src/tools/clippy/clippy_lints/src/derive.rs

   1 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_note, span_lint_and_sugg, span_lint_and_then};
   2 use clippy_utils::ty::{implements_trait, implements_trait_with_env, is_copy};
   3 use clippy_utils::{is_lint_allowed, match_def_path, paths};
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_hir::intravisit::{walk_expr, walk_fn, walk_item, FnKind, Visitor};
   8 use rustc_hir::{
   9     self as hir, BlockCheckMode, BodyId, Expr, ExprKind, FnDecl, Impl, Item, ItemKind, UnsafeSource, Unsafety,
  10 };
  11 use rustc_lint::{LateContext, LateLintPass};
  12 use rustc_middle::hir::nested_filter;
  13 use rustc_middle::traits::Reveal;
  14 use rustc_middle::ty::{
  15     self, ClauseKind, GenericArgKind, GenericParamDefKind, ImplPolarity, ParamEnv, ToPredicate, TraitPredicate, Ty,
  16     TyCtxt,
  17 };
  18 use rustc_session::{declare_lint_pass, declare_tool_lint};
  19 use rustc_span::def_id::LocalDefId;
  20 use rustc_span::source_map::Span;
  21 use rustc_span::sym;
  22
  23 declare_clippy_lint! {
  24     /// ### What it does
  25     /// Lints against manual `PartialEq` implementations for types with a derived `Hash`
  26     /// implementation.
  27     ///
  28     /// ### Why is this bad?
  29     /// The implementation of these traits must agree (for
  30     /// example for use with `HashMap`) so it’s probably a bad idea to use a
  31     /// default-generated `Hash` implementation with an explicitly defined
  32     /// `PartialEq`. In particular, the following must hold for any type:
  33     ///
  34     /// ```text
  35     /// k1 == k2 ⇒ hash(k1) == hash(k2)
  36     /// ```
  37     ///
  38     /// ### Example
  39     /// ```ignore
  40     /// #[derive(Hash)]
  41     /// struct Foo;
  42     ///
  43     /// impl PartialEq for Foo {
  44     ///     ...
  45     /// }
  46     /// ```
  47     #[clippy::version = "pre 1.29.0"]
  48     pub DERIVED_HASH_WITH_MANUAL_EQ,
  49     correctness,
  50     "deriving `Hash` but implementing `PartialEq` explicitly"
  51 }
  52
  53 declare_clippy_lint! {
  54     /// ### What it does
  55     /// Lints against manual `PartialOrd` and `Ord` implementations for types with a derived `Ord`
  56     /// or `PartialOrd` implementation.
  57     ///
  58     /// ### Why is this bad?
  59     /// The implementation of these traits must agree (for
  60     /// example for use with `sort`) so it’s probably a bad idea to use a
  61     /// default-generated `Ord` implementation with an explicitly defined
  62     /// `PartialOrd`. In particular, the following must hold for any type
  63     /// implementing `Ord`:
  64     ///
  65     /// ```text
  66     /// k1.cmp(&k2) == k1.partial_cmp(&k2).unwrap()
  67     /// ```
  68     ///
  69     /// ### Example
  70     /// ```rust,ignore
  71     /// #[derive(Ord, PartialEq, Eq)]
  72     /// struct Foo;
  73     ///
  74     /// impl PartialOrd for Foo {
  75     ///     ...
  76     /// }
  77     /// ```
  78     /// Use instead:
  79     /// ```rust,ignore
  80     /// #[derive(PartialEq, Eq)]
  81     /// struct Foo;
  82     ///
  83     /// impl PartialOrd for Foo {
  84     ///     fn partial_cmp(&self, other: &Foo) -> Option<Ordering> {
  85     ///        Some(self.cmp(other))
  86     ///     }
  87     /// }
  88     ///
  89     /// impl Ord for Foo {
  90     ///     ...
  91     /// }
  92     /// ```
  93     /// or, if you don't need a custom ordering:
  94     /// ```rust,ignore
  95     /// #[derive(Ord, PartialOrd, PartialEq, Eq)]
  96     /// struct Foo;
  97     /// ```
  98     #[clippy::version = "1.47.0"]
  99     pub DERIVE_ORD_XOR_PARTIAL_ORD,
 100     correctness,
 101     "deriving `Ord` but implementing `PartialOrd` explicitly"
 102 }
 103
 104 declare_clippy_lint! {
 105     /// ### What it does
 106     /// Checks for explicit `Clone` implementations for `Copy`
 107     /// types.
 108     ///
 109     /// ### Why is this bad?
