src/tools/clippy/clippy_lints/src/await_holding_invalid.rs

   1 use clippy_config::types::DisallowedPath;
   2 use clippy_utils::diagnostics::span_lint_and_then;
   3 use clippy_utils::{match_def_path, paths};
   4 use rustc_data_structures::fx::FxHashMap;
   5 use rustc_hir as hir;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_middle::mir::CoroutineLayout;
   9 use rustc_session::impl_lint_pass;
  10 use rustc_span::{sym, Span};
  11
  12 declare_clippy_lint! {
  13     /// ### What it does
  14     /// Checks for calls to await while holding a non-async-aware MutexGuard.
  15     ///
  16     /// ### Why is this bad?
  17     /// The Mutex types found in std::sync and parking_lot
  18     /// are not designed to operate in an async context across await points.
  19     ///
  20     /// There are two potential solutions. One is to use an async-aware Mutex
  21     /// type. Many asynchronous foundation crates provide such a Mutex type. The
  22     /// other solution is to ensure the mutex is unlocked before calling await,
  23     /// either by introducing a scope or an explicit call to Drop::drop.
  24     ///
  25     /// ### Known problems
  26     /// Will report false positive for explicitly dropped guards
  27     /// ([#6446](https://github.com/rust-lang/rust-clippy/issues/6446)). A workaround for this is
  28     /// to wrap the `.lock()` call in a block instead of explicitly dropping the guard.
  29     ///
  30     /// ### Example
  31     /// ```no_run
  32     /// # use std::sync::Mutex;
  33     /// # async fn baz() {}
  34     /// async fn foo(x: &Mutex<u32>) {
  35     ///   let mut guard = x.lock().unwrap();
  36     ///   *guard += 1;
  37     ///   baz().await;
  38     /// }
  39     ///
  40     /// async fn bar(x: &Mutex<u32>) {
  41     ///   let mut guard = x.lock().unwrap();
  42     ///   *guard += 1;
  43     ///   drop(guard); // explicit drop
  44     ///   baz().await;
  45     /// }
  46     /// ```
  47     ///
  48     /// Use instead:
  49     /// ```no_run
  50     /// # use std::sync::Mutex;
  51     /// # async fn baz() {}
  52     /// async fn foo(x: &Mutex<u32>) {
  53     ///   {
  54     ///     let mut guard = x.lock().unwrap();
  55     ///     *guard += 1;
  56     ///   }
  57     ///   baz().await;
  58     /// }
  59     ///
  60     /// async fn bar(x: &Mutex<u32>) {
  61     ///   {
  62     ///     let mut guard = x.lock().unwrap();
  63     ///     *guard += 1;
  64     ///   } // guard dropped here at end of scope
  65     ///   baz().await;
  66     /// }
  67     /// ```
  68     #[clippy::version = "1.45.0"]
  69     pub AWAIT_HOLDING_LOCK,
  70     suspicious,
  71     "inside an async function, holding a `MutexGuard` while calling `await`"
  72 }
  73
  74 declare_clippy_lint! {
  75     /// ### What it does
  76     /// Checks for calls to await while holding a `RefCell` `Ref` or `RefMut`.
  77     ///
  78     /// ### Why is this bad?
  79     /// `RefCell` refs only check for exclusive mutable access
  80     /// at runtime. Holding onto a `RefCell` ref across an `await` suspension point
  81     /// risks panics from a mutable ref shared while other refs are outstanding.
  82     ///
  83     /// ### Known problems
  84     /// Will report false positive for explicitly dropped refs
  85     /// ([#6353](https://github.com/rust-lang/rust-clippy/issues/6353)). A workaround for this is
  86     /// to wrap the `.borrow[_mut]()` call in a block instead of explicitly dropping the ref.
