compiler/rustc_lint/src/late.rs

   1 //! Implementation of lint checking.
   2 //!
   3 //! The lint checking is mostly consolidated into one pass which runs
   4 //! after all other analyses. Throughout compilation, lint warnings
   5 //! can be added via the `add_lint` method on the Session structure. This
   6 //! requires a span and an ID of the node that the lint is being added to. The
   7 //! lint isn't actually emitted at that time because it is unknown what the
   8 //! actual lint level at that location is.
   9 //!
  10 //! To actually emit lint warnings/errors, a separate pass is used.
  11 //! A context keeps track of the current state of all lint levels.
  12 //! Upon entering a node of the ast which can modify the lint settings, the
  13 //! previous lint state is pushed onto a stack and the ast is then recursed
  14 //! upon. As the ast is traversed, this keeps track of the current lint level
  15 //! for all lint attributes.
  16
  17 use crate::{passes::LateLintPassObject, LateContext, LateLintPass, LintStore};
  18 use rustc_ast as ast;
  19 use rustc_data_structures::sync::join;
  20 use rustc_hir as hir;
  21 use rustc_hir::def_id::LocalDefId;
  22 use rustc_hir::intravisit as hir_visit;
  23 use rustc_hir::intravisit::Visitor;
  24 use rustc_middle::hir::nested_filter;
  25 use rustc_middle::ty::{self, TyCtxt};
  26 use rustc_session::lint::LintPass;
  27 use rustc_span::Span;
  28
  29 use std::any::Any;
  30 use std::cell::Cell;
  31
  32 /// Extract the `LintStore` from the query context.
  33 /// This function exists because we've erased `LintStore` as `dyn Any` in the context.
  34 pub fn unerased_lint_store(tcx: TyCtxt<'_>) -> &LintStore {
  35     let store: &dyn Any = &*tcx.lint_store;
  36     store.downcast_ref().unwrap()
  37 }
  38
  39 macro_rules! lint_callback { ($cx:expr, $f:ident, $($args:expr),*) => ({
  40     $cx.pass.$f(&$cx.context, $($args),*);
  41 }) }
  42
  43 /// Implements the AST traversal for late lint passes. `T` provides the
  44 /// `check_*` methods.
  45 pub struct LateContextAndPass<'tcx, T: LateLintPass<'tcx>> {
  46     context: LateContext<'tcx>,
  47     pass: T,
  48 }
  49
  50 impl<'tcx, T: LateLintPass<'tcx>> LateContextAndPass<'tcx, T> {
  51     /// Merge the lints specified by any lint attributes into the
  52     /// current lint context, call the provided function, then reset the
  53     /// lints in effect to their previous state.
  54     fn with_lint_attrs<F>(&mut self, id: hir::HirId, f: F)
  55     where
  56         F: FnOnce(&mut Self),
  57     {
  58         let attrs = self.context.tcx.hir().attrs(id);
  59         let prev = self.context.last_node_with_lint_attrs;
  60         self.context.last_node_with_lint_attrs = id;
  61         debug!("late context: enter_attrs({:?})", attrs);
  62         lint_callback!(self, enter_lint_attrs, attrs);
  63         f(self);
  64         debug!("late context: exit_attrs({:?})", attrs);
  65         lint_callback!(self, exit_lint_attrs, attrs);
  66         self.context.last_node_with_lint_attrs = prev;
  67     }
  68
  69     fn with_param_env<F>(&mut self, id: hir::HirId, f: F)
  70     where
  71         F: FnOnce(&mut Self),
  72     {
  73         let old_param_env = self.context.param_env;
  74         self.context.param_env =
  75             self.context.tcx.param_env(self.context.tcx.hir().local_def_id(id));
  76         f(self);
  77         self.context.param_env = old_param_env;
  78     }
  79
  80     fn process_mod(&mut self, m: &'tcx hir::Mod<'tcx>, n: hir::HirId) {
  81         lint_callback!(self, check_mod, m, n);
  82         hir_visit::walk_mod(self, m, n);
  83     }
  84 }
  85
  86 impl<'tcx, T: LateLintPass<'tcx>> hir_visit::Visitor<'tcx> for LateContextAndPass<'tcx, T> {
  87     type NestedFilter = nested_filter::All;
  88
  89     /// Because lints are scoped lexically, we want to walk nested
  90     /// items in the context of the outer item, so enable
  91     /// deep-walking.
