clippy_lints/src/use_self.rs

   1 use crate::utils::span_lint_and_sugg;
   2 use if_chain::if_chain;
   3 use rustc::hir::def::{CtorKind, Def};
   4 use rustc::hir::intravisit::{walk_item, walk_path, walk_ty, NestedVisitorMap, Visitor};
   5 use rustc::hir::*;
   6 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
   7 use rustc::ty;
   8 use rustc::{declare_tool_lint, lint_array};
   9 use rustc_errors::Applicability;
  10 use syntax_pos::symbol::keywords::SelfUpper;
  11
  12 /// **What it does:** Checks for unnecessary repetition of structure name when a
  13 /// replacement with `Self` is applicable.
  14 ///
  15 /// **Why is this bad?** Unnecessary repetition. Mixed use of `Self` and struct
  16 /// name
  17 /// feels inconsistent.
  18 ///
  19 /// **Known problems:**
  20 /// - False positive when using associated types (#2843)
  21 /// - False positives in some situations when using generics (#3410)
  22 ///
  23 /// **Example:**
  24 /// ```rust
  25 /// struct Foo {}
  26 /// impl Foo {
  27 ///     fn new() -> Foo {
  28 ///         Foo {}
  29 ///     }
  30 /// }
  31 /// ```
  32 /// could be
  33 /// ```rust
  34 /// struct Foo {}
  35 /// impl Foo {
  36 ///     fn new() -> Self {
  37 ///         Self {}
  38 ///     }
  39 /// }
  40 /// ```
  41 declare_clippy_lint! {
  42     pub USE_SELF,
  43     pedantic,
  44     "Unnecessary structure name repetition whereas `Self` is applicable"
  45 }
  46
  47 #[derive(Copy, Clone, Default)]
  48 pub struct UseSelf;
  49
  50 impl LintPass for UseSelf {
  51     fn get_lints(&self) -> LintArray {
  52         lint_array!(USE_SELF)
  53     }
  54 }
  55
  56 const SEGMENTS_MSG: &str = "segments should be composed of at least 1 element";
  57
  58 fn span_use_self_lint(cx: &LateContext<'_, '_>, path: &Path) {
  59     // path segments only include actual path, no methods or fields
  60     let last_path_span = path.segments.last().expect(SEGMENTS_MSG).ident.span;
  61     // only take path up to the end of last_path_span
  62     let span = path.span.with_hi(last_path_span.hi());
  63
  64     span_lint_and_sugg(
  65         cx,
  66         USE_SELF,
  67         span,
  68         "unnecessary structure name repetition",
  69         "use the applicable keyword",
  70         "Self".to_owned(),
  71         Applicability::MachineApplicable,
  72     );
  73 }
  74
  75 struct TraitImplTyVisitor<'a, 'tcx: 'a> {
  76     item_type: ty::Ty<'tcx>,
  77     cx: &'a LateContext<'a, 'tcx>,
  78     trait_type_walker: ty::walk::TypeWalker<'tcx>,
  79     impl_type_walker: ty::walk::TypeWalker<'tcx>,
  80 }
  81
  82 impl<'a, 'tcx> Visitor<'tcx> for TraitImplTyVisitor<'a, 'tcx> {
  83     fn visit_ty(&mut self, t: &'tcx Ty) {
  84         let trait_ty = self.trait_type_walker.next();
  85         let impl_ty = self.impl_type_walker.next();
  86
  87         if let TyKind::Path(QPath::Resolved(_, path)) = &t.node {
  88             // The implementation and trait types don't match which means that
  89             // the concrete type was specified by the implementation
  90             if impl_ty != trait_ty {
  91                 if let Some(impl_ty) = impl_ty {
  92                     if self.item_type == impl_ty {
  93                         let is_self_ty = if let def::Def::SelfTy(..) = path.def {
  94                             true
  95                         } else {
  96                             false
  97                         };
  98
  99                         if !is_self_ty {
 100                             span_use_self_lint(self.cx, path);
 101                         }
 102                     }
 103                 }
 104             }
 105         }
 106
 107         walk_ty(self, t)
 108     }
 109
 110     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 111         NestedVisitorMap::None
 112     }
 113 }
 114
 115 fn check_trait_method_impl_decl<'a, 'tcx: 'a>(
 116     cx: &'a LateContext<'a, 'tcx>,
 117     item_type: ty::Ty<'tcx>,
 118     impl_item: &ImplItem,
 119     impl_decl: &'tcx FnDecl,
 120     impl_trait_ref: &ty::TraitRef<'_>,
 121 ) {
 122     let trait_method = cx
 123         .tcx
 124         .associated_items(impl_trait_ref.def_id)
 125         .find(|assoc_item| {
 126             assoc_item.kind == ty::AssociatedKind::Method
 127                 && cx
 128                     .tcx
 129                     .hygienic_eq(impl_item.ident, assoc_item.ident, impl_trait_ref.def_id)
 130         })
 131         .expect("impl method matches a trait method");
 132
 133     let trait_method_sig = cx.tcx.fn_sig(trait_method.def_id);
 134     let trait_method_sig = cx.tcx.erase_late_bound_regions(&trait_method_sig);
 135
 136     let impl_method_def_id = cx.tcx.hir().local_def_id(impl_item.id);
 137     let impl_method_sig = cx.tcx.fn_sig(impl_method_def_id);
 138     let impl_method_sig = cx.tcx.erase_late_bound_regions(&impl_method_sig);
 139
 140     let output_ty = if let FunctionRetTy::Return(ty) = &impl_decl.output {
 141         Some(&**ty)
 142     } else {
 143         None
 144     };
 145
 146     // `impl_decl_ty` (of type `hir::Ty`) represents the type declared in the signature.
