Add initial flake8-trio rule (#8439)

## Summary

This pull request adds
[flake8-trio](https://github.com/Zac-HD/flake8-trio) support to ruff,
which is a very useful plugin for trio users to avoid very common
mistakes.

Part of #8451.

## Test Plan

Traditional rule testing, as [described in the
documentation](https://docs.astral.sh/ruff/contributing/#rule-testing-fixtures-and-snapshots).

LICENSE

@@ -1269,6 +1269,31 @@ are:
     SOFTWARE.
   """
 
+- flake8-trio, licensed as follows:
+  """
+    MIT License
+
+    Copyright (c) 2022 Zac Hatfield-Dodds
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in all
+    copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+    SOFTWARE.
+  """
+
 - Pyright, licensed as follows:
   """
     MIT License

README.md

@@ -314,6 +314,7 @@ quality tools, including:
 - [flake8-super](https://pypi.org/project/flake8-super/)
 - [flake8-tidy-imports](https://pypi.org/project/flake8-tidy-imports/)
 - [flake8-todos](https://pypi.org/project/flake8-todos/)
+- [flake8-trio](https://pypi.org/project/flake8-trio/)
 - [flake8-type-checking](https://pypi.org/project/flake8-type-checking/)
 - [flake8-use-pathlib](https://pypi.org/project/flake8-use-pathlib/)
 - [flynt](https://pypi.org/project/flynt/) ([#2102](https://github.com/astral-sh/ruff/issues/2102))

crates/ruff_linter/resources/test/fixtures/flake8_trio/TRIO100.py

@@ -0,0 +1,18 @@
+import trio
+
+
+async def foo():
+    with trio.fail_after():
+        ...
+
+async def foo():
+    with trio.fail_at():
+        await ...
+
+async def foo():
+    with trio.move_on_after():
+        ...
+
+async def foo():
+    with trio.move_at():
+        await ...

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

@@ -12,8 +12,8 @@ use crate::rules::{
     airflow, flake8_bandit, flake8_boolean_trap, flake8_bugbear, flake8_builtins, flake8_debugger,
     flake8_django, flake8_errmsg, flake8_import_conventions, flake8_pie, flake8_pyi,
     flake8_pytest_style, flake8_raise, flake8_return, flake8_simplify, flake8_slots,
-    flake8_tidy_imports, flake8_type_checking, mccabe, pandas_vet, pep8_naming, perflint,
-    pycodestyle, pyflakes, pygrep_hooks, pylint, pyupgrade, refurb, ruff, tryceratops,
+    flake8_tidy_imports, flake8_trio, flake8_type_checking, mccabe, pandas_vet, pep8_naming,
+    perflint, pycodestyle, pyflakes, pygrep_hooks, pylint, pyupgrade, refurb, ruff, tryceratops,
 };
 use crate::settings::types::PythonVersion;
 
@@ -1195,6 +1195,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             if checker.enabled(Rule::UselessWithLock) {
                 pylint::rules::useless_with_lock(checker, with_stmt);
             }
+            if checker.enabled(Rule::TrioTimeoutWithoutAwait) {
+                flake8_trio::rules::timeout_without_await(checker, with_stmt, items);
+            }
         }
         Stmt::While(ast::StmtWhile { body, orelse, .. }) => {
             if checker.enabled(Rule::FunctionUsesLoopVariable) {

crates/ruff_linter/src/codes.rs

@@ -290,6 +290,9 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8Async, "101") => (RuleGroup::Stable, rules::flake8_async::rules::OpenSleepOrSubprocessInAsyncFunction),
         (Flake8Async, "102") => (RuleGroup::Stable, rules::flake8_async::rules::BlockingOsCallInAsyncFunction),
 
