src/tools/clippy/clippy_lints/src/implicit_hasher.rs

   1 #![allow(rustc::default_hash_types)]
   2
   3 use std::borrow::Cow;
   4 use std::collections::BTreeMap;
   5
   6 use rustc_errors::DiagnosticBuilder;
   7 use rustc_hir as hir;
   8 use rustc_hir::intravisit::{walk_body, walk_expr, walk_ty, NestedVisitorMap, Visitor};
   9 use rustc_hir::{Body, Expr, ExprKind, GenericArg, Item, ItemKind, QPath, TyKind};
  10 use rustc_lint::{LateContext, LateLintPass, LintContext};
  11 use rustc_middle::hir::map::Map;
  12 use rustc_middle::lint::in_external_macro;
  13 use rustc_middle::ty::{Ty, TyS, TypeckResults};
  14 use rustc_session::{declare_lint_pass, declare_tool_lint};
  15 use rustc_span::source_map::Span;
  16 use rustc_span::symbol::sym;
  17 use rustc_typeck::hir_ty_to_ty;
  18
  19 use if_chain::if_chain;
  20
  21 use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
  22 use clippy_utils::paths;
  23 use clippy_utils::source::{snippet, snippet_opt};
  24 use clippy_utils::ty::is_type_diagnostic_item;
  25 use clippy_utils::{differing_macro_contexts, match_def_path};
  26
  27 declare_clippy_lint! {
  28     /// **What it does:** Checks for public `impl` or `fn` missing generalization
  29     /// over different hashers and implicitly defaulting to the default hashing
  30     /// algorithm (`SipHash`).
  31     ///
  32     /// **Why is this bad?** `HashMap` or `HashSet` with custom hashers cannot be
  33     /// used with them.
  34     ///
  35     /// **Known problems:** Suggestions for replacing constructors can contain
  36     /// false-positives. Also applying suggestions can require modification of other
  37     /// pieces of code, possibly including external crates.
  38     ///
  39     /// **Example:**
  40     /// ```rust
  41     /// # use std::collections::HashMap;
  42     /// # use std::hash::{Hash, BuildHasher};
  43     /// # trait Serialize {};
  44     /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
  45     ///
  46     /// pub fn foo(map: &mut HashMap<i32, i32>) { }
  47     /// ```
  48     /// could be rewritten as
  49     /// ```rust
  50     /// # use std::collections::HashMap;
  51     /// # use std::hash::{Hash, BuildHasher};
  52     /// # trait Serialize {};
  53     /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
  54     ///
  55     /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
  56     /// ```
  57     pub IMPLICIT_HASHER,
  58     pedantic,
  59     "missing generalization over different hashers"
  60 }
  61
  62 declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
  63
  64 impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
  65     #[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
  66     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
  67         use rustc_span::BytePos;
  68
  69         fn suggestion<'tcx>(
  70             cx: &LateContext<'tcx>,
  71             diag: &mut DiagnosticBuilder<'_>,
  72             generics_span: Span,
  73             generics_suggestion_span: Span,
  74             target: &ImplicitHasherType<'_>,
  75             vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
  76         ) {
  77             let generics_snip = snippet(cx, generics_span, "");
  78             // trim `<` `>`
  79             let generics_snip = if generics_snip.is_empty() {
  80                 ""
  81             } else {
  82                 &generics_snip[1..generics_snip.len() - 1]
  83             };
  84
  85             multispan_sugg(
  86                 diag,
  87                 "consider adding a type parameter",
  88                 vec![
  89                     (
  90                         generics_suggestion_span,
  91                         format!(
  92                             "<{}{}S: ::std::hash::BuildHasher{}>",
  93                             generics_snip,
  94                             if generics_snip.is_empty() { "" } else { ", " },
  95                             if vis.suggestions.is_empty() {
  96                                 ""
  97                             } else {
  98                                 // request users to add `Default` bound so that generic constructors can be used
  99                                 " + Default"
 100                             },
 101                         ),
 102                     ),
 103                     (
 104                         target.span(),
 105                         format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
 106                     ),
 107                 ],
 108             );
 109
 110             if !vis.suggestions.is_empty() {
 111                 multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
