src/tools/clippy/clippy_lints/src/use_self.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::is_from_proc_macro;
   3 use clippy_utils::msrvs::{self, Msrv};
   4 use clippy_utils::ty::same_type_and_consts;
   5 use if_chain::if_chain;
   6 use rustc_data_structures::fx::FxHashSet;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::{
   9     self as hir,
  10     def::{CtorOf, DefKind, Res},
  11     def_id::LocalDefId,
  12     intravisit::{walk_inf, walk_ty, Visitor},
  13     Expr, ExprKind, FnRetTy, FnSig, GenericArg, HirId, Impl, ImplItemKind, Item, ItemKind, Pat, PatKind, Path, QPath,
  14     TyKind,
  15 };
  16 use rustc_hir_analysis::hir_ty_to_ty;
  17 use rustc_lint::{LateContext, LateLintPass};
  18 use rustc_session::{declare_tool_lint, impl_lint_pass};
  19 use rustc_span::Span;
  20
  21 declare_clippy_lint! {
  22     /// ### What it does
  23     /// Checks for unnecessary repetition of structure name when a
  24     /// replacement with `Self` is applicable.
  25     ///
  26     /// ### Why is this bad?
  27     /// Unnecessary repetition. Mixed use of `Self` and struct
  28     /// name
  29     /// feels inconsistent.
  30     ///
  31     /// ### Known problems
  32     /// - Unaddressed false negative in fn bodies of trait implementations
  33     ///
  34     /// ### Example
  35     /// ```rust
  36     /// struct Foo;
  37     /// impl Foo {
  38     ///     fn new() -> Foo {
  39     ///         Foo {}
  40     ///     }
  41     /// }
  42     /// ```
  43     /// could be
  44     /// ```rust
  45     /// struct Foo;
  46     /// impl Foo {
  47     ///     fn new() -> Self {
  48     ///         Self {}
  49     ///     }
  50     /// }
  51     /// ```
  52     #[clippy::version = "pre 1.29.0"]
  53     pub USE_SELF,
  54     nursery,
  55     "unnecessary structure name repetition whereas `Self` is applicable"
  56 }
  57
  58 #[derive(Default)]
  59 pub struct UseSelf {
  60     msrv: Msrv,
  61     stack: Vec<StackItem>,
  62 }
  63
  64 impl UseSelf {
  65     #[must_use]
  66     pub fn new(msrv: Msrv) -> Self {
  67         Self {
  68             msrv,
  69             ..Self::default()
  70         }
  71     }
  72 }
  73
  74 #[derive(Debug)]
  75 enum StackItem {
  76     Check {
  77         impl_id: LocalDefId,
  78         in_body: u32,
  79         types_to_skip: FxHashSet<HirId>,
  80     },
  81     NoCheck,
  82 }
  83
  84 impl_lint_pass!(UseSelf => [USE_SELF]);
  85
  86 const SEGMENTS_MSG: &str = "segments should be composed of at least 1 element";
  87
  88 impl<'tcx> LateLintPass<'tcx> for UseSelf {
  89     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &Item<'tcx>) {
  90         if matches!(item.kind, ItemKind::OpaqueTy(_)) {
  91             // skip over `ItemKind::OpaqueTy` in order to lint `foo() -> impl <..>`
  92             return;
  93         }
  94         // We push the self types of `impl`s on a stack here. Only the top type on the stack is
  95         // relevant for linting, since this is the self type of the `impl` we're currently in. To
  96         // avoid linting on nested items, we push `StackItem::NoCheck` on the stack to signal, that
  97         // we're in an `impl` or nested item, that we don't want to lint
  98         let stack_item = if_chain! {
  99             if let ItemKind::Impl(Impl { self_ty, .. }) = item.kind;
 100             if let TyKind::Path(QPath::Resolved(_, item_path)) = self_ty.kind;
 101             let parameters = &item_path.segments.last().expect(SEGMENTS_MSG).args;
 102             if parameters.as_ref().map_or(true, |params| {
 103                 !params.parenthesized && !params.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)))
 104             });
 105             if !item.span.from_expansion();
 106             if !is_from_proc_macro(cx, item); // expensive, should be last check
 107             then {
 108                 StackItem::Check {
 109                     impl_id: item.owner_id.def_id,
 110                     in_body: 0,
 111                     types_to_skip: std::iter::once(self_ty.hir_id).collect(),
 112                 }
 113             } else {
 114                 StackItem::NoCheck
 115             }
 116         };
 117         self.stack.push(stack_item);
 118     }
 119
 120     fn check_item_post(&mut self, _: &LateContext<'_>, item: &Item<'_>) {
 121         if !matches!(item.kind, ItemKind::OpaqueTy(_)) {
 122             self.stack.pop();
 123         }
 124     }
 125
 126     fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
 127         // We want to skip types in trait `impl`s that aren't declared as `Self` in the trait
 128         // declaration. The collection of those types is all this method implementation does.
