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

   1 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_note, span_lint_and_then};
   2 use clippy_utils::paths;
   3 use clippy_utils::ty::{implements_trait, is_copy};
   4 use clippy_utils::{is_lint_allowed, match_def_path};
   5 use if_chain::if_chain;
   6 use rustc_hir::intravisit::{walk_expr, walk_fn, walk_item, FnKind, Visitor};
   7 use rustc_hir::{
   8     BlockCheckMode, BodyId, Expr, ExprKind, FnDecl, HirId, Impl, Item, ItemKind, TraitRef, UnsafeSource, Unsafety,
   9 };
  10 use rustc_lint::{LateContext, LateLintPass};
  11 use rustc_middle::hir::nested_filter;
  12 use rustc_middle::ty::{self, Ty};
  13 use rustc_session::{declare_lint_pass, declare_tool_lint};
  14 use rustc_span::source_map::Span;
  15 use rustc_span::sym;
  16
  17 declare_clippy_lint! {
  18     /// ### What it does
  19     /// Checks for deriving `Hash` but implementing `PartialEq`
  20     /// explicitly or vice versa.
  21     ///
  22     /// ### Why is this bad?
  23     /// The implementation of these traits must agree (for
  24     /// example for use with `HashMap`) so it’s probably a bad idea to use a
  25     /// default-generated `Hash` implementation with an explicitly defined
  26     /// `PartialEq`. In particular, the following must hold for any type:
  27     ///
  28     /// ```text
  29     /// k1 == k2 ⇒ hash(k1) == hash(k2)
  30     /// ```
  31     ///
  32     /// ### Example
  33     /// ```ignore
  34     /// #[derive(Hash)]
  35     /// struct Foo;
  36     ///
  37     /// impl PartialEq for Foo {
  38     ///     ...
  39     /// }
  40     /// ```
  41     #[clippy::version = "pre 1.29.0"]
  42     pub DERIVE_HASH_XOR_EQ,
  43     correctness,
  44     "deriving `Hash` but implementing `PartialEq` explicitly"
  45 }
  46
  47 declare_clippy_lint! {
  48     /// ### What it does
  49     /// Checks for deriving `Ord` but implementing `PartialOrd`
  50     /// explicitly or vice versa.
  51     ///
  52     /// ### Why is this bad?
  53     /// The implementation of these traits must agree (for
  54     /// example for use with `sort`) so it’s probably a bad idea to use a
  55     /// default-generated `Ord` implementation with an explicitly defined
  56     /// `PartialOrd`. In particular, the following must hold for any type
  57     /// implementing `Ord`:
  58     ///
  59     /// ```text
  60     /// k1.cmp(&k2) == k1.partial_cmp(&k2).unwrap()
  61     /// ```
  62     ///
  63     /// ### Example
  64     /// ```rust,ignore
  65     /// #[derive(Ord, PartialEq, Eq)]
  66     /// struct Foo;
  67     ///
  68     /// impl PartialOrd for Foo {
  69     ///     ...
  70     /// }
  71     /// ```
  72     /// Use instead:
  73     /// ```rust,ignore
  74     /// #[derive(PartialEq, Eq)]
  75     /// struct Foo;
  76     ///
  77     /// impl PartialOrd for Foo {
  78     ///     fn partial_cmp(&self, other: &Foo) -> Option<Ordering> {
  79     ///        Some(self.cmp(other))
  80     ///     }
  81     /// }
  82     ///
  83     /// impl Ord for Foo {
  84     ///     ...
  85     /// }
  86     /// ```
  87     /// or, if you don't need a custom ordering:
  88     /// ```rust,ignore
  89     /// #[derive(Ord, PartialOrd, PartialEq, Eq)]
  90     /// struct Foo;
  91     /// ```
  92     #[clippy::version = "1.47.0"]
  93     pub DERIVE_ORD_XOR_PARTIAL_ORD,
  94     correctness,
  95     "deriving `Ord` but implementing `PartialOrd` explicitly"
  96 }
  97
  98 declare_clippy_lint! {
  99     /// ### What it does
 100     /// Checks for explicit `Clone` implementations for `Copy`
 101     /// types.
 102     ///
 103     /// ### Why is this bad?