 112             }
 113         }
 114
 115         if !cx.access_levels.is_exported(item.hir_id()) {
 116             return;
 117         }
 118
 119         match item.kind {
 120             ItemKind::Impl(ref impl_) => {
 121                 let mut vis = ImplicitHasherTypeVisitor::new(cx);
 122                 vis.visit_ty(impl_.self_ty);
 123
 124                 for target in &vis.found {
 125                     if differing_macro_contexts(item.span, target.span()) {
 126                         return;
 127                     }
 128
 129                     let generics_suggestion_span = impl_.generics.span.substitute_dummy({
 130                         let pos = snippet_opt(cx, item.span.until(target.span()))
 131                             .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
 132                         if let Some(pos) = pos {
 133                             Span::new(pos, pos, item.span.data().ctxt)
 134                         } else {
 135                             return;
 136                         }
 137                     });
 138
 139                     let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
 140                     for item in impl_.items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
 141                         ctr_vis.visit_impl_item(item);
 142                     }
 143
 144                     span_lint_and_then(
 145                         cx,
 146                         IMPLICIT_HASHER,
 147                         target.span(),
 148                         &format!(
 149                             "impl for `{}` should be generalized over different hashers",
 150                             target.type_name()
 151                         ),
 152                         move |diag| {
 153                             suggestion(cx, diag, impl_.generics.span, generics_suggestion_span, target, ctr_vis);
 154                         },
 155                     );
 156                 }
 157             },
 158             ItemKind::Fn(ref sig, ref generics, body_id) => {
 159                 let body = cx.tcx.hir().body(body_id);
 160
 161                 for ty in sig.decl.inputs {
 162                     let mut vis = ImplicitHasherTypeVisitor::new(cx);
 163                     vis.visit_ty(ty);
 164
 165                     for target in &vis.found {
 166                         if in_external_macro(cx.sess(), generics.span) {
 167                             continue;
 168                         }
 169                         let generics_suggestion_span = generics.span.substitute_dummy({
 170                             let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
 171                                 .and_then(|snip| {
 172                                     let i = snip.find("fn")?;
 173                                     Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
 174                                 })
 175                                 .expect("failed to create span for type parameters");
 176                             Span::new(pos, pos, item.span.data().ctxt)
 177                         });
 178
 179                         let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
 180                         ctr_vis.visit_body(body);
 181
 182                         span_lint_and_then(
 183                             cx,
 184                             IMPLICIT_HASHER,
 185                             target.span(),
 186                             &format!(
 187                                 "parameter of type `{}` should be generalized over different hashers",
 188                                 target.type_name()
 189                             ),
 190                             move |diag| {
 191                                 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
 192                             },
 193                         );
 194                     }
 195                 }
 196             },
 197             _ => {},
 198         }
 199     }
 200 }
 201
 202 enum ImplicitHasherType<'tcx> {
 203     HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
 204     HashSet(Span, Ty<'tcx>, Cow<'static, str>),
 205 }
 206
 207 impl<'tcx> ImplicitHasherType<'tcx> {
 208     /// Checks that `ty` is a target type without a `BuildHasher`.
 209     fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
 210         if let TyKind::Path(QPath::Resolved(None, path)) = hir_ty.kind {
 211             let params: Vec<_> = path
 212                 .segments
 213                 .last()
 214                 .as_ref()?
 215                 .args
 216                 .as_ref()?
