[TRIO] Add TRIO109 rule

crates/ruff_linter/resources/test/fixtures/flake8_trio/TRIO109.py

@@ -0,0 +1,10 @@
+async def func():
+    ...
+
+
+async def func(timeout):
+    ...
+
+
+async def func(timeout=10):
+    ...

crates/ruff_linter/src/checkers/ast/analyze/statement.rs

@@ -356,6 +356,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                     flake8_builtins::rules::builtin_variable_shadowing(checker, name, name.range());
                 }
             }
+            if checker.enabled(Rule::TrioAsyncFunctionWithTimeout) {
+                flake8_trio::rules::async_function_with_timeout(checker, function_def);
+            }
             #[cfg(feature = "unreachable-code")]
             if checker.enabled(Rule::UnreachableCode) {
                 checker

crates/ruff_linter/src/codes.rs

@@ -293,6 +293,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         // flake8-trio
         (Flake8Trio, "100") => (RuleGroup::Preview, rules::flake8_trio::rules::TrioTimeoutWithoutAwait),
         (Flake8Trio, "105") => (RuleGroup::Preview, rules::flake8_trio::rules::TrioSyncCall),
+        (Flake8Trio, "109") => (RuleGroup::Preview, rules::flake8_trio::rules::TrioAsyncFunctionWithTimeout),
         (Flake8Trio, "115") => (RuleGroup::Preview, rules::flake8_trio::rules::TrioZeroSleepCall),
 
         // flake8-builtins

crates/ruff_linter/src/rules/flake8_trio/mod.rs

@@ -16,6 +16,7 @@ mod tests {
 
     #[test_case(Rule::TrioTimeoutWithoutAwait, Path::new("TRIO100.py"))]
     #[test_case(Rule::TrioSyncCall, Path::new("TRIO105.py"))]
+    #[test_case(Rule::TrioAsyncFunctionWithTimeout, Path::new("TRIO109.py"))]
     #[test_case(Rule::TrioZeroSleepCall, Path::new("TRIO115.py"))]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());

crates/ruff_linter/src/rules/flake8_trio/rules/async_function_with_timeout.rs

@@ -0,0 +1,53 @@
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast as ast;
+use ruff_text_size::Ranged;
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Checks for `async` functions with a `timeout` argument.
+///
+/// ## Why is this bad?
+/// Rather than implementing asynchronous timeout behavior manually, prefer
+/// trio's built-in timeout functionality, available as `trio.fail_after`,
+/// `trio.move_on_after`, `trio.fail_at`, and `trio.move_on_at`.
+///
+/// ## Example
+/// ```python
+/// async def func():
+///     await long_running_task(timeout=2)
+/// ```
+///
+/// Use instead:
+/// ```python
+/// async def func():
+///     with trio.fail_after(2):
+///         await long_running_task()
+/// ```
+#[violation]
+pub struct TrioAsyncFunctionWithTimeout;
+
+impl Violation for TrioAsyncFunctionWithTimeout {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("Prefer `trio.fail_after` and `trio.move_on_after` over manual `async` timeout behavior")
+    }
+}
+
+/// TRIO109
+pub(crate) fn async_function_with_timeout(
+    checker: &mut Checker,
+    function_def: &ast::StmtFunctionDef,
+) {
+    if !function_def.is_async {
+        return;
+    }
+    let Some(timeout) = function_def.parameters.find("timeout") else {
+        return;
+    };
+    checker.diagnostics.push(Diagnostic::new(
+        TrioAsyncFunctionWithTimeout,
+        timeout.range(),
+    ));
+}

crates/ruff_linter/src/rules/flake8_trio/rules/mod.rs

@@ -1,7 +1,9 @@
+pub(crate) use async_function_with_timeout::*;
 pub(crate) use sync_call::*;
 pub(crate) use timeout_without_await::*;
 pub(crate) use zero_sleep_call::*;
 
+mod async_function_with_timeout;
 mod sync_call;
 mod timeout_without_await;
 mod zero_sleep_call;

crates/ruff_linter/src/rules/flake8_trio/snapshots/ruff_linter__rules__flake8_trio__tests__TRIO109_TRIO109.py.snap

@@ -0,0 +1,18 @@
+---
+source: crates/ruff_linter/src/rules/flake8_trio/mod.rs
+---
+TRIO109.py:5:16: TRIO109 Prefer `trio.fail_after` and `trio.move_on_after` over manual `async` timeout behavior
+  |
+5 | async def func(timeout):
+  |                ^^^^^^^ TRIO109
+6 |     ...
+  |
+
+TRIO109.py:9:16: TRIO109 Prefer `trio.fail_after` and `trio.move_on_after` over manual `async` timeout behavior
+   |
+ 9 | async def func(timeout=10):
+   |                ^^^^^^^^^^ TRIO109
+10 |     ...
+   |
+
+

crates/ruff_python_ast/src/nodes.rs

@@ -2281,6 +2281,15 @@ pub struct Parameters {
 }
 
 impl Parameters {
+    /// Returns the [`ParameterWithDefault`] with the given name, or `None` if no such [`ParameterWithDefault`] exists.
+    pub fn find(&self, name: &str) -> Option<&ParameterWithDefault> {
+        self.posonlyargs
+            .iter()
+            .chain(&self.args)
+            .chain(&self.kwonlyargs)
+            .find(|arg| arg.parameter.name.as_str() == name)
+    }
+
     /// Returns `true` if a parameter with the given name included in this [`Parameters`].
     pub fn includes(&self, name: &str) -> bool {
         if self