  87     ///
  88     /// ### Example
  89     /// ```no_run
  90     /// # use std::cell::RefCell;
  91     /// # async fn baz() {}
  92     /// async fn foo(x: &RefCell<u32>) {
  93     ///   let mut y = x.borrow_mut();
  94     ///   *y += 1;
  95     ///   baz().await;
  96     /// }
  97     ///
  98     /// async fn bar(x: &RefCell<u32>) {
  99     ///   let mut y = x.borrow_mut();
 100     ///   *y += 1;
 101     ///   drop(y); // explicit drop
 102     ///   baz().await;
 103     /// }
 104     /// ```
 105     ///
 106     /// Use instead:
 107     /// ```no_run
 108     /// # use std::cell::RefCell;
 109     /// # async fn baz() {}
 110     /// async fn foo(x: &RefCell<u32>) {
 111     ///   {
 112     ///      let mut y = x.borrow_mut();
 113     ///      *y += 1;
 114     ///   }
 115     ///   baz().await;
 116     /// }
 117     ///
 118     /// async fn bar(x: &RefCell<u32>) {
 119     ///   {
 120     ///     let mut y = x.borrow_mut();
 121     ///     *y += 1;
 122     ///   } // y dropped here at end of scope
 123     ///   baz().await;
 124     /// }
 125     /// ```
 126     #[clippy::version = "1.49.0"]
 127     pub AWAIT_HOLDING_REFCELL_REF,
 128     suspicious,
 129     "inside an async function, holding a `RefCell` ref while calling `await`"
 130 }
 131
 132 declare_clippy_lint! {
 133     /// ### What it does
 134     /// Allows users to configure types which should not be held across `await`
 135     /// suspension points.
 136     ///
 137     /// ### Why is this bad?
 138     /// There are some types which are perfectly "safe" to be used concurrently
 139     /// from a memory access perspective but will cause bugs at runtime if they
 140     /// are held in such a way.
 141     ///
 142     /// ### Example
 143     ///
 144     /// ```toml
 145     /// await-holding-invalid-types = [
 146     ///   # You can specify a type name
 147     ///   "CustomLockType",
 148     ///   # You can (optionally) specify a reason
 149     ///   { path = "OtherCustomLockType", reason = "Relies on a thread local" }
 150     /// ]
 151     /// ```
 152     ///
 153     /// ```no_run
 154     /// # async fn baz() {}
 155     /// struct CustomLockType;
 156     /// struct OtherCustomLockType;
 157     /// async fn foo() {
 158     ///   let _x = CustomLockType;
 159     ///   let _y = OtherCustomLockType;
 160     ///   baz().await; // Lint violation
 161     /// }
 162     /// ```
 163     #[clippy::version = "1.62.0"]
 164     pub AWAIT_HOLDING_INVALID_TYPE,
 165     suspicious,
 166     "holding a type across an await point which is not allowed to be held as per the configuration"
 167 }
 168
 169 impl_lint_pass!(AwaitHolding => [AWAIT_HOLDING_LOCK, AWAIT_HOLDING_REFCELL_REF, AWAIT_HOLDING_INVALID_TYPE]);
 170
 171 #[derive(Debug)]
 172 pub struct AwaitHolding {
 173     conf_invalid_types: Vec<DisallowedPath>,
 174     def_ids: FxHashMap<DefId, DisallowedPath>,
 175 }
 176
 177 impl AwaitHolding {
 178     pub(crate) fn new(conf_invalid_types: Vec<DisallowedPath>) -> Self {
 179         Self {
 180             conf_invalid_types,
 181             def_ids: FxHashMap::default(),
 182         }
 183     }
 184 }
 185
 186 impl<'tcx> LateLintPass<'tcx> for AwaitHolding {
 187     fn check_crate(&mut self, cx: &LateContext<'tcx>) {
 188         for conf in &self.conf_invalid_types {
 189             let segs: Vec<_> = conf.path().split("::").collect();
 190             for id in clippy_utils::def_path_def_ids(cx, &segs) {
 191                 self.def_ids.insert(id, conf.clone());
 192             }
 193         }
 194     }
 195
 196     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
 197         if let hir::ExprKind::Closure(hir::Closure {
 198             kind: hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Async, _)),
 199             def_id,
 200             ..
