rust-clippy/clippy_lints/src/derive.rs

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use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_note, span_lint_and_sugg, span_lint_and_then};
use clippy_utils::paths;
use clippy_utils::ty::{implements_trait, implements_trait_with_env, is_copy};
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use clippy_utils::{is_lint_allowed, match_def_path};
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use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::def_id::DefId;
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use rustc_hir::intravisit::{walk_expr, walk_fn, walk_item, FnKind, Visitor};
use rustc_hir::{
self as hir, BlockCheckMode, BodyId, Constness, Expr, ExprKind, FnDecl, HirId, Impl, Item, ItemKind, UnsafeSource,
Unsafety,
};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::hir::nested_filter;
use rustc_middle::traits::Reveal;
use rustc_middle::ty::{
self, Binder, BoundConstness, GenericParamDefKind, ImplPolarity, ParamEnv, PredicateKind, TraitPredicate, TraitRef,
Ty, TyCtxt,
};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
use rustc_span::sym;
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declare_clippy_lint! {
/// ### What it does
/// Checks for deriving `Hash` but implementing `PartialEq`
/// explicitly or vice versa.
///
/// ### Why is this bad?
/// The implementation of these traits must agree (for
/// example for use with `HashMap`) so its probably a bad idea to use a
/// default-generated `Hash` implementation with an explicitly defined
/// `PartialEq`. In particular, the following must hold for any type:
///
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/// ```text
/// k1 == k2 ⇒ hash(k1) == hash(k2)
/// ```
///
/// ### Example
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/// ```ignore
/// #[derive(Hash)]
/// struct Foo;
///
/// impl PartialEq for Foo {
/// ...
/// }
/// ```
#[clippy::version = "pre 1.29.0"]
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pub DERIVE_HASH_XOR_EQ,
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correctness,
"deriving `Hash` but implementing `PartialEq` explicitly"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for deriving `Ord` but implementing `PartialOrd`
/// explicitly or vice versa.
///
/// ### Why is this bad?
/// The implementation of these traits must agree (for
/// example for use with `sort`) so its probably a bad idea to use a
/// default-generated `Ord` implementation with an explicitly defined
/// `PartialOrd`. In particular, the following must hold for any type
/// implementing `Ord`:
///
/// ```text
/// k1.cmp(&k2) == k1.partial_cmp(&k2).unwrap()
/// ```
///
/// ### Example
/// ```rust,ignore
/// #[derive(Ord, PartialEq, Eq)]
/// struct Foo;
///
/// impl PartialOrd for Foo {
/// ...
/// }
/// ```
/// Use instead:
/// ```rust,ignore
/// #[derive(PartialEq, Eq)]
/// struct Foo;
///
/// impl PartialOrd for Foo {
/// fn partial_cmp(&self, other: &Foo) -> Option<Ordering> {
/// Some(self.cmp(other))
/// }
/// }
///
/// impl Ord for Foo {
/// ...
/// }
/// ```
/// or, if you don't need a custom ordering:
/// ```rust,ignore
/// #[derive(Ord, PartialOrd, PartialEq, Eq)]
/// struct Foo;
/// ```
#[clippy::version = "1.47.0"]
pub DERIVE_ORD_XOR_PARTIAL_ORD,
correctness,
"deriving `Ord` but implementing `PartialOrd` explicitly"
}
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declare_clippy_lint! {
/// ### What it does
/// Checks for explicit `Clone` implementations for `Copy`
/// types.
///
/// ### Why is this bad?
/// To avoid surprising behavior, these traits should
/// agree and the behavior of `Copy` cannot be overridden. In almost all
/// situations a `Copy` type should have a `Clone` implementation that does
/// nothing more than copy the object, which is what `#[derive(Copy, Clone)]`
/// gets you.
///
/// ### Example
/// ```rust,ignore
/// #[derive(Copy)]
/// struct Foo;
///
/// impl Clone for Foo {
/// // ..
/// }
/// ```
#[clippy::version = "pre 1.29.0"]
pub EXPL_IMPL_CLONE_ON_COPY,
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pedantic,
"implementing `Clone` explicitly on `Copy` types"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for deriving `serde::Deserialize` on a type that
/// has methods using `unsafe`.
///
/// ### Why is this bad?
/// Deriving `serde::Deserialize` will create a constructor
/// that may violate invariants hold by another constructor.
///
/// ### Example
/// ```rust,ignore
/// use serde::Deserialize;
///
/// #[derive(Deserialize)]
/// pub struct Foo {
/// // ..
