252 lines
10 KiB
Rust
252 lines
10 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::source::snippet;
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use clippy_utils::ty::{implements_trait, is_copy};
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use clippy_utils::{is_lint_allowed, match_def_path, paths};
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use rustc_ast::ImplPolarity;
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use rustc_hir::def_id::DefId;
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use rustc_hir::{FieldDef, Item, ItemKind, Node};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::lint::in_external_macro;
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use rustc_middle::ty::{self, subst::GenericArgKind, Ty};
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::sym;
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declare_clippy_lint! {
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/// ### What it does
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/// This lint warns about a `Send` implementation for a type that
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/// contains fields that are not safe to be sent across threads.
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/// It tries to detect fields that can cause a soundness issue
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/// when sent to another thread (e.g., `Rc`) while allowing `!Send` fields
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/// that are expected to exist in a `Send` type, such as raw pointers.
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///
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/// ### Why is this bad?
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/// Sending the struct to another thread effectively sends all of its fields,
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/// and the fields that do not implement `Send` can lead to soundness bugs
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/// such as data races when accessed in a thread
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/// that is different from the thread that created it.
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///
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/// See:
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/// * [*The Rustonomicon* about *Send and Sync*](https://doc.rust-lang.org/nomicon/send-and-sync.html)
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/// * [The documentation of `Send`](https://doc.rust-lang.org/std/marker/trait.Send.html)
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///
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/// ### Known Problems
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/// This lint relies on heuristics to distinguish types that are actually
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/// unsafe to be sent across threads and `!Send` types that are expected to
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/// exist in `Send` type. Its rule can filter out basic cases such as
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/// `Vec<*const T>`, but it's not perfect. Feel free to create an issue if
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/// you have a suggestion on how this heuristic can be improved.
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///
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/// ### Example
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/// ```rust,ignore
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/// struct ExampleStruct<T> {
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/// rc_is_not_send: Rc<String>,
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/// unbounded_generic_field: T,
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/// }
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///
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/// // This impl is unsound because it allows sending `!Send` types through `ExampleStruct`
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/// unsafe impl<T> Send for ExampleStruct<T> {}
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/// ```
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/// Use thread-safe types like [`std::sync::Arc`](https://doc.rust-lang.org/std/sync/struct.Arc.html)
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/// or specify correct bounds on generic type parameters (`T: Send`).
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#[clippy::version = "1.57.0"]
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pub NON_SEND_FIELDS_IN_SEND_TY,
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nursery,
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"there is a field that is not safe to be sent to another thread in a `Send` struct"
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}
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#[derive(Copy, Clone)]
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pub struct NonSendFieldInSendTy {
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enable_raw_pointer_heuristic: bool,
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}
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impl NonSendFieldInSendTy {
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pub fn new(enable_raw_pointer_heuristic: bool) -> Self {
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Self {
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enable_raw_pointer_heuristic,
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}
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}
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}
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impl_lint_pass!(NonSendFieldInSendTy => [NON_SEND_FIELDS_IN_SEND_TY]);
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impl<'tcx> LateLintPass<'tcx> for NonSendFieldInSendTy {
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fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
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let ty_allowed_in_send = if self.enable_raw_pointer_heuristic {
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ty_allowed_with_raw_pointer_heuristic
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} else {
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ty_allowed_without_raw_pointer_heuristic
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};
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// Checks if we are in `Send` impl item.
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// We start from `Send` impl instead of `check_field_def()` because
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// single `AdtDef` may have multiple `Send` impls due to generic
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// parameters, and the lint is much easier to implement in this way.
