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

   1 use crate::utils::paths;
   2 use crate::utils::{
   3     is_automatically_derived, is_copy, match_path, span_lint_and_help, span_lint_and_note, span_lint_and_then,
   4 };
   5 use if_chain::if_chain;
   6 use rustc_hir::def_id::DefId;
   7 use rustc_hir::intravisit::{walk_expr, walk_fn, walk_item, FnKind, NestedVisitorMap, Visitor};
   8 use rustc_hir::{
   9     BlockCheckMode, BodyId, Expr, ExprKind, FnDecl, HirId, Item, ItemKind, TraitRef, UnsafeSource, Unsafety,
  10 };
  11 use rustc_lint::{LateContext, LateLintPass};
  12 use rustc_middle::hir::map::Map;
  13 use rustc_middle::ty::{self, Ty};
  14 use rustc_session::{declare_lint_pass, declare_tool_lint};
  15 use rustc_span::source_map::Span;
  16
  17 declare_clippy_lint! {
  18     /// **What it does:** Checks for deriving `Hash` but implementing `PartialEq`
  19     /// explicitly or vice versa.
  20     ///
  21     /// **Why is this bad?** The implementation of these traits must agree (for
  22     /// example for use with `HashMap`) so it’s probably a bad idea to use a
  23     /// default-generated `Hash` implementation with an explicitly defined
  24     /// `PartialEq`. In particular, the following must hold for any type:
  25     ///
  26     /// ```text
  27     /// k1 == k2 ⇒ hash(k1) == hash(k2)
  28     /// ```
  29     ///
  30     /// **Known problems:** None.
  31     ///
  32     /// **Example:**
  33     /// ```ignore
  34     /// #[derive(Hash)]
  35     /// struct Foo;
  36     ///
  37     /// impl PartialEq for Foo {
  38     ///     ...
  39     /// }
  40     /// ```
  41     pub DERIVE_HASH_XOR_EQ,
  42     correctness,
  43     "deriving `Hash` but implementing `PartialEq` explicitly"
  44 }
  45
  46 declare_clippy_lint! {
  47     /// **What it does:** Checks for explicit `Clone` implementations for `Copy`
  48     /// types.
  49     ///
  50     /// **Why is this bad?** To avoid surprising behaviour, these traits should
  51     /// agree and the behaviour of `Copy` cannot be overridden. In almost all
  52     /// situations a `Copy` type should have a `Clone` implementation that does
  53     /// nothing more than copy the object, which is what `#[derive(Copy, Clone)]`
  54     /// gets you.
  55     ///
  56     /// **Known problems:** Bounds of generic types are sometimes wrong: https://github.com/rust-lang/rust/issues/26925
  57     ///
  58     /// **Example:**
  59     /// ```rust,ignore
  60     /// #[derive(Copy)]
  61     /// struct Foo;
  62     ///
  63     /// impl Clone for Foo {
  64     ///     // ..
  65     /// }
  66     /// ```
  67     pub EXPL_IMPL_CLONE_ON_COPY,
  68     pedantic,
  69     "implementing `Clone` explicitly on `Copy` types"
  70 }
  71
  72 declare_clippy_lint! {
  73     /// **What it does:** Checks for deriving `serde::Deserialize` on a type that
  74     /// has methods using `unsafe`.
  75     ///
  76     /// **Why is this bad?** Deriving `serde::Deserialize` will create a constructor
  77     /// that may violate invariants hold by another constructor.
  78     ///
  79     /// **Known problems:** None.
  80     ///
  81     /// **Example:**
  82     ///
  83     /// ```rust,ignore
  84     /// use serde::Deserialize;
  85     ///
  86     /// #[derive(Deserialize)]
  87     /// pub struct Foo {
  88     ///     // ..
  89     /// }
  90     ///
  91     /// impl Foo {
  92     ///     pub fn new() -> Self {
  93     ///         // setup here ..