/// }
///
/// impl Foo {
/// pub fn new() -> Self {
/// // setup here ..
/// }
///
/// pub unsafe fn parts() -> (&str, &str) {
/// // assumes invariants hold
/// }
/// }
/// ```
#[clippy::version = "1.45.0"]
pub UNSAFE_DERIVE_DESERIALIZE,
pedantic,
"deriving `serde::Deserialize` on a type that has methods using `unsafe`"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for types that derive `PartialEq` and could implement `Eq`.
///
/// ### Why is this bad?
/// If a type `T` derives `PartialEq` and all of its members implement `Eq`,
/// then `T` can always implement `Eq`. Implementing `Eq` allows `T` to be used
/// in APIs that require `Eq` types. It also allows structs containing `T` to derive
/// `Eq` themselves.
///
/// ### Example
/// ```rust
/// #[derive(PartialEq)]
/// struct Foo {
/// i_am_eq: i32,
/// i_am_eq_too: Vec<String>,
/// }
/// ```
/// Use instead:
/// ```rust
/// #[derive(PartialEq, Eq)]
/// struct Foo {
/// i_am_eq: i32,
/// i_am_eq_too: Vec<String>,
/// }
/// ```
#[clippy::version = "1.63.0"]
pub DERIVE_PARTIAL_EQ_WITHOUT_EQ,
style,
"deriving `PartialEq` on a type that can implement `Eq`, without implementing `Eq`"
}
declare_lint_pass!(Derive => [
EXPL_IMPL_CLONE_ON_COPY,
DERIVE_HASH_XOR_EQ,
DERIVE_ORD_XOR_PARTIAL_ORD,
UNSAFE_DERIVE_DESERIALIZE,
DERIVE_PARTIAL_EQ_WITHOUT_EQ
]);
impl<'tcx> LateLintPass<'tcx> for Derive {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
if let ItemKind::Impl(Impl {
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of_trait: Some(ref trait_ref),
..
}) = item.kind
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{
let ty = cx.tcx.type_of(item.def_id);
let is_automatically_derived = cx.tcx.has_attr(item.def_id.to_def_id(), sym::automatically_derived);
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check_hash_peq(cx, item.span, trait_ref, ty, is_automatically_derived);
check_ord_partial_ord(cx, item.span, trait_ref, ty, is_automatically_derived);
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if is_automatically_derived {
check_unsafe_derive_deserialize(cx, item, trait_ref, ty);
check_partial_eq_without_eq(cx, item.span, trait_ref, ty);
} else {
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check_copy_clone(cx, item, trait_ref, ty);
}
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}
}
}
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/// Implementation of the `DERIVE_HASH_XOR_EQ` lint.
fn check_hash_peq<'tcx>(
cx: &LateContext<'tcx>,
span: Span,
trait_ref: &hir::TraitRef<'_>,
ty: Ty<'tcx>,
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hash_is_automatically_derived: bool,
) {
if_chain! {
if let Some(peq_trait_def_id) = cx.tcx.lang_items().eq_trait();
if let Some(def_id) = trait_ref.trait_def_id();
if cx.tcx.is_diagnostic_item(sym::Hash, def_id);
then {
// Look for the PartialEq implementations for `ty`
cx.tcx.for_each_relevant_impl(peq_trait_def_id, ty, |impl_id| {
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let peq_is_automatically_derived = cx.tcx.has_attr(impl_id, sym::automatically_derived);
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if peq_is_automatically_derived == hash_is_automatically_derived {
return;
}
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let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
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// Only care about `impl PartialEq<Foo> for Foo`
// For `impl PartialEq<B> for A, input_types is [A, B]
if trait_ref.substs.type_at(1) == ty {
let mess = if peq_is_automatically_derived {
"you are implementing `Hash` explicitly but have derived `PartialEq`"
} else {
"you are deriving `Hash` but have implemented `PartialEq` explicitly"
};
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span_lint_and_then(
cx,
DERIVE_HASH_XOR_EQ,
span,
mess,
|diag| {
if let Some(local_def_id) = impl_id.as_local() {
let hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
diag.span_note(
cx.tcx.hir().span(hir_id),
"`PartialEq` implemented here"
);
}
}
);
}
});
}
}
}
/// Implementation of the `DERIVE_ORD_XOR_PARTIAL_ORD` lint.
