Fix FBT001 false negative with unions and optional (#7501)

## Summary

- Close #7487

In the spirit of `flake8-boolean-trap`, any positional argument that can
accept a boolean should raise `FBT001`.
Raise `FBT001` for all annotations that accept booleans (e.g.
`Optional[bool]`, `Union[int, bool]`).

## Test Plan

Add a fixture, with an annotation using `|`, `Optional`, and `Union`,
and containing a boolean.

crates/ruff_linter/resources/test/fixtures/flake8_boolean_trap/FBT.py

@@ -91,3 +91,18 @@ def foo(self, value: bool) -> None:
 
     def foo(self) -> None:
         object.__setattr__(self, "flag", True)
+
+
+from typing import Optional, Union
+
+
+def func(x: Union[list, Optional[int | str | float | bool]]):
+    pass
+
+
+def func(x: bool | str):
+    pass
+
+
+def func(x: int | str):
+    pass

crates/ruff_linter/src/rules/flake8_boolean_trap/mod.rs

@@ -10,6 +10,7 @@ mod tests {
     use test_case::test_case;
 
     use crate::registry::Rule;
+    use crate::settings::types::PreviewMode;
     use crate::test::test_path;
     use crate::{assert_messages, settings};
 
@@ -25,4 +26,22 @@ mod tests {
         assert_messages!(snapshot, diagnostics);
         Ok(())
     }
+
+    #[test_case(Rule::BooleanTypeHintPositionalArgument, Path::new("FBT.py"))]
+    fn preview_rules(rule_code: Rule, path: &Path) -> Result<()> {
+        let snapshot = format!(
+            "preview__{}_{}",
+            rule_code.noqa_code(),
+            path.to_string_lossy()
+        );
+        let diagnostics = test_path(
+            Path::new("flake8_boolean_trap").join(path).as_path(),
+            &settings::LinterSettings {
+                preview: PreviewMode::Enabled,
+                ..settings::LinterSettings::for_rule(rule_code)
+            },
+        )?;
+        assert_messages!(snapshot, diagnostics);
+        Ok(())
+    }
 }

crates/ruff_linter/src/rules/flake8_boolean_trap/rules/boolean_type_hint_positional_argument.rs

@@ -4,6 +4,7 @@ use ruff_diagnostics::Diagnostic;
 use ruff_diagnostics::Violation;
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::call_path::collect_call_path;
+use ruff_python_semantic::SemanticModel;
 use ruff_text_size::Ranged;
 
 use crate::checkers::ast::Checker;
@@ -26,6 +27,9 @@ use crate::rules::flake8_boolean_trap::helpers::is_allowed_func_def;
 /// keyword-only argument, to force callers to be explicit when providing
 /// the argument.
 ///
+/// In [preview], this rule will also flag annotations that include boolean
+/// variants, like `bool | int`.
+///
 /// ## Example
 /// ```python
 /// from math import ceil, floor
@@ -86,6 +90,8 @@ use crate::rules::flake8_boolean_trap::helpers::is_allowed_func_def;
 /// ## References
 /// - [Python documentation: Calls](https://docs.python.org/3/reference/expressions.html#calls)
 /// - [_How to Avoid “The Boolean Trap”_ by Adam Johnson](https://adamj.eu/tech/2021/07/10/python-type-hints-how-to-avoid-the-boolean-trap/)
+///
+/// [preview]: https://docs.astral.sh/ruff/preview/
 #[violation]
 pub struct BooleanTypeHintPositionalArgument;
 
@@ -96,6 +102,7 @@ impl Violation for BooleanTypeHintPositionalArgument {
     }
 }
 
+/// FBT001
 pub(crate) fn boolean_type_hint_positional_argument(
     checker: &mut Checker,
     name: &str,
@@ -122,19 +129,70 @@ pub(crate) fn boolean_type_hint_positional_argument(
         let Some(annotation) = parameter.annotation.as_ref() else {
             continue;
         };
-
-        // check for both bool (python class) and 'bool' (string annotation)
-        let hint = match annotation.as_ref() {
-            Expr::Name(name) => &name.id == "bool",
-            Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) => value == "bool",
-            _ => false,
-        };
-        if !hint || !checker.semantic().is_builtin("bool") {
-            continue;
+        if checker.settings.preview.is_enabled() {
+            if !match_annotation_to_complex_bool(annotation, checker.semantic()) {
+                continue;
+            }
+        } else {
+            if !match_annotation_to_literal_bool(annotation) {
+                continue;
+            }
+        }
+        if !checker.semantic().is_builtin("bool") {
+            return;
         }
         checker.diagnostics.push(Diagnostic::new(
             BooleanTypeHintPositionalArgument,
             parameter.name.range(),
         ));
     }
 }
+
+/// Returns `true` if the annotation is a boolean type hint (e.g., `bool`).
+fn match_annotation_to_literal_bool(annotation: &Expr) -> bool {
+    match annotation {
+        // Ex) `True`
+        Expr::Name(name) => &name.id == "bool",
+        // Ex) `"True"`
+        Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) => value == "bool",
+        _ => false,
+    }
+}
+
+/// Returns `true` if the annotation is a boolean type hint (e.g., `bool`), or a type hint that
+/// includes boolean as a variant (e.g., `bool | int`).
+fn match_annotation_to_complex_bool(annotation: &Expr, semantic: &SemanticModel) -> bool {
+    match annotation {
+        // Ex) `bool`
+        Expr::Name(name) => &name.id == "bool",
+        // Ex) `"bool"`
+        Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) => value == "bool",
+        // Ex) `bool | int`
+        Expr::BinOp(ast::ExprBinOp {
+            left,
+            op: ast::Operator::BitOr,
+            right,
+            ..
+        }) => {
+            match_annotation_to_complex_bool(left, semantic)
+                || match_annotation_to_complex_bool(right, semantic)
+        }
+        // Ex) `typing.Union[bool, int]`
+        Expr::Subscript(ast::ExprSubscript { value, slice, .. }) => {
+            if semantic.match_typing_expr(value, "Union") {
+                if let Expr::Tuple(ast::ExprTuple { elts, .. }) = slice.as_ref() {
+                    elts.iter()
+                        .any(|elt| match_annotation_to_complex_bool(elt, semantic))
+                } else {
+                    // Union with a single type is an invalid type annotation
+                    false
+                }
+            } else if semantic.match_typing_expr(value, "Optional") {
+                match_annotation_to_complex_bool(slice, semantic)
+            } else {
+                false
+            }
+        }
+        _ => false,
+    }
+}

