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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::ty::is_type_diagnostic_item;
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind, Mutability};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for `&mut Mutex::lock` calls
///
/// ### Why is this bad?
/// `Mutex::lock` is less efficient than
/// calling `Mutex::get_mut`. In addition you also have a statically
/// guarantee that the mutex isn't locked, instead of just a runtime
/// guarantee.
///
/// ### Example
/// ```rust
/// use std::sync::{Arc, Mutex};
///
/// 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.lock().unwrap();
/// *value += 1;
/// ```
/// Use instead:
/// ```rust
/// use std::sync::{Arc, Mutex};
///
/// let mut value_rc = Arc::new(Mutex::new(42_u8));
/// let value_mutex = Arc::get_mut(&mut value_rc).unwrap();
///
/// let value = value_mutex.get_mut().unwrap();
/// *value += 1;
/// ```
#[clippy::version = "1.49.0"]
pub MUT_MUTEX_LOCK,
style,
"`&mut Mutex::lock` does unnecessary locking"
}
declare_lint_pass!(MutMutexLock => [MUT_MUTEX_LOCK]);
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, [self_arg, ..], _) = &ex.kind;
if path.ident.name == sym!(lock);
let ty = cx.typeck_results().expr_ty(self_arg);
if let ty::Ref(_, inner_ty, Mutability::Mut) = ty.kind();
if is_type_diagnostic_item(cx, *inner_ty, sym::Mutex);
then {
span_lint_and_sugg(
cx,
MUT_MUTEX_LOCK,
path.ident.span,
"calling `&mut Mutex::lock` unnecessarily locks an exclusive (mutable) reference",
"change this to",
"get_mut".to_owned(),
Applicability::MaybeIncorrect,
);
}
}
}
}
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