fn check_ord_partial_ord<'tcx>(
cx: &LateContext<'tcx>,
span: Span,
trait_ref: &hir::TraitRef<'_>,
ty: Ty<'tcx>,
ord_is_automatically_derived: bool,
) {
if_chain! {
if let Some(ord_trait_def_id) = cx.tcx.get_diagnostic_item(sym::Ord);
if let Some(partial_ord_trait_def_id) = cx.tcx.lang_items().partial_ord_trait();
if let Some(def_id) = &trait_ref.trait_def_id();
if *def_id == ord_trait_def_id;
then {
// Look for the PartialOrd implementations for `ty`
cx.tcx.for_each_relevant_impl(partial_ord_trait_def_id, ty, |impl_id| {
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let partial_ord_is_automatically_derived = cx.tcx.has_attr(impl_id, sym::automatically_derived);
if partial_ord_is_automatically_derived == ord_is_automatically_derived {
return;
}
let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
// Only care about `impl PartialOrd<Foo> for Foo`
// For `impl PartialOrd<B> for A, input_types is [A, B]
if trait_ref.substs.type_at(1) == ty {
let mess = if partial_ord_is_automatically_derived {
"you are implementing `Ord` explicitly but have derived `PartialOrd`"
} else {
"you are deriving `Ord` but have implemented `PartialOrd` explicitly"
};
span_lint_and_then(
cx,
DERIVE_ORD_XOR_PARTIAL_ORD,
span,
mess,
|diag| {
if let Some(local_def_id) = impl_id.as_local() {
let hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
diag.span_note(
cx.tcx.hir().span(hir_id),
"`PartialOrd` implemented here"
);
}
}
);
}
});
}
}
}
/// Implementation of the `EXPL_IMPL_CLONE_ON_COPY` lint.
fn check_copy_clone<'tcx>(cx: &LateContext<'tcx>, item: &Item<'_>, trait_ref: &hir::TraitRef<'_>, ty: Ty<'tcx>) {
let clone_id = match cx.tcx.lang_items().clone_trait() {
Some(id) if trait_ref.trait_def_id() == Some(id) => id,
_ => return,
};
let copy_id = match cx.tcx.lang_items().copy_trait() {
Some(id) => id,
None => return,
};
let (ty_adt, ty_subs) = match *ty.kind() {
// Unions can't derive clone.
ty::Adt(adt, subs) if !adt.is_union() => (adt, subs),
_ => return,
};
// If the current self type doesn't implement Copy (due to generic constraints), search to see if
// there's a Copy impl for any instance of the adt.
if !is_copy(cx, ty) {
if ty_subs.non_erasable_generics().next().is_some() {
let has_copy_impl = cx.tcx.all_local_trait_impls(()).get(&copy_id).map_or(false, |impls| {
impls
.iter()
.any(|&id| matches!(cx.tcx.type_of(id).kind(), ty::Adt(adt, _) if ty_adt.did() == adt.did()))
});
if !has_copy_impl {
return;
}
} else {
return;
}
}
// Derive constrains all generic types to requiring Clone. Check if any type is not constrained for
// this impl.
if ty_subs.types().any(|ty| !implements_trait(cx, ty, clone_id, &[])) {
return;
}
span_lint_and_note(
cx,
EXPL_IMPL_CLONE_ON_COPY,
item.span,
"you are implementing `Clone` explicitly on a `Copy` type",
Some(item.span),
"consider deriving `Clone` or removing `Copy`",
);
}
/// Implementation of the `UNSAFE_DERIVE_DESERIALIZE` lint.
