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

   1 use crate::utils::paths;
   2 use crate::utils::{
   3     get_trait_def_id, is_allowed, is_automatically_derived, is_copy, match_path, span_lint_and_help,
   4     span_lint_and_note, span_lint_and_then,
   5 };
   6 use if_chain::if_chain;
   7 use rustc_hir::def_id::DefId;
   8 use rustc_hir::intravisit::{walk_expr, walk_fn, walk_item, FnKind, NestedVisitorMap, Visitor};
   9 use rustc_hir::{
  10     BlockCheckMode, BodyId, Expr, ExprKind, FnDecl, HirId, Item, ItemKind, TraitRef, UnsafeSource, Unsafety,
  11 };
  12 use rustc_lint::{LateContext, LateLintPass};
  13 use rustc_middle::hir::map::Map;
  14 use rustc_middle::ty::{self, Ty};
  15 use rustc_session::{declare_lint_pass, declare_tool_lint};
  16 use rustc_span::source_map::Span;
  17
  18 declare_clippy_lint! {
  19     /// **What it does:** Checks for deriving `Hash` but implementing `PartialEq`
  20     /// explicitly or vice versa.
  21     ///
  22     /// **Why is this bad?** The implementation of these traits must agree (for
  23     /// example for use with `HashMap`) so it’s probably a bad idea to use a
  24     /// default-generated `Hash` implementation with an explicitly defined
  25     /// `PartialEq`. In particular, the following must hold for any type:
  26     ///
  27     /// ```text
  28     /// k1 == k2 ⇒ hash(k1) == hash(k2)
  29     /// ```
  30     ///
  31     /// **Known problems:** None.
  32     ///
  33     /// **Example:**
  34     /// ```ignore
  35     /// #[derive(Hash)]
  36     /// struct Foo;
  37     ///
  38     /// impl PartialEq for Foo {
  39     ///     ...
  40     /// }
  41     /// ```
  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:** Checks for deriving `Ord` but implementing `PartialOrd`
  49     /// explicitly or vice versa.
  50     ///
  51     /// **Why is this bad?** The implementation of these traits must agree (for
  52     /// example for use with `sort`) so it’s probably a bad idea to use a
  53     /// default-generated `Ord` implementation with an explicitly defined
  54     /// `PartialOrd`. In particular, the following must hold for any type
  55     /// implementing `Ord`:
  56     ///
  57     /// ```text
  58     /// k1.cmp(&k2) == k1.partial_cmp(&k2).unwrap()
  59     /// ```
  60     ///
  61     /// **Known problems:** None.
  62     ///
  63     /// **Example:**
  64     ///
  65     /// ```rust,ignore
  66     /// #[derive(Ord, PartialEq, Eq)]
  67     /// struct Foo;
  68     ///
  69     /// impl PartialOrd for Foo {
  70     ///     ...
  71     /// }
  72     /// ```
  73     /// Use instead:
  74     /// ```rust,ignore
  75     /// #[derive(PartialEq, Eq)]
  76     /// struct Foo;
  77     ///
  78     /// impl PartialOrd for Foo {
  79     ///     fn partial_cmp(&self, other: &Foo) -> Option<Ordering> {
  80     ///        Some(self.cmp(other))
  81     ///     }
  82     /// }
  83     ///
  84     /// impl Ord for Foo {
  85     ///     ...
  86     /// }
  87     /// ```
  88     /// or, if you don't need a custom ordering:
  89     /// ```rust,ignore
  90     /// #[derive(Ord, PartialOrd, PartialEq, Eq)]
  91     /// struct Foo;
  92     /// ```
  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:** Checks for explicit `Clone` implementations for `Copy`
 100     /// types.
 101     ///
 102     /// **Why is this bad?** To avoid surprising behaviour, these traits should
 103     /// agree and the behaviour of `Copy` cannot be overridden. In almost all
 104     /// situations a `Copy` type should have a `Clone` implementation that does
 105     /// nothing more than copy the object, which is what `#[derive(Copy, Clone)]`
 106     /// gets you.
