compiler/rustc_lint/src/levels.rs

   1 use crate::context::{CheckLintNameResult, LintStore};
   2 use crate::late::unerased_lint_store;
   3 use rustc_ast as ast;
   4 use rustc_ast::attr;
   5 use rustc_ast::unwrap_or;
   6 use rustc_ast_pretty::pprust;
   7 use rustc_data_structures::fx::FxHashMap;
   8 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
   9 use rustc_hir as hir;
  10 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
  11 use rustc_hir::{intravisit, HirId};
  12 use rustc_middle::hir::map::Map;
  13 use rustc_middle::lint::LevelAndSource;
  14 use rustc_middle::lint::LintDiagnosticBuilder;
  15 use rustc_middle::lint::{
  16     struct_lint_level, LintLevelMap, LintLevelSets, LintLevelSource, LintSet,
  17 };
  18 use rustc_middle::ty::query::Providers;
  19 use rustc_middle::ty::TyCtxt;
  20 use rustc_session::lint::{
  21     builtin::{self, FORBIDDEN_LINT_GROUPS},
  22     Level, Lint, LintId,
  23 };
  24 use rustc_session::parse::feature_err;
  25 use rustc_session::Session;
  26 use rustc_span::symbol::{sym, Symbol};
  27 use rustc_span::{source_map::MultiSpan, Span, DUMMY_SP};
  28 use tracing::debug;
  29
  30 use std::cmp;
  31
  32 fn lint_levels(tcx: TyCtxt<'_>, cnum: CrateNum) -> LintLevelMap {
  33     assert_eq!(cnum, LOCAL_CRATE);
  34     let store = unerased_lint_store(tcx);
  35     let levels = LintLevelsBuilder::new(tcx.sess, false, &store);
  36     let mut builder = LintLevelMapBuilder { levels, tcx, store };
  37     let krate = tcx.hir().krate();
  38
  39     builder.levels.id_to_set.reserve(krate.exported_macros.len() + 1);
  40
  41     let push = builder.levels.push(tcx.hir().attrs(hir::CRATE_HIR_ID), &store, true);
  42     builder.levels.register_id(hir::CRATE_HIR_ID);
  43     for macro_def in krate.exported_macros {
  44         builder.levels.register_id(macro_def.hir_id());
  45     }
  46     intravisit::walk_crate(&mut builder, krate);
  47     builder.levels.pop(push);
  48
  49     builder.levels.build_map()
  50 }
  51
  52 pub struct LintLevelsBuilder<'s> {
  53     sess: &'s Session,
  54     sets: LintLevelSets,
  55     id_to_set: FxHashMap<HirId, u32>,
  56     cur: u32,
  57     warn_about_weird_lints: bool,
  58     store: &'s LintStore,
  59 }
  60
  61 pub struct BuilderPush {
  62     prev: u32,
  63     pub changed: bool,
  64 }
  65
  66 impl<'s> LintLevelsBuilder<'s> {
  67     pub fn new(sess: &'s Session, warn_about_weird_lints: bool, store: &'s LintStore) -> Self {
  68         let mut builder = LintLevelsBuilder {
  69             sess,
  70             sets: LintLevelSets::new(),
  71             cur: 0,
  72             id_to_set: Default::default(),
  73             warn_about_weird_lints,
  74             store,
  75         };
  76         builder.process_command_line(sess, store);
  77         assert_eq!(builder.sets.list.len(), 1);
  78         builder
  79     }
  80
  81     fn process_command_line(&mut self, sess: &Session, store: &LintStore) {
  82         let mut specs = FxHashMap::default();
  83         self.sets.lint_cap = sess.opts.lint_cap.unwrap_or(Level::Forbid);
  84
  85         for &(ref lint_name, level) in &sess.opts.lint_opts {
  86             store.check_lint_name_cmdline(sess, &lint_name, level);
  87             let orig_level = level;
  88
  89             // If the cap is less than this specified level, e.g., if we've got
  90             // `--cap-lints allow` but we've also got `-D foo` then we ignore
  91             // this specification as the lint cap will set it to allow anyway.
