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::unwrap_or;
   5 use rustc_ast_pretty::pprust;
   6 use rustc_data_structures::fx::FxHashMap;
   7 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
   8 use rustc_hir as hir;
   9 use rustc_hir::def_id::{CrateNum, DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  10 use rustc_hir::{intravisit, HirId};
  11 use rustc_middle::hir::map::Map;
  12 use rustc_middle::lint::LevelAndSource;
  13 use rustc_middle::lint::LintDiagnosticBuilder;
  14 use rustc_middle::lint::{
  15     struct_lint_level, LintLevelMap, LintLevelSets, LintLevelSource, LintSet,
  16 };
  17 use rustc_middle::ty::query::Providers;
  18 use rustc_middle::ty::TyCtxt;
  19 use rustc_session::lint::{
  20     builtin::{self, FORBIDDEN_LINT_GROUPS},
  21     Level, Lint, LintId,
  22 };
  23 use rustc_session::parse::feature_err;
  24 use rustc_session::Session;
  25 use rustc_span::symbol::{sym, Symbol};
  26 use rustc_span::{source_map::MultiSpan, Span, DUMMY_SP};
  27 use tracing::debug;
  28
  29 use std::cmp;
  30
  31 fn lint_levels(tcx: TyCtxt<'_>, cnum: CrateNum) -> LintLevelMap {
  32     assert_eq!(cnum, LOCAL_CRATE);
  33     let store = unerased_lint_store(tcx);
  34     let crate_attrs = tcx.get_attrs(DefId { krate: cnum, index: CRATE_DEF_INDEX });
  35     let levels = LintLevelsBuilder::new(tcx.sess, false, &store, crate_attrs);
  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     crate_attrs: &'s [ast::Attribute],
  60 }
  61
  62 pub struct BuilderPush {
  63     prev: u32,
  64     pub changed: bool,
  65 }
  66
  67 impl<'s> LintLevelsBuilder<'s> {
  68     pub fn new(
  69         sess: &'s Session,
  70         warn_about_weird_lints: bool,
  71         store: &'s LintStore,
  72         crate_attrs: &'s [ast::Attribute],
  73     ) -> Self {
  74         let mut builder = LintLevelsBuilder {
  75             sess,
  76             sets: LintLevelSets::new(),
  77             cur: 0,
  78             id_to_set: Default::default(),
  79             warn_about_weird_lints,
  80             store,
  81             crate_attrs,
  82         };
  83         builder.process_command_line(sess, store);
  84         assert_eq!(builder.sets.list.len(), 1);
  85         builder
  86     }
  87
  88     fn process_command_line(&mut self, sess: &Session, store: &LintStore) {
  89         let mut specs = FxHashMap::default();
  90         self.sets.lint_cap = sess.opts.lint_cap.unwrap_or(Level::Forbid);
  91
  92         for &(ref lint_name, level) in &sess.opts.lint_opts {
  93             store.check_lint_name_cmdline(sess, &lint_name, level);
  94             let orig_level = level;
  95
  96             // If the cap is less than this specified level, e.g., if we've got
  97             // `--cap-lints allow` but we've also got `-D foo` then we ignore
  98             // this specification as the lint cap will set it to allow anyway.
  99             let level = cmp::min(level, self.sets.lint_cap);
 100
 101             let lint_flag_val = Symbol::intern(lint_name);
 102
 103             let ids = match store.find_lints(&lint_name) {
 104                 Ok(ids) => ids,
 105                 Err(_) => continue, // errors handled in check_lint_name_cmdline above
 106             };
 107             for id in ids {
 108                 self.check_gated_lint(id, DUMMY_SP);
 109                 let src = LintLevelSource::CommandLine(lint_flag_val, orig_level);
 110                 specs.insert(id, (level, src));
 111             }
 112         }
 113
 114         self.sets.list.push(LintSet::CommandLine { specs });
 115     }
 116
 117     /// Attempts to insert the `id` to `level_src` map entry. If unsuccessful
 118     /// (e.g. if a forbid was already inserted on the same scope), then emits a
 119     /// diagnostic with no change to `specs`.
 120     fn insert_spec(
 121         &mut self,
 122         specs: &mut FxHashMap<LintId, LevelAndSource>,
 123         id: LintId,
 124         (level, src): LevelAndSource,
 125     ) {
 126         // Setting to a non-forbid level is an error if the lint previously had
 127         // a forbid level. Note that this is not necessarily true even with a
 128         // `#[forbid(..)]` attribute present, as that is overriden by `--cap-lints`.
