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|
use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::higher;
use clippy_utils::ty::is_type_diagnostic_item;
use clippy_utils::SpanlessEq;
use if_chain::if_chain;
use rustc_hir::intravisit::{self as visit, Visitor};
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for `Mutex::lock` calls in `if let` expression
/// with lock calls in any of the else blocks.
///
/// ### Why is this bad?
/// The Mutex lock remains held for the whole
/// `if let ... else` block and deadlocks.
///
/// ### Example
/// ```rust,ignore
/// if let Ok(thing) = mutex.lock() {
/// do_thing();
/// } else {
/// mutex.lock();
/// }
/// ```
/// Should be written
/// ```rust,ignore
/// let locked = mutex.lock();
/// if let Ok(thing) = locked {
/// do_thing(thing);
/// } else {
/// use_locked(locked);
/// }
/// ```
#[clippy::version = "1.45.0"]
pub IF_LET_MUTEX,
correctness,
"locking a `Mutex` in an `if let` block can cause deadlocks"
}
declare_lint_pass!(IfLetMutex => [IF_LET_MUTEX]);
impl<'tcx> LateLintPass<'tcx> for IfLetMutex {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
let mut arm_visit = ArmVisitor {
mutex_lock_called: false,
found_mutex: None,
cx,
};
let mut op_visit = OppVisitor {
mutex_lock_called: false,
found_mutex: None,
cx,
};
if let Some(higher::IfLet {
let_expr,
if_then,
if_else: Some(if_else),
..
}) = higher::IfLet::hir(cx, expr)
{
op_visit.visit_expr(let_expr);
if op_visit.mutex_lock_called {
arm_visit.visit_expr(if_then);
arm_visit.visit_expr(if_else);
if arm_visit.mutex_lock_called && arm_visit.same_mutex(cx, op_visit.found_mutex.unwrap()) {
span_lint_and_help(
cx,
IF_LET_MUTEX,
expr.span,
"calling `Mutex::lock` inside the scope of another `Mutex::lock` causes a deadlock",
None,
"move the lock call outside of the `if let ...` expression",
);
}
}
}
}
}
/// Checks if `Mutex::lock` is called in the `if let` expr.
pub struct OppVisitor<'a, 'tcx> {
mutex_lock_called: bool,
found_mutex: Option<&'tcx Expr<'tcx>>,
cx: &'a LateContext<'tcx>,
}
impl<'tcx> Visitor<'tcx> for OppVisitor<'_, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
if let Some(mutex) = is_mutex_lock_call(self.cx, expr) {
self.found_mutex = Some(mutex);
self.mutex_lock_called = true;
return;
}
visit::walk_expr(self, expr);
}
}
/// Checks if `Mutex::lock` is called in any of the branches.
pub struct ArmVisitor<'a, 'tcx> {
mutex_lock_called: bool,
found_mutex: Option<&'tcx Expr<'tcx>>,
cx: &'a LateContext<'tcx>,
}
impl<'tcx> Visitor<'tcx> for ArmVisitor<'_, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
if let Some(mutex) = is_mutex_lock_call(self.cx, expr) {
self.found_mutex = Some(mutex);
self.mutex_lock_called = true;
return;
}
visit::walk_expr(self, expr);
}
}
impl<'tcx, 'l> ArmVisitor<'tcx, 'l> {
fn same_mutex(&self, cx: &LateContext<'_>, op_mutex: &Expr<'_>) -> bool {
self.found_mutex
.map_or(false, |arm_mutex| SpanlessEq::new(cx).eq_expr(op_mutex, arm_mutex))
}
}
fn is_mutex_lock_call<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
if_chain! {
if let ExprKind::MethodCall(path, [self_arg, ..], _) = &expr.kind;
if path.ident.as_str() == "lock";
let ty = cx.typeck_results().expr_ty(self_arg);
if is_type_diagnostic_item(cx, ty, sym::Mutex);
then {
Some(self_arg)
} else {
None
}
}
}
|
