-use crate::utils::{is_type_diagnostic_item, span_lint_and_help};
+use crate::utils::{is_type_diagnostic_item, span_lint_and_sugg};
use if_chain::if_chain;
+use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind, Mutability};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
/// **What it does:** Checks for `&mut Mutex::lock` calls
///
/// **Why is this bad?** `Mutex::lock` is less efficient than
- /// calling `Mutex::get_mut`
+ /// calling `Mutex::get_mut`. In addition you also have a statically
+ /// guarantee that the mutex isn't locked, instead of just a runtime
+ /// guarantee.
///
/// **Known problems:** None.
///
impl<'tcx> LateLintPass<'tcx> for MutMutexLock {
fn check_expr(&mut self, cx: &LateContext<'tcx>, ex: &'tcx Expr<'tcx>) {
if_chain! {
- if let ExprKind::MethodCall(path, _span, args, _) = &ex.kind;
+ if let ExprKind::MethodCall(path, method_span, args, _) = &ex.kind;
if path.ident.name == sym!(lock);
let ty = cx.typeck_results().expr_ty(&args[0]);
if let ty::Ref(_, inner_ty, Mutability::Mut) = ty.kind();
if is_type_diagnostic_item(cx, inner_ty, sym!(mutex_type));
then {
- span_lint_and_help(
+ span_lint_and_sugg(
cx,
MUT_MUTEX_LOCK,
- ex.span,
+ *method_span,
"calling `&mut Mutex::lock` unnecessarily locks an exclusive (mutable) reference",
- None,
- "use `&mut Mutex::get_mut` instead",
+ "change this to",
+ "get_mut".to_owned(),
+ Applicability::MachineApplicable,
);
}
}
--- /dev/null
+// run-rustfix
+#![allow(dead_code, unused_mut)]
+#![warn(clippy::mut_mutex_lock)]
+
+use std::sync::{Arc, Mutex};
+
+fn mut_mutex_lock() {
+ let mut value_rc = Arc::new(Mutex::new(42_u8));
+ let value_mutex = Arc::get_mut(&mut value_rc).unwrap();
+
+ let mut value = value_mutex.get_mut().unwrap();
+ *value += 1;
+}
+
+fn no_owned_mutex_lock() {
+ let mut value_rc = Arc::new(Mutex::new(42_u8));
+ let mut value = value_rc.lock().unwrap();
+ *value += 1;
+}
+
+fn main() {}
error: calling `&mut Mutex::lock` unnecessarily locks an exclusive (mutable) reference
- --> $DIR/mut_mutex_lock.rs:9:21
+ --> $DIR/mut_mutex_lock.rs:11:33
|
LL | let mut value = value_mutex.lock().unwrap();
- | ^^^^^^^^^^^^^^^^^^
+ | ^^^^ help: change this to: `get_mut`
|
= note: `-D clippy::mut-mutex-lock` implied by `-D warnings`
- = help: use `&mut Mutex::get_mut` instead
error: aborting due to previous error