 129         //
 130         // This means that this only errors if we're truly lowering the lint
 131         // level from forbid.
 132         if level != Level::Forbid {
 133             if let (Level::Forbid, old_src) =
 134                 self.sets.get_lint_level(id.lint, self.cur, Some(&specs), &self.sess)
 135             {
 136                 // Backwards compatibility check:
 137                 //
 138                 // We used to not consider `forbid(lint_group)`
 139                 // as preventing `allow(lint)` for some lint `lint` in
 140                 // `lint_group`. For now, issue a future-compatibility
 141                 // warning for this case.
 142                 let id_name = id.lint.name_lower();
 143                 let fcw_warning = match old_src {
 144                     LintLevelSource::Default => false,
 145                     LintLevelSource::Node(symbol, _, _) => self.store.is_lint_group(symbol),
 146                     LintLevelSource::CommandLine(symbol, _) => self.store.is_lint_group(symbol),
 147                 };
 148                 debug!(
 149                     "fcw_warning={:?}, specs.get(&id) = {:?}, old_src={:?}, id_name={:?}",
 150                     fcw_warning, specs, old_src, id_name
 151                 );
 152
 153                 let decorate_diag_builder = |mut diag_builder: DiagnosticBuilder<'_>| {
 154                     diag_builder.span_label(src.span(), "overruled by previous forbid");
 155                     match old_src {
 156                         LintLevelSource::Default => {
 157                             diag_builder.note(&format!(
 158                                 "`forbid` lint level is the default for {}",
 159                                 id.to_string()
 160                             ));
 161                         }
 162                         LintLevelSource::Node(_, forbid_source_span, reason) => {
 163                             diag_builder.span_label(forbid_source_span, "`forbid` level set here");
 164                             if let Some(rationale) = reason {
 165                                 diag_builder.note(&rationale.as_str());
 166                             }
 167                         }
 168                         LintLevelSource::CommandLine(_, _) => {
 169                             diag_builder.note("`forbid` lint level was set on command line");
 170                         }
 171                     }
 172                     diag_builder.emit();
 173                 };
 174                 if !fcw_warning {
 175                     let diag_builder = struct_span_err!(
 176                         self.sess,
 177                         src.span(),
 178                         E0453,
 179                         "{}({}) incompatible with previous forbid",
 180                         level.as_str(),
 181                         src.name(),
 182                     );
 183                     decorate_diag_builder(diag_builder);
 184                 } else {
 185                     self.struct_lint(
 186                         FORBIDDEN_LINT_GROUPS,
 187                         Some(src.span().into()),
 188                         |diag_builder| {
 189                             let diag_builder = diag_builder.build(&format!(
 190                                 "{}({}) incompatible with previous forbid",
 191                                 level.as_str(),
 192                                 src.name(),
 193                             ));
 194                             decorate_diag_builder(diag_builder);
 195                         },
 196                     );
 197                 }
 198
 199                 // Retain the forbid lint level, unless we are
 200                 // issuing a FCW. In the FCW case, we want to
 201                 // respect the new setting.
 202                 if !fcw_warning {
 203                     return;
 204                 }
 205             }
 206         }
 207         specs.insert(id, (level, src));
 208     }
 209
 210     /// Pushes a list of AST lint attributes onto this context.
 211     ///
 212     /// This function will return a `BuilderPush` object which should be passed
 213     /// to `pop` when this scope for the attributes provided is exited.
 214     ///
 215     /// This function will perform a number of tasks:
 216     ///
 217     /// * It'll validate all lint-related attributes in `attrs`
 218     /// * It'll mark all lint-related attributes as used
 219     /// * Lint levels will be updated based on the attributes provided
 220     /// * Lint attributes are validated, e.g., a `#[forbid]` can't be switched to
 221     ///   `#[allow]`
 222     ///
 223     /// Don't forget to call `pop`!
