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::{in_macro, span_lint_and_sugg};
  11 use if_chain::if_chain;
  12 use rustc::hir::intravisit::{walk_path, walk_ty, NestedVisitorMap, Visitor};
  13 use rustc::hir::*;
  14 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  15 use rustc::ty;
  16 use rustc::{declare_tool_lint, lint_array};
  17 use rustc_errors::Applicability;
  18 use syntax::ast::NodeId;
  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 /// - Does not trigger within locally defined macros (#2098)
  30 /// - False positive when using associated types (#2843)
  31 /// - False positives in some situations when using generics (#3410)
  32 /// - False positive when type from outer function can't be used (#3463)
  33 /// - Does not diagnose tuple structs (#3498)
  34 /// - Does not trigger in lifetimed struct
  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 declare_clippy_lint! {
  55     pub USE_SELF,
  56     pedantic,
  57     "Unnecessary structure name repetition whereas `Self` is applicable"
  58 }
  59
  60 #[derive(Copy, Clone, Default)]
  61 pub struct UseSelf;
  62
  63 impl LintPass for UseSelf {
  64     fn get_lints(&self) -> LintArray {
  65         lint_array!(USE_SELF)
  66     }
  67 }
  68
  69 const SEGMENTS_MSG: &str = "segments should be composed of at least 1 element";
  70
  71 fn span_use_self_lint(cx: &LateContext<'_, '_>, path: &Path) {
  72     span_lint_and_sugg(
  73         cx,
  74         USE_SELF,
  75         path.span,
  76         "unnecessary structure name repetition",
  77         "use the applicable keyword",
  78         "Self".to_owned(),
  79         Applicability::MachineApplicable,
  80     );
  81 }
  82
  83 struct TraitImplTyVisitor<'a, 'tcx: 'a> {
  84     item_type: ty::Ty<'tcx>,
  85     cx: &'a LateContext<'a, 'tcx>,
  86     trait_type_walker: ty::walk::TypeWalker<'tcx>,
  87     impl_type_walker: ty::walk::TypeWalker<'tcx>,
  88 }
  89
  90 impl<'a, 'tcx> Visitor<'tcx> for TraitImplTyVisitor<'a, 'tcx> {
  91     fn visit_ty(&mut self, t: &'tcx Ty) {
  92         let trait_ty = self.trait_type_walker.next();
  93         let impl_ty = self.impl_type_walker.next();
  94
  95         if let TyKind::Path(QPath::Resolved(_, path)) = &t.node {
  96             // The implementation and trait types don't match which means that
  97             // the concrete type was specified by the implementation
  98             if impl_ty != trait_ty {
  99                 if let Some(impl_ty) = impl_ty {
 100                     if self.item_type == impl_ty {
 101                         let is_self_ty = if let def::Def::SelfTy(..) = path.def {
 102                             true
 103                         } else {
 104                             false
 105                         };
 106
 107                         if !is_self_ty {
 108                             span_use_self_lint(self.cx, path);
 109                         }
 110                     }
 111                 }
 112             }
 113         }
 114
 115         walk_ty(self, t)
 116     }
 117
 118     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 119         NestedVisitorMap::None
 120     }
 121 }
 122
 123 fn check_trait_method_impl_decl<'a, 'tcx: 'a>(
 124     cx: &'a LateContext<'a, 'tcx>,
 125     item_type: ty::Ty<'tcx>,
 126     impl_item: &ImplItem,
 127     impl_decl: &'tcx FnDecl,
 128     impl_trait_ref: &ty::TraitRef<'_>,
 129 ) {
 130     let trait_method = cx
 131         .tcx
 132         .associated_items(impl_trait_ref.def_id)
 133         .find(|assoc_item| {
 134             assoc_item.kind == ty::AssociatedKind::Method
 135                 && cx
 136                     .tcx
 137                     .hygienic_eq(impl_item.ident, assoc_item.ident, impl_trait_ref.def_id)
 138         })
 139         .expect("impl method matches a trait method");
 140
 141     let trait_method_sig = cx.tcx.fn_sig(trait_method.def_id);
 142     let trait_method_sig = cx.tcx.erase_late_bound_regions(&trait_method_sig);
 143
 144     let impl_method_def_id = cx.tcx.hir().local_def_id(impl_item.id);
 145     let impl_method_sig = cx.tcx.fn_sig(impl_method_def_id);
 146     let impl_method_sig = cx.tcx.erase_late_bound_regions(&impl_method_sig);
 147
 148     let output_ty = if let FunctionRetTy::Return(ty) = &impl_decl.output {
 149         Some(&**ty)
 150     } else {
 151         None
 152     };
 153
 154     // `impl_decl_ty` (of type `hir::Ty`) represents the type declared in the signature.