 110     /// To avoid surprising behavior, these traits should
 111     /// agree and the behavior of `Copy` cannot be overridden. In almost all
 112     /// situations a `Copy` type should have a `Clone` implementation that does
 113     /// nothing more than copy the object, which is what `#[derive(Copy, Clone)]`
 114     /// gets you.
 115     ///
 116     /// ### Example
 117     /// ```rust,ignore
 118     /// #[derive(Copy)]
 119     /// struct Foo;
 120     ///
 121     /// impl Clone for Foo {
 122     ///     // ..
 123     /// }
 124     /// ```
 125     #[clippy::version = "pre 1.29.0"]
 126     pub EXPL_IMPL_CLONE_ON_COPY,
 127     pedantic,
 128     "implementing `Clone` explicitly on `Copy` types"
 129 }
 130
 131 declare_clippy_lint! {
 132     /// ### What it does
 133     /// Checks for deriving `serde::Deserialize` on a type that
 134     /// has methods using `unsafe`.
 135     ///
 136     /// ### Why is this bad?
 137     /// Deriving `serde::Deserialize` will create a constructor
 138     /// that may violate invariants hold by another constructor.
 139     ///
 140     /// ### Example
 141     /// ```rust,ignore
 142     /// use serde::Deserialize;
 143     ///
 144     /// #[derive(Deserialize)]
 145     /// pub struct Foo {
 146     ///     // ..
 147     /// }
 148     ///
 149     /// impl Foo {
 150     ///     pub fn new() -> Self {
 151     ///         // setup here ..
 152     ///     }
 153     ///
 154     ///     pub unsafe fn parts() -> (&str, &str) {
 155     ///         // assumes invariants hold
 156     ///     }
 157     /// }
 158     /// ```
 159     #[clippy::version = "1.45.0"]
 160     pub UNSAFE_DERIVE_DESERIALIZE,
 161     pedantic,
 162     "deriving `serde::Deserialize` on a type that has methods using `unsafe`"
 163 }
 164
 165 declare_clippy_lint! {
 166     /// ### What it does
 167     /// Checks for types that derive `PartialEq` and could implement `Eq`.
 168     ///
 169     /// ### Why is this bad?
 170     /// If a type `T` derives `PartialEq` and all of its members implement `Eq`,
 171     /// then `T` can always implement `Eq`. Implementing `Eq` allows `T` to be used
 172     /// in APIs that require `Eq` types. It also allows structs containing `T` to derive
 173     /// `Eq` themselves.
 174     ///
 175     /// ### Example
 176     /// ```rust
 177     /// #[derive(PartialEq)]
 178     /// struct Foo {
 179     ///     i_am_eq: i32,
 180     ///     i_am_eq_too: Vec<String>,
 181     /// }
 182     /// ```
 183     /// Use instead:
 184     /// ```rust
 185     /// #[derive(PartialEq, Eq)]
 186     /// struct Foo {
 187     ///     i_am_eq: i32,
 188     ///     i_am_eq_too: Vec<String>,
 189     /// }
 190     /// ```
 191     #[clippy::version = "1.63.0"]
 192     pub DERIVE_PARTIAL_EQ_WITHOUT_EQ,
 193     nursery,
 194     "deriving `PartialEq` on a type that can implement `Eq`, without implementing `Eq`"
 195 }
 196
 197 declare_lint_pass!(Derive => [
 198     EXPL_IMPL_CLONE_ON_COPY,
 199     DERIVED_HASH_WITH_MANUAL_EQ,
 200     DERIVE_ORD_XOR_PARTIAL_ORD,
 201     UNSAFE_DERIVE_DESERIALIZE,
 202     DERIVE_PARTIAL_EQ_WITHOUT_EQ
 203 ]);
 204
 205 impl<'tcx> LateLintPass<'tcx> for Derive {
 206     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 207         if let ItemKind::Impl(Impl {
 208             of_trait: Some(ref trait_ref),
 209             ..
 210         }) = item.kind
 211         {
 212             let ty = cx.tcx.type_of(item.owner_id).instantiate_identity();
 213             let is_automatically_derived = cx.tcx.has_attr(item.owner_id, sym::automatically_derived);
 214
 215             check_hash_peq(cx, item.span, trait_ref, ty, is_automatically_derived);
 216             check_ord_partial_ord(cx, item.span, trait_ref, ty, is_automatically_derived);
 217
 218             if is_automatically_derived {
 219                 check_unsafe_derive_deserialize(cx, item, trait_ref, ty);
 220                 check_partial_eq_without_eq(cx, item.span, trait_ref, ty);
 221             } else {
 222                 check_copy_clone(cx, item, trait_ref, ty);
 223             }
 224         }
 225     }
 226 }
 227
 228 /// Implementation of the `DERIVED_HASH_WITH_MANUAL_EQ` lint.