  92     fn nested_visit_map(&mut self) -> Self::Map {
  93         self.context.tcx.hir()
  94     }
  95
  96     fn visit_nested_body(&mut self, body_id: hir::BodyId) {
  97         let old_enclosing_body = self.context.enclosing_body.replace(body_id);
  98         let old_cached_typeck_results = self.context.cached_typeck_results.get();
  99
 100         // HACK(eddyb) avoid trashing `cached_typeck_results` when we're
 101         // nested in `visit_fn`, which may have already resulted in them
 102         // being queried.
 103         if old_enclosing_body != Some(body_id) {
 104             self.context.cached_typeck_results.set(None);
 105         }
 106
 107         let body = self.context.tcx.hir().body(body_id);
 108         self.visit_body(body);
 109         self.context.enclosing_body = old_enclosing_body;
 110
 111         // See HACK comment above.
 112         if old_enclosing_body != Some(body_id) {
 113             self.context.cached_typeck_results.set(old_cached_typeck_results);
 114         }
 115     }
 116
 117     fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
 118         self.with_lint_attrs(param.hir_id, |cx| {
 119             hir_visit::walk_param(cx, param);
 120         });
 121     }
 122
 123     fn visit_body(&mut self, body: &'tcx hir::Body<'tcx>) {
 124         lint_callback!(self, check_body, body);
 125         hir_visit::walk_body(self, body);
 126         lint_callback!(self, check_body_post, body);
 127     }
 128
 129     fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) {
 130         let generics = self.context.generics.take();
 131         self.context.generics = it.kind.generics();
 132         let old_cached_typeck_results = self.context.cached_typeck_results.take();
 133         let old_enclosing_body = self.context.enclosing_body.take();
 134         self.with_lint_attrs(it.hir_id(), |cx| {
 135             cx.with_param_env(it.hir_id(), |cx| {
 136                 lint_callback!(cx, check_item, it);
 137                 hir_visit::walk_item(cx, it);
 138                 lint_callback!(cx, check_item_post, it);
 139             });
 140         });
 141         self.context.enclosing_body = old_enclosing_body;
 142         self.context.cached_typeck_results.set(old_cached_typeck_results);
 143         self.context.generics = generics;
 144     }
 145
 146     fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {
 147         self.with_lint_attrs(it.hir_id(), |cx| {
 148             cx.with_param_env(it.hir_id(), |cx| {
 149                 lint_callback!(cx, check_foreign_item, it);
 150                 hir_visit::walk_foreign_item(cx, it);
 151             });
 152         })
 153     }
 154
 155     fn visit_pat(&mut self, p: &'tcx hir::Pat<'tcx>) {
 156         lint_callback!(self, check_pat, p);
 157         hir_visit::walk_pat(self, p);
 158     }
 159
 160     fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
 161         self.with_lint_attrs(e.hir_id, |cx| {
 162             lint_callback!(cx, check_expr, e);
 163             hir_visit::walk_expr(cx, e);
 164             lint_callback!(cx, check_expr_post, e);
 165         })
 166     }
 167
 168     fn visit_stmt(&mut self, s: &'tcx hir::Stmt<'tcx>) {
 169         // See `EarlyContextAndPass::visit_stmt` for an explanation
 170         // of why we call `walk_stmt` outside of `with_lint_attrs`
 171         self.with_lint_attrs(s.hir_id, |cx| {
 172             lint_callback!(cx, check_stmt, s);
 173         });
 174         hir_visit::walk_stmt(self, s);
 175     }
 176
 177     fn visit_fn(
 178         &mut self,
 179         fk: hir_visit::FnKind<'tcx>,
 180         decl: &'tcx hir::FnDecl<'tcx>,
 181         body_id: hir::BodyId,
 182         span: Span,
 183         id: hir::HirId,
 184     ) {
 185         // Wrap in typeck results here, not just in visit_nested_body,
 186         // in order for `check_fn` to be able to use them.
