compiler/rustc_lint/src/context.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 self::TargetLint::*;
  18
  19 use crate::levels::{is_known_lint_tool, LintLevelsBuilder};
  20 use crate::passes::{EarlyLintPassObject, LateLintPassObject};
  21 use rustc_ast as ast;
  22 use rustc_data_structures::fx::FxHashMap;
  23 use rustc_data_structures::sync;
  24 use rustc_errors::{
  25     add_elided_lifetime_in_path_suggestion, struct_span_err, Applicability, SuggestionStyle,
  26 };
  27 use rustc_hir as hir;
  28 use rustc_hir::def::Res;
  29 use rustc_hir::def_id::{CrateNum, DefId};
  30 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
  31 use rustc_middle::lint::LintDiagnosticBuilder;
  32 use rustc_middle::middle::privacy::AccessLevels;
  33 use rustc_middle::middle::stability;
  34 use rustc_middle::ty::layout::{LayoutError, TyAndLayout};
  35 use rustc_middle::ty::print::with_no_trimmed_paths;
  36 use rustc_middle::ty::{self, print::Printer, subst::GenericArg, Ty, TyCtxt};
  37 use rustc_serialize::json::Json;
  38 use rustc_session::lint::{BuiltinLintDiagnostics, ExternDepSpec};
  39 use rustc_session::lint::{FutureIncompatibleInfo, Level, Lint, LintBuffer, LintId};
  40 use rustc_session::Session;
  41 use rustc_session::SessionLintStore;
  42 use rustc_span::lev_distance::find_best_match_for_name;
  43 use rustc_span::{symbol::Symbol, MultiSpan, Span, DUMMY_SP};
  44 use rustc_target::abi::LayoutOf;
  45 use tracing::debug;
  46
  47 use std::cell::Cell;
  48 use std::iter;
  49 use std::slice;
  50
  51 /// Information about the registered lints.
  52 ///
  53 /// This is basically the subset of `Context` that we can
  54 /// build early in the compile pipeline.
  55 pub struct LintStore {
  56     /// Registered lints.
  57     lints: Vec<&'static Lint>,
  58
  59     /// Constructor functions for each variety of lint pass.
  60     ///
  61     /// These should only be called once, but since we want to avoid locks or
  62     /// interior mutability, we don't enforce this (and lints should, in theory,
  63     /// be compatible with being constructed more than once, though not
  64     /// necessarily in a sane manner. This is safe though.)
  65     pub pre_expansion_passes: Vec<Box<dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync>>,
  66     pub early_passes: Vec<Box<dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync>>,
  67     pub late_passes: Vec<Box<dyn Fn() -> LateLintPassObject + sync::Send + sync::Sync>>,
  68     /// This is unique in that we construct them per-module, so not once.
  69     pub late_module_passes: Vec<Box<dyn Fn() -> LateLintPassObject + sync::Send + sync::Sync>>,
  70
  71     /// Lints indexed by name.
  72     by_name: FxHashMap<String, TargetLint>,
  73
  74     /// Map of registered lint groups to what lints they expand to.
  75     lint_groups: FxHashMap<&'static str, LintGroup>,
  76 }
  77
  78 impl SessionLintStore for LintStore {
  79     fn name_to_lint(&self, lint_name: &str) -> LintId {
  80         let lints = self
  81             .find_lints(lint_name)
  82             .unwrap_or_else(|_| panic!("Failed to find lint with name `{}`", lint_name));
  83
  84         if let &[lint] = lints.as_slice() {
  85             return lint;
  86         } else {
  87             panic!("Found mutliple lints with name `{}`: {:?}", lint_name, lints);
  88         }
  89     }
  90 }
  91
  92 /// The target of the `by_name` map, which accounts for renaming/deprecation.
  93 #[derive(Debug)]
  94 enum TargetLint {
  95     /// A direct lint target
  96     Id(LintId),
  97
  98     /// Temporary renaming, used for easing migration pain; see #16545
  99     Renamed(String, LintId),
 100
 101     /// Lint with this name existed previously, but has been removed/deprecated.