 104     /// To avoid surprising behaviour, these traits should
 105     /// agree and the behaviour of `Copy` cannot be overridden. In almost all
 106     /// situations a `Copy` type should have a `Clone` implementation that does
 107     /// nothing more than copy the object, which is what `#[derive(Copy, Clone)]`
 108     /// gets you.
 109     ///
 110     /// ### Example
 111     /// ```rust,ignore
 112     /// #[derive(Copy)]
 113     /// struct Foo;
 114     ///
 115     /// impl Clone for Foo {
 116     ///     // ..
 117     /// }
 118     /// ```
 119     #[clippy::version = "pre 1.29.0"]
 120     pub EXPL_IMPL_CLONE_ON_COPY,
 121     pedantic,
 122     "implementing `Clone` explicitly on `Copy` types"
 123 }
 124
 125 declare_clippy_lint! {
 126     /// ### What it does
 127     /// Checks for deriving `serde::Deserialize` on a type that
 128     /// has methods using `unsafe`.
 129     ///
 130     /// ### Why is this bad?
 131     /// Deriving `serde::Deserialize` will create a constructor
 132     /// that may violate invariants hold by another constructor.
 133     ///
 134     /// ### Example
 135     /// ```rust,ignore
 136     /// use serde::Deserialize;
 137     ///
 138     /// #[derive(Deserialize)]
 139     /// pub struct Foo {
 140     ///     // ..
 141     /// }
 142     ///
 143     /// impl Foo {
 144     ///     pub fn new() -> Self {
 145     ///         // setup here ..
 146     ///     }
 147     ///
 148     ///     pub unsafe fn parts() -> (&str, &str) {
 149     ///         // assumes invariants hold
 150     ///     }
 151     /// }
 152     /// ```
 153     #[clippy::version = "1.45.0"]
 154     pub UNSAFE_DERIVE_DESERIALIZE,
 155     pedantic,
 156     "deriving `serde::Deserialize` on a type that has methods using `unsafe`"
 157 }
 158
 159 declare_lint_pass!(Derive => [
 160     EXPL_IMPL_CLONE_ON_COPY,
 161     DERIVE_HASH_XOR_EQ,
 162     DERIVE_ORD_XOR_PARTIAL_ORD,
 163     UNSAFE_DERIVE_DESERIALIZE
 164 ]);
 165
 166 impl<'tcx> LateLintPass<'tcx> for Derive {
 167     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 168         if let ItemKind::Impl(Impl {
 169             of_trait: Some(ref trait_ref),
 170             ..
 171         }) = item.kind
 172         {
 173             let ty = cx.tcx.type_of(item.def_id);
 174             let is_automatically_derived =
 175                 cx.tcx.has_attr(item.def_id.to_def_id(), sym::automatically_derived);
 176
 177             check_hash_peq(cx, item.span, trait_ref, ty, is_automatically_derived);
 178             check_ord_partial_ord(cx, item.span, trait_ref, ty, is_automatically_derived);
 179
 180             if is_automatically_derived {
 181                 check_unsafe_derive_deserialize(cx, item, trait_ref, ty);
 182             } else {
 183                 check_copy_clone(cx, item, trait_ref, ty);
 184             }
 185         }
 186     }
 187 }
 188
 189 /// Implementation of the `DERIVE_HASH_XOR_EQ` lint.