 229 fn check_hash_peq<'tcx>(
 230     cx: &LateContext<'tcx>,
 231     span: Span,
 232     trait_ref: &hir::TraitRef<'_>,
 233     ty: Ty<'tcx>,
 234     hash_is_automatically_derived: bool,
 235 ) {
 236     if_chain! {
 237         if let Some(peq_trait_def_id) = cx.tcx.lang_items().eq_trait();
 238         if let Some(def_id) = trait_ref.trait_def_id();
 239         if cx.tcx.is_diagnostic_item(sym::Hash, def_id);
 240         then {
 241             // Look for the PartialEq implementations for `ty`
 242             cx.tcx.for_each_relevant_impl(peq_trait_def_id, ty, |impl_id| {
 243                 let peq_is_automatically_derived = cx.tcx.has_attr(impl_id, sym::automatically_derived);
 244
 245                 if !hash_is_automatically_derived || peq_is_automatically_derived {
 246                     return;
 247                 }
 248
 249                 let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
 250
 251                 // Only care about `impl PartialEq<Foo> for Foo`
 252                 // For `impl PartialEq<B> for A, input_types is [A, B]
 253                 if trait_ref.instantiate_identity().args.type_at(1) == ty {
 254                     span_lint_and_then(
 255                         cx,
 256                         DERIVED_HASH_WITH_MANUAL_EQ,
 257                         span,
 258                         "you are deriving `Hash` but have implemented `PartialEq` explicitly",
 259                         |diag| {
 260                             if let Some(local_def_id) = impl_id.as_local() {
 261                                 let hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
 262                                 diag.span_note(
 263                                     cx.tcx.hir().span(hir_id),
 264                                     "`PartialEq` implemented here"
 265                                 );
 266                             }
 267                         }
 268                     );
 269                 }
 270             });
 271         }
 272     }
 273 }
 274
 275 /// Implementation of the `DERIVE_ORD_XOR_PARTIAL_ORD` lint.
 276 fn check_ord_partial_ord<'tcx>(
 277     cx: &LateContext<'tcx>,
 278     span: Span,
 279     trait_ref: &hir::TraitRef<'_>,
 280     ty: Ty<'tcx>,
 281     ord_is_automatically_derived: bool,
 282 ) {
 283     if_chain! {
 284         if let Some(ord_trait_def_id) = cx.tcx.get_diagnostic_item(sym::Ord);
 285         if let Some(partial_ord_trait_def_id) = cx.tcx.lang_items().partial_ord_trait();
 286         if let Some(def_id) = &trait_ref.trait_def_id();
 287         if *def_id == ord_trait_def_id;
 288         then {
 289             // Look for the PartialOrd implementations for `ty`
 290             cx.tcx.for_each_relevant_impl(partial_ord_trait_def_id, ty, |impl_id| {
 291                 let partial_ord_is_automatically_derived = cx.tcx.has_attr(impl_id, sym::automatically_derived);
 292
 293                 if partial_ord_is_automatically_derived == ord_is_automatically_derived {
 294                     return;
 295                 }
 296
 297                 let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
 298
 299                 // Only care about `impl PartialOrd<Foo> for Foo`
 300                 // For `impl PartialOrd<B> for A, input_types is [A, B]
 301                 if trait_ref.instantiate_identity().args.type_at(1) == ty {
 302                     let mess = if partial_ord_is_automatically_derived {
 303                         "you are implementing `Ord` explicitly but have derived `PartialOrd`"
 304                     } else {
 305                         "you are deriving `Ord` but have implemented `PartialOrd` explicitly"
 306                     };
 307
 308                     span_lint_and_then(
 309                         cx,
 310                         DERIVE_ORD_XOR_PARTIAL_ORD,
 311                         span,
 312                         mess,
 313                         |diag| {
 314                             if let Some(local_def_id) = impl_id.as_local() {
 315                                 let hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
 316                                 diag.span_note(
 317                                     cx.tcx.hir().span(hir_id),
 318                                     "`PartialOrd` implemented here"
 319                                 );
 320                             }
 321                         }
 322                     );
 323                 }
 324             });
 325         }
 326     }
 327 }
 328
 329 /// Implementation of the `EXPL_IMPL_CLONE_ON_COPY` lint.
