src/librustc/lint/internal.rs

   1 //! Some lints that are only useful in the compiler or crates that use compiler internals, such as
   2 //! Clippy.
   3
   4 use crate::hir::{GenericArg, HirId, MutTy, Mutability, Path, PathSegment, QPath, Ty, TyKind};
   5 use crate::lint::{
   6     EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintArray, LintContext, LintPass,
   7 };
   8 use errors::Applicability;
   9 use rustc_data_structures::fx::FxHashMap;
  10 use syntax::ast::Ident;
  11 use syntax::symbol::{sym, Symbol};
  12
  13 declare_lint! {
  14     pub DEFAULT_HASH_TYPES,
  15     Allow,
  16     "forbid HashMap and HashSet and suggest the FxHash* variants"
  17 }
  18
  19 pub struct DefaultHashTypes {
  20     map: FxHashMap<Symbol, Symbol>,
  21 }
  22
  23 impl DefaultHashTypes {
  24     // we are allowed to use `HashMap` and `HashSet` as identifiers for implementing the lint itself
  25     #[allow(internal)]
  26     pub fn new() -> Self {
  27         let mut map = FxHashMap::default();
  28         map.insert(sym::HashMap, sym::FxHashMap);
  29         map.insert(sym::HashSet, sym::FxHashSet);
  30         Self { map }
  31     }
  32 }
  33
  34 impl_lint_pass!(DefaultHashTypes => [DEFAULT_HASH_TYPES]);
  35
  36 impl EarlyLintPass for DefaultHashTypes {
  37     fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
  38         if let Some(replace) = self.map.get(&ident.name) {
  39             let msg = format!(
  40                 "Prefer {} over {}, it has better performance",
  41                 replace, ident
  42             );
  43             let mut db = cx.struct_span_lint(DEFAULT_HASH_TYPES, ident.span, &msg);
  44             db.span_suggestion(
  45                 ident.span,
  46                 "use",
  47                 replace.to_string(),
  48                 Applicability::MaybeIncorrect, // FxHashMap, ... needs another import
  49             );
  50             db.note(&format!(
  51                 "a `use rustc_data_structures::fx::{}` may be necessary",
  52                 replace
  53             ))
  54             .emit();
  55         }
  56     }
  57 }
  58
  59 declare_lint! {
  60     pub USAGE_OF_TY_TYKIND,
  61     Allow,
  62     "usage of `ty::TyKind` outside of the `ty::sty` module"
  63 }
  64
  65 declare_lint! {
  66     pub TY_PASS_BY_REFERENCE,
  67     Allow,
  68     "passing `Ty` or `TyCtxt` by reference"
  69 }
  70
  71 declare_lint! {
  72     pub USAGE_OF_QUALIFIED_TY,
  73     Allow,
  74     "using `ty::{Ty,TyCtxt}` instead of importing it"
  75 }
  76
  77 declare_lint_pass!(TyTyKind => [
  78     USAGE_OF_TY_TYKIND,
  79     TY_PASS_BY_REFERENCE,
  80     USAGE_OF_QUALIFIED_TY,
  81 ]);
  82
  83 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TyTyKind {
  84     fn check_path(&mut self, cx: &LateContext<'_, '_>, path: &'tcx Path, _: HirId) {
  85         let segments = path.segments.iter().rev().skip(1).rev();
  86
  87         if let Some(last) = segments.last() {
  88             let span = path.span.with_hi(last.ident.span.hi());
  89             if lint_ty_kind_usage(cx, last) {
  90                 cx.struct_span_lint(USAGE_OF_TY_TYKIND, span, "usage of `ty::TyKind::<kind>`")
  91                     .span_suggestion(
  92                         span,
  93                         "try using ty::<kind> directly",
  94                         "ty".to_string(),
  95                         Applicability::MaybeIncorrect, // ty maybe needs an import
  96                     )
  97                     .emit();
  98             }
  99         }
 100     }
 101
 102     fn check_ty(&mut self, cx: &LateContext<'_, '_>, ty: &'tcx Ty) {
 103         match &ty.node {
 104             TyKind::Path(qpath) => {
 105                 if let QPath::Resolved(_, path) = qpath {
 106                     if let Some(last) = path.segments.iter().last() {
 107                         if lint_ty_kind_usage(cx, last) {
 108                             cx.struct_span_lint(
 109                                 USAGE_OF_TY_TYKIND,
 110                                 path.span,
 111                                 "usage of `ty::TyKind`",
 112                             )
 113                             .help("try using `Ty` instead")
 114                             .emit();
 115                         } else {
 116                             if ty.span.ctxt().outer().expn_info().is_some() {