  92             let level = cmp::min(level, self.sets.lint_cap);
  93
  94             let lint_flag_val = Symbol::intern(lint_name);
  95
  96             let ids = match store.find_lints(&lint_name) {
  97                 Ok(ids) => ids,
  98                 Err(_) => continue, // errors handled in check_lint_name_cmdline above
  99             };
 100             for id in ids {
 101                 self.check_gated_lint(id, DUMMY_SP);
 102                 let src = LintLevelSource::CommandLine(lint_flag_val, orig_level);
 103                 specs.insert(id, (level, src));
 104             }
 105         }
 106
 107         self.sets.list.push(LintSet::CommandLine { specs });
 108     }
 109
 110     /// Attempts to insert the `id` to `level_src` map entry. If unsuccessful
 111     /// (e.g. if a forbid was already inserted on the same scope), then emits a
 112     /// diagnostic with no change to `specs`.
 113     fn insert_spec(
 114         &mut self,
 115         specs: &mut FxHashMap<LintId, LevelAndSource>,
 116         id: LintId,
 117         (level, src): LevelAndSource,
 118     ) {
 119         // Setting to a non-forbid level is an error if the lint previously had
 120         // a forbid level. Note that this is not necessarily true even with a
 121         // `#[forbid(..)]` attribute present, as that is overriden by `--cap-lints`.
 122         //
 123         // This means that this only errors if we're truly lowering the lint
 124         // level from forbid.
 125         if level != Level::Forbid {
 126             if let (Level::Forbid, old_src) =
 127                 self.sets.get_lint_level(id.lint, self.cur, Some(&specs), &self.sess)
 128             {
 129                 // Backwards compatibility check:
 130                 //
 131                 // We used to not consider `forbid(lint_group)`
 132                 // as preventing `allow(lint)` for some lint `lint` in
 133                 // `lint_group`. For now, issue a future-compatibility
 134                 // warning for this case.
 135                 let id_name = id.lint.name_lower();
 136                 let fcw_warning = match old_src {
 137                     LintLevelSource::Default => false,
 138                     LintLevelSource::Node(symbol, _, _) => self.store.is_lint_group(symbol),
 139                     LintLevelSource::CommandLine(symbol, _) => self.store.is_lint_group(symbol),
 140                 };
 141                 debug!(
 142                     "fcw_warning={:?}, specs.get(&id) = {:?}, old_src={:?}, id_name={:?}",
 143                     fcw_warning, specs, old_src, id_name
 144                 );
 145
 146                 let decorate_diag_builder = |mut diag_builder: DiagnosticBuilder<'_>| {
 147                     diag_builder.span_label(src.span(), "overruled by previous forbid");
 148                     match old_src {
 149                         LintLevelSource::Default => {
 150                             diag_builder.note(&format!(
 151                                 "`forbid` lint level is the default for {}",
 152                                 id.to_string()
 153                             ));
 154                         }
 155                         LintLevelSource::Node(_, forbid_source_span, reason) => {
 156                             diag_builder.span_label(forbid_source_span, "`forbid` level set here");
 157                             if let Some(rationale) = reason {
 158                                 diag_builder.note(&rationale.as_str());
 159                             }
 160                         }
 161                         LintLevelSource::CommandLine(_, _) => {
 162                             diag_builder.note("`forbid` lint level was set on command line");
 163                         }
 164                     }
 165                     diag_builder.emit();
 166                 };
 167                 if !fcw_warning {
 168                     let diag_builder = struct_span_err!(
 169                         self.sess,
 170                         src.span(),
 171                         E0453,
 172                         "{}({}) incompatible with previous forbid",
 173                         level.as_str(),
 174                         src.name(),
 175                     );
 176                     decorate_diag_builder(diag_builder);
 177                 } else {
 178                     self.struct_lint(
 179                         FORBIDDEN_LINT_GROUPS,
 180                         Some(src.span().into()),
 181                         |diag_builder| {
 182                             let diag_builder = diag_builder.build(&format!(
 183                                 "{}({}) incompatible with previous forbid",
 184                                 level.as_str(),
 185                                 src.name(),
 186                             ));
 187                             decorate_diag_builder(diag_builder);
 188                         },
 189                     );
 190                 }
 191
 192                 // Retain the forbid lint level, unless we are
 193                 // issuing a FCW. In the FCW case, we want to
 194                 // respect the new setting.
 195                 if !fcw_warning {
 196                     return;
 197                 }
 198             }
 199         }
 200         specs.insert(id, (level, src));
 201     }
 202
 203     /// Pushes a list of AST lint attributes onto this context.