 107     ///
 108     /// **Known problems:** Bounds of generic types are sometimes wrong: https://github.com/rust-lang/rust/issues/26925
 109     ///
 110     /// **Example:**
 111     /// ```rust,ignore
 112     /// #[derive(Copy)]
 113     /// struct Foo;
 114     ///
 115     /// impl Clone for Foo {
 116     ///     // ..
 117     /// }
 118     /// ```
 119     pub EXPL_IMPL_CLONE_ON_COPY,
 120     pedantic,
 121     "implementing `Clone` explicitly on `Copy` types"
 122 }
 123
 124 declare_clippy_lint! {
 125     /// **What it does:** Checks for deriving `serde::Deserialize` on a type that
 126     /// has methods using `unsafe`.
 127     ///
 128     /// **Why is this bad?** Deriving `serde::Deserialize` will create a constructor
 129     /// that may violate invariants hold by another constructor.
 130     ///
 131     /// **Known problems:** None.
 132     ///
 133     /// **Example:**
 134     ///
 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     pub UNSAFE_DERIVE_DESERIALIZE,
 154     pedantic,
 155     "deriving `serde::Deserialize` on a type that has methods using `unsafe`"
 156 }
 157
 158 declare_lint_pass!(Derive => [
 159     EXPL_IMPL_CLONE_ON_COPY,
 160     DERIVE_HASH_XOR_EQ,
 161     DERIVE_ORD_XOR_PARTIAL_ORD,
 162     UNSAFE_DERIVE_DESERIALIZE
 163 ]);
 164
 165 impl<'tcx> LateLintPass<'tcx> for Derive {
 166     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 167         if let ItemKind::Impl {
 168             of_trait: Some(ref trait_ref),
 169             ..
 170         } = item.kind
 171         {
 172             let ty = cx.tcx.type_of(cx.tcx.hir().local_def_id(item.hir_id));
 173             let is_automatically_derived = is_automatically_derived(&*item.attrs);
 174
 175             check_hash_peq(cx, item.span, trait_ref, ty, is_automatically_derived);
 176             check_ord_partial_ord(cx, item.span, trait_ref, ty, is_automatically_derived);
 177
 178             if is_automatically_derived {
 179                 check_unsafe_derive_deserialize(cx, item, trait_ref, ty);
 180             } else {
 181                 check_copy_clone(cx, item, trait_ref, ty);
 182             }
 183         }
 184     }
 185 }
 186
 187 /// Implementation of the `DERIVE_HASH_XOR_EQ` lint.
 188 fn check_hash_peq<'tcx>(
 189     cx: &LateContext<'tcx>,
 190     span: Span,
 191     trait_ref: &TraitRef<'_>,
 192     ty: Ty<'tcx>,
 193     hash_is_automatically_derived: bool,
 194 ) {
 195     if_chain! {
 196         if match_path(&trait_ref.path, &paths::HASH);
 197         if let Some(peq_trait_def_id) = cx.tcx.lang_items().eq_trait();
 198         if let Some(def_id) = &trait_ref.trait_def_id();
 199         if !def_id.is_local();
 200         then {
 201             // Look for the PartialEq implementations for `ty`
 202             cx.tcx.for_each_relevant_impl(peq_trait_def_id, ty, |impl_id| {
 203                 let peq_is_automatically_derived = is_automatically_derived(&cx.tcx.get_attrs(impl_id));
 204
 205                 if peq_is_automatically_derived == hash_is_automatically_derived {
 206                     return;
 207                 }
 208
 209                 let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
 210
 211                 // Only care about `impl PartialEq<Foo> for Foo`
 212                 // For `impl PartialEq<B> for A, input_types is [A, B]
 213                 if trait_ref.substs.type_at(1) == ty {
 214                     let mess = if peq_is_automatically_derived {
 215                         "you are implementing `Hash` explicitly but have derived `PartialEq`"
 216                     } else {
 217                         "you are deriving `Hash` but have implemented `PartialEq` explicitly"
 218                     };
 219
 220                     span_lint_and_then(
 221                         cx,
 222                         DERIVE_HASH_XOR_EQ,
 223                         span,
 224                         mess,
 225                         |diag| {
 226                             if let Some(local_def_id) = impl_id.as_local() {
 227                                 let hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
 228                                 diag.span_note(
 229                                     cx.tcx.hir().span(hir_id),
 230                                     "`PartialEq` implemented here"
 231                                 );
 232                             }
 233                         }
 234                     );
 235                 }
 236             });
 237         }
 238     }
 239 }
 240
 241 /// Implementation of the `DERIVE_ORD_XOR_PARTIAL_ORD` lint.