 117                                 return;
 118                             }
 119                             if let Some(t) = is_ty_or_ty_ctxt(cx, ty) {
 120                                 if path.segments.len() > 1 {
 121                                     cx.struct_span_lint(
 122                                         USAGE_OF_QUALIFIED_TY,
 123                                         path.span,
 124                                         &format!("usage of qualified `ty::{}`", t),
 125                                     )
 126                                     .span_suggestion(
 127                                         path.span,
 128                                         "try using it unqualified",
 129                                         t,
 130                                         // The import probably needs to be changed
 131                                         Applicability::MaybeIncorrect,
 132                                     )
 133                                     .emit();
 134                                 }
 135                             }
 136                         }
 137                     }
 138                 }
 139             }
 140             TyKind::Rptr(
 141                 _,
 142                 MutTy {
 143                     ty: inner_ty,
 144                     mutbl: Mutability::MutImmutable,
 145                 },
 146             ) => {
 147                 if let Some(impl_did) = cx.tcx.impl_of_method(ty.hir_id.owner_def_id()) {
 148                     if cx.tcx.impl_trait_ref(impl_did).is_some() {
 149                         return;
 150                     }
 151                 }
 152                 if let Some(t) = is_ty_or_ty_ctxt(cx, &inner_ty) {
 153                     cx.struct_span_lint(
 154                         TY_PASS_BY_REFERENCE,
 155                         ty.span,
 156                         &format!("passing `{}` by reference", t),
 157                     )
 158                     .span_suggestion(
 159                         ty.span,
 160                         "try passing by value",
 161                         t,
 162                         // Changing type of function argument
 163                         Applicability::MaybeIncorrect,
 164                     )
 165                     .emit();
 166                 }
 167             }
 168             _ => {}
 169         }
 170     }
 171 }
 172
 173 fn lint_ty_kind_usage(cx: &LateContext<'_, '_>, segment: &PathSegment) -> bool {
 174     if segment.ident.name == sym::TyKind {
 175         if let Some(res) = segment.res {
 176             if let Some(did) = res.opt_def_id() {
 177                 return cx.match_def_path(did, TYKIND_PATH);
 178             }
 179         }
 180     }
 181
 182     false
 183 }
 184
 185 const TYKIND_PATH: &[Symbol] = &[sym::rustc, sym::ty, sym::sty, sym::TyKind];
 186 const TY_PATH: &[Symbol] = &[sym::rustc, sym::ty, sym::Ty];
 187 const TYCTXT_PATH: &[Symbol] = &[sym::rustc, sym::ty, sym::context, sym::TyCtxt];
 188
 189 fn is_ty_or_ty_ctxt(cx: &LateContext<'_, '_>, ty: &Ty) -> Option<String> {
 190     match &ty.node {
 191         TyKind::Path(qpath) => {
 192             if let QPath::Resolved(_, path) = qpath {
 193                 let did = path.res.opt_def_id()?;
 194                 if cx.match_def_path(did, TY_PATH) {
 195                     return Some(format!("Ty{}", gen_args(path.segments.last().unwrap())));
 196                 } else if cx.match_def_path(did, TYCTXT_PATH) {
 197                     return Some(format!("TyCtxt{}", gen_args(path.segments.last().unwrap())));
 198                 }
 199             }
 200         }
 201         _ => {}
 202     }
 203
 204     None
 205 }
 206
 207 fn gen_args(segment: &PathSegment) -> String {
 208     if let Some(args) = &segment.args {
 209         let lifetimes = args
 210             .args
 211             .iter()
 212             .filter_map(|arg| {
 213                 if let GenericArg::Lifetime(lt) = arg {
 214                     Some(lt.name.ident().to_string())
 215                 } else {
 216                     None
 217                 }
 218             })
 219             .collect::<Vec<_>>();
 220
 221         if !lifetimes.is_empty() {
 222             return format!("<{}>", lifetimes.join(", "));
 223         }
 224     }
 225
 226     String::new()
 227 }