src/tools/clippy/clippy_lints/src/non_send_fields_in_send_ty.rs

   1 use clippy_utils::diagnostics::span_lint_and_then;
   2 use clippy_utils::source::snippet;
   3 use clippy_utils::ty::{implements_trait, is_copy};
   4 use clippy_utils::{is_lint_allowed, match_def_path, paths};
   5 use rustc_ast::ImplPolarity;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_hir::{FieldDef, Item, ItemKind, Node};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_middle::lint::in_external_macro;
  10 use rustc_middle::ty::{self, subst::GenericArgKind, Ty};
  11 use rustc_session::{declare_tool_lint, impl_lint_pass};
  12 use rustc_span::sym;
  13
  14 declare_clippy_lint! {
  15     /// ### What it does
  16     /// Warns about fields in struct implementing `Send` that are neither `Send` nor `Copy`.
  17     ///
  18     /// ### Why is this bad?
  19     /// Sending the struct to another thread will transfer the ownership to
  20     /// the new thread by dropping in the current thread during the transfer.
  21     /// This causes soundness issues for non-`Send` fields, as they are also
  22     /// dropped and might not be set up to handle this.
  23     ///
  24     /// See:
  25     /// * [*The Rustonomicon* about *Send and Sync*](https://doc.rust-lang.org/nomicon/send-and-sync.html)
  26     /// * [The documentation of `Send`](https://doc.rust-lang.org/std/marker/trait.Send.html)
  27     ///
  28     /// ### Known Problems
  29     /// Data structures that contain raw pointers may cause false positives.
  30     /// They are sometimes safe to be sent across threads but do not implement
  31     /// the `Send` trait. This lint has a heuristic to filter out basic cases
  32     /// such as `Vec<*const T>`, but it's not perfect. Feel free to create an
  33     /// issue if you have a suggestion on how this heuristic can be improved.
  34     ///
  35     /// ### Example
  36     /// ```rust,ignore
  37     /// struct ExampleStruct<T> {
  38     ///     rc_is_not_send: Rc<String>,
  39     ///     unbounded_generic_field: T,
  40     /// }
  41     ///
  42     /// // This impl is unsound because it allows sending `!Send` types through `ExampleStruct`
  43     /// unsafe impl<T> Send for ExampleStruct<T> {}
  44     /// ```
  45     /// Use thread-safe types like [`std::sync::Arc`](https://doc.rust-lang.org/std/sync/struct.Arc.html)
  46     /// or specify correct bounds on generic type parameters (`T: Send`).
  47     #[clippy::version = "1.57.0"]
  48     pub NON_SEND_FIELDS_IN_SEND_TY,
  49     suspicious,
  50     "there is field that does not implement `Send` in a `Send` struct"
  51 }
  52
  53 #[derive(Copy, Clone)]
  54 pub struct NonSendFieldInSendTy {
  55     enable_raw_pointer_heuristic: bool,
  56 }
  57
  58 impl NonSendFieldInSendTy {
  59     pub fn new(enable_raw_pointer_heuristic: bool) -> Self {
  60         Self {
  61             enable_raw_pointer_heuristic,
  62         }
  63     }
  64 }
  65
  66 impl_lint_pass!(NonSendFieldInSendTy => [NON_SEND_FIELDS_IN_SEND_TY]);
  67
  68 impl<'tcx> LateLintPass<'tcx> for NonSendFieldInSendTy {
  69     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
  70         let ty_allowed_in_send = if self.enable_raw_pointer_heuristic {
  71             ty_allowed_with_raw_pointer_heuristic
  72         } else {
  73             ty_allowed_without_raw_pointer_heuristic
  74         };
  75
  76         // Checks if we are in `Send` impl item.
  77         // We start from `Send` impl instead of `check_field_def()` because
  78         // single `AdtDef` may have multiple `Send` impls due to generic
  79         // parameters, and the lint is much easier to implement in this way.