 129         if_chain! {
 130             if let ImplItemKind::Fn(FnSig { decl, .. }, ..) = impl_item.kind;
 131             if let Some(&mut StackItem::Check {
 132                 impl_id,
 133                 ref mut types_to_skip,
 134                 ..
 135             }) = self.stack.last_mut();
 136             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_id);
 137             then {
 138                 // `self_ty` is the semantic self type of `impl <trait> for <type>`. This cannot be
 139                 // `Self`.
 140                 let self_ty = impl_trait_ref.subst_identity().self_ty();
 141
 142                 // `trait_method_sig` is the signature of the function, how it is declared in the
 143                 // trait, not in the impl of the trait.
 144                 let trait_method = cx
 145                     .tcx
 146                     .associated_item(impl_item.owner_id)
 147                     .trait_item_def_id
 148                     .expect("impl method matches a trait method");
 149                 let trait_method_sig = cx.tcx.fn_sig(trait_method);
 150                 let trait_method_sig = cx.tcx.erase_late_bound_regions(trait_method_sig);
 151
 152                 // `impl_inputs_outputs` is an iterator over the types (`hir::Ty`) declared in the
 153                 // implementation of the trait.
 154                 let output_hir_ty = if let FnRetTy::Return(ty) = &decl.output {
 155                     Some(&**ty)
 156                 } else {
 157                     None
 158                 };
 159                 let impl_inputs_outputs = decl.inputs.iter().chain(output_hir_ty);
 160
 161                 // `impl_hir_ty` (of type `hir::Ty`) represents the type written in the signature.
 162                 //
 163                 // `trait_sem_ty` (of type `ty::Ty`) is the semantic type for the signature in the
 164                 // trait declaration. This is used to check if `Self` was used in the trait
 165                 // declaration.
 166                 //
 167                 // If `any`where in the `trait_sem_ty` the `self_ty` was used verbatim (as opposed
 168                 // to `Self`), we want to skip linting that type and all subtypes of it. This
 169                 // avoids suggestions to e.g. replace `Vec<u8>` with `Vec<Self>`, in an `impl Trait
 170                 // for u8`, when the trait always uses `Vec<u8>`.
 171                 //
 172                 // See also https://github.com/rust-lang/rust-clippy/issues/2894.
 173                 for (impl_hir_ty, trait_sem_ty) in impl_inputs_outputs.zip(trait_method_sig.inputs_and_output) {
 174                     if trait_sem_ty.walk().any(|inner| inner == self_ty.into()) {
 175                         let mut visitor = SkipTyCollector::default();
 176                         visitor.visit_ty(impl_hir_ty);
 177                         types_to_skip.extend(visitor.types_to_skip);
 178                     }
 179                 }
 180             }
 181         }
 182     }
 183
 184     fn check_body(&mut self, _: &LateContext<'_>, _: &hir::Body<'_>) {
 185         // `hir_ty_to_ty` cannot be called in `Body`s or it will panic (sometimes). But in bodies
 186         // we can use `cx.typeck_results.node_type(..)` to get the `ty::Ty` from a `hir::Ty`.
 187         // However the `node_type()` method can *only* be called in bodies.
