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//! Checks for uses of mutex where an atomic value could be used
//!
//! This lint is **warn** by default
use clippy_utils::diagnostics::span_lint;
use clippy_utils::ty::is_type_diagnostic_item;
use rustc_hir::Expr;
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::{self, Ty};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for usages of `Mutex<X>` where an atomic will do.
///
/// ### Why is this bad?
/// Using a mutex just to make access to a plain bool or
/// reference sequential is shooting flies with cannons.
/// `std::sync::atomic::AtomicBool` and `std::sync::atomic::AtomicPtr` are leaner and
/// faster.
///
/// ### Known problems
/// This lint cannot detect if the mutex is actually used
/// for waiting before a critical section.
///
/// ### Example
/// ```rust
/// # let y = true;
/// # use std::sync::Mutex;
/// let x = Mutex::new(&y);
/// ```
///
/// Use instead:
/// ```rust
/// # let y = true;
/// # use std::sync::atomic::AtomicBool;
/// let x = AtomicBool::new(y);
/// ```
#[clippy::version = "pre 1.29.0"]
pub MUTEX_ATOMIC,
nursery,
"using a mutex where an atomic value could be used instead"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for usages of `Mutex<X>` where `X` is an integral
/// type.
///
/// ### Why is this bad?
/// Using a mutex just to make access to a plain integer
/// sequential is
/// shooting flies with cannons. `std::sync::atomic::AtomicUsize` is leaner and faster.
///
/// ### Known problems
/// This lint cannot detect if the mutex is actually used
/// for waiting before a critical section.
///
/// ### Example
/// ```rust
/// # use std::sync::Mutex;
/// let x = Mutex::new(0usize);
/// ```
///
/// Use instead:
/// ```rust
/// # use std::sync::atomic::AtomicUsize;
/// let x = AtomicUsize::new(0usize);
/// ```
#[clippy::version = "pre 1.29.0"]
pub MUTEX_INTEGER,
nursery,
"using a mutex for an integer type"
}
declare_lint_pass!(Mutex => [MUTEX_ATOMIC, MUTEX_INTEGER]);
impl<'tcx> LateLintPass<'tcx> for Mutex {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
let ty = cx.typeck_results().expr_ty(expr);
if let ty::Adt(_, subst) = ty.kind() {
if is_type_diagnostic_item(cx, ty, sym::Mutex) {
let mutex_param = subst.type_at(0);
if let Some(atomic_name) = get_atomic_name(mutex_param) {
let msg = format!(
"consider using an `{atomic_name}` instead of a `Mutex` here; if you just want the locking \
behavior and not the internal type, consider using `Mutex<()>`"
);
match *mutex_param.kind() {
ty::Uint(t) if t != ty::UintTy::Usize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg),
ty::Int(t) if t != ty::IntTy::Isize => span_lint(cx, MUTEX_INTEGER, expr.span, &msg),
_ => span_lint(cx, MUTEX_ATOMIC, expr.span, &msg),
};
}
}
}
}
}
fn get_atomic_name(ty: Ty<'_>) -> Option<&'static str> {
match ty.kind() {
ty::Bool => Some("AtomicBool"),
ty::Uint(_) => Some("AtomicUsize"),
ty::Int(_) => Some("AtomicIsize"),
ty::RawPtr(_) => Some("AtomicPtr"),
_ => None,
}
}
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