 242 fn check_ord_partial_ord<'tcx>(
 243     cx: &LateContext<'tcx>,
 244     span: Span,
 245     trait_ref: &TraitRef<'_>,
 246     ty: Ty<'tcx>,
 247     ord_is_automatically_derived: bool,
 248 ) {
 249     if_chain! {
 250         if let Some(ord_trait_def_id) = get_trait_def_id(cx, &paths::ORD);
 251         if let Some(partial_ord_trait_def_id) = cx.tcx.lang_items().partial_ord_trait();
 252         if let Some(def_id) = &trait_ref.trait_def_id();
 253         if *def_id == ord_trait_def_id;
 254         then {
 255             // Look for the PartialOrd implementations for `ty`
 256             cx.tcx.for_each_relevant_impl(partial_ord_trait_def_id, ty, |impl_id| {
 257                 let partial_ord_is_automatically_derived = is_automatically_derived(&cx.tcx.get_attrs(impl_id));
 258
 259                 if partial_ord_is_automatically_derived == ord_is_automatically_derived {
 260                     return;
 261                 }
 262
 263                 let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
 264
 265                 // Only care about `impl PartialOrd<Foo> for Foo`
 266                 // For `impl PartialOrd<B> for A, input_types is [A, B]
 267                 if trait_ref.substs.type_at(1) == ty {
 268                     let mess = if partial_ord_is_automatically_derived {
 269                         "you are implementing `Ord` explicitly but have derived `PartialOrd`"
 270                     } else {
 271                         "you are deriving `Ord` but have implemented `PartialOrd` explicitly"
 272                     };
 273
 274                     span_lint_and_then(
 275                         cx,
 276                         DERIVE_ORD_XOR_PARTIAL_ORD,
 277                         span,
 278                         mess,
 279                         |diag| {
 280                             if let Some(local_def_id) = impl_id.as_local() {
 281                                 let hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
 282                                 diag.span_note(
 283                                     cx.tcx.hir().span(hir_id),
 284                                     "`PartialOrd` implemented here"
 285                                 );
 286                             }
 287                         }
 288                     );
 289                 }
 290             });
 291         }
 292     }
 293 }
 294
 295 /// Implementation of the `EXPL_IMPL_CLONE_ON_COPY` lint.
 296 fn check_copy_clone<'tcx>(cx: &LateContext<'tcx>, item: &Item<'_>, trait_ref: &TraitRef<'_>, ty: Ty<'tcx>) {
 297     if match_path(&trait_ref.path, &paths::CLONE_TRAIT) {
 298         if !is_copy(cx, ty) {
 299             return;
 300         }
 301
 302         match ty.kind {
 303             ty::Adt(def, _) if def.is_union() => return,
 304
 305             // Some types are not Clone by default but could be cloned “by hand” if necessary
 306             ty::Adt(def, substs) => {
 307                 for variant in &def.variants {
 308                     for field in &variant.fields {
 309                         if let ty::FnDef(..) = field.ty(cx.tcx, substs).kind {
 310                             return;
 311                         }
 312                     }
 313                     for subst in substs {
 314                         if let ty::subst::GenericArgKind::Type(subst) = subst.unpack() {
 315                             if let ty::Param(_) = subst.kind {
 316                                 return;
 317                             }
 318                         }
 319                     }
 320                 }
 321             },
 322             _ => (),
 323         }
 324
 325         span_lint_and_note(
 326             cx,
 327             EXPL_IMPL_CLONE_ON_COPY,
 328             item.span,
 329             "you are implementing `Clone` explicitly on a `Copy` type",
 330             Some(item.span),
 331             "consider deriving `Clone` or removing `Copy`",
 332         );
 333     }
 334 }
 335
 336 /// Implementation of the `UNSAFE_DERIVE_DESERIALIZE` lint.