 188         if let Some(&mut StackItem::Check { ref mut in_body, .. }) = self.stack.last_mut() {
 189             *in_body = in_body.saturating_add(1);
 190         }
 191     }
 192
 193     fn check_body_post(&mut self, _: &LateContext<'_>, _: &hir::Body<'_>) {
 194         if let Some(&mut StackItem::Check { ref mut in_body, .. }) = self.stack.last_mut() {
 195             *in_body = in_body.saturating_sub(1);
 196         }
 197     }
 198
 199     fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>) {
 200         if_chain! {
 201             if !hir_ty.span.from_expansion();
 202             if self.msrv.meets(msrvs::TYPE_ALIAS_ENUM_VARIANTS);
 203             if let Some(&StackItem::Check {
 204                 impl_id,
 205                 in_body,
 206                 ref types_to_skip,
 207             }) = self.stack.last();
 208             if let TyKind::Path(QPath::Resolved(_, path)) = hir_ty.kind;
 209             if !matches!(
 210                 path.res,
 211                 Res::SelfTyParam { .. }
 212                 | Res::SelfTyAlias { .. }
 213                 | Res::Def(DefKind::TyParam, _)
 214             );
 215             if !types_to_skip.contains(&hir_ty.hir_id);
 216             let ty = if in_body > 0 {
 217                 cx.typeck_results().node_type(hir_ty.hir_id)
 218             } else {
 219                 hir_ty_to_ty(cx.tcx, hir_ty)
 220             };
 221             if same_type_and_consts(ty, cx.tcx.type_of(impl_id));
 222             then {
 223                 span_lint(cx, hir_ty.span);
 224             }
 225         }
 226     }
 227
 228     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
 229         if_chain! {
 230             if !expr.span.from_expansion();
 231             if self.msrv.meets(msrvs::TYPE_ALIAS_ENUM_VARIANTS);
 232             if let Some(&StackItem::Check { impl_id, .. }) = self.stack.last();
 233             if cx.typeck_results().expr_ty(expr) == cx.tcx.type_of(impl_id);
 234             then {} else { return; }
 235         }
 236         match expr.kind {
 237             ExprKind::Struct(QPath::Resolved(_, path), ..) => check_path(cx, path),
 238             ExprKind::Call(fun, _) => {
 239                 if let ExprKind::Path(QPath::Resolved(_, path)) = fun.kind {
 240                     check_path(cx, path);
 241                 }
 242             },
 243             ExprKind::Path(QPath::Resolved(_, path)) => check_path(cx, path),
 244             _ => (),
 245         }
 246     }
 247
 248     fn check_pat(&mut self, cx: &LateContext<'_>, pat: &Pat<'_>) {
 249         if_chain! {
 250             if !pat.span.from_expansion();
 251             if self.msrv.meets(msrvs::TYPE_ALIAS_ENUM_VARIANTS);
 252             if let Some(&StackItem::Check { impl_id, .. }) = self.stack.last();
 253             // get the path from the pattern
 254             if let PatKind::Path(QPath::Resolved(_, path))
 255                  | PatKind::TupleStruct(QPath::Resolved(_, path), _, _)
 256                  | PatKind::Struct(QPath::Resolved(_, path), _, _) = pat.kind;
 257             if cx.typeck_results().pat_ty(pat) == cx.tcx.type_of(impl_id);
 258             then {
 259                 check_path(cx, path);
 260             }
 261         }
 262     }
 263
 264     extract_msrv_attr!(LateContext);
 265 }
 266
 267 #[derive(Default)]
 268 struct SkipTyCollector {
 269     types_to_skip: Vec<HirId>,
 270 }
 271
 272 impl<'tcx> Visitor<'tcx> for SkipTyCollector {
 273     fn visit_infer(&mut self, inf: &hir::InferArg) {
 274         self.types_to_skip.push(inf.hir_id);
 275
 276         walk_inf(self, inf);
 277     }
 278     fn visit_ty(&mut self, hir_ty: &hir::Ty<'_>) {
 279         self.types_to_skip.push(hir_ty.hir_id);
 280
 281         walk_ty(self, hir_ty);
 282     }
 283 }
 284
 285 fn span_lint(cx: &LateContext<'_>, span: Span) {
 286     span_lint_and_sugg(
 287         cx,
 288         USE_SELF,
 289         span,
 290         "unnecessary structure name repetition",
 291         "use the applicable keyword",
 292         "Self".to_owned(),
 293         Applicability::MachineApplicable,
 294     );
 295 }
 296
 297 fn check_path(cx: &LateContext<'_>, path: &Path<'_>) {
 298     match path.res {
 299         Res::Def(DefKind::Ctor(CtorOf::Variant, _) | DefKind::Variant, ..) => {
 300             lint_path_to_variant(cx, path);
 301         },
 302         Res::Def(DefKind::Ctor(CtorOf::Struct, _) | DefKind::Struct, ..) => span_lint(cx, path.span),
 303         _ => (),
 304     }
 305 }
 306
 307 fn lint_path_to_variant(cx: &LateContext<'_>, path: &Path<'_>) {
 308     if let [.., self_seg, _variant] = path.segments {
 309         let span = path
 310             .span
 311             .with_hi(self_seg.args().span_ext().unwrap_or(self_seg.ident.span).hi());
 312         span_lint(cx, span);
 313     }
 314 }