+        // flake8-trio
+        (Flake8Trio, "100") => (RuleGroup::Preview, rules::flake8_trio::rules::TrioTimeoutWithoutAwait),
+
         // flake8-builtins
         (Flake8Builtins, "001") => (RuleGroup::Stable, rules::flake8_builtins::rules::BuiltinVariableShadowing),
         (Flake8Builtins, "002") => (RuleGroup::Stable, rules::flake8_builtins::rules::BuiltinArgumentShadowing),

crates/ruff_linter/src/registry.rs

@@ -64,6 +64,9 @@ pub enum Linter {
     /// [flake8-async](https://pypi.org/project/flake8-async/)
     #[prefix = "ASYNC"]
     Flake8Async,
+    /// [flake8-trio](https://pypi.org/project/flake8-trio/)
+    #[prefix = "TRIO"]
+    Flake8Trio,
     /// [flake8-bandit](https://pypi.org/project/flake8-bandit/)
     #[prefix = "S"]
     Flake8Bandit,

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

@@ -0,0 +1,26 @@
+//! Rules from [flake8-trio](https://pypi.org/project/flake8-trio/).
+pub(crate) mod rules;
+
+#[cfg(test)]
+mod tests {
+    use std::path::Path;
+
+    use anyhow::Result;
+    use test_case::test_case;
+
+    use crate::assert_messages;
+    use crate::registry::Rule;
+    use crate::settings::LinterSettings;
+    use crate::test::test_path;
+
+    #[test_case(Rule::TrioTimeoutWithoutAwait, Path::new("TRIO100.py"))]
+    fn rules(rule_code: Rule, path: &Path) -> Result<()> {
+        let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
+        let diagnostics = test_path(
+            Path::new("flake8_trio").join(path).as_path(),
+            &LinterSettings::for_rule(rule_code),
+        )?;
+        assert_messages!(snapshot, diagnostics);
+        Ok(())
+    }
+}

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

@@ -0,0 +1,3 @@
+pub(crate) use timeout_without_await::*;
+
+mod timeout_without_await;

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

@@ -0,0 +1,125 @@
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::call_path::CallPath;
+use ruff_python_ast::visitor::{walk_expr, walk_stmt, Visitor};
+use ruff_python_ast::{Expr, ExprAwait, Stmt, StmtWith, WithItem};
+
+use crate::checkers::ast::Checker;
+
+/// ## What it does
+/// Checks for trio functions that should contain await but don't.
+///
+/// ## Why is this bad?
+/// Some trio context managers, such as `trio.fail_after` and
+/// `trio.move_on_after`, have no effect unless they contain an `await`
+/// statement. The use of such functions without an `await` statement is
+/// likely a mistake.
+///
+/// ## Example
+/// ```python
+/// async def func():
+///     with trio.move_on_after(2):
+///         do_something()
+/// ```
+///
+/// Use instead:
+/// ```python
+/// async def func():
+///     with trio.move_on_after(2):
+///         do_something()
+///         await awaitable()
+/// ```
+#[violation]
+pub struct TrioTimeoutWithoutAwait {
+    method_name: MethodName,
+}
+
+impl Violation for TrioTimeoutWithoutAwait {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let Self { method_name } = self;
+        format!("A `with {method_name}(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.")
+    }
+}
+
+/// TRIO100
+pub(crate) fn timeout_without_await(
+    checker: &mut Checker,
+    with_stmt: &StmtWith,
+    with_items: &[WithItem],
+) {
+    let Some(method_name) = with_items.iter().find_map(|item| {
+        let call = item.context_expr.as_call_expr()?;
+        let call_path = checker.semantic().resolve_call_path(call.func.as_ref())?;
+        MethodName::try_from(&call_path)
+    }) else {
+        return;
+    };
+
+    let mut visitor = AwaitVisitor::default();
+    visitor.visit_body(&with_stmt.body);
+    if visitor.seen_await {
+        return;
+    }
+
+    checker.diagnostics.push(Diagnostic::new(
+        TrioTimeoutWithoutAwait { method_name },
+        with_stmt.range,
+    ));
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+enum MethodName {
+    MoveOnAfter,
+    MoveOnAt,
+    FailAfter,
+    FailAt,
+    CancelScope,
+}
+
+impl MethodName {
+    fn try_from(call_path: &CallPath<'_>) -> Option<Self> {
+        match call_path.as_slice() {
+            ["trio", "move_on_after"] => Some(Self::MoveOnAfter),
+            ["trio", "move_on_at"] => Some(Self::MoveOnAt),
+            ["trio", "fail_after"] => Some(Self::FailAfter),
+            ["trio", "fail_at"] => Some(Self::FailAt),
+            ["trio", "CancelScope"] => Some(Self::CancelScope),
+            _ => None,
+        }
+    }
+}
+
+impl std::fmt::Display for MethodName {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            MethodName::MoveOnAfter => write!(f, "trio.move_on_after"),
+            MethodName::MoveOnAt => write!(f, "trio.move_on_at"),
+            MethodName::FailAfter => write!(f, "trio.fail_after"),
+            MethodName::FailAt => write!(f, "trio.fail_at"),
+            MethodName::CancelScope => write!(f, "trio.CancelScope"),
+        }
+    }
+}
+
+#[derive(Debug, Default)]
+struct AwaitVisitor {
+    seen_await: bool,
+}
+
+impl Visitor<'_> for AwaitVisitor {
+    fn visit_stmt(&mut self, stmt: &Stmt) {
+        match stmt {
+            Stmt::FunctionDef(_) | Stmt::ClassDef(_) => (),
+            _ => walk_stmt(self, stmt),
+        }
+    }
+
+    fn visit_expr(&mut self, expr: &Expr) {
+        if let Expr::Await(ExprAwait { .. }) = expr {
+            self.seen_await = true;
+        } else {
+            walk_expr(self, expr);
+        }
+    }
+}