 337 fn check_unsafe_derive_deserialize<'tcx>(
 338     cx: &LateContext<'tcx>,
 339     item: &Item<'_>,
 340     trait_ref: &TraitRef<'_>,
 341     ty: Ty<'tcx>,
 342 ) {
 343     fn item_from_def_id<'tcx>(cx: &LateContext<'tcx>, def_id: DefId) -> &'tcx Item<'tcx> {
 344         let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
 345         cx.tcx.hir().expect_item(hir_id)
 346     }
 347
 348     fn has_unsafe<'tcx>(cx: &LateContext<'tcx>, item: &'tcx Item<'_>) -> bool {
 349         let mut visitor = UnsafeVisitor { cx, has_unsafe: false };
 350         walk_item(&mut visitor, item);
 351         visitor.has_unsafe
 352     }
 353
 354     if_chain! {
 355         if match_path(&trait_ref.path, &paths::SERDE_DESERIALIZE);
 356         if let ty::Adt(def, _) = ty.kind;
 357         if let Some(local_def_id) = def.did.as_local();
 358         let adt_hir_id = cx.tcx.hir().local_def_id_to_hir_id(local_def_id);
 359         if !is_allowed(cx, UNSAFE_DERIVE_DESERIALIZE, adt_hir_id);
 360         if cx.tcx.inherent_impls(def.did)
 361             .iter()
 362             .map(|imp_did| item_from_def_id(cx, *imp_did))
 363             .any(|imp| has_unsafe(cx, imp));
 364         then {
 365             span_lint_and_help(
 366                 cx,
 367                 UNSAFE_DERIVE_DESERIALIZE,
 368                 item.span,
 369                 "you are deriving `serde::Deserialize` on a type that has methods using `unsafe`",
 370                 None,
 371                 "consider implementing `serde::Deserialize` manually. See https://serde.rs/impl-deserialize.html"
 372             );
 373         }
 374     }
 375 }
 376
 377 struct UnsafeVisitor<'a, 'tcx> {
 378     cx: &'a LateContext<'tcx>,
 379     has_unsafe: bool,
 380 }
 381
 382 impl<'tcx> Visitor<'tcx> for UnsafeVisitor<'_, 'tcx> {
 383     type Map = Map<'tcx>;
 384
 385     fn visit_fn(&mut self, kind: FnKind<'tcx>, decl: &'tcx FnDecl<'_>, body_id: BodyId, span: Span, id: HirId) {
 386         if self.has_unsafe {
 387             return;
 388         }
 389
 390         if_chain! {
 391             if let Some(header) = kind.header();
 392             if let Unsafety::Unsafe = header.unsafety;
 393             then {
 394                 self.has_unsafe = true;
 395             }
 396         }
 397
 398         walk_fn(self, kind, decl, body_id, span, id);
 399     }
 400
 401     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 402         if self.has_unsafe {
 403             return;
 404         }
 405
 406         if let ExprKind::Block(block, _) = expr.kind {
 407             match block.rules {
 408                 BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided)
 409                 | BlockCheckMode::PushUnsafeBlock(UnsafeSource::UserProvided)
 410                 | BlockCheckMode::PopUnsafeBlock(UnsafeSource::UserProvided) => {
 411                     self.has_unsafe = true;
 412                 },
 413                 _ => {},
 414             }
 415         }
 416
 417         walk_expr(self, expr);
 418     }
 419
 420     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 421         NestedVisitorMap::All(self.cx.tcx.hir())
 422     }
 423 }