clippy_lints/src/loops/missing_spin_loop.rs

   1 use super::MISSING_SPIN_LOOP;
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use clippy_utils::is_no_std_crate;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{Block, Expr, ExprKind};
   6 use rustc_lint::LateContext;
   7 use rustc_middle::ty;
   8 use rustc_span::sym;
   9
  10 fn unpack_cond<'tcx>(cond: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
  11     match &cond.kind {
  12         ExprKind::Block(
  13             Block {
  14                 stmts: [],
  15                 expr: Some(e),
  16                 ..
  17             },
  18             _,
  19         )
  20         | ExprKind::Unary(_, e) => unpack_cond(e),
  21         ExprKind::Binary(_, l, r) => {
  22             let l = unpack_cond(l);
  23             if let ExprKind::MethodCall(..) = l.kind {
  24                 l
  25             } else {
  26                 unpack_cond(r)
  27             }
  28         },
  29         _ => cond,
  30     }
  31 }
  32
  33 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, body: &'tcx Expr<'_>) {
  34     if_chain! {
  35         if let ExprKind::Block(Block { stmts: [], expr: None, ..}, _) = body.kind;
  36         if let ExprKind::MethodCall(method, [callee, ..], _) = unpack_cond(cond).kind;
  37         if [sym::load, sym::compare_exchange, sym::compare_exchange_weak].contains(&method.ident.name);
  38         if let ty::Adt(def, _substs) = cx.typeck_results().expr_ty(callee).kind();
  39         if cx.tcx.is_diagnostic_item(sym::AtomicBool, def.did());
  40         then {
  41             span_lint_and_sugg(
  42                 cx,
  43                 MISSING_SPIN_LOOP,
  44                 body.span,
  45                 "busy-waiting loop should at least have a spin loop hint",
  46                 "try this",
  47                 (if is_no_std_crate(cx) {
  48                     "{ core::hint::spin_loop() }"
  49                 } else {
  50                     "{ std::hint::spin_loop() }"
  51                 }).into(),
  52                 Applicability::MachineApplicable
  53             );
  54         }
  55     }
  56 }