 187         let old_enclosing_body = self.context.enclosing_body.replace(body_id);
 188         let old_cached_typeck_results = self.context.cached_typeck_results.take();
 189         let body = self.context.tcx.hir().body(body_id);
 190         lint_callback!(self, check_fn, fk, decl, body, span, id);
 191         hir_visit::walk_fn(self, fk, decl, body_id, id);
 192         self.context.enclosing_body = old_enclosing_body;
 193         self.context.cached_typeck_results.set(old_cached_typeck_results);
 194     }
 195
 196     fn visit_variant_data(&mut self, s: &'tcx hir::VariantData<'tcx>) {
 197         lint_callback!(self, check_struct_def, s);
 198         hir_visit::walk_struct_def(self, s);
 199     }
 200
 201     fn visit_field_def(&mut self, s: &'tcx hir::FieldDef<'tcx>) {
 202         self.with_lint_attrs(s.hir_id, |cx| {
 203             lint_callback!(cx, check_field_def, s);
 204             hir_visit::walk_field_def(cx, s);
 205         })
 206     }
 207
 208     fn visit_variant(&mut self, v: &'tcx hir::Variant<'tcx>) {
 209         self.with_lint_attrs(v.hir_id, |cx| {
 210             lint_callback!(cx, check_variant, v);
 211             hir_visit::walk_variant(cx, v);
 212         })
 213     }
 214
 215     fn visit_ty(&mut self, t: &'tcx hir::Ty<'tcx>) {
 216         lint_callback!(self, check_ty, t);
 217         hir_visit::walk_ty(self, t);
 218     }
 219
 220     fn visit_infer(&mut self, inf: &'tcx hir::InferArg) {
 221         hir_visit::walk_inf(self, inf);
 222     }
 223
 224     fn visit_mod(&mut self, m: &'tcx hir::Mod<'tcx>, _: Span, n: hir::HirId) {
 225         if !self.context.only_module {
 226             self.process_mod(m, n);
 227         }
 228     }
 229
 230     fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>) {
 231         self.with_lint_attrs(l.hir_id, |cx| {
 232             lint_callback!(cx, check_local, l);
 233             hir_visit::walk_local(cx, l);
 234         })
 235     }
 236
 237     fn visit_block(&mut self, b: &'tcx hir::Block<'tcx>) {
 238         lint_callback!(self, check_block, b);
 239         hir_visit::walk_block(self, b);
 240         lint_callback!(self, check_block_post, b);
 241     }
 242
 243     fn visit_arm(&mut self, a: &'tcx hir::Arm<'tcx>) {
 244         lint_callback!(self, check_arm, a);
 245         hir_visit::walk_arm(self, a);
 246     }
 247
 248     fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
 249         lint_callback!(self, check_generic_param, p);
 250         hir_visit::walk_generic_param(self, p);
 251     }
 252
 253     fn visit_generics(&mut self, g: &'tcx hir::Generics<'tcx>) {
 254         lint_callback!(self, check_generics, g);
 255         hir_visit::walk_generics(self, g);
 256     }
 257
 258     fn visit_where_predicate(&mut self, p: &'tcx hir::WherePredicate<'tcx>) {
 259         hir_visit::walk_where_predicate(self, p);
 260     }
 261
 262     fn visit_poly_trait_ref(&mut self, t: &'tcx hir::PolyTraitRef<'tcx>) {
 263         lint_callback!(self, check_poly_trait_ref, t);
 264         hir_visit::walk_poly_trait_ref(self, t);
 265     }
 266
 267     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
 268         let generics = self.context.generics.take();
 269         self.context.generics = Some(&trait_item.generics);
 270         self.with_lint_attrs(trait_item.hir_id(), |cx| {