 224     pub(crate) fn push(
 225         &mut self,
 226         attrs: &[ast::Attribute],
 227         store: &LintStore,
 228         is_crate_node: bool,
 229     ) -> BuilderPush {
 230         let mut specs = FxHashMap::default();
 231         let sess = self.sess;
 232         let bad_attr = |span| struct_span_err!(sess, span, E0452, "malformed lint attribute input");
 233         for attr in attrs {
 234             let level = match Level::from_symbol(attr.name_or_empty()) {
 235                 None => continue,
 236                 Some(lvl) => lvl,
 237             };
 238
 239             let meta = unwrap_or!(attr.meta(), continue);
 240             self.sess.mark_attr_used(attr);
 241
 242             let mut metas = unwrap_or!(meta.meta_item_list(), continue);
 243
 244             if metas.is_empty() {
 245                 // FIXME (#55112): issue unused-attributes lint for `#[level()]`
 246                 continue;
 247             }
 248
 249             // Before processing the lint names, look for a reason (RFC 2383)
 250             // at the end.
 251             let mut reason = None;
 252             let tail_li = &metas[metas.len() - 1];
 253             if let Some(item) = tail_li.meta_item() {
 254                 match item.kind {
 255                     ast::MetaItemKind::Word => {} // actual lint names handled later
 256                     ast::MetaItemKind::NameValue(ref name_value) => {
 257                         if item.path == sym::reason {
 258                             // found reason, reslice meta list to exclude it
 259                             metas = &metas[0..metas.len() - 1];
 260                             // FIXME (#55112): issue unused-attributes lint if we thereby
 261                             // don't have any lint names (`#[level(reason = "foo")]`)
 262                             if let ast::LitKind::Str(rationale, _) = name_value.kind {
 263                                 if !self.sess.features_untracked().lint_reasons {
 264                                     feature_err(
 265                                         &self.sess.parse_sess,
 266                                         sym::lint_reasons,
 267                                         item.span,
 268                                         "lint reasons are experimental",
 269                                     )
 270                                     .emit();
 271                                 }
 272                                 reason = Some(rationale);
 273                             } else {
 274                                 bad_attr(name_value.span)
 275                                     .span_label(name_value.span, "reason must be a string literal")
 276                                     .emit();
 277                             }
 278                         } else {
 279                             bad_attr(item.span)
 280                                 .span_label(item.span, "bad attribute argument")
 281                                 .emit();
 282                         }
 283                     }
 284                     ast::MetaItemKind::List(_) => {
 285                         bad_attr(item.span).span_label(item.span, "bad attribute argument").emit();
 286                     }
 287                 }
 288             }
 289
 290             for li in metas {
 291                 let meta_item = match li.meta_item() {
 292                     Some(meta_item) if meta_item.is_word() => meta_item,
 293                     _ => {
 294                         let sp = li.span();
 295                         let mut err = bad_attr(sp);
 296                         let mut add_label = true;
 297                         if let Some(item) = li.meta_item() {
 298                             if let ast::MetaItemKind::NameValue(_) = item.kind {
 299                                 if item.path == sym::reason {
 300                                     err.span_label(sp, "reason in lint attribute must come last");
 301                                     add_label = false;
 302                                 }
 303                             }
 304                         }
 305                         if add_label {
 306                             err.span_label(sp, "bad attribute argument");
 307                         }
 308                         err.emit();
 309                         continue;
 310                     }
 311                 };
 312                 let tool_name = if meta_item.path.segments.len() > 1 {
 313                     let tool_ident = meta_item.path.segments[0].ident;
 314                     if !is_known_lint_tool(tool_ident.name, sess, &self.crate_attrs) {
 315                         let mut err = struct_span_err!(
 316                             sess,
 317                             tool_ident.span,
 318                             E0710,
 319                             "unknown tool name `{}` found in scoped lint: `{}`",
 320                             tool_ident.name,
 321                             pprust::path_to_string(&meta_item.path),
 322                         );
 323                         if sess.is_nightly_build() {
 324                             err.help(&format!(
 325                                 "add `#![register_tool({})]` to the crate root",
 326                                 tool_ident.name
 327                             ));
 328                         }
 329                         err.emit();
 330                         continue;
 331                     }
 332
 333                     Some(tool_ident.name)
 334                 } else {
 335                     None
 336                 };
 337                 let name = meta_item.path.segments.last().expect("empty lint name").ident.name;
 338                 let lint_result = store.check_lint_name(&name.as_str(), tool_name);
 339                 match &lint_result {
 340                     CheckLintNameResult::Ok(ids) => {
 341                         let src = LintLevelSource::Node(name, li.span(), reason);
 342                         for &id in *ids {
 343                             self.check_gated_lint(id, attr.span);
 344                             self.insert_spec(&mut specs, id, (level, src));
 345                         }
 346                     }
 347
 348                     CheckLintNameResult::Tool(result) => {
 349                         match *result {