 155     // `impl_ty` (of type `ty:TyS`) is the concrete type that the compiler has determined for
 156     // that declaration.  We use `impl_decl_ty` to see if the type was declared as `Self`
 157     // and use `impl_ty` to check its concrete type.
 158     for (impl_decl_ty, (impl_ty, trait_ty)) in impl_decl.inputs.iter().chain(output_ty).zip(
 159         impl_method_sig
 160             .inputs_and_output
 161             .iter()
 162             .zip(trait_method_sig.inputs_and_output),
 163     ) {
 164         let mut visitor = TraitImplTyVisitor {
 165             cx,
 166             item_type,
 167             trait_type_walker: trait_ty.walk(),
 168             impl_type_walker: impl_ty.walk(),
 169         };
 170
 171         visitor.visit_ty(&impl_decl_ty);
 172     }
 173 }
 174
 175 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UseSelf {
 176     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
 177         if in_macro(item.span) {
 178             return;
 179         }
 180         if_chain! {
 181             if let ItemKind::Impl(.., ref item_type, ref refs) = item.node;
 182             if let TyKind::Path(QPath::Resolved(_, ref item_path)) = item_type.node;
 183             then {
 184                 let parameters = &item_path.segments.last().expect(SEGMENTS_MSG).args;
 185                 let should_check = if let Some(ref params) = *parameters {
 186                     !params.parenthesized && !params.args.iter().any(|arg| match arg {
 187                         GenericArg::Lifetime(_) => true,
 188                         GenericArg::Type(_) => false,
 189                     })
 190                 } else {
 191                     true
 192                 };
 193
 194                 if should_check {
 195                     let visitor = &mut UseSelfVisitor {
 196                         item_path,
 197                         cx,
 198                     };
 199                     let impl_def_id = cx.tcx.hir().local_def_id(item.id);
 200                     let impl_trait_ref = cx.tcx.impl_trait_ref(impl_def_id);
 201
 202                     if let Some(impl_trait_ref) = impl_trait_ref {
 203                         for impl_item_ref in refs {
 204                             let impl_item = cx.tcx.hir().impl_item(impl_item_ref.id);
 205                             if let ImplItemKind::Method(MethodSig{ decl: impl_decl, .. }, impl_body_id)
 206                                     = &impl_item.node {
 207                                 let item_type = cx.tcx.type_of(impl_def_id);
 208                                 check_trait_method_impl_decl(cx, item_type, impl_item, impl_decl, &impl_trait_ref);
 209
 210                                 let body = cx.tcx.hir().body(*impl_body_id);
 211                                 visitor.visit_body(body);
 212                             } else {
 213                                 visitor.visit_impl_item(impl_item);
 214                             }
 215                         }
 216                     } else {
 217                         for impl_item_ref in refs {
 218                             let impl_item = cx.tcx.hir().impl_item(impl_item_ref.id);
 219                             visitor.visit_impl_item(impl_item);
 220                         }
 221                     }
 222                 }
 223             }
 224         }
 225     }
 226 }
 227
 228 struct UseSelfVisitor<'a, 'tcx: 'a> {
 229     item_path: &'a Path,
 230     cx: &'a LateContext<'a, 'tcx>,
 231 }
 232
 233 impl<'a, 'tcx> Visitor<'tcx> for UseSelfVisitor<'a, 'tcx> {
 234     fn visit_path(&mut self, path: &'tcx Path, _id: HirId) {
 235         if self.item_path.def == path.def && path.segments.last().expect(SEGMENTS_MSG).ident.name != SelfUpper.name() {
 236             span_use_self_lint(self.cx, path);
 237         }
 238
 239         walk_path(self, path);
 240     }
 241
 242     fn visit_use(&mut self, _path: &'tcx Path, _id: NodeId, _hir_id: HirId) {
 243         // Don't check use statements
 244     }
 245
 246     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 247         NestedVisitorMap::All(&self.cx.tcx.hir())
 248     }
 249 }