  80         if_chain! {
  81             if !in_external_macro(cx.tcx.sess, item.span);
  82             if let Some(send_trait) = cx.tcx.get_diagnostic_item(sym::Send);
  83             if let ItemKind::Impl(hir_impl) = &item.kind;
  84             if let Some(trait_ref) = &hir_impl.of_trait;
  85             if let Some(trait_id) = trait_ref.trait_def_id();
  86             if send_trait == trait_id;
  87             if hir_impl.polarity == ImplPolarity::Positive;
  88             if let Some(ty_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
  89             if let self_ty = ty_trait_ref.self_ty();
  90             if let ty::Adt(adt_def, impl_trait_substs) = self_ty.kind();
  91             then {
  92                 let mut non_send_fields = Vec::new();
  93
  94                 let hir_map = cx.tcx.hir();
  95                 for variant in &adt_def.variants {
  96                     for field in &variant.fields {
  97                         if_chain! {
  98                             if let Some(field_hir_id) = field
  99                                 .did
 100                                 .as_local()
 101                                 .map(|local_def_id| hir_map.local_def_id_to_hir_id(local_def_id));
 102                             if !is_lint_allowed(cx, NON_SEND_FIELDS_IN_SEND_TY, field_hir_id);
 103                             if let field_ty = field.ty(cx.tcx, impl_trait_substs);
 104                             if !ty_allowed_in_send(cx, field_ty, send_trait);
 105                             if let Node::Field(field_def) = hir_map.get(field_hir_id);
 106                             then {
 107                                 non_send_fields.push(NonSendField {
 108                                     def: field_def,
 109                                     ty: field_ty,
 110                                     generic_params: collect_generic_params(cx, field_ty),
 111                                 })
 112                             }
 113                         }
 114                     }
 115                 }
 116
 117                 if !non_send_fields.is_empty() {
 118                     span_lint_and_then(
 119                         cx,
 120                         NON_SEND_FIELDS_IN_SEND_TY,
 121                         item.span,
 122                         &format!(
 123                             "this implementation is unsound, as some fields in `{}` are `!Send`",
 124                             snippet(cx, hir_impl.self_ty.span, "Unknown")
 125                         ),
 126                         |diag| {
 127                             for field in non_send_fields {
 128                                 diag.span_note(
 129                                     field.def.span,
 130                                     &format!("the type of field `{}` is `!Send`", field.def.ident.name),
 131                                 );
 132
 133                                 match field.generic_params.len() {
 134                                     0 => diag.help("use a thread-safe type that implements `Send`"),
 135                                     1 if is_ty_param(field.ty) => diag.help(&format!("add `{}: Send` bound in `Send` impl", field.ty)),
 136                                     _ => diag.help(&format!(
 137                                         "add bounds on type parameter{} `{}` that satisfy `{}: Send`",
 138                                         if field.generic_params.len() > 1 { "s" } else { "" },
 139                                         field.generic_params_string(),
 140                                         snippet(cx, field.def.ty.span, "Unknown"),
 141                                     )),
 142                                 };
 143                             }
 144                         },
 145                     );
 146                 }
 147             }
 148         }
 149     }
 150 }
 151
 152 struct NonSendField<'tcx> {
 153     def: &'tcx FieldDef<'tcx>,
 154     ty: Ty<'tcx>,
 155     generic_params: Vec<Ty<'tcx>>,
 156 }
 157
 158 impl<'tcx> NonSendField<'tcx> {
 159     fn generic_params_string(&self) -> String {
 160         self.generic_params
 161             .iter()
 162             .map(ToString::to_string)
 163             .collect::<Vec<_>>()
 164             .join(", ")
 165     }
 166 }
 167
 168 /// Given a type, collect all of its generic parameters.
 169 /// Example: `MyStruct<P, Box<Q, R>>` => `vec![P, Q, R]`
 170 fn collect_generic_params<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Vec<Ty<'tcx>> {
 171     ty.walk(cx.tcx)
 172         .filter_map(|inner| match inner.unpack() {
 173             GenericArgKind::Type(inner_ty) => Some(inner_ty),
 174             _ => None,
 175         })
 176         .filter(|&inner_ty| is_ty_param(inner_ty))
 177         .collect()
 178 }
 179
 180 /// Be more strict when the heuristic is disabled
 181 fn ty_allowed_without_raw_pointer_heuristic<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, send_trait: DefId) -> bool {
 182     if implements_trait(cx, ty, send_trait, &[]) {
 183         return true;
 184     }
 185
 186     if is_copy(cx, ty) && !contains_pointer_like(cx, ty) {
 187         return true;
 188     }
 189
 190     false
 191 }
 192
 193 /// Heuristic to allow cases like `Vec<*const u8>`
 194 fn ty_allowed_with_raw_pointer_heuristic<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, send_trait: DefId) -> bool {
 195     if implements_trait(cx, ty, send_trait, &[]) || is_copy(cx, ty) {
 196         return true;
 197     }
 198
 199     // The type is known to be `!Send` and `!Copy`
 200     match ty.kind() {
 201         ty::Tuple(_) => ty
 202             .tuple_fields()
 203             .all(|ty| ty_allowed_with_raw_pointer_heuristic(cx, ty, send_trait)),
 204         ty::Array(ty, _) | ty::Slice(ty) => ty_allowed_with_raw_pointer_heuristic(cx, ty, send_trait),
 205         ty::Adt(_, substs) => {
 206             if contains_pointer_like(cx, ty) {
 207                 // descends only if ADT contains any raw pointers
 208                 substs.iter().all(|generic_arg| match generic_arg.unpack() {
 209                     GenericArgKind::Type(ty) => ty_allowed_with_raw_pointer_heuristic(cx, ty, send_trait),
 210                     // Lifetimes and const generics are not solid part of ADT and ignored
 211                     GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => true,
 212                 })
 213             } else {
 214                 false
 215             }
 216         },
 217         // Raw pointers are `!Send` but allowed by the heuristic
 218         ty::RawPtr(_) => true,
 219         _ => false,
 220     }
 221 }
 222
 223 /// Checks if the type contains any pointer-like types in substs (including nested ones)
 224 fn contains_pointer_like<'tcx>(cx: &LateContext<'tcx>, target_ty: Ty<'tcx>) -> bool {
 225     for ty_node in target_ty.walk(cx.tcx) {
 226         if let GenericArgKind::Type(inner_ty) = ty_node.unpack() {
 227             match inner_ty.kind() {
 228                 ty::RawPtr(_) => {
 229                     return true;
 230                 },
 231                 ty::Adt(adt_def, _) => {
 232                     if match_def_path(cx, adt_def.did, &paths::PTR_NON_NULL) {
 233                         return true;
 234                     }
 235                 },
 236                 _ => (),
 237             }
 238         }
 239     }
 240
 241     false
 242 }
 243
 244 /// Returns `true` if the type is a type parameter such as `T`.
 245 fn is_ty_param(target_ty: Ty<'_>) -> bool {
 246     matches!(target_ty.kind(), ty::Param(_))
 247 }