 201         }) = expr.kind
 202         {
 203             if let Some(coroutine_layout) = cx.tcx.mir_coroutine_witnesses(*def_id) {
 204                 self.check_interior_types(cx, coroutine_layout);
 205             }
 206         }
 207     }
 208 }
 209
 210 impl AwaitHolding {
 211     fn check_interior_types(&self, cx: &LateContext<'_>, coroutine: &CoroutineLayout<'_>) {
 212         for (ty_index, ty_cause) in coroutine.field_tys.iter_enumerated() {
 213             if let rustc_middle::ty::Adt(adt, _) = ty_cause.ty.kind() {
 214                 let await_points = || {
 215                     coroutine
 216                         .variant_source_info
 217                         .iter_enumerated()
 218                         .filter_map(|(variant, source_info)| {
 219                             coroutine.variant_fields[variant]
 220                                 .raw
 221                                 .contains(&ty_index)
 222                                 .then_some(source_info.span)
 223                         })
 224                         .collect::<Vec<_>>()
 225                 };
 226                 if is_mutex_guard(cx, adt.did()) {
 227                     span_lint_and_then(
 228                         cx,
 229                         AWAIT_HOLDING_LOCK,
 230                         ty_cause.source_info.span,
 231                         "this `MutexGuard` is held across an `await` point",
 232                         |diag| {
 233                             diag.help(
 234                                 "consider using an async-aware `Mutex` type or ensuring the \
 235                                 `MutexGuard` is dropped before calling await",
 236                             );
 237                             diag.span_note(
 238                                 await_points(),
 239                                 "these are all the `await` points this lock is held through",
 240                             );
 241                         },
 242                     );
 243                 } else if is_refcell_ref(cx, adt.did()) {
 244                     span_lint_and_then(
 245                         cx,
 246                         AWAIT_HOLDING_REFCELL_REF,
 247                         ty_cause.source_info.span,
 248                         "this `RefCell` reference is held across an `await` point",
 249                         |diag| {
 250                             diag.help("ensure the reference is dropped before calling `await`");
 251                             diag.span_note(
 252                                 await_points(),
 253                                 "these are all the `await` points this reference is held through",
 254                             );
 255                         },
 256                     );
 257                 } else if let Some(disallowed) = self.def_ids.get(&adt.did()) {
 258                     emit_invalid_type(cx, ty_cause.source_info.span, disallowed);
 259                 }
 260             }
 261         }
 262     }
 263 }
 264
 265 fn emit_invalid_type(cx: &LateContext<'_>, span: Span, disallowed: &DisallowedPath) {
 266     span_lint_and_then(
 267         cx,
 268         AWAIT_HOLDING_INVALID_TYPE,
 269         span,
 270         format!(
 271             "`{}` may not be held across an `await` point per `clippy.toml`",
 272             disallowed.path()
 273         ),
 274         |diag| {
 275             if let Some(reason) = disallowed.reason() {
 276                 diag.note(reason);
 277             }
 278         },
 279     );
 280 }
 281
 282 fn is_mutex_guard(cx: &LateContext<'_>, def_id: DefId) -> bool {
 283     cx.tcx.is_diagnostic_item(sym::MutexGuard, def_id)
 284         || cx.tcx.is_diagnostic_item(sym::RwLockReadGuard, def_id)
 285         || cx.tcx.is_diagnostic_item(sym::RwLockWriteGuard, def_id)
 286         || match_def_path(cx, def_id, &paths::PARKING_LOT_MUTEX_GUARD)
 287         || match_def_path(cx, def_id, &paths::PARKING_LOT_RWLOCK_READ_GUARD)
 288         || match_def_path(cx, def_id, &paths::PARKING_LOT_RWLOCK_WRITE_GUARD)
 289 }
 290
 291 fn is_refcell_ref(cx: &LateContext<'_>, def_id: DefId) -> bool {
 292     matches!(
 293         cx.tcx.get_diagnostic_name(def_id),
 294         Some(sym::RefCellRef | sym::RefCellRefMut)
 295     )
 296 }