 271             cx.with_param_env(trait_item.hir_id(), |cx| {
 272                 lint_callback!(cx, check_trait_item, trait_item);
 273                 hir_visit::walk_trait_item(cx, trait_item);
 274             });
 275         });
 276         self.context.generics = generics;
 277     }
 278
 279     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 280         let generics = self.context.generics.take();
 281         self.context.generics = Some(&impl_item.generics);
 282         self.with_lint_attrs(impl_item.hir_id(), |cx| {
 283             cx.with_param_env(impl_item.hir_id(), |cx| {
 284                 lint_callback!(cx, check_impl_item, impl_item);
 285                 hir_visit::walk_impl_item(cx, impl_item);
 286                 lint_callback!(cx, check_impl_item_post, impl_item);
 287             });
 288         });
 289         self.context.generics = generics;
 290     }
 291
 292     fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
 293         hir_visit::walk_lifetime(self, lt);
 294     }
 295
 296     fn visit_path(&mut self, p: &hir::Path<'tcx>, id: hir::HirId) {
 297         lint_callback!(self, check_path, p, id);
 298         hir_visit::walk_path(self, p);
 299     }
 300
 301     fn visit_attribute(&mut self, attr: &'tcx ast::Attribute) {
 302         lint_callback!(self, check_attribute, attr);
 303     }
 304 }
 305
 306 // Combines multiple lint passes into a single pass, at runtime. Each
 307 // `check_foo` method in `$methods` within this pass simply calls `check_foo`
 308 // once per `$pass`. Compare with `declare_combined_late_lint_pass`, which is
 309 // similar, but combines lint passes at compile time.
 310 struct RuntimeCombinedLateLintPass<'a, 'tcx> {
 311     passes: &'a mut [LateLintPassObject<'tcx>],
 312 }
 313
 314 #[allow(rustc::lint_pass_impl_without_macro)]
 315 impl LintPass for RuntimeCombinedLateLintPass<'_, '_> {
 316     fn name(&self) -> &'static str {
 317         panic!()
 318     }
 319 }
 320
 321 macro_rules! impl_late_lint_pass {
 322     ([], [$($(#[$attr:meta])* fn $f:ident($($param:ident: $arg:ty),*);)*]) => {
 323         impl<'tcx> LateLintPass<'tcx> for RuntimeCombinedLateLintPass<'_, 'tcx> {
 324             $(fn $f(&mut self, context: &LateContext<'tcx>, $($param: $arg),*) {
 325                 for pass in self.passes.iter_mut() {
 326                     pass.$f(context, $($param),*);
 327                 }
 328             })*
 329         }
 330     };
 331 }
 332
 333 crate::late_lint_methods!(impl_late_lint_pass, []);
 334
 335 pub(super) fn late_lint_mod<'tcx, T: LateLintPass<'tcx> + 'tcx>(
 336     tcx: TyCtxt<'tcx>,
 337     module_def_id: LocalDefId,
 338     builtin_lints: T,
 339 ) {
 340     let context = LateContext {
 341         tcx,
 342         enclosing_body: None,
 343         cached_typeck_results: Cell::new(None),
 344         param_env: ty::ParamEnv::empty(),
 345         effective_visibilities: &tcx.effective_visibilities(()),
 346         lint_store: unerased_lint_store(tcx),
 347         last_node_with_lint_attrs: tcx.hir().local_def_id_to_hir_id(module_def_id),
 348         generics: None,
 349         only_module: true,
 350     };
 351
 352     // Note: `passes` is often empty. In that case, it's faster to run
 353     // `builtin_lints` directly rather than bundling it up into the
 354     // `RuntimeCombinedLateLintPass`.