 204     ///
 205     /// This function will return a `BuilderPush` object which should be passed
 206     /// to `pop` when this scope for the attributes provided is exited.
 207     ///
 208     /// This function will perform a number of tasks:
 209     ///
 210     /// * It'll validate all lint-related attributes in `attrs`
 211     /// * It'll mark all lint-related attributes as used
 212     /// * Lint levels will be updated based on the attributes provided
 213     /// * Lint attributes are validated, e.g., a `#[forbid]` can't be switched to
 214     ///   `#[allow]`
 215     ///
 216     /// Don't forget to call `pop`!
 217     pub(crate) fn push(
 218         &mut self,
 219         attrs: &[ast::Attribute],
 220         store: &LintStore,
 221         is_crate_node: bool,
 222     ) -> BuilderPush {
 223         let mut specs = FxHashMap::default();
 224         let sess = self.sess;
 225         let bad_attr = |span| struct_span_err!(sess, span, E0452, "malformed lint attribute input");
 226         for attr in attrs {
 227             let level = match Level::from_symbol(attr.name_or_empty()) {
 228                 None => continue,
 229                 Some(lvl) => lvl,
 230             };
 231
 232             let meta = unwrap_or!(attr.meta(), continue);
 233             self.sess.mark_attr_used(attr);
 234
 235             let mut metas = unwrap_or!(meta.meta_item_list(), continue);
 236
 237             if metas.is_empty() {
 238                 // FIXME (#55112): issue unused-attributes lint for `#[level()]`
 239                 continue;
 240             }
 241
 242             // Before processing the lint names, look for a reason (RFC 2383)
 243             // at the end.
 244             let mut reason = None;
 245             let tail_li = &metas[metas.len() - 1];
 246             if let Some(item) = tail_li.meta_item() {
 247                 match item.kind {
 248                     ast::MetaItemKind::Word => {} // actual lint names handled later
 249                     ast::MetaItemKind::NameValue(ref name_value) => {
 250                         if item.path == sym::reason {
 251                             // found reason, reslice meta list to exclude it
 252                             metas = &metas[0..metas.len() - 1];
 253                             // FIXME (#55112): issue unused-attributes lint if we thereby
 254                             // don't have any lint names (`#[level(reason = "foo")]`)
 255                             if let ast::LitKind::Str(rationale, _) = name_value.kind {
 256                                 if !self.sess.features_untracked().lint_reasons {
 257                                     feature_err(
 258                                         &self.sess.parse_sess,
 259                                         sym::lint_reasons,
 260                                         item.span,
 261                                         "lint reasons are experimental",
 262                                     )
 263                                     .emit();
 264                                 }
 265                                 reason = Some(rationale);
 266                             } else {
 267                                 bad_attr(name_value.span)
 268                                     .span_label(name_value.span, "reason must be a string literal")
 269                                     .emit();
 270                             }
 271                         } else {
 272                             bad_attr(item.span)
 273                                 .span_label(item.span, "bad attribute argument")
 274                                 .emit();
 275                         }
 276                     }
 277                     ast::MetaItemKind::List(_) => {
 278                         bad_attr(item.span).span_label(item.span, "bad attribute argument").emit();
 279                     }
 280                 }
 281             }
 282
 283             for li in metas {
 284                 let meta_item = match li.meta_item() {
 285                     Some(meta_item) if meta_item.is_word() => meta_item,
 286                     _ => {
 287                         let sp = li.span();
 288                         let mut err = bad_attr(sp);
 289                         let mut add_label = true;
 290                         if let Some(item) = li.meta_item() {
 291                             if let ast::MetaItemKind::NameValue(_) = item.kind {
 292                                 if item.path == sym::reason {
 293                                     err.span_label(sp, "reason in lint attribute must come last");
 294                                     add_label = false;
 295                                 }
 296                             }
 297                         }
 298                         if add_label {
 299                             err.span_label(sp, "bad attribute argument");
 300                         }
 301                         err.emit();
 302                         continue;
 303                     }
 304                 };
 305                 let tool_name = if meta_item.path.segments.len() > 1 {
 306                     let tool_ident = meta_item.path.segments[0].ident;
 307                     if !attr::is_known_lint_tool(tool_ident) {
 308                         struct_span_err!(
 309                             sess,
 310                             tool_ident.span,
 311                             E0710,
 312                             "an unknown tool name found in scoped lint: `{}`",
 313                             pprust::path_to_string(&meta_item.path),
 314                         )
 315                         .emit();
 316                         continue;
 317                     }
 318
 319                     Some(tool_ident.name)
 320                 } else {
 321                     None
 322                 };
 323                 let name = meta_item.path.segments.last().expect("empty lint name").ident.name;
 324                 let lint_result = store.check_lint_name(&name.as_str(), tool_name);
 325                 match &lint_result {
 326                     CheckLintNameResult::Ok(ids) => {
 327                         let src = LintLevelSource::Node(name, li.span(), reason);
 328                         for &id in *ids {
 329                             self.check_gated_lint(id, attr.span);
 330                             self.insert_spec(&mut specs, id, (level, src));
 331                         }
 332                     }
 333