 350                             Ok(ids) => {
 351                                 let complete_name = &format!("{}::{}", tool_name.unwrap(), name);
 352                                 let src = LintLevelSource::Node(
 353                                     Symbol::intern(complete_name),
 354                                     li.span(),
 355                                     reason,
 356                                 );
 357                                 for id in ids {
 358                                     self.insert_spec(&mut specs, *id, (level, src));
 359                                 }
 360                             }
 361                             Err((Some(ids), ref new_lint_name)) => {
 362                                 let lint = builtin::RENAMED_AND_REMOVED_LINTS;
 363                                 let (lvl, src) =
 364                                     self.sets.get_lint_level(lint, self.cur, Some(&specs), &sess);
 365                                 struct_lint_level(
 366                                     self.sess,
 367                                     lint,
 368                                     lvl,
 369                                     src,
 370                                     Some(li.span().into()),
 371                                     |lint| {
 372                                         let msg = format!(
 373                                             "lint name `{}` is deprecated \
 374                                              and may not have an effect in the future.",
 375                                             name
 376                                         );
 377                                         lint.build(&msg)
 378                                             .span_suggestion(
 379                                                 li.span(),
 380                                                 "change it to",
 381                                                 new_lint_name.to_string(),
 382                                                 Applicability::MachineApplicable,
 383                                             )
 384                                             .emit();
 385                                     },
 386                                 );
 387
 388                                 let src = LintLevelSource::Node(
 389                                     Symbol::intern(&new_lint_name),
 390                                     li.span(),
 391                                     reason,
 392                                 );
 393                                 for id in ids {
 394                                     self.insert_spec(&mut specs, *id, (level, src));
 395                                 }
 396                             }
 397                             Err((None, _)) => {
 398                                 // If Tool(Err(None, _)) is returned, then either the lint does not
 399                                 // exist in the tool or the code was not compiled with the tool and
 400                                 // therefore the lint was never added to the `LintStore`. To detect
 401                                 // this is the responsibility of the lint tool.
 402                             }
 403                         }
 404                     }
 405
 406                     _ if !self.warn_about_weird_lints => {}
 407
 408                     CheckLintNameResult::Warning(msg, renamed) => {
 409                         let lint = builtin::RENAMED_AND_REMOVED_LINTS;
 410                         let (renamed_lint_level, src) =
 411                             self.sets.get_lint_level(lint, self.cur, Some(&specs), &sess);
 412                         struct_lint_level(
 413                             self.sess,
 414                             lint,
 415                             renamed_lint_level,
 416                             src,
 417                             Some(li.span().into()),
 418                             |lint| {
 419                                 let mut err = lint.build(&msg);
 420                                 if let Some(new_name) = &renamed {
 421                                     err.span_suggestion(
 422                                         li.span(),
 423                                         "use the new name",
 424                                         new_name.to_string(),
 425                                         Applicability::MachineApplicable,
 426                                     );
 427                                 }
 428                                 err.emit();
 429                             },
 430                         );
 431                     }
 432                     CheckLintNameResult::NoLint(suggestion) => {
 433                         let lint = builtin::UNKNOWN_LINTS;
 434                         let (level, src) =
 435                             self.sets.get_lint_level(lint, self.cur, Some(&specs), self.sess);
 436                         struct_lint_level(
 437                             self.sess,
 438                             lint,
 439                             level,
 440                             src,
 441                             Some(li.span().into()),
 442                             |lint| {
 443                                 let name = if let Some(tool_name) = tool_name {
 444                                     format!("{}::{}", tool_name, name)
 445                                 } else {
 446                                     name.to_string()
 447                                 };
 448                                 let mut db = lint.build(&format!("unknown lint: `{}`", name));
 449                                 if let Some(suggestion) = suggestion {
 450                                     db.span_suggestion(
 451                                         li.span(),
 452                                         "did you mean",
 453                                         suggestion.to_string(),
 454                                         Applicability::MachineApplicable,
 455                                     );
 456                                 }
 457                                 db.emit();
 458                             },
 459                         );
 460                     }
 461                 }
 462                 // If this lint was renamed, apply the new lint instead of ignoring the attribute.