 217                 .args
 218                 .iter()
 219                 .filter_map(|arg| match arg {
 220                     GenericArg::Type(ty) => Some(ty),
 221                     _ => None,
 222                 })
 223                 .collect();
 224             let params_len = params.len();
 225
 226             let ty = hir_ty_to_ty(cx.tcx, hir_ty);
 227
 228             if is_type_diagnostic_item(cx, ty, sym::hashmap_type) && params_len == 2 {
 229                 Some(ImplicitHasherType::HashMap(
 230                     hir_ty.span,
 231                     ty,
 232                     snippet(cx, params[0].span, "K"),
 233                     snippet(cx, params[1].span, "V"),
 234                 ))
 235             } else if is_type_diagnostic_item(cx, ty, sym::hashset_type) && params_len == 1 {
 236                 Some(ImplicitHasherType::HashSet(
 237                     hir_ty.span,
 238                     ty,
 239                     snippet(cx, params[0].span, "T"),
 240                 ))
 241             } else {
 242                 None
 243             }
 244         } else {
 245             None
 246         }
 247     }
 248
 249     fn type_name(&self) -> &'static str {
 250         match *self {
 251             ImplicitHasherType::HashMap(..) => "HashMap",
 252             ImplicitHasherType::HashSet(..) => "HashSet",
 253         }
 254     }
 255
 256     fn type_arguments(&self) -> String {
 257         match *self {
 258             ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
 259             ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
 260         }
 261     }
 262
 263     fn ty(&self) -> Ty<'tcx> {
 264         match *self {
 265             ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
 266         }
 267     }
 268
 269     fn span(&self) -> Span {
 270         match *self {
 271             ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
 272         }
 273     }
 274 }
 275
 276 struct ImplicitHasherTypeVisitor<'a, 'tcx> {
 277     cx: &'a LateContext<'tcx>,
 278     found: Vec<ImplicitHasherType<'tcx>>,
 279 }
 280
 281 impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
 282     fn new(cx: &'a LateContext<'tcx>) -> Self {
 283         Self { cx, found: vec![] }
 284     }
 285 }
 286
 287 impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
 288     type Map = Map<'tcx>;
 289
 290     fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
 291         if let Some(target) = ImplicitHasherType::new(self.cx, t) {
 292             self.found.push(target);
 293         }
 294
 295         walk_ty(self, t);
 296     }
 297
 298     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 299         NestedVisitorMap::None
 300     }
 301 }
 302
 303 /// Looks for default-hasher-dependent constructors like `HashMap::new`.
 304 struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
 305     cx: &'a LateContext<'tcx>,
 306     maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
 307     target: &'b ImplicitHasherType<'tcx>,
 308     suggestions: BTreeMap<Span, String>,
 309 }
 310
 311 impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
 312     fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
 313         Self {
 314             cx,
 315             maybe_typeck_results: cx.maybe_typeck_results(),
 316             target,
 317             suggestions: BTreeMap::new(),
 318         }
 319     }
 320 }
 321
 322 impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
 323     type Map = Map<'tcx>;
 324
 325     fn visit_body(&mut self, body: &'tcx Body<'_>) {
 326         let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
 327         walk_body(self, body);
 328         self.maybe_typeck_results = old_maybe_typeck_results;
 329     }
 330
 331     fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
 332         if_chain! {
 333             if let ExprKind::Call(fun, args) = e.kind;
 334             if let ExprKind::Path(QPath::TypeRelative(ty, method)) = fun.kind;
 335             if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
 336             if let Some(ty_did) = ty_path.res.opt_def_id();
 337             then {
 338                 if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
 339                     return;
 340                 }
 341
 342                 if match_def_path(self.cx, ty_did, &paths::HASHMAP) {
 343                     if method.ident.name == sym::new {
 344                         self.suggestions
 345                             .insert(e.span, "HashMap::default()".to_string());
 346                     } else if method.ident.name == sym!(with_capacity) {
 347                         self.suggestions.insert(
 348                             e.span,
 349                             format!(
 350                                 "HashMap::with_capacity_and_hasher({}, Default::default())",
 351                                 snippet(self.cx, args[0].span, "capacity"),
 352                             ),
 353                         );
 354                     }
 355                 } else if match_def_path(self.cx, ty_did, &paths::HASHSET) {
 356                     if method.ident.name == sym::new {
 357                         self.suggestions
 358                             .insert(e.span, "HashSet::default()".to_string());
 359                     } else if method.ident.name == sym!(with_capacity) {
 360                         self.suggestions.insert(
 361                             e.span,
 362                             format!(
 363                                 "HashSet::with_capacity_and_hasher({}, Default::default())",
 364                                 snippet(self.cx, args[0].span, "capacity"),
 365                             ),
 366                         );
 367                     }
 368                 }
 369             }
 370         }
 371
 372         walk_expr(self, e);
 373     }
 374
 375     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 376         NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
 377     }
 378 }