  94     ///     }
  95     ///
  96     ///     pub unsafe fn parts() -> (&str, &str) {
  97     ///         // assumes invariants hold
  98     ///     }
  99     /// }
 100     /// ```
 101     pub UNSAFE_DERIVE_DESERIALIZE,
 102     pedantic,
 103     "deriving `serde::Deserialize` on a type that has methods using `unsafe`"
 104 }
 105
 106 declare_lint_pass!(Derive => [EXPL_IMPL_CLONE_ON_COPY, DERIVE_HASH_XOR_EQ, UNSAFE_DERIVE_DESERIALIZE]);
 107
 108 impl<'tcx> LateLintPass<'tcx> for Derive {
 109     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
 110         if let ItemKind::Impl {
 111             of_trait: Some(ref trait_ref),
 112             ..
 113         } = item.kind
 114         {
 115             let ty = cx.tcx.type_of(cx.tcx.hir().local_def_id(item.hir_id));
 116             let is_automatically_derived = is_automatically_derived(&*item.attrs);
 117
 118             check_hash_peq(cx, item.span, trait_ref, ty, is_automatically_derived);
 119
 120             if is_automatically_derived {
 121                 check_unsafe_derive_deserialize(cx, item, trait_ref, ty);
 122             } else {
 123                 check_copy_clone(cx, item, trait_ref, ty);
 124             }
 125         }
 126     }
 127 }
 128
 129 /// Implementation of the `DERIVE_HASH_XOR_EQ` lint.
 130 fn check_hash_peq<'tcx>(
 131     cx: &LateContext<'tcx>,
 132     span: Span,
 133     trait_ref: &TraitRef<'_>,
 134     ty: Ty<'tcx>,
 135     hash_is_automatically_derived: bool,
 136 ) {
 137     if_chain! {
 138         if match_path(&trait_ref.path, &paths::HASH);
 139         if let Some(peq_trait_def_id) = cx.tcx.lang_items().eq_trait();
 140         if let Some(def_id) = &trait_ref.trait_def_id();
 141         if !def_id.is_local();
 142         then {
 143             // Look for the PartialEq implementations for `ty`
 144             cx.tcx.for_each_relevant_impl(peq_trait_def_id, ty, |impl_id| {
 145                 let peq_is_automatically_derived = is_automatically_derived(&cx.tcx.get_attrs(impl_id));
 146
 147                 if peq_is_automatically_derived == hash_is_automatically_derived {
 148                     return;
 149                 }
 150
 151                 let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
 152
 153                 // Only care about `impl PartialEq<Foo> for Foo`
 154                 // For `impl PartialEq<B> for A, input_types is [A, B]
 155                 if trait_ref.substs.type_at(1) == ty {
 156                     let mess = if peq_is_automatically_derived {
 157                         "you are implementing `Hash` explicitly but have derived `PartialEq`"
 158                     } else {
 159                         "you are deriving `Hash` but have implemented `PartialEq` explicitly"
 160                     };
 161
 162                     span_lint_and_then(
 163                         cx,
 164                         DERIVE_HASH_XOR_EQ,
 165                         span,
 166                         mess,
 167                         |diag| {
 168                             if let Some(local_def_id) = impl_id.as_local() {
 169                                 let hir_id = cx.tcx.hir().as_local_hir_id(local_def_id);
 170                                 diag.span_note(
 171                                     cx.tcx.hir().span(hir_id),
 172                                     "`PartialEq` implemented here"
 173                                 );
 174                             }
 175                         }
 176                     );
 177                 }
 178             });
 179         }
 180     }
 181 }
 182
 183 /// Implementation of the `EXPL_IMPL_CLONE_ON_COPY` lint.