 330 fn check_copy_clone<'tcx>(cx: &LateContext<'tcx>, item: &Item<'_>, trait_ref: &hir::TraitRef<'_>, ty: Ty<'tcx>) {
 331     let clone_id = match cx.tcx.lang_items().clone_trait() {
 332         Some(id) if trait_ref.trait_def_id() == Some(id) => id,
 333         _ => return,
 334     };
 335     let Some(copy_id) = cx.tcx.lang_items().copy_trait() else {
 336         return;
 337     };
 338     let (ty_adt, ty_subs) = match *ty.kind() {
 339         // Unions can't derive clone.
 340         ty::Adt(adt, subs) if !adt.is_union() => (adt, subs),
 341         _ => return,
 342     };
 343     // If the current self type doesn't implement Copy (due to generic constraints), search to see if
 344     // there's a Copy impl for any instance of the adt.
 345     if !is_copy(cx, ty) {
 346         if ty_subs.non_erasable_generics(cx.tcx, ty_adt.did()).next().is_some() {
 347             let has_copy_impl = cx.tcx.all_local_trait_impls(()).get(&copy_id).map_or(false, |impls| {
 348                 impls.iter().any(|&id| {
 349                     matches!(cx.tcx.type_of(id).instantiate_identity().kind(), ty::Adt(adt, _)
 350                                         if ty_adt.did() == adt.did())
 351                 })
 352             });
 353             if !has_copy_impl {
 354                 return;
 355             }
 356         } else {
 357             return;
 358         }
 359     }
 360     // Derive constrains all generic types to requiring Clone. Check if any type is not constrained for
 361     // this impl.
 362     if ty_subs.types().any(|ty| !implements_trait(cx, ty, clone_id, &[])) {
 363         return;
 364     }
 365     // `#[repr(packed)]` structs with type/const parameters can't derive `Clone`.
 366     // https://github.com/rust-lang/rust-clippy/issues/10188
 367     if ty_adt.repr().packed()
 368         && ty_subs
 369             .iter()
 370             .any(|arg| matches!(arg.unpack(), GenericArgKind::Type(_) | GenericArgKind::Const(_)))
 371     {
 372         return;
 373     }
 374
 375     span_lint_and_note(
 376         cx,
 377         EXPL_IMPL_CLONE_ON_COPY,
 378         item.span,
 379         "you are implementing `Clone` explicitly on a `Copy` type",
 380         Some(item.span),
 381         "consider deriving `Clone` or removing `Copy`",
 382     );
 383 }
 384
 385 /// Implementation of the `UNSAFE_DERIVE_DESERIALIZE` lint.
 386 fn check_unsafe_derive_deserialize<'tcx>(
 387     cx: &LateContext<'tcx>,
 388     item: &Item<'_>,
 389     trait_ref: &hir::TraitRef<'_>,
 390     ty: Ty<'tcx>,
 391 ) {
 392     fn has_unsafe<'tcx>(cx: &LateContext<'tcx>, item: &'tcx Item<'_>) -> bool {
 393         let mut visitor = UnsafeVisitor { cx, has_unsafe: false };
 394         walk_item(&mut visitor, item);
 395         visitor.has_unsafe
 396     }
 397
 398     if_chain! {
 399         if let Some(trait_def_id) = trait_ref.trait_def_id();
 400         if match_def_path(cx, trait_def_id, &paths::SERDE_DESERIALIZE);
 401         if let ty::Adt(def, _) = ty.kind();
 402         if let Some(local_def_id) = def.did().as_local();
 403         let adt_hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
 404         if !is_lint_allowed(cx, UNSAFE_DERIVE_DESERIALIZE, adt_hir_id);
 405         if cx.tcx.inherent_impls(def.did())
 406             .iter()
 407             .map(|imp_did| cx.tcx.hir().expect_item(imp_did.expect_local()))
 408             .any(|imp| has_unsafe(cx, imp));
 409         then {
 410             span_lint_and_help(
 411                 cx,
 412                 UNSAFE_DERIVE_DESERIALIZE,
 413                 item.span,
 414                 "you are deriving `serde::Deserialize` on a type that has methods using `unsafe`",
 415                 None,
 416                 "consider implementing `serde::Deserialize` manually. See https://serde.rs/impl-deserialize.html"
 417             );
 418         }
 419     }
 420 }
 421
 422 struct UnsafeVisitor<'a, 'tcx> {
 423     cx: &'a LateContext<'tcx>,
 424     has_unsafe: bool,
 425 }
 426
 427 impl<'tcx> Visitor<'tcx> for UnsafeVisitor<'_, 'tcx> {
 428     type NestedFilter = nested_filter::All;
 429
 430     fn visit_fn(&mut self, kind: FnKind<'tcx>, decl: &'tcx FnDecl<'_>, body_id: BodyId, _: Span, id: LocalDefId) {
 431         if self.has_unsafe {
 432             return;
 433         }
 434
 435         if_chain! {
 436             if let Some(header) = kind.header();
 437             if header.unsafety == Unsafety::Unsafe;
 438             then {
 439                 self.has_unsafe = true;
 440             }
 441         }
 442
 443         walk_fn(self, kind, decl, body_id, id);
 444     }
 445
 446     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 447         if self.has_unsafe {
 448             return;
 449         }
 450
 451         if let ExprKind::Block(block, _) = expr.kind {
 452             if block.rules == BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided) {
 453                 self.has_unsafe = true;
 454             }
 455         }
 456
 457         walk_expr(self, expr);
 458     }
 459
 460     fn nested_visit_map(&mut self) -> Self::Map {
 461         self.cx.tcx.hir()
 462     }
 463 }
 464
 465 /// Implementation of the `DERIVE_PARTIAL_EQ_WITHOUT_EQ` lint.