crates/ruff_linter/src/rules/flake8_boolean_trap/snapshots/ruff_linter__rules__flake8_boolean_trap__tests__preview__FBT001_FBT.py.snap

@@ -0,0 +1,106 @@
+---
+source: crates/ruff_linter/src/rules/flake8_boolean_trap/mod.rs
+---
+FBT.py:4:5: FBT001 Boolean-typed positional argument in function definition
+  |
+2 |     posonly_nohint,
+3 |     posonly_nonboolhint: int,
+4 |     posonly_boolhint: bool,
+  |     ^^^^^^^^^^^^^^^^ FBT001
+5 |     posonly_boolstrhint: "bool",
+6 |     /,
+  |
+
+FBT.py:5:5: FBT001 Boolean-typed positional argument in function definition
+  |
+3 |     posonly_nonboolhint: int,
+4 |     posonly_boolhint: bool,
+5 |     posonly_boolstrhint: "bool",
+  |     ^^^^^^^^^^^^^^^^^^^ FBT001
+6 |     /,
+7 |     offset,
+  |
+
+FBT.py:10:5: FBT001 Boolean-typed positional argument in function definition
+   |
+ 8 |     posorkw_nonvalued_nohint,
+ 9 |     posorkw_nonvalued_nonboolhint: int,
+10 |     posorkw_nonvalued_boolhint: bool,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ FBT001
+11 |     posorkw_nonvalued_boolstrhint: "bool",
+12 |     posorkw_boolvalued_nohint=True,
+   |
+
+FBT.py:11:5: FBT001 Boolean-typed positional argument in function definition
+   |
+ 9 |     posorkw_nonvalued_nonboolhint: int,
+10 |     posorkw_nonvalued_boolhint: bool,
+11 |     posorkw_nonvalued_boolstrhint: "bool",
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ FBT001
+12 |     posorkw_boolvalued_nohint=True,
+13 |     posorkw_boolvalued_nonboolhint: int = True,
+   |
+
+FBT.py:14:5: FBT001 Boolean-typed positional argument in function definition
+   |
+12 |     posorkw_boolvalued_nohint=True,
+13 |     posorkw_boolvalued_nonboolhint: int = True,
+14 |     posorkw_boolvalued_boolhint: bool = True,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ FBT001
+15 |     posorkw_boolvalued_boolstrhint: "bool" = True,
+16 |     posorkw_nonboolvalued_nohint=1,
+   |
+
+FBT.py:15:5: FBT001 Boolean-typed positional argument in function definition
+   |
+13 |     posorkw_boolvalued_nonboolhint: int = True,
+14 |     posorkw_boolvalued_boolhint: bool = True,
+15 |     posorkw_boolvalued_boolstrhint: "bool" = True,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ FBT001
+16 |     posorkw_nonboolvalued_nohint=1,
+17 |     posorkw_nonboolvalued_nonboolhint: int = 2,
+   |
+
+FBT.py:18:5: FBT001 Boolean-typed positional argument in function definition
+   |
+16 |     posorkw_nonboolvalued_nohint=1,
+17 |     posorkw_nonboolvalued_nonboolhint: int = 2,
+18 |     posorkw_nonboolvalued_boolhint: bool = 3,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ FBT001
+19 |     posorkw_nonboolvalued_boolstrhint: "bool" = 4,
+20 |     *,
+   |
+
+FBT.py:19:5: FBT001 Boolean-typed positional argument in function definition
+   |
+17 |     posorkw_nonboolvalued_nonboolhint: int = 2,
+18 |     posorkw_nonboolvalued_boolhint: bool = 3,
+19 |     posorkw_nonboolvalued_boolstrhint: "bool" = 4,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ FBT001
+20 |     *,
+21 |     kwonly_nonvalued_nohint,
+   |
+
+FBT.py:89:19: FBT001 Boolean-typed positional argument in function definition
+   |
+88 |     # FBT001: Boolean positional arg in function definition
+89 |     def foo(self, value: bool) -> None:
+   |                   ^^^^^ FBT001
+90 |         pass
+   |
+
+FBT.py:99:10: FBT001 Boolean-typed positional argument in function definition
+    |
+ 99 | def func(x: Union[list, Optional[int | str | float | bool]]):
+    |          ^ FBT001
+100 |     pass
+    |
+
+FBT.py:103:10: FBT001 Boolean-typed positional argument in function definition
+    |
+103 | def func(x: bool | str):
+    |          ^ FBT001
+104 |     pass
+    |
+
+