clippy_lints/src/use_self.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10 use crate::utils::span_lint_and_sugg;
  11 use if_chain::if_chain;
  12 use rustc::hir::def::{CtorKind, Def};
  13 use rustc::hir::intravisit::{walk_item, walk_path, walk_ty, NestedVisitorMap, Visitor};
  14 use rustc::hir::*;
  15 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
  16 use rustc::ty;
  17 use rustc::{declare_tool_lint, lint_array};
  18 use rustc_errors::Applicability;
  19 use syntax_pos::symbol::keywords::SelfUpper;
  20
  21 /// **What it does:** Checks for unnecessary repetition of structure name when a
  22 /// replacement with `Self` is applicable.
  23 ///
  24 /// **Why is this bad?** Unnecessary repetition. Mixed use of `Self` and struct
  25 /// name
  26 /// feels inconsistent.
  27 ///
  28 /// **Known problems:**
  29 /// - False positive when using associated types (#2843)
  30 /// - False positives in some situations when using generics (#3410)
  31 ///
  32 /// **Example:**
  33 /// ```rust
  34 /// struct Foo {}
  35 /// impl Foo {
  36 ///     fn new() -> Foo {
  37 ///         Foo {}
  38 ///     }
  39 /// }
  40 /// ```
  41 /// could be
  42 /// ```rust
  43 /// struct Foo {}
  44 /// impl Foo {
  45 ///     fn new() -> Self {
  46 ///         Self {}
  47 ///     }
  48 /// }
  49 /// ```
  50 declare_clippy_lint! {
  51     pub USE_SELF,
  52     pedantic,
  53     "Unnecessary structure name repetition whereas `Self` is applicable"
  54 }
  55
  56 #[derive(Copy, Clone, Default)]
  57 pub struct UseSelf;
  58
  59 impl LintPass for UseSelf {
  60     fn get_lints(&self) -> LintArray {
  61         lint_array!(USE_SELF)
  62     }
  63 }
  64
  65 const SEGMENTS_MSG: &str = "segments should be composed of at least 1 element";
  66
  67 fn span_use_self_lint(cx: &LateContext<'_, '_>, path: &Path) {
  68     span_lint_and_sugg(
  69         cx,
  70         USE_SELF,
  71         path.span,
  72         "unnecessary structure name repetition",
  73         "use the applicable keyword",
  74         "Self".to_owned(),
  75         Applicability::MachineApplicable,
  76     );
  77 }
  78
  79 struct TraitImplTyVisitor<'a, 'tcx: 'a> {
  80     item_type: ty::Ty<'tcx>,
  81     cx: &'a LateContext<'a, 'tcx>,
  82     trait_type_walker: ty::walk::TypeWalker<'tcx>,
  83     impl_type_walker: ty::walk::TypeWalker<'tcx>,
  84 }
  85
  86 impl<'a, 'tcx> Visitor<'tcx> for TraitImplTyVisitor<'a, 'tcx> {
  87     fn visit_ty(&mut self, t: &'tcx Ty) {
  88         let trait_ty = self.trait_type_walker.next();
  89         let impl_ty = self.impl_type_walker.next();
  90
  91         if let TyKind::Path(QPath::Resolved(_, path)) = &t.node {
  92             // The implementation and trait types don't match which means that
  93             // the concrete type was specified by the implementation
  94             if impl_ty != trait_ty {
  95                 if let Some(impl_ty) = impl_ty {
  96                     if self.item_type == impl_ty {
  97                         let is_self_ty = if let def::Def::SelfTy(..) = path.def {
  98                             true
  99                         } else {
 100                             false
 101                         };
 102
 103                         if !is_self_ty {
 104                             span_use_self_lint(self.cx, path);
 105                         }
 106                     }
 107                 }
 108             }
 109         }
 110
 111         walk_ty(self, t)
 112     }
 113
 114     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 115         NestedVisitorMap::None
 116     }
 117 }
 118
 119 fn check_trait_method_impl_decl<'a, 'tcx: 'a>(
 120     cx: &'a LateContext<'a, 'tcx>,
 121     item_type: ty::Ty<'tcx>,
 122     impl_item: &ImplItem,
 123     impl_decl: &'tcx FnDecl,
 124     impl_trait_ref: &ty::TraitRef<'_>,
 125 ) {
 126     let trait_method = cx
 127         .tcx
 128         .associated_items(impl_trait_ref.def_id)
 129         .find(|assoc_item| {
 130             assoc_item.kind == ty::AssociatedKind::Method
 131                 && cx
 132                     .tcx
 133                     .hygienic_eq(impl_item.ident, assoc_item.ident, impl_trait_ref.def_id)
 134         })
 135         .expect("impl method matches a trait method");
 136
 137     let trait_method_sig = cx.tcx.fn_sig(trait_method.def_id);
 138     let trait_method_sig = cx.tcx.erase_late_bound_regions(&trait_method_sig);
 139
 140     let impl_method_def_id = cx.tcx.hir().local_def_id(impl_item.id);
 141     let impl_method_sig = cx.tcx.fn_sig(impl_method_def_id);
 142     let impl_method_sig = cx.tcx.erase_late_bound_regions(&impl_method_sig);
 143
 144     let output_ty = if let FunctionRetTy::Return(ty) = &impl_decl.output {
 145         Some(&**ty)
 146     } else {
 147         None
 148     };
 149
 150     // `impl_decl_ty` (of type `hir::Ty`) represents the type declared in the signature.
