rust/clippy_lints/src/arc_with_non_send_sync.rs

91 lines
4.0 KiB
Rust

use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
use clippy_utils::{is_from_proc_macro, last_path_segment};
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_middle::ty::print::with_forced_trimmed_paths;
use rustc_middle::ty::GenericArgKind;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::symbol::sym;
declare_clippy_lint! {
/// ### What it does.
/// This lint warns when you use `Arc` with a type that does not implement `Send` or `Sync`.
///
/// ### Why is this bad?
/// `Arc<T>` is an Atomic `RC<T>` and guarantees that updates to the reference counter are
/// Atomic. This is useful in multiprocessing scenarios. To send an `Arc<T>` across processes
/// and make use of the atomic ref counter, `T` must be [both `Send` and `Sync`](https://doc.rust-lang.org/std/sync/struct.Arc.html#impl-Send-for-Arc%3CT%3E),
/// either `T` should be made `Send + Sync` or an `Rc` should be used instead of an `Arc`
///
/// ### Example
/// ```no_run
/// # use std::cell::RefCell;
/// # use std::sync::Arc;
///
/// fn main() {
/// // This is fine, as `i32` implements `Send` and `Sync`.
/// let a = Arc::new(42);
///
/// // `RefCell` is `!Sync`, so either the `Arc` should be replaced with an `Rc`
/// // or the `RefCell` replaced with something like a `RwLock`
/// let b = Arc::new(RefCell::new(42));
/// }
/// ```
#[clippy::version = "1.72.0"]
pub ARC_WITH_NON_SEND_SYNC,
suspicious,
"using `Arc` with a type that does not implement `Send` and `Sync`"
}
declare_lint_pass!(ArcWithNonSendSync => [ARC_WITH_NON_SEND_SYNC]);
impl<'tcx> LateLintPass<'tcx> for ArcWithNonSendSync {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
if !expr.span.from_expansion()
&& let ty = cx.typeck_results().expr_ty(expr)
&& is_type_diagnostic_item(cx, ty, sym::Arc)
&& let ExprKind::Call(func, [arg]) = expr.kind
&& let ExprKind::Path(func_path) = func.kind
&& last_path_segment(&func_path).ident.name == sym::new
&& let arg_ty = cx.typeck_results().expr_ty(arg)
// make sure that the type is not and does not contain any type parameters
&& arg_ty.walk().all(|arg| {
!matches!(arg.unpack(), GenericArgKind::Type(ty) if matches!(ty.kind(), ty::Param(_)))
})
&& let Some(send) = cx.tcx.get_diagnostic_item(sym::Send)
&& let Some(sync) = cx.tcx.lang_items().sync_trait()
&& let [is_send, is_sync] = [send, sync].map(|id| implements_trait(cx, arg_ty, id, &[]))
&& !(is_send && is_sync)
&& !is_from_proc_macro(cx, expr)
{
span_lint_and_then(
cx,
ARC_WITH_NON_SEND_SYNC,
expr.span,
"usage of an `Arc` that is not `Send` and `Sync`",
|diag| {
with_forced_trimmed_paths!({
diag.note(format!("`Arc<{arg_ty}>` is not `Send` and `Sync` as:"));
if !is_send {
diag.note(format!("- the trait `Send` is not implemented for `{arg_ty}`"));
}
if !is_sync {
diag.note(format!("- the trait `Sync` is not implemented for `{arg_ty}`"));
}
diag.help("consider using an `Rc` instead. `Arc` does not provide benefits for non `Send` and `Sync` types");
diag.note("if you intend to use `Arc` with `Send` and `Sync` traits");
diag.note(format!(
"wrap the inner type with a `Mutex` or implement `Send` and `Sync` for `{arg_ty}`"
));
});
},
);
}
}
}