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

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::ty::same_type_and_consts;
   3 use clippy_utils::{meets_msrv, msrvs};
   4 use if_chain::if_chain;
   5 use rustc_data_structures::fx::FxHashSet;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::{
   8     self as hir,
   9     def::{CtorOf, DefKind, Res},
  10     def_id::LocalDefId,
  11     intravisit::{walk_inf, walk_ty, NestedVisitorMap, Visitor},
  12     Expr, ExprKind, FnRetTy, FnSig, GenericArg, HirId, Impl, ImplItemKind, Item, ItemKind, Path, QPath, TyKind,
  13 };
  14 use rustc_lint::{LateContext, LateLintPass, LintContext};
  15 use rustc_middle::hir::map::Map;
  16 use rustc_middle::ty::AssocKind;
  17 use rustc_semver::RustcVersion;
  18 use rustc_session::{declare_tool_lint, impl_lint_pass};
  19 use rustc_span::Span;
  20 use rustc_typeck::hir_ty_to_ty;
  21
  22 declare_clippy_lint! {
  23     /// ### What it does
  24     /// Checks for unnecessary repetition of structure name when a
  25     /// replacement with `Self` is applicable.
  26     ///
  27     /// ### Why is this bad?
  28     /// Unnecessary repetition. Mixed use of `Self` and struct
  29     /// name
  30     /// feels inconsistent.
  31     ///
  32     /// ### Known problems
  33     /// - Unaddressed false negative in fn bodies of trait implementations
  34     /// - False positive with assotiated types in traits (#4140)
  35     ///
  36     /// ### Example
  37     /// ```rust
  38     /// struct Foo {}
  39     /// impl Foo {
  40     ///     fn new() -> Foo {
  41     ///         Foo {}
  42     ///     }
  43     /// }
  44     /// ```
  45     /// could be
  46     /// ```rust
  47     /// struct Foo {}
  48     /// impl Foo {
  49     ///     fn new() -> Self {
  50     ///         Self {}
  51     ///     }
  52     /// }
  53     /// ```
  54     #[clippy::version = "pre 1.29.0"]
  55     pub USE_SELF,
  56     nursery,
  57     "unnecessary structure name repetition whereas `Self` is applicable"
  58 }
  59
  60 #[derive(Default)]
  61 pub struct UseSelf {
  62     msrv: Option<RustcVersion>,
  63     stack: Vec<StackItem>,
  64 }
  65
  66 impl UseSelf {
  67     #[must_use]
  68     pub fn new(msrv: Option<RustcVersion>) -> Self {
  69         Self {
  70             msrv,
  71             ..Self::default()
  72         }
  73     }
  74 }
  75
  76 #[derive(Debug)]
  77 enum StackItem {
  78     Check {
  79         impl_id: LocalDefId,
  80         in_body: u32,
  81         types_to_skip: FxHashSet<HirId>,
  82     },
  83     NoCheck,
  84 }
  85
  86 impl_lint_pass!(UseSelf => [USE_SELF]);
  87
  88 const SEGMENTS_MSG: &str = "segments should be composed of at least 1 element";
  89
  90 impl<'tcx> LateLintPass<'tcx> for UseSelf {
  91     fn check_item(&mut self, _cx: &LateContext<'_>, item: &Item<'_>) {
  92         if matches!(item.kind, ItemKind::OpaqueTy(_)) {
  93             // skip over `ItemKind::OpaqueTy` in order to lint `foo() -> impl <..>`
  94             return;
  95         }
  96         // We push the self types of `impl`s on a stack here. Only the top type on the stack is
  97         // relevant for linting, since this is the self type of the `impl` we're currently in. To
  98         // avoid linting on nested items, we push `StackItem::NoCheck` on the stack to signal, that
  99         // we're in an `impl` or nested item, that we don't want to lint
 100         let stack_item = if_chain! {
 101             if let ItemKind::Impl(Impl { self_ty, .. }) = item.kind;
 102             if let TyKind::Path(QPath::Resolved(_, item_path)) = self_ty.kind;
 103             let parameters = &item_path.segments.last().expect(SEGMENTS_MSG).args;
 104             if parameters.as_ref().map_or(true, |params| {
 105                 !params.parenthesized && !params.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)))
 106             });
 107             then {
 108                 StackItem::Check {
 109                     impl_id: item.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.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_items(impl_trait_ref.def_id)