 334                     CheckLintNameResult::Tool(result) => {
 335                         match *result {
 336                             Ok(ids) => {
 337                                 let complete_name = &format!("{}::{}", tool_name.unwrap(), name);
 338                                 let src = LintLevelSource::Node(
 339                                     Symbol::intern(complete_name),
 340                                     li.span(),
 341                                     reason,
 342                                 );
 343                                 for id in ids {
 344                                     self.insert_spec(&mut specs, *id, (level, src));
 345                                 }
 346                             }
 347                             Err((Some(ids), ref new_lint_name)) => {
 348                                 let lint = builtin::RENAMED_AND_REMOVED_LINTS;
 349                                 let (lvl, src) =
 350                                     self.sets.get_lint_level(lint, self.cur, Some(&specs), &sess);
 351                                 struct_lint_level(
 352                                     self.sess,
 353                                     lint,
 354                                     lvl,
 355                                     src,
 356                                     Some(li.span().into()),
 357                                     |lint| {
 358                                         let msg = format!(
 359                                             "lint name `{}` is deprecated \
 360                                              and may not have an effect in the future.",
 361                                             name
 362                                         );
 363                                         lint.build(&msg)
 364                                             .span_suggestion(
 365                                                 li.span(),
 366                                                 "change it to",
 367                                                 new_lint_name.to_string(),
 368                                                 Applicability::MachineApplicable,
 369                                             )
 370                                             .emit();
 371                                     },
 372                                 );
 373
 374                                 let src = LintLevelSource::Node(
 375                                     Symbol::intern(&new_lint_name),
 376                                     li.span(),
 377                                     reason,
 378                                 );
 379                                 for id in ids {
 380                                     self.insert_spec(&mut specs, *id, (level, src));
 381                                 }
 382                             }
 383                             Err((None, _)) => {
 384                                 // If Tool(Err(None, _)) is returned, then either the lint does not
 385                                 // exist in the tool or the code was not compiled with the tool and
 386                                 // therefore the lint was never added to the `LintStore`. To detect
 387                                 // this is the responsibility of the lint tool.
 388                             }
 389                         }
 390                     }
 391
 392                     _ if !self.warn_about_weird_lints => {}
 393
 394                     CheckLintNameResult::Warning(msg, renamed) => {
 395                         let lint = builtin::RENAMED_AND_REMOVED_LINTS;
 396                         let (renamed_lint_level, src) =
 397                             self.sets.get_lint_level(lint, self.cur, Some(&specs), &sess);
 398                         struct_lint_level(
 399                             self.sess,
 400                             lint,
 401                             renamed_lint_level,
 402                             src,
 403                             Some(li.span().into()),
 404                             |lint| {
 405                                 let mut err = lint.build(&msg);
 406                                 if let Some(new_name) = &renamed {
 407                                     err.span_suggestion(
 408                                         li.span(),
 409                                         "use the new name",
 410                                         new_name.to_string(),
 411                                         Applicability::MachineApplicable,
 412                                     );
 413                                 }
 414                                 err.emit();
 415                             },
 416                         );
 417                     }
 418                     CheckLintNameResult::NoLint(suggestion) => {
 419                         let lint = builtin::UNKNOWN_LINTS;
 420                         let (level, src) =
 421                             self.sets.get_lint_level(lint, self.cur, Some(&specs), self.sess);
 422                         struct_lint_level(
 423                             self.sess,
 424                             lint,
 425                             level,
 426                             src,
 427                             Some(li.span().into()),
 428                             |lint| {
 429                                 let name = if let Some(tool_name) = tool_name {
 430                                     format!("{}::{}", tool_name, name)
 431                                 } else {
 432                                     name.to_string()
 433                                 };
 434                                 let mut db = lint.build(&format!("unknown lint: `{}`", name));
 435                                 if let Some(suggestion) = suggestion {
 436                                     db.span_suggestion(
 437                                         li.span(),
 438                                         "did you mean",
 439                                         suggestion.to_string(),
 440                                         Applicability::MachineApplicable,
 441                                     );
 442                                 }
 443                                 db.emit();
 444                             },
 445                         );
 446                     }
 447                 }
 448                 // If this lint was renamed, apply the new lint instead of ignoring the attribute.