 151     // `impl_ty` (of type `ty:TyS`) is the concrete type that the compiler has determined for
 152     // that declaration.  We use `impl_decl_ty` to see if the type was declared as `Self`
 153     // and use `impl_ty` to check its concrete type.
 154     for (impl_decl_ty, (impl_ty, trait_ty)) in impl_decl.inputs.iter().chain(output_ty).zip(
 155         impl_method_sig
 156             .inputs_and_output
 157             .iter()
 158             .zip(trait_method_sig.inputs_and_output),
 159     ) {
 160         let mut visitor = TraitImplTyVisitor {
 161             cx,
 162             item_type,
 163             trait_type_walker: trait_ty.walk(),
 164             impl_type_walker: impl_ty.walk(),
 165         };
 166
 167         visitor.visit_ty(&impl_decl_ty);
 168     }
 169 }
 170
 171 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UseSelf {
 172     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
 173         if in_external_macro(cx.sess(), item.span) {
 174             return;
 175         }
 176         if_chain! {
 177             if let ItemKind::Impl(.., ref item_type, ref refs) = item.node;
 178             if let TyKind::Path(QPath::Resolved(_, ref item_path)) = item_type.node;
 179             then {
 180                 let parameters = &item_path.segments.last().expect(SEGMENTS_MSG).args;
 181                 let should_check = if let Some(ref params) = *parameters {
 182                     !params.parenthesized && !params.args.iter().any(|arg| match arg {
 183                         GenericArg::Lifetime(_) => true,
 184                         GenericArg::Type(_) => false,
 185                     })
 186                 } else {
 187                     true
 188                 };
 189
 190                 if should_check {
 191                     let visitor = &mut UseSelfVisitor {
 192                         item_path,
 193                         cx,
 194                     };
 195                     let impl_def_id = cx.tcx.hir().local_def_id(item.id);
 196                     let impl_trait_ref = cx.tcx.impl_trait_ref(impl_def_id);
 197
 198                     if let Some(impl_trait_ref) = impl_trait_ref {
 199                         for impl_item_ref in refs {
 200                             let impl_item = cx.tcx.hir().impl_item(impl_item_ref.id);
 201                             if let ImplItemKind::Method(MethodSig{ decl: impl_decl, .. }, impl_body_id)
 202                                     = &impl_item.node {
 203                                 let item_type = cx.tcx.type_of(impl_def_id);
 204                                 check_trait_method_impl_decl(cx, item_type, impl_item, impl_decl, &impl_trait_ref);
 205
 206                                 let body = cx.tcx.hir().body(*impl_body_id);
 207                                 visitor.visit_body(body);
 208                             } else {
 209                                 visitor.visit_impl_item(impl_item);
 210                             }
 211                         }
 212                     } else {
 213                         for impl_item_ref in refs {
 214                             let impl_item = cx.tcx.hir().impl_item(impl_item_ref.id);
 215                             visitor.visit_impl_item(impl_item);
 216                         }
 217                     }
 218                 }
 219             }
 220         }
 221     }
 222 }
 223
 224 struct UseSelfVisitor<'a, 'tcx: 'a> {
 225     item_path: &'a Path,
 226     cx: &'a LateContext<'a, 'tcx>,
 227 }
 228
 229 impl<'a, 'tcx> Visitor<'tcx> for UseSelfVisitor<'a, 'tcx> {
 230     fn visit_path(&mut self, path: &'tcx Path, _id: HirId) {
 231         if path.segments.last().expect(SEGMENTS_MSG).ident.name != SelfUpper.name() {
 232             if self.item_path.def == path.def {
 233                 span_use_self_lint(self.cx, path);
 234             } else if let Def::StructCtor(ctor_did, CtorKind::Fn) = path.def {
 235                 if self.item_path.def.opt_def_id() == self.cx.tcx.parent_def_id(ctor_did) {
 236                     span_use_self_lint(self.cx, path);
 237                 }
 238             }
 239         }
 240         walk_path(self, path);
 241     }
 242
 243     fn visit_item(&mut self, item: &'tcx Item) {
 244         match item.node {
 245             ItemKind::Use(..)
 246             | ItemKind::Static(..)
 247             | ItemKind::Enum(..)
 248             | ItemKind::Struct(..)
 249             | ItemKind::Union(..) => {
 250                 // Don't check statements that shadow `Self` or where `Self` can't be used
 251             },
 252             _ => walk_item(self, item),
 253         }
 254     }
 255
 256     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 257         NestedVisitorMap::All(&self.cx.tcx.hir())
 258     }
 259 }