 102     /// The string argument is the reason for removal.
 103     Removed(String),
 104
 105     /// A lint name that should give no warnings and have no effect.
 106     ///
 107     /// This is used by rustc to avoid warning about old rustdoc lints before rustdoc registers them as tool lints.
 108     Ignored,
 109 }
 110
 111 pub enum FindLintError {
 112     NotFound,
 113     Removed,
 114 }
 115
 116 struct LintAlias {
 117     name: &'static str,
 118     /// Whether deprecation warnings should be suppressed for this alias.
 119     silent: bool,
 120 }
 121
 122 struct LintGroup {
 123     lint_ids: Vec<LintId>,
 124     from_plugin: bool,
 125     depr: Option<LintAlias>,
 126 }
 127
 128 pub enum CheckLintNameResult<'a> {
 129     Ok(&'a [LintId]),
 130     /// Lint doesn't exist. Potentially contains a suggestion for a correct lint name.
 131     NoLint(Option<Symbol>),
 132     /// The lint refers to a tool that has not been registered.
 133     NoTool,
 134     /// The lint is either renamed or removed. This is the warning
 135     /// message, and an optional new name (`None` if removed).
 136     Warning(String, Option<String>),
 137     /// The lint is from a tool. If the Option is None, then either
 138     /// the lint does not exist in the tool or the code was not
 139     /// compiled with the tool and therefore the lint was never
 140     /// added to the `LintStore`. Otherwise the `LintId` will be
 141     /// returned as if it where a rustc lint.
 142     Tool(Result<&'a [LintId], (Option<&'a [LintId]>, String)>),
 143 }
 144
 145 impl LintStore {
 146     pub fn new() -> LintStore {
 147         LintStore {
 148             lints: vec![],
 149             pre_expansion_passes: vec![],
 150             early_passes: vec![],
 151             late_passes: vec![],
 152             late_module_passes: vec![],
 153             by_name: Default::default(),
 154             lint_groups: Default::default(),
 155         }
 156     }
 157
 158     pub fn get_lints<'t>(&'t self) -> &'t [&'static Lint] {
 159         &self.lints
 160     }
 161
 162     pub fn get_lint_groups<'t>(&'t self) -> Vec<(&'static str, Vec<LintId>, bool)> {
 163         self.lint_groups
 164             .iter()
 165             .filter(|(_, LintGroup { depr, .. })| {
 166                 // Don't display deprecated lint groups.
 167                 depr.is_none()
 168             })
 169             .map(|(k, LintGroup { lint_ids, from_plugin, .. })| {
 170                 (*k, lint_ids.clone(), *from_plugin)
 171             })
 172             .collect()
 173     }
 174
 175     pub fn register_early_pass(
 176         &mut self,
 177         pass: impl Fn() -> EarlyLintPassObject + 'static + sync::Send + sync::Sync,
 178     ) {
 179         self.early_passes.push(Box::new(pass));
 180     }
 181
 182     /// Used by clippy.
 183     pub fn register_pre_expansion_pass(
 184         &mut self,
 185         pass: impl Fn() -> EarlyLintPassObject + 'static + sync::Send + sync::Sync,
 186     ) {
 187         self.pre_expansion_passes.push(Box::new(pass));
 188     }
 189
 190     pub fn register_late_pass(
 191         &mut self,
 192         pass: impl Fn() -> LateLintPassObject + 'static + sync::Send + sync::Sync,
 193     ) {
 194         self.late_passes.push(Box::new(pass));
 195     }
 196
 197     pub fn register_late_mod_pass(
 198         &mut self,
 199         pass: impl Fn() -> LateLintPassObject + 'static + sync::Send + sync::Sync,
 200     ) {
 201         self.late_module_passes.push(Box::new(pass));
 202     }
 203
 204     // Helper method for register_early/late_pass
 205     pub fn register_lints(&mut self, lints: &[&'static Lint]) {
 206         for lint in lints {
 207             self.lints.push(lint);
 208
 209             let id = LintId::of(lint);
 210             if self.by_name.insert(lint.name_lower(), Id(id)).is_some() {
 211                 bug!("duplicate specification of lint {}", lint.name_lower())
 212             }
 213
 214             if let Some(FutureIncompatibleInfo { reason, .. }) = lint.future_incompatible {
 215                 if let Some(edition) = reason.edition() {
 216                     self.lint_groups
 217                         .entry(edition.lint_name())
 218                         .or_insert(LintGroup {
 219                             lint_ids: vec![],
 220                             from_plugin: lint.is_plugin,
 221                             depr: None,
 222                         })
 223                         .lint_ids
 224                         .push(id);
 225                 } else {
 226                     // Lints belonging to the `future_incompatible` lint group are lints where a
 227                     // future version of rustc will cause existing code to stop compiling.