 449                 // This happens outside of the match because the new lint should be applied even if
 450                 // we don't warn about the name change.
 451                 if let CheckLintNameResult::Warning(_, Some(new_name)) = lint_result {
 452                     // Ignore any errors or warnings that happen because the new name is inaccurate
 453                     if let CheckLintNameResult::Ok(ids) =
 454                         store.check_lint_name(&new_name, tool_name)
 455                     {
 456                         let src =
 457                             LintLevelSource::Node(Symbol::intern(&new_name), li.span(), reason);
 458                         for &id in ids {
 459                             self.check_gated_lint(id, attr.span);
 460                             self.insert_spec(&mut specs, id, (level, src));
 461                         }
 462                     }
 463                 }
 464             }
 465         }
 466
 467         if !is_crate_node {
 468             for (id, &(level, ref src)) in specs.iter() {
 469                 if !id.lint.crate_level_only {
 470                     continue;
 471                 }
 472
 473                 let (lint_attr_name, lint_attr_span) = match *src {
 474                     LintLevelSource::Node(name, span, _) => (name, span),
 475                     _ => continue,
 476                 };
 477
 478                 let lint = builtin::UNUSED_ATTRIBUTES;
 479                 let (lint_level, lint_src) =
 480                     self.sets.get_lint_level(lint, self.cur, Some(&specs), self.sess);
 481                 struct_lint_level(
 482                     self.sess,
 483                     lint,
 484                     lint_level,
 485                     lint_src,
 486                     Some(lint_attr_span.into()),
 487                     |lint| {
 488                         let mut db = lint.build(&format!(
 489                             "{}({}) is ignored unless specified at crate level",
 490                             level.as_str(),
 491                             lint_attr_name
 492                         ));
 493                         db.emit();
 494                     },
 495                 );
 496                 // don't set a separate error for every lint in the group
 497                 break;
 498             }
 499         }
 500
 501         let prev = self.cur;
 502         if !specs.is_empty() {
 503             self.cur = self.sets.list.len() as u32;
 504             self.sets.list.push(LintSet::Node { specs, parent: prev });
 505         }
 506
 507         BuilderPush { prev, changed: prev != self.cur }
 508     }
 509
 510     /// Checks if the lint is gated on a feature that is not enabled.
 511     fn check_gated_lint(&self, lint_id: LintId, span: Span) {
 512         if let Some(feature) = lint_id.lint.feature_gate {
 513             if !self.sess.features_untracked().enabled(feature) {
 514                 feature_err(
 515                     &self.sess.parse_sess,
 516                     feature,
 517                     span,
 518                     &format!("the `{}` lint is unstable", lint_id.lint.name_lower()),
 519                 )
 520                 .emit();
 521             }
 522         }
 523     }
 524
 525     /// Called after `push` when the scope of a set of attributes are exited.
 526     pub fn pop(&mut self, push: BuilderPush) {
 527         self.cur = push.prev;
 528     }
 529
 530     /// Find the lint level for a lint.
 531     pub fn lint_level(&self, lint: &'static Lint) -> (Level, LintLevelSource) {
 532         self.sets.get_lint_level(lint, self.cur, None, self.sess)
 533     }
 534
 535     /// Used to emit a lint-related diagnostic based on the current state of
 536     /// this lint context.