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if_chain! {
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if !in_external_macro(cx.tcx.sess, item.span);
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if let Some(send_trait) = cx.tcx.get_diagnostic_item(sym::Send);
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if let ItemKind::Impl(hir_impl) = &item.kind;
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if let Some(trait_ref) = &hir_impl.of_trait;
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if let Some(trait_id) = trait_ref.trait_def_id();
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if send_trait == trait_id;
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if hir_impl.polarity == ImplPolarity::Positive;
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if let Some(ty_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
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if let self_ty = ty_trait_ref.self_ty();
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if let ty::Adt(adt_def, impl_trait_substs) = self_ty.kind();
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then {
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let mut non_send_fields = Vec::new();
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let hir_map = cx.tcx.hir();
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for variant in &adt_def.variants {
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for field in &variant.fields {
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if_chain! {
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if let Some(field_hir_id) = field
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.did
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.as_local()
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.map(|local_def_id| hir_map.local_def_id_to_hir_id(local_def_id));
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if !is_lint_allowed(cx, NON_SEND_FIELDS_IN_SEND_TY, field_hir_id);
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if let field_ty = field.ty(cx.tcx, impl_trait_substs);
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if !ty_allowed_in_send(cx, field_ty, send_trait);
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if let Node::Field(field_def) = hir_map.get(field_hir_id);
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then {
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non_send_fields.push(NonSendField {
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def: field_def,
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ty: field_ty,
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generic_params: collect_generic_params(cx, field_ty),
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})
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}
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}
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}
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}
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if !non_send_fields.is_empty() {
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span_lint_and_then(
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cx,
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NON_SEND_FIELDS_IN_SEND_TY,
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item.span,
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&format!(
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"some fields in `{}` are not safe to be sent to another thread",
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snippet(cx, hir_impl.self_ty.span, "Unknown")
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),
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|diag| {
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for field in non_send_fields {
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diag.span_note(
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field.def.span,
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&format!("it is not safe to send field `{}` to another thread", field.def.ident.name),
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);
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match field.generic_params.len() {
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0 => diag.help("use a thread-safe type that implements `Send`"),
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1 if is_ty_param(field.ty) => diag.help(&format!("add `{}: Send` bound in `Send` impl", field.ty)),
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_ => diag.help(&format!(
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"add bounds on type parameter{} `{}` that satisfy `{}: Send`",
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if field.generic_params.len() > 1 { "s" } else { "" },
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field.generic_params_string(),
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snippet(cx, field.def.ty.span, "Unknown"),
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)),
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};
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}
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},
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);
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}
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}
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}
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}
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}
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struct NonSendField<'tcx> {
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def: &'tcx FieldDef<'tcx>,
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ty: Ty<'tcx>,
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generic_params: Vec<Ty<'tcx>>,
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}
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impl<'tcx> NonSendField<'tcx> {
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fn generic_params_string(&self) -> String {
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self.generic_params
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.iter()
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.map(ToString::to_string)
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.collect::<Vec<_>>()
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.join(", ")
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}
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}
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/// Given a type, collect all of its generic parameters.
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/// Example: `MyStruct<P, Box<Q, R>>` => `vec![P, Q, R]`
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fn collect_generic_params<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Vec<Ty<'tcx>> {
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ty.walk(cx.tcx)
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.filter_map(|inner| match inner.unpack() {
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GenericArgKind::Type(inner_ty) => Some(inner_ty),
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_ => None,
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})
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.filter(|&inner_ty| is_ty_param(inner_ty))
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.collect()
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}
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/// Be more strict when the heuristic is disabled
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fn ty_allowed_without_raw_pointer_heuristic<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, send_trait: DefId) -> bool {
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if implements_trait(cx, ty, send_trait, &[]) {
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return true;
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}
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if is_copy(cx, ty) && !contains_pointer_like(cx, ty) {
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return true;
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}
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false
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}
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/// Heuristic to allow cases like `Vec<*const u8>`
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fn ty_allowed_with_raw_pointer_heuristic<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, send_trait: DefId) -> bool {
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if implements_trait(cx, ty, send_trait, &[]) || is_copy(cx, ty) {
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return true;
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}
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// The type is known to be `!Send` and `!Copy`
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match ty.kind() {
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ty::Tuple(_) => ty
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.tuple_fields()
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.all(|ty| ty_allowed_with_raw_pointer_heuristic(cx, ty, send_trait)),
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ty::Array(ty, _) | ty::Slice(ty) => ty_allowed_with_raw_pointer_heuristic(cx, ty, send_trait),
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ty::Adt(_, substs) => {
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if contains_pointer_like(cx, ty) {
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// descends only if ADT contains any raw pointers
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substs.iter().all(|generic_arg| match generic_arg.unpack() {
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GenericArgKind::Type(ty) => ty_allowed_with_raw_pointer_heuristic(cx, ty, send_trait),
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// Lifetimes and const generics are not solid part of ADT and ignored
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GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => true,
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})
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} else {
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false
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}
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},
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// Raw pointers are `!Send` but allowed by the heuristic
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ty::RawPtr(_) => true,
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_ => false,
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}
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}
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/// Checks if the type contains any pointer-like types in substs (including nested ones)
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fn contains_pointer_like<'tcx>(cx: &LateContext<'tcx>, target_ty: Ty<'tcx>) -> bool {
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for ty_node in target_ty.walk(cx.tcx) {
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if let GenericArgKind::Type(inner_ty) = ty_node.unpack() {
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match inner_ty.kind() {
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ty::RawPtr(_) => {
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return true;
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},
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ty::Adt(adt_def, _) => {
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if match_def_path(cx, adt_def.did, &paths::PTR_NON_NULL) {
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return true;
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}
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},
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_ => (),
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}
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}
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}
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false
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}
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/// Returns `true` if the type is a type parameter such as `T`.
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fn is_ty_param(target_ty: Ty<'_>) -> bool {
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matches!(target_ty.kind(), ty::Param(_))
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}
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