 147     // `impl_ty` (of type `ty:TyS`) is the concrete type that the compiler has determined for
 148     // that declaration.  We use `impl_decl_ty` to see if the type was declared as `Self`
 149     // and use `impl_ty` to check its concrete type.
 150     for (impl_decl_ty, (impl_ty, trait_ty)) in impl_decl.inputs.iter().chain(output_ty).zip(
 151         impl_method_sig
 152             .inputs_and_output
 153             .iter()
 154             .zip(trait_method_sig.inputs_and_output),
 155     ) {
 156         let mut visitor = TraitImplTyVisitor {
 157             cx,
 158             item_type,
 159             trait_type_walker: trait_ty.walk(),
 160             impl_type_walker: impl_ty.walk(),
 161         };
 162
 163         visitor.visit_ty(&impl_decl_ty);
 164     }
 165 }
 166
 167 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UseSelf {
 168     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
 169         if in_external_macro(cx.sess(), item.span) {
 170             return;
 171         }
 172         if_chain! {
 173             if let ItemKind::Impl(.., ref item_type, ref refs) = item.node;
 174             if let TyKind::Path(QPath::Resolved(_, ref item_path)) = item_type.node;
 175             then {
 176                 let parameters = &item_path.segments.last().expect(SEGMENTS_MSG).args;
 177                 let should_check = if let Some(ref params) = *parameters {
 178                     !params.parenthesized && !params.args.iter().any(|arg| match arg {
 179                         GenericArg::Lifetime(_) => true,
 180                         GenericArg::Type(_) => false,
 181                     })
 182                 } else {
 183                     true
 184                 };
 185
 186                 if should_check {
 187                     let visitor = &mut UseSelfVisitor {
 188                         item_path,
 189                         cx,
 190                     };
 191                     let impl_def_id = cx.tcx.hir().local_def_id(item.id);
 192                     let impl_trait_ref = cx.tcx.impl_trait_ref(impl_def_id);
 193
 194                     if let Some(impl_trait_ref) = impl_trait_ref {
 195                         for impl_item_ref in refs {
 196                             let impl_item = cx.tcx.hir().impl_item(impl_item_ref.id);
 197                             if let ImplItemKind::Method(MethodSig{ decl: impl_decl, .. }, impl_body_id)
 198                                     = &impl_item.node {
 199                                 let item_type = cx.tcx.type_of(impl_def_id);
 200                                 check_trait_method_impl_decl(cx, item_type, impl_item, impl_decl, &impl_trait_ref);
 201
 202                                 let body = cx.tcx.hir().body(*impl_body_id);
 203                                 visitor.visit_body(body);
 204                             } else {
 205                                 visitor.visit_impl_item(impl_item);
 206                             }
 207                         }
 208                     } else {
 209                         for impl_item_ref in refs {
 210                             let impl_item = cx.tcx.hir().impl_item(impl_item_ref.id);
 211                             visitor.visit_impl_item(impl_item);
 212                         }
 213                     }
 214                 }
 215             }
 216         }
 217     }
 218 }
 219
 220 struct UseSelfVisitor<'a, 'tcx: 'a> {
 221     item_path: &'a Path,
 222     cx: &'a LateContext<'a, 'tcx>,
 223 }
 224
 225 impl<'a, 'tcx> Visitor<'tcx> for UseSelfVisitor<'a, 'tcx> {
 226     fn visit_path(&mut self, path: &'tcx Path, _id: HirId) {
 227         if path.segments.last().expect(SEGMENTS_MSG).ident.name != SelfUpper.name() {
 228             if self.item_path.def == path.def {
 229                 span_use_self_lint(self.cx, path);
 230             } else if let Def::StructCtor(ctor_did, CtorKind::Fn) = path.def {
 231                 if self.item_path.def.opt_def_id() == self.cx.tcx.parent_def_id(ctor_did) {
 232                     span_use_self_lint(self.cx, path);
 233                 }
 234             }
 235         }
 236         walk_path(self, path);
 237     }
 238
 239     fn visit_item(&mut self, item: &'tcx Item) {
 240         match item.node {
 241             ItemKind::Use(..)
 242             | ItemKind::Static(..)
 243             | ItemKind::Enum(..)
 244             | ItemKind::Struct(..)
 245             | ItemKind::Union(..)
 246             | ItemKind::Impl(..) => {
 247                 // Don't check statements that shadow `Self` or where `Self` can't be used
 248             },
 249             _ => walk_item(self, item),
 250         }
 251     }
 252
 253     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 254         NestedVisitorMap::All(&self.cx.tcx.hir())
 255     }
 256 }