Only flag flake8-trio rule when trio is present (#8550)

## Summary

Hoping to avoid some false positives by narrowing the scope of
https://github.com/astral-sh/ruff/pull/8534.

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

@@ -1,3 +1,6 @@
+import trio
+
+
 async def func():
     ...
 

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

@@ -13,6 +13,10 @@ use crate::checkers::ast::Checker;
 /// trio's built-in timeout functionality, available as `trio.fail_after`,
 /// `trio.move_on_after`, `trio.fail_at`, and `trio.move_on_at`.
 ///
+/// ## Known problems
+/// To avoid false positives, this rule is only enabled if `trio` is imported
+/// in the module.
+///
 /// ## Example
 /// ```python
 /// async def func():
@@ -40,12 +44,19 @@ pub(crate) fn async_function_with_timeout(
     checker: &mut Checker,
     function_def: &ast::StmtFunctionDef,
 ) {
+    // Detect `async` calls with a `timeout` argument.
     if !function_def.is_async {
         return;
     }
     let Some(timeout) = function_def.parameters.find("timeout") else {
         return;
     };
+
+    // If `trio` isn't in scope, avoid raising the diagnostic.
+    if !checker.semantic().seen(&["trio"]) {
+        return;
+    }
+
     checker.diagnostics.push(Diagnostic::new(
         TrioAsyncFunctionWithTimeout,
         timeout.range(),

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

@@ -1,18 +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
+TRIO109.py:8:16: TRIO109 Prefer `trio.fail_after` and `trio.move_on_after` over manual `async` timeout behavior
   |
-5 | async def func(timeout):
+8 | async def func(timeout):
   |                ^^^^^^^ TRIO109
-6 |     ...
+9 |     ...
   |
 
-TRIO109.py:9:16: TRIO109 Prefer `trio.fail_after` and `trio.move_on_after` over manual `async` timeout behavior
+TRIO109.py:12:16: TRIO109 Prefer `trio.fail_after` and `trio.move_on_after` over manual `async` timeout behavior
    |
- 9 | async def func(timeout=10):
+12 | async def func(timeout=10):
    |                ^^^^^^^^^^ TRIO109
-10 |     ...
+13 |     ...
    |
 
 

crates/ruff_python_semantic/src/model.rs

@@ -1207,6 +1207,16 @@ impl<'a> SemanticModel<'a> {
         exceptions
     }
 
+    /// Return `true` if the module at the given path was seen anywhere in the semantic model.
+    /// This includes both direct imports (`import trio`) and member imports (`from trio import
+    /// TrioTask`).
+    pub fn seen(&self, module: &[&str]) -> bool {
+        self.bindings
+            .iter()
+            .filter_map(Binding::as_any_import)
+            .any(|import| import.call_path().starts_with(module))
+    }
+
     /// Generate a [`Snapshot`] of the current semantic model.
     pub fn snapshot(&self) -> Snapshot {
         Snapshot {