 190 fn check_hash_peq<'tcx>(
 191     cx: &LateContext<'tcx>,
 192     span: Span,
 193     trait_ref: &TraitRef<'_>,
 194     ty: Ty<'tcx>,
 195     hash_is_automatically_derived: bool,
 196 ) {
 197     if_chain! {
 198         if let Some(peq_trait_def_id) = cx.tcx.lang_items().eq_trait();
 199         if let Some(def_id) = trait_ref.trait_def_id();
 200         if cx.tcx.is_diagnostic_item(sym::Hash, def_id);
 201         then {
 202             // Look for the PartialEq implementations for `ty`
 203             cx.tcx.for_each_relevant_impl(peq_trait_def_id, ty, |impl_id| {
 204                 let peq_is_automatically_derived = cx.tcx.has_attr(impl_id, sym::automatically_derived);
 205
 206                 if peq_is_automatically_derived == hash_is_automatically_derived {
 207                     return;
 208                 }
 209
 210                 let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
 211
 212                 // Only care about `impl PartialEq<Foo> for Foo`
 213                 // For `impl PartialEq<B> for A, input_types is [A, B]
 214                 if trait_ref.substs.type_at(1) == ty {
 215                     let mess = if peq_is_automatically_derived {
 216                         "you are implementing `Hash` explicitly but have derived `PartialEq`"
 217                     } else {
 218                         "you are deriving `Hash` but have implemented `PartialEq` explicitly"
 219                     };
 220
 221                     span_lint_and_then(
 222                         cx,
 223                         DERIVE_HASH_XOR_EQ,
 224                         span,
 225                         mess,
 226                         |diag| {
 227                             if let Some(local_def_id) = impl_id.as_local() {
 228                                 let hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
 229                                 diag.span_note(
 230                                     cx.tcx.hir().span(hir_id),
 231                                     "`PartialEq` implemented here"
 232                                 );
 233                             }
 234                         }
 235                     );
 236                 }
 237             });
 238         }
 239     }
 240 }
 241
 242 /// Implementation of the `DERIVE_ORD_XOR_PARTIAL_ORD` lint.
 243 fn check_ord_partial_ord<'tcx>(
 244     cx: &LateContext<'tcx>,
 245     span: Span,
 246     trait_ref: &TraitRef<'_>,
 247     ty: Ty<'tcx>,
 248     ord_is_automatically_derived: bool,
 249 ) {
 250     if_chain! {
 251         if let Some(ord_trait_def_id) = cx.tcx.get_diagnostic_item(sym::Ord);
 252         if let Some(partial_ord_trait_def_id) = cx.tcx.lang_items().partial_ord_trait();
 253         if let Some(def_id) = &trait_ref.trait_def_id();
 254         if *def_id == ord_trait_def_id;
 255         then {
 256             // Look for the PartialOrd implementations for `ty`
 257             cx.tcx.for_each_relevant_impl(partial_ord_trait_def_id, ty, |impl_id| {
 258                 let partial_ord_is_automatically_derived = cx.tcx.has_attr(impl_id, sym::automatically_derived);
 259
 260                 if partial_ord_is_automatically_derived == ord_is_automatically_derived {
 261                     return;
 262                 }
 263
 264                 let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
 265
 266                 // Only care about `impl PartialOrd<Foo> for Foo`
 267                 // For `impl PartialOrd<B> for A, input_types is [A, B]
 268                 if trait_ref.substs.type_at(1) == ty {
 269                     let mess = if partial_ord_is_automatically_derived {
 270                         "you are implementing `Ord` explicitly but have derived `PartialOrd`"
 271                     } else {
 272                         "you are deriving `Ord` but have implemented `PartialOrd` explicitly"
 273                     };
 274
 275                     span_lint_and_then(
 276                         cx,
 277                         DERIVE_ORD_XOR_PARTIAL_ORD,
 278                         span,
 279                         mess,
 280                         |diag| {
 281                             if let Some(local_def_id) = impl_id.as_local() {
 282                                 let hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
 283                                 diag.span_note(
 284                                     cx.tcx.hir().span(hir_id),
 285                                     "`PartialOrd` implemented here"
 286                                 );
 287                             }
 288                         }
 289                     );
 290                 }
 291             });
 292         }
 293     }
 294 }
 295
 296 /// Implementation of the `EXPL_IMPL_CLONE_ON_COPY` lint.
 297 fn check_copy_clone<'tcx>(cx: &LateContext<'tcx>, item: &Item<'_>, trait_ref: &TraitRef<'_>, ty: Ty<'tcx>) {
 298     let clone_id = match cx.tcx.lang_items().clone_trait() {
 299         Some(id) if trait_ref.trait_def_id() == Some(id) => id,
 300         _ => return,
 301     };
 302     let copy_id = match cx.tcx.lang_items().copy_trait() {
 303         Some(id) => id,
 304         None => return,
 305     };
 306     let (ty_adt, ty_subs) = match *ty.kind() {
 307         // Unions can't derive clone.
 308         ty::Adt(adt, subs) if !adt.is_union() => (adt, subs),
 309         _ => return,
 310     };
 311     // If the current self type doesn't implement Copy (due to generic constraints), search to see if
 312     // there's a Copy impl for any instance of the adt.
