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