | def f0(arg1: float | int) -> None: ...  # PYI041
+   |              ^^^^^^^^^^^ PYI041
+   |
+
+PYI041.pyi:24:30: PYI041 Use `complex` instead of `float | complex`
+   |
+24 | def f1(arg1: float, *, arg2: float | list[str] | type[bool] | complex) -> None: ...  # PYI041
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PYI041
+   |
+
+PYI041.pyi:27:28: PYI041 Use `float` instead of `int | float`
+   |
+27 | def f2(arg1: int, /, arg2: int | int | float) -> None: ...  # PYI041
+   |                            ^^^^^^^^^^^^^^^^^ PYI041
+   |
+
+PYI041.pyi:33:24: PYI041 Use `float` instead of `int | float`
+   |
+33 | async def f4(**kwargs: int | int | float) -> None: ...  # PYI041
+   |                        ^^^^^^^^^^^^^^^^^ PYI041
+   |
+
+PYI041.pyi:39:24: PYI041 Use `complex` instead of `float | complex`
+   |
+37 |     def good(self, arg: int) -> None: ...
+38 | 
+39 |     def bad(self, arg: int | float | complex) -> None: ...  # PYI041
+   |                        ^^^^^^^^^^^^^^^^^^^^^ PYI041
+   |
+
+PYI041.pyi:39:24: PYI041 Use `complex` instead of `int | complex`
+   |
+37 |     def good(self, arg: int) -> None: ...
+38 | 
+39 |     def bad(self, arg: int | float | complex) -> None: ...  # PYI041
+   |                        ^^^^^^^^^^^^^^^^^^^^^ PYI041
+   |
+
+