 355     let mut passes: Vec<_> =
 356         unerased_lint_store(tcx).late_module_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();
 357     if passes.is_empty() {
 358         late_lint_mod_inner(tcx, module_def_id, context, builtin_lints);
 359     } else {
 360         passes.push(Box::new(builtin_lints));
 361         let pass = RuntimeCombinedLateLintPass { passes: &mut passes[..] };
 362         late_lint_mod_inner(tcx, module_def_id, context, pass);
 363     }
 364 }
 365
 366 fn late_lint_mod_inner<'tcx, T: LateLintPass<'tcx>>(
 367     tcx: TyCtxt<'tcx>,
 368     module_def_id: LocalDefId,
 369     context: LateContext<'tcx>,
 370     pass: T,
 371 ) {
 372     let mut cx = LateContextAndPass { context, pass };
 373
 374     let (module, _span, hir_id) = tcx.hir().get_module(module_def_id);
 375     cx.process_mod(module, hir_id);
 376
 377     // Visit the crate attributes
 378     if hir_id == hir::CRATE_HIR_ID {
 379         for attr in tcx.hir().attrs(hir::CRATE_HIR_ID).iter() {
 380             cx.visit_attribute(attr)
 381         }
 382     }
 383 }
 384
 385 fn late_lint_crate<'tcx, T: LateLintPass<'tcx> + 'tcx>(tcx: TyCtxt<'tcx>, builtin_lints: T) {
 386     let context = LateContext {
 387         tcx,
 388         enclosing_body: None,
 389         cached_typeck_results: Cell::new(None),
 390         param_env: ty::ParamEnv::empty(),
 391         effective_visibilities: &tcx.effective_visibilities(()),
 392         lint_store: unerased_lint_store(tcx),
 393         last_node_with_lint_attrs: hir::CRATE_HIR_ID,
 394         generics: None,
 395         only_module: false,
 396     };
 397
 398     // Note: `passes` is often empty. In that case, it's faster to run
 399     // `builtin_lints` directly rather than bundling it up into the
 400     // `RuntimeCombinedLateLintPass`.
 401     let mut passes: Vec<_> =
 402         unerased_lint_store(tcx).late_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();
 403     if passes.is_empty() {
 404         late_lint_crate_inner(tcx, context, builtin_lints);
 405     } else {
 406         passes.push(Box::new(builtin_lints));
 407         let pass = RuntimeCombinedLateLintPass { passes: &mut passes[..] };
 408         late_lint_crate_inner(tcx, context, pass);
 409     }
 410 }
 411
 412 fn late_lint_crate_inner<'tcx, T: LateLintPass<'tcx>>(
 413     tcx: TyCtxt<'tcx>,
 414     context: LateContext<'tcx>,
 415     pass: T,
 416 ) {
 417     let mut cx = LateContextAndPass { context, pass };
 418
 419     // Visit the whole crate.
 420     cx.with_lint_attrs(hir::CRATE_HIR_ID, |cx| {
 421         // Since the root module isn't visited as an item (because it isn't an
 422         // item), warn for it here.
 423         lint_callback!(cx, check_crate,);
 424         tcx.hir().walk_toplevel_module(cx);
 425         tcx.hir().walk_attributes(cx);
 426         lint_callback!(cx, check_crate_post,);
 427     })
 428 }
 429
 430 /// Performs lint checking on a crate.
 431 pub fn check_crate<'tcx, T: LateLintPass<'tcx> + 'tcx>(
 432     tcx: TyCtxt<'tcx>,
 433     builtin_lints: impl FnOnce() -> T + Send,
 434 ) {
 435     join(
 436         || {
 437             tcx.sess.time("crate_lints", || {
 438                 // Run whole crate non-incremental lints
 439                 late_lint_crate(tcx, builtin_lints());
 440             });
 441         },
 442         || {
 443             tcx.sess.time("module_lints", || {
 444                 // Run per-module lints
 445                 tcx.hir().par_for_each_module(|module| tcx.ensure().lint_mod(module));
 446             });
 447         },
 448     );
 449 }