 228                     // Lints tied to an edition don't count because they are opt-in.
 229                     self.lint_groups
 230                         .entry("future_incompatible")
 231                         .or_insert(LintGroup {
 232                             lint_ids: vec![],
 233                             from_plugin: lint.is_plugin,
 234                             depr: None,
 235                         })
 236                         .lint_ids
 237                         .push(id);
 238                 }
 239             }
 240         }
 241     }
 242
 243     pub fn register_group_alias(&mut self, lint_name: &'static str, alias: &'static str) {
 244         self.lint_groups.insert(
 245             alias,
 246             LintGroup {
 247                 lint_ids: vec![],
 248                 from_plugin: false,
 249                 depr: Some(LintAlias { name: lint_name, silent: true }),
 250             },
 251         );
 252     }
 253
 254     pub fn register_group(
 255         &mut self,
 256         from_plugin: bool,
 257         name: &'static str,
 258         deprecated_name: Option<&'static str>,
 259         to: Vec<LintId>,
 260     ) {
 261         let new = self
 262             .lint_groups
 263             .insert(name, LintGroup { lint_ids: to, from_plugin, depr: None })
 264             .is_none();
 265         if let Some(deprecated) = deprecated_name {
 266             self.lint_groups.insert(
 267                 deprecated,
 268                 LintGroup {
 269                     lint_ids: vec![],
 270                     from_plugin,
 271                     depr: Some(LintAlias { name, silent: false }),
 272                 },
 273             );
 274         }
 275
 276         if !new {
 277             bug!("duplicate specification of lint group {}", name);
 278         }
 279     }
 280
 281     /// This lint should give no warning and have no effect.
 282     ///
 283     /// This is used by rustc to avoid warning about old rustdoc lints before rustdoc registers them as tool lints.
 284     #[track_caller]
 285     pub fn register_ignored(&mut self, name: &str) {
 286         if self.by_name.insert(name.to_string(), Ignored).is_some() {
 287             bug!("duplicate specification of lint {}", name);
 288         }
 289     }
 290
 291     /// This lint has been renamed; warn about using the new name and apply the lint.
 292     #[track_caller]
 293     pub fn register_renamed(&mut self, old_name: &str, new_name: &str) {
 294         let target = match self.by_name.get(new_name) {
 295             Some(&Id(lint_id)) => lint_id,
 296             _ => bug!("invalid lint renaming of {} to {}", old_name, new_name),
 297         };
 298         self.by_name.insert(old_name.to_string(), Renamed(new_name.to_string(), target));
 299     }
 300
 301     pub fn register_removed(&mut self, name: &str, reason: &str) {
 302         self.by_name.insert(name.into(), Removed(reason.into()));
 303     }
 304
 305     pub fn find_lints(&self, mut lint_name: &str) -> Result<Vec<LintId>, FindLintError> {
 306         match self.by_name.get(lint_name) {
 307             Some(&Id(lint_id)) => Ok(vec![lint_id]),
 308             Some(&Renamed(_, lint_id)) => Ok(vec![lint_id]),
 309             Some(&Removed(_)) => Err(FindLintError::Removed),
 310             Some(&Ignored) => Ok(vec![]),
 311             None => loop {
 312                 return match self.lint_groups.get(lint_name) {
 313                     Some(LintGroup { lint_ids, depr, .. }) => {
 314                         if let Some(LintAlias { name, .. }) = depr {
 315                             lint_name = name;
 316                             continue;
 317                         }
 318                         Ok(lint_ids.clone())
 319                     }
 320                     None => Err(FindLintError::Removed),
 321                 };
 322             },
 323         }
 324     }
 325
 326     /// Checks the validity of lint names derived from the command line.