 147                     .find_by_name_and_kind(cx.tcx, impl_item.ident, AssocKind::Fn, impl_trait_ref.def_id)
 148                     .expect("impl method matches a trait method");
 149                 let trait_method_sig = cx.tcx.fn_sig(trait_method.def_id);
 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(cx.tcx).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 meets_msrv(self.msrv.as_ref(), &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!(path.res, Res::SelfTy(..) | Res::Def(DefKind::TyParam, _));
 210             if !types_to_skip.contains(&hir_ty.hir_id);
 211             let ty = if in_body > 0 {
 212                 cx.typeck_results().node_type(hir_ty.hir_id)
 213             } else {
 214                 hir_ty_to_ty(cx.tcx, hir_ty)
 215             };
 216             if same_type_and_consts(ty, cx.tcx.type_of(impl_id));
 217             let hir = cx.tcx.hir();
 218             // prevents false positive on `#[derive(serde::Deserialize)]`
 219             if !hir.span(hir.get_parent_node(hir_ty.hir_id)).in_derive_expansion();
 220             then {
 221                 span_lint(cx, hir_ty.span);
 222             }
 223         }
 224     }
 225
 226     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
 227         if_chain! {
 228             if !expr.span.from_expansion();
 229             if meets_msrv(self.msrv.as_ref(), &msrvs::TYPE_ALIAS_ENUM_VARIANTS);
 230             if let Some(&StackItem::Check { impl_id, .. }) = self.stack.last();
 231             if cx.typeck_results().expr_ty(expr) == cx.tcx.type_of(impl_id);
 232             then {} else { return; }
 233         }
 234         match expr.kind {
 235             ExprKind::Struct(QPath::Resolved(_, path), ..) => match path.res {
 236                 Res::SelfTy(..) => (),
 237                 Res::Def(DefKind::Variant, _) => lint_path_to_variant(cx, path),
 238                 _ => span_lint(cx, path.span),
 239             },
 240             // tuple struct instantiation (`Foo(arg)` or `Enum::Foo(arg)`)
 241             ExprKind::Call(fun, _) => {
 242                 if let ExprKind::Path(QPath::Resolved(_, path)) = fun.kind {
 243                     if let Res::Def(DefKind::Ctor(ctor_of, _), ..) = path.res {
 244                         match ctor_of {
 245                             CtorOf::Variant => lint_path_to_variant(cx, path),
 246                             CtorOf::Struct => span_lint(cx, path.span),
 247                         }
 248                     }
 249                 }
 250             },
 251             // unit enum variants (`Enum::A`)
 252             ExprKind::Path(QPath::Resolved(_, path)) => lint_path_to_variant(cx, path),
 253             _ => (),
 254         }
 255     }
 256
 257     extract_msrv_attr!(LateContext);
 258 }
 259
 260 #[derive(Default)]
 261 struct SkipTyCollector {
 262     types_to_skip: Vec<HirId>,
 263 }
 264
 265 impl<'tcx> Visitor<'tcx> for SkipTyCollector {
 266     type Map = Map<'tcx>;
 267
 268     fn visit_infer(&mut self, inf: &hir::InferArg) {
 269         self.types_to_skip.push(inf.hir_id);
 270
 271         walk_inf(self, inf);
 272     }
 273     fn visit_ty(&mut self, hir_ty: &hir::Ty<'_>) {
 274         self.types_to_skip.push(hir_ty.hir_id);
 275
 276         walk_ty(self, hir_ty);
 277     }
 278
 279     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 280         NestedVisitorMap::None
 281     }
 282 }
 283
 284 fn span_lint(cx: &LateContext<'_>, span: Span) {
 285     span_lint_and_sugg(
 286         cx,
 287         USE_SELF,
 288         span,
 289         "unnecessary structure name repetition",
 290         "use the applicable keyword",
 291         "Self".to_owned(),
 292         Applicability::MachineApplicable,
 293     );
 294 }
 295
 296 fn lint_path_to_variant(cx: &LateContext<'_>, path: &Path<'_>) {
 297     if let [.., self_seg, _variant] = path.segments {
 298         let span = path
 299             .span
 300             .with_hi(self_seg.args().span_ext().unwrap_or(self_seg.ident.span).hi());
 301         span_lint(cx, span);
 302     }
 303 }