fn check_unsafe_derive_deserialize<'tcx>(
cx: &LateContext<'tcx>,
item: &Item<'_>,
trait_ref: &hir::TraitRef<'_>,
ty: Ty<'tcx>,
) {
fn has_unsafe<'tcx>(cx: &LateContext<'tcx>, item: &'tcx Item<'_>) -> bool {
let mut visitor = UnsafeVisitor { cx, has_unsafe: false };
walk_item(&mut visitor, item);
visitor.has_unsafe
}
if_chain! {
if let Some(trait_def_id) = trait_ref.trait_def_id();
if match_def_path(cx, trait_def_id, &paths::SERDE_DESERIALIZE);
if let ty::Adt(def, _) = ty.kind();
if let Some(local_def_id) = def.did().as_local();
let adt_hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
if !is_lint_allowed(cx, UNSAFE_DERIVE_DESERIALIZE, adt_hir_id);
if cx.tcx.inherent_impls(def.did())
.iter()
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.map(|imp_did| cx.tcx.hir().expect_item(imp_did.expect_local()))
.any(|imp| has_unsafe(cx, imp));
then {
span_lint_and_help(
cx,
UNSAFE_DERIVE_DESERIALIZE,
item.span,
"you are deriving `serde::Deserialize` on a type that has methods using `unsafe`",
None,
"consider implementing `serde::Deserialize` manually. See https://serde.rs/impl-deserialize.html"
);
}
}
}
struct UnsafeVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
has_unsafe: bool,
}
impl<'tcx> Visitor<'tcx> for UnsafeVisitor<'_, 'tcx> {
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type NestedFilter = nested_filter::All;
fn visit_fn(&mut self, kind: FnKind<'tcx>, decl: &'tcx FnDecl<'_>, body_id: BodyId, _: Span, id: HirId) {
if self.has_unsafe {
return;
}
if_chain! {
if let Some(header) = kind.header();
if header.unsafety == Unsafety::Unsafe;
then {
self.has_unsafe = true;
}
}
walk_fn(self, kind, decl, body_id, id);
}
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
if self.has_unsafe {
return;
}
if let ExprKind::Block(block, _) = expr.kind {
if block.rules == BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided) {
self.has_unsafe = true;
}
}
walk_expr(self, expr);
}
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fn nested_visit_map(&mut self) -> Self::Map {
self.cx.tcx.hir()
}
}
/// Implementation of the `DERIVE_PARTIAL_EQ_WITHOUT_EQ` lint.
fn check_partial_eq_without_eq<'tcx>(cx: &LateContext<'tcx>, span: Span, trait_ref: &hir::TraitRef<'_>, ty: Ty<'tcx>) {
if_chain! {
if let ty::Adt(adt, substs) = ty.kind();
if cx.tcx.visibility(adt.did()).is_public();
if let Some(eq_trait_def_id) = cx.tcx.get_diagnostic_item(sym::Eq);
if let Some(def_id) = trait_ref.trait_def_id();
if cx.tcx.is_diagnostic_item(sym::PartialEq, def_id);
let param_env = param_env_for_derived_eq(cx.tcx, adt.did(), eq_trait_def_id);
if !implements_trait_with_env(cx.tcx, param_env, ty, eq_trait_def_id, &[]);
// If all of our fields implement `Eq`, we can implement `Eq` too
if adt
.all_fields()
.map(|f| f.ty(cx.tcx, substs))
.all(|ty| implements_trait_with_env(cx.tcx, param_env, ty, eq_trait_def_id, &[]));
then {
span_lint_and_sugg(
cx,
DERIVE_PARTIAL_EQ_WITHOUT_EQ,
span.ctxt().outer_expn_data().call_site,
"you are deriving `PartialEq` and can implement `Eq`",
"consider deriving `Eq` as well",
"PartialEq, Eq".to_string(),
Applicability::MachineApplicable,
)
}
}
}
/// Creates the `ParamEnv` used for the give type's derived `Eq` impl.
fn param_env_for_derived_eq(tcx: TyCtxt<'_>, did: DefId, eq_trait_id: DefId) -> ParamEnv<'_> {
// Initial map from generic index to param def.
// Vec<(param_def, needs_eq)>
let mut params = tcx
.generics_of(did)
.params
.iter()
.map(|p| (p, matches!(p.kind, GenericParamDefKind::Type { .. })))
.collect::<Vec<_>>();
let ty_predicates = tcx.predicates_of(did).predicates;
for (p, _) in ty_predicates {
if let PredicateKind::Trait(p) = p.kind().skip_binder()
&& p.trait_ref.def_id == eq_trait_id
&& let ty::Param(self_ty) = p.trait_ref.self_ty().kind()
&& p.constness == BoundConstness::NotConst
{
// Flag types which already have an `Eq` bound.
params[self_ty.index as usize].1 = false;
}
}
ParamEnv::new(
tcx.mk_predicates(ty_predicates.iter().map(|&(p, _)| p).chain(
params.iter().filter(|&&(_, needs_eq)| needs_eq).map(|&(param, _)| {
tcx.mk_predicate(Binder::dummy(PredicateKind::Trait(TraitPredicate {
trait_ref: TraitRef::new(
eq_trait_id,
tcx.mk_substs(std::iter::once(tcx.mk_param_from_def(param))),
),
constness: BoundConstness::NotConst,
polarity: ImplPolarity::Positive,
})))
}),
)),
Reveal::UserFacing,
Constness::NotConst,
)
}