 184 fn check_copy_clone<'tcx>(cx: &LateContext<'tcx>, item: &Item<'_>, trait_ref: &TraitRef<'_>, ty: Ty<'tcx>) {
 185     if match_path(&trait_ref.path, &paths::CLONE_TRAIT) {
 186         if !is_copy(cx, ty) {
 187             return;
 188         }
 189
 190         match ty.kind {
 191             ty::Adt(def, _) if def.is_union() => return,
 192
 193             // Some types are not Clone by default but could be cloned “by hand” if necessary
 194             ty::Adt(def, substs) => {
 195                 for variant in &def.variants {
 196                     for field in &variant.fields {
 197                         if let ty::FnDef(..) = field.ty(cx.tcx, substs).kind {
 198                             return;
 199                         }
 200                     }
 201                     for subst in substs {
 202                         if let ty::subst::GenericArgKind::Type(subst) = subst.unpack() {
 203                             if let ty::Param(_) = subst.kind {
 204                                 return;
 205                             }
 206                         }
 207                     }
 208                 }
 209             },
 210             _ => (),
 211         }
 212
 213         span_lint_and_note(
 214             cx,
 215             EXPL_IMPL_CLONE_ON_COPY,
 216             item.span,
 217             "you are implementing `Clone` explicitly on a `Copy` type",
 218             Some(item.span),
 219             "consider deriving `Clone` or removing `Copy`",
 220         );
 221     }
 222 }
 223
 224 /// Implementation of the `UNSAFE_DERIVE_DESERIALIZE` lint.
 225 fn check_unsafe_derive_deserialize<'tcx>(
 226     cx: &LateContext<'tcx>,
 227     item: &Item<'_>,
 228     trait_ref: &TraitRef<'_>,
 229     ty: Ty<'tcx>,
 230 ) {
 231     fn item_from_def_id<'tcx>(cx: &LateContext<'tcx>, def_id: DefId) -> &'tcx Item<'tcx> {
 232         let hir_id = cx.tcx.hir().as_local_hir_id(def_id.expect_local());
 233         cx.tcx.hir().expect_item(hir_id)
 234     }
 235
 236     fn has_unsafe<'tcx>(cx: &LateContext<'tcx>, item: &'tcx Item<'_>) -> bool {
 237         let mut visitor = UnsafeVisitor { cx, has_unsafe: false };
 238         walk_item(&mut visitor, item);
 239         visitor.has_unsafe
 240     }
 241
 242     if_chain! {
 243         if match_path(&trait_ref.path, &paths::SERDE_DESERIALIZE);
 244         if let ty::Adt(def, _) = ty.kind;
 245         if def.did.is_local();
 246         if cx.tcx.inherent_impls(def.did)
 247             .iter()
 248             .map(|imp_did| item_from_def_id(cx, *imp_did))
 249             .any(|imp| has_unsafe(cx, imp));
 250         then {
 251             span_lint_and_help(
 252                 cx,
 253                 UNSAFE_DERIVE_DESERIALIZE,
 254                 item.span,
 255                 "you are deriving `serde::Deserialize` on a type that has methods using `unsafe`",
 256                 None,
 257                 "consider implementing `serde::Deserialize` manually. See https://serde.rs/impl-deserialize.html"
 258             );
 259         }
 260     }
 261 }
 262
 263 struct UnsafeVisitor<'a, 'tcx> {
 264     cx: &'a LateContext<'tcx>,
 265     has_unsafe: bool,
 266 }
 267
 268 impl<'tcx> Visitor<'tcx> for UnsafeVisitor<'_, 'tcx> {
 269     type Map = Map<'tcx>;
 270
 271     fn visit_fn(&mut self, kind: FnKind<'tcx>, decl: &'tcx FnDecl<'_>, body_id: BodyId, span: Span, id: HirId) {
 272         if self.has_unsafe {
 273             return;
 274         }
 275
 276         if_chain! {
 277             if let Some(header) = kind.header();
 278             if let Unsafety::Unsafe = header.unsafety;
 279             then {
 280                 self.has_unsafe = true;
 281             }
 282         }
 283
 284         walk_fn(self, kind, decl, body_id, span, id);
 285     }
 286
 287     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 288         if self.has_unsafe {
 289             return;
 290         }
 291
 292         if let ExprKind::Block(block, _) = expr.kind {
 293             match block.rules {
 294                 BlockCheckMode::UnsafeBlock(UnsafeSource::UserProvided)
 295                 | BlockCheckMode::PushUnsafeBlock(UnsafeSource::UserProvided)
 296                 | BlockCheckMode::PopUnsafeBlock(UnsafeSource::UserProvided) => {
 297                     self.has_unsafe = true;
 298                 },
 299                 _ => {},
 300             }
 301         }
 302
 303         walk_expr(self, expr);
 304     }
 305
 306     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 307         NestedVisitorMap::All(self.cx.tcx.hir())
 308     }
 309 }