 463                 // This happens outside of the match because the new lint should be applied even if
 464                 // we don't warn about the name change.
 465                 if let CheckLintNameResult::Warning(_, Some(new_name)) = lint_result {
 466                     // Ignore any errors or warnings that happen because the new name is inaccurate
 467                     if let CheckLintNameResult::Ok(ids) =
 468                         store.check_lint_name(&new_name, tool_name)
 469                     {
 470                         let src =
 471                             LintLevelSource::Node(Symbol::intern(&new_name), li.span(), reason);
 472                         for &id in ids {
 473                             self.check_gated_lint(id, attr.span);
 474                             self.insert_spec(&mut specs, id, (level, src));
 475                         }
 476                     }
 477                 }
 478             }
 479         }
 480
 481         if !is_crate_node {
 482             for (id, &(level, ref src)) in specs.iter() {
 483                 if !id.lint.crate_level_only {
 484                     continue;
 485                 }
 486
 487                 let (lint_attr_name, lint_attr_span) = match *src {
 488                     LintLevelSource::Node(name, span, _) => (name, span),
 489                     _ => continue,
 490                 };
 491
 492                 let lint = builtin::UNUSED_ATTRIBUTES;
 493                 let (lint_level, lint_src) =
 494                     self.sets.get_lint_level(lint, self.cur, Some(&specs), self.sess);
 495                 struct_lint_level(
 496                     self.sess,
 497                     lint,
 498                     lint_level,
 499                     lint_src,
 500                     Some(lint_attr_span.into()),
 501                     |lint| {
 502                         let mut db = lint.build(&format!(
 503                             "{}({}) is ignored unless specified at crate level",
 504                             level.as_str(),
 505                             lint_attr_name
 506                         ));
 507                         db.emit();
 508                     },
 509                 );
 510                 // don't set a separate error for every lint in the group
 511                 break;
 512             }
 513         }
 514
 515         let prev = self.cur;
 516         if !specs.is_empty() {
 517             self.cur = self.sets.list.len() as u32;
 518             self.sets.list.push(LintSet::Node { specs, parent: prev });
 519         }
 520
 521         BuilderPush { prev, changed: prev != self.cur }
 522     }
 523
 524     /// Checks if the lint is gated on a feature that is not enabled.
 525     fn check_gated_lint(&self, lint_id: LintId, span: Span) {
 526         if let Some(feature) = lint_id.lint.feature_gate {
 527             if !self.sess.features_untracked().enabled(feature) {
 528                 feature_err(
 529                     &self.sess.parse_sess,
 530                     feature,
 531                     span,
 532                     &format!("the `{}` lint is unstable", lint_id.lint.name_lower()),
 533                 )
 534                 .emit();
 535             }
 536         }
 537     }
 538
 539     /// Called after `push` when the scope of a set of attributes are exited.
 540     pub fn pop(&mut self, push: BuilderPush) {
 541         self.cur = push.prev;
 542     }
 543
 544     /// Find the lint level for a lint.
 545     pub fn lint_level(&self, lint: &'static Lint) -> (Level, LintLevelSource) {
 546         self.sets.get_lint_level(lint, self.cur, None, self.sess)
 547     }
 548
 549     /// Used to emit a lint-related diagnostic based on the current state of
 550     /// this lint context.
 551     pub fn struct_lint(
 552         &self,
 553         lint: &'static Lint,
 554         span: Option<MultiSpan>,
 555         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 556     ) {
 557         let (level, src) = self.lint_level(lint);
 558         struct_lint_level(self.sess, lint, level, src, span, decorate)
 559     }
 560
 561     /// Registers the ID provided with the current set of lints stored in
 562     /// this context.
 563     pub fn register_id(&mut self, id: HirId) {
 564         self.id_to_set.insert(id, self.cur);
 565     }
 566
 567     pub fn build_map(self) -> LintLevelMap {
 568         LintLevelMap { sets: self.sets, id_to_set: self.id_to_set }
 569     }
 570 }
 571
 572 fn is_known_lint_tool(m_item: Symbol, sess: &Session, attrs: &[ast::Attribute]) -> bool {
 573     if [sym::clippy, sym::rustc, sym::rustdoc].contains(&m_item) {
 574         return true;
 575     }
 576     // Look for registered tools
 577     // NOTE: does no error handling; error handling is done by rustc_resolve.