 466 fn check_partial_eq_without_eq<'tcx>(cx: &LateContext<'tcx>, span: Span, trait_ref: &hir::TraitRef<'_>, ty: Ty<'tcx>) {
 467     if_chain! {
 468         if let ty::Adt(adt, args) = ty.kind();
 469         if cx.tcx.visibility(adt.did()).is_public();
 470         if let Some(eq_trait_def_id) = cx.tcx.get_diagnostic_item(sym::Eq);
 471         if let Some(def_id) = trait_ref.trait_def_id();
 472         if cx.tcx.is_diagnostic_item(sym::PartialEq, def_id);
 473         let param_env = param_env_for_derived_eq(cx.tcx, adt.did(), eq_trait_def_id);
 474         if !implements_trait_with_env(cx.tcx, param_env, ty, eq_trait_def_id, &[]);
 475         // If all of our fields implement `Eq`, we can implement `Eq` too
 476         if adt
 477             .all_fields()
 478             .map(|f| f.ty(cx.tcx, args))
 479             .all(|ty| implements_trait_with_env(cx.tcx, param_env, ty, eq_trait_def_id, &[]));
 480         then {
 481             span_lint_and_sugg(
 482                 cx,
 483                 DERIVE_PARTIAL_EQ_WITHOUT_EQ,
 484                 span.ctxt().outer_expn_data().call_site,
 485                 "you are deriving `PartialEq` and can implement `Eq`",
 486                 "consider deriving `Eq` as well",
 487                 "PartialEq, Eq".to_string(),
 488                 Applicability::MachineApplicable,
 489             )
 490         }
 491     }
 492 }
 493
 494 /// Creates the `ParamEnv` used for the give type's derived `Eq` impl.
 495 fn param_env_for_derived_eq(tcx: TyCtxt<'_>, did: DefId, eq_trait_id: DefId) -> ParamEnv<'_> {
 496     // Initial map from generic index to param def.
 497     // Vec<(param_def, needs_eq)>
 498     let mut params = tcx
 499         .generics_of(did)
 500         .params
 501         .iter()
 502         .map(|p| (p, matches!(p.kind, GenericParamDefKind::Type { .. })))
 503         .collect::<Vec<_>>();
 504
 505     let ty_predicates = tcx.predicates_of(did).predicates;
 506     for (p, _) in ty_predicates {
 507         if let ClauseKind::Trait(p) = p.kind().skip_binder()
 508             && p.trait_ref.def_id == eq_trait_id
 509             && let ty::Param(self_ty) = p.trait_ref.self_ty().kind()
 510         {
 511             // Flag types which already have an `Eq` bound.
 512             params[self_ty.index as usize].1 = false;
 513         }
 514     }
 515
 516     ParamEnv::new(
 517         tcx.mk_clauses_from_iter(ty_predicates.iter().map(|&(p, _)| p).chain(
 518             params.iter().filter(|&&(_, needs_eq)| needs_eq).map(|&(param, _)| {
 519                 ClauseKind::Trait(TraitPredicate {
 520                     trait_ref: ty::TraitRef::new(tcx, eq_trait_id, [tcx.mk_param_from_def(param)]),
 521                     polarity: ImplPolarity::Positive,
 522                 })
 523                 .to_predicate(tcx)
 524             }),
 525         )),
 526         Reveal::UserFacing,
 527     )
 528 }