 313     if !is_copy(cx, ty) {
 314         if ty_subs.non_erasable_generics().next().is_some() {
 315             let has_copy_impl = cx.tcx.all_local_trait_impls(()).get(&copy_id).map_or(false, |impls| {
 316                 impls
 317                     .iter()
 318                     .any(|&id| matches!(cx.tcx.type_of(id).kind(), ty::Adt(adt, _) if ty_adt.did() == adt.did()))
 319             });
 320             if !has_copy_impl {
 321                 return;
 322             }
 323         } else {
 324             return;
 325         }
 326     }
 327     // Derive constrains all generic types to requiring Clone. Check if any type is not constrained for
 328     // this impl.
 329     if ty_subs.types().any(|ty| !implements_trait(cx, ty, clone_id, &[])) {
 330         return;
 331     }
 332
 333     span_lint_and_note(
 334         cx,
 335         EXPL_IMPL_CLONE_ON_COPY,
 336         item.span,
 337         "you are implementing `Clone` explicitly on a `Copy` type",
 338         Some(item.span),
 339         "consider deriving `Clone` or removing `Copy`",
 340     );
 341 }
 342
 343 /// Implementation of the `UNSAFE_DERIVE_DESERIALIZE` lint.
 344 fn check_unsafe_derive_deserialize<'tcx>(
 345     cx: &LateContext<'tcx>,
 346     item: &Item<'_>,
 347     trait_ref: &TraitRef<'_>,
 348     ty: Ty<'tcx>,
 349 ) {
 350     fn has_unsafe<'tcx>(cx: &LateContext<'tcx>, item: &'tcx Item<'_>) -> bool {
 351         let mut visitor = UnsafeVisitor { cx, has_unsafe: false };
 352         walk_item(&mut visitor, item);
 353         visitor.has_unsafe
 354     }
 355
 356     if_chain! {
 357         if let Some(trait_def_id) = trait_ref.trait_def_id();
 358         if match_def_path(cx, trait_def_id, &paths::SERDE_DESERIALIZE);
 359         if let ty::Adt(def, _) = ty.kind();
 360         if let Some(local_def_id) = def.did().as_local();
 361         let adt_hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
 362         if !is_lint_allowed(cx, UNSAFE_DERIVE_DESERIALIZE, adt_hir_id);
 363         if cx.tcx.inherent_impls(def.did())
 364             .iter()
 365             .map(|imp_did| cx.tcx.hir().expect_item(imp_did.expect_local()))
 366             .any(|imp| has_unsafe(cx, imp));
 367         then {
 368             span_lint_and_help(
 369                 cx,
 370                 UNSAFE_DERIVE_DESERIALIZE,
 371                 item.span,
 372                 "you are deriving `serde::Deserialize` on a type that has methods using `unsafe`",
 373                 None,
 374                 "consider implementing `serde::Deserialize` manually. See https://serde.rs/impl-deserialize.html"
 375             );
 376         }
 377     }
 378 }
 379
 380 struct UnsafeVisitor<'a, 'tcx> {
 381     cx: &'a LateContext<'tcx>,
 382     has_unsafe: bool,
 383 }
 384
 385 impl<'tcx> Visitor<'tcx> for UnsafeVisitor<'_, 'tcx> {
 386     type NestedFilter = nested_filter::All;
 387
 388     fn visit_fn(&mut self, kind: FnKind<'tcx>, decl: &'tcx FnDecl<'_>, body_id: BodyId, span: Span, id: HirId) {
 389         if self.has_unsafe {
 390             return;
 391         }
 392
 393         if_chain! {
 394             if let Some(header) = kind.header();
 395             if header.unsafety == Unsafety::Unsafe;
 396             then {
 397                 self.has_unsafe = true;
 398             }
 399         }
 400
 401         walk_fn(self, kind, decl, body_id, span, id);
 402     }
 403
 404     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 405         if self.has_unsafe {
 406             return;
 407         }
 408
 409         if let ExprKind::Block(block, _) = expr.kind {
 410             if block.rules == BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided) {
 411                 self.has_unsafe = true;
 412             }
 413         }
 414
 415         walk_expr(self, expr);
 416     }
 417
 418     fn nested_visit_map(&mut self) -> Self::Map {
 419         self.cx.tcx.hir()
 420     }
 421 }