 578     sess.filter_by_name(attrs, sym::register_tool)
 579         .filter_map(|attr| attr.meta_item_list())
 580         .flat_map(std::convert::identity)
 581         .filter_map(|nested_meta| nested_meta.ident())
 582         .map(|ident| ident.name)
 583         .any(|name| name == m_item)
 584 }
 585
 586 struct LintLevelMapBuilder<'a, 'tcx> {
 587     levels: LintLevelsBuilder<'tcx>,
 588     tcx: TyCtxt<'tcx>,
 589     store: &'a LintStore,
 590 }
 591
 592 impl LintLevelMapBuilder<'_, '_> {
 593     fn with_lint_attrs<F>(&mut self, id: hir::HirId, f: F)
 594     where
 595         F: FnOnce(&mut Self),
 596     {
 597         let is_crate_hir = id == hir::CRATE_HIR_ID;
 598         let attrs = self.tcx.hir().attrs(id);
 599         let push = self.levels.push(attrs, self.store, is_crate_hir);
 600         if push.changed {
 601             self.levels.register_id(id);
 602         }
 603         f(self);
 604         self.levels.pop(push);
 605     }
 606 }
 607
 608 impl<'tcx> intravisit::Visitor<'tcx> for LintLevelMapBuilder<'_, 'tcx> {
 609     type Map = Map<'tcx>;
 610
 611     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
 612         intravisit::NestedVisitorMap::All(self.tcx.hir())
 613     }
 614
 615     fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
 616         self.with_lint_attrs(param.hir_id, |builder| {
 617             intravisit::walk_param(builder, param);
 618         });
 619     }
 620
 621     fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) {
 622         self.with_lint_attrs(it.hir_id(), |builder| {
 623             intravisit::walk_item(builder, it);
 624         });
 625     }
 626
 627     fn visit_foreign_item(&mut self, it: &'tcx hir::ForeignItem<'tcx>) {
 628         self.with_lint_attrs(it.hir_id(), |builder| {
 629             intravisit::walk_foreign_item(builder, it);
 630         })
 631     }
 632
 633     fn visit_stmt(&mut self, e: &'tcx hir::Stmt<'tcx>) {
 634         // We will call `with_lint_attrs` when we walk
 635         // the `StmtKind`. The outer statement itself doesn't
 636         // define the lint levels.
 637         intravisit::walk_stmt(self, e);
 638     }
 639
 640     fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
 641         self.with_lint_attrs(e.hir_id, |builder| {
 642             intravisit::walk_expr(builder, e);
 643         })
 644     }
 645
 646     fn visit_field_def(&mut self, s: &'tcx hir::FieldDef<'tcx>) {
 647         self.with_lint_attrs(s.hir_id, |builder| {
 648             intravisit::walk_field_def(builder, s);
 649         })
 650     }
 651
 652     fn visit_variant(
 653         &mut self,
 654         v: &'tcx hir::Variant<'tcx>,
 655         g: &'tcx hir::Generics<'tcx>,
 656         item_id: hir::HirId,
 657     ) {
 658         self.with_lint_attrs(v.id, |builder| {
 659             intravisit::walk_variant(builder, v, g, item_id);
 660         })
 661     }
 662
 663     fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>) {
 664         self.with_lint_attrs(l.hir_id, |builder| {
 665             intravisit::walk_local(builder, l);
 666         })
 667     }
 668
 669     fn visit_arm(&mut self, a: &'tcx hir::Arm<'tcx>) {
 670         self.with_lint_attrs(a.hir_id, |builder| {
 671             intravisit::walk_arm(builder, a);
 672         })
 673     }
 674
 675     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
 676         self.with_lint_attrs(trait_item.hir_id(), |builder| {
 677             intravisit::walk_trait_item(builder, trait_item);
 678         });
 679     }
 680
 681     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 682         self.with_lint_attrs(impl_item.hir_id(), |builder| {
 683             intravisit::walk_impl_item(builder, impl_item);
 684         });
 685     }
 686 }
 687
 688 pub fn provide(providers: &mut Providers) {
 689     providers.lint_levels = lint_levels;
 690 }