 537     pub fn struct_lint(
 538         &self,
 539         lint: &'static Lint,
 540         span: Option<MultiSpan>,
 541         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 542     ) {
 543         let (level, src) = self.lint_level(lint);
 544         struct_lint_level(self.sess, lint, level, src, span, decorate)
 545     }
 546
 547     /// Registers the ID provided with the current set of lints stored in
 548     /// this context.
 549     pub fn register_id(&mut self, id: HirId) {
 550         self.id_to_set.insert(id, self.cur);
 551     }
 552
 553     pub fn build(self) -> LintLevelSets {
 554         self.sets
 555     }
 556
 557     pub fn build_map(self) -> LintLevelMap {
 558         LintLevelMap { sets: self.sets, id_to_set: self.id_to_set }
 559     }
 560 }
 561
 562 struct LintLevelMapBuilder<'a, 'tcx> {
 563     levels: LintLevelsBuilder<'tcx>,
 564     tcx: TyCtxt<'tcx>,
 565     store: &'a LintStore,
 566 }
 567
 568 impl LintLevelMapBuilder<'_, '_> {
 569     fn with_lint_attrs<F>(&mut self, id: hir::HirId, f: F)
 570     where
 571         F: FnOnce(&mut Self),
 572     {
 573         let is_crate_hir = id == hir::CRATE_HIR_ID;
 574         let attrs = self.tcx.hir().attrs(id);
 575         let push = self.levels.push(attrs, self.store, is_crate_hir);
 576         if push.changed {
 577             self.levels.register_id(id);
 578         }
 579         f(self);
 580         self.levels.pop(push);
 581     }
 582 }
 583
 584 impl<'tcx> intravisit::Visitor<'tcx> for LintLevelMapBuilder<'_, 'tcx> {
 585     type Map = Map<'tcx>;
 586
 587     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
 588         intravisit::NestedVisitorMap::All(self.tcx.hir())
 589     }
 590
 591     fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
 592         self.with_lint_attrs(param.hir_id, |builder| {
 593             intravisit::walk_param(builder, param);
 594         });
 595     }
 596
 597     fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) {
 598         self.with_lint_attrs(it.hir_id(), |builder| {
 599             intravisit::walk_item(builder, it);
 600         });
 601     }
 602
 603     fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {
 604         self.with_lint_attrs(it.hir_id(), |builder| {
 605             intravisit::walk_foreign_item(builder, it);
 606         })
 607     }
 608
 609     fn visit_stmt(&mut self, e: &'tcx hir::Stmt<'tcx>) {
 610         // We will call `with_lint_attrs` when we walk
 611         // the `StmtKind`. The outer statement itself doesn't
 612         // define the lint levels.
 613         intravisit::walk_stmt(self, e);
 614     }
 615
 616     fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
 617         self.with_lint_attrs(e.hir_id, |builder| {
 618             intravisit::walk_expr(builder, e);
 619         })
 620     }
 621
 622     fn visit_struct_field(&mut self, s: &'tcx hir::StructField<'tcx>) {
 623         self.with_lint_attrs(s.hir_id, |builder| {
 624             intravisit::walk_struct_field(builder, s);
 625         })
 626     }
 627
 628     fn visit_variant(
 629         &mut self,
 630         v: &'tcx hir::Variant<'tcx>,
 631         g: &'tcx hir::Generics<'tcx>,
 632         item_id: hir::HirId,
 633     ) {
 634         self.with_lint_attrs(v.id, |builder| {
 635             intravisit::walk_variant(builder, v, g, item_id);
 636         })
 637     }
 638
 639     fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>) {
 640         self.with_lint_attrs(l.hir_id, |builder| {
 641             intravisit::walk_local(builder, l);
 642         })
 643     }
 644
 645     fn visit_arm(&mut self, a: &'tcx hir::Arm<'tcx>) {
 646         self.with_lint_attrs(a.hir_id, |builder| {
 647             intravisit::walk_arm(builder, a);
 648         })
 649     }
 650
 651     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
 652         self.with_lint_attrs(trait_item.hir_id(), |builder| {
 653             intravisit::walk_trait_item(builder, trait_item);
 654         });
 655     }
 656
 657     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 658         self.with_lint_attrs(impl_item.hir_id(), |builder| {
 659             intravisit::walk_impl_item(builder, impl_item);
 660         });
 661     }
 662 }
 663
 664 pub fn provide(providers: &mut Providers) {
 665     providers.lint_levels = lint_levels;
 666 }