crates/ruff_linter/src/rules/flake8_trio/snapshots/ruff_linter__rules__flake8_trio__tests__TRIO100_TRIO100.py.snap

@@ -0,0 +1,26 @@
+---
+source: crates/ruff_linter/src/rules/flake8_trio/mod.rs
+---
+TRIO100.py:5:5: TRIO100 A `with trio.fail_after(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
+  |
+4 |   async def foo():
+5 |       with trio.fail_after():
+  |  _____^
+6 | |         ...
+  | |___________^ TRIO100
+7 |   
+8 |   async def foo():
+  |
+
+TRIO100.py:13:5: TRIO100 A `with trio.move_on_after(...):` context does not contain any `await` statements. This makes it pointless, as the timeout can only be triggered by a checkpoint.
+   |
+12 |   async def foo():
+13 |       with trio.move_on_after():
+   |  _____^
+14 | |         ...
+   | |___________^ TRIO100
+15 |   
+16 |   async def foo():
+   |
+
+

crates/ruff_linter/src/rules/mod.rs

@@ -37,6 +37,7 @@ pub mod flake8_simplify;
 pub mod flake8_slots;
 pub mod flake8_tidy_imports;
 pub mod flake8_todos;
+pub mod flake8_trio;
 pub mod flake8_type_checking;
 pub mod flake8_unused_arguments;
 pub mod flake8_use_pathlib;

docs/faq.md

@@ -81,6 +81,7 @@ natively, including:
 - [flake8-super](https://pypi.org/project/flake8-super/)
 - [flake8-tidy-imports](https://pypi.org/project/flake8-tidy-imports/)
 - [flake8-todos](https://pypi.org/project/flake8-todos/)
+- [flake8-trio](https://pypi.org/project/flake8-trio/) ([#8451](https://github.com/astral-sh/ruff/issues/8451))
 - [flake8-type-checking](https://pypi.org/project/flake8-type-checking/)
 - [flake8-use-pathlib](https://pypi.org/project/flake8-use-pathlib/)
 - [flynt](https://pypi.org/project/flynt/) ([#2102](https://github.com/astral-sh/ruff/issues/2102))
@@ -185,6 +186,7 @@ Today, Ruff can be used to replace Flake8 when used with any of the following pl
 - [flake8-super](https://pypi.org/project/flake8-super/)
 - [flake8-tidy-imports](https://pypi.org/project/flake8-tidy-imports/)
 - [flake8-todos](https://pypi.org/project/flake8-todos/)
+- [flake8-trio](https://pypi.org/project/flake8-trio/) ([#8451](https://github.com/astral-sh/ruff/issues/8451))
 - [flake8-type-checking](https://pypi.org/project/flake8-type-checking/)
 - [flake8-use-pathlib](https://pypi.org/project/flake8-use-pathlib/)
 - [flynt](https://pypi.org/project/flynt/) ([#2102](https://github.com/astral-sh/ruff/issues/2102))