 327     pub fn check_lint_name_cmdline(
 328         &self,
 329         sess: &Session,
 330         lint_name: &str,
 331         level: Level,
 332         crate_attrs: &[ast::Attribute],
 333     ) {
 334         let (tool_name, lint_name_only) = parse_lint_and_tool_name(lint_name);
 335
 336         let db = match self.check_lint_name(sess, lint_name_only, tool_name, crate_attrs) {
 337             CheckLintNameResult::Ok(_) => None,
 338             CheckLintNameResult::Warning(ref msg, _) => Some(sess.struct_warn(msg)),
 339             CheckLintNameResult::NoLint(suggestion) => {
 340                 let mut err =
 341                     struct_span_err!(sess, DUMMY_SP, E0602, "unknown lint: `{}`", lint_name);
 342
 343                 if let Some(suggestion) = suggestion {
 344                     err.help(&format!("did you mean: `{}`", suggestion));
 345                 }
 346
 347                 Some(err)
 348             }
 349             CheckLintNameResult::Tool(result) => match result {
 350                 Err((Some(_), new_name)) => Some(sess.struct_warn(&format!(
 351                     "lint name `{}` is deprecated \
 352                      and does not have an effect anymore. \
 353                      Use: {}",
 354                     lint_name, new_name
 355                 ))),
 356                 _ => None,
 357             },
 358             CheckLintNameResult::NoTool => Some(struct_span_err!(
 359                 sess,
 360                 DUMMY_SP,
 361                 E0602,
 362                 "unknown lint tool: `{}`",
 363                 tool_name.unwrap()
 364             )),
 365         };
 366
 367         if let Some(mut db) = db {
 368             let msg = format!(
 369                 "requested on the command line with `{} {}`",
 370                 match level {
 371                     Level::Allow => "-A",
 372                     Level::Warn => "-W",
 373                     Level::ForceWarn => "--force-warn",
 374                     Level::Deny => "-D",
 375                     Level::Forbid => "-F",
 376                 },
 377                 lint_name
 378             );
 379             db.note(&msg);
 380             db.emit();
 381         }
 382     }
 383
 384     /// True if this symbol represents a lint group name.
 385     pub fn is_lint_group(&self, lint_name: Symbol) -> bool {
 386         debug!(
 387             "is_lint_group(lint_name={:?}, lint_groups={:?})",
 388             lint_name,
 389             self.lint_groups.keys().collect::<Vec<_>>()
 390         );
 391         let lint_name_str = &*lint_name.as_str();
 392         self.lint_groups.contains_key(&lint_name_str) || {
 393             let warnings_name_str = crate::WARNINGS.name_lower();
 394             lint_name_str == &*warnings_name_str
 395         }
 396     }
 397
 398     /// Checks the name of a lint for its existence, and whether it was
 399     /// renamed or removed. Generates a DiagnosticBuilder containing a
 400     /// warning for renamed and removed lints. This is over both lint
 401     /// names from attributes and those passed on the command line. Since
 402     /// it emits non-fatal warnings and there are *two* lint passes that
 403     /// inspect attributes, this is only run from the late pass to avoid
 404     /// printing duplicate warnings.
 405     pub fn check_lint_name(
 406         &self,
 407         sess: &Session,
 408         lint_name: &str,
 409         tool_name: Option<Symbol>,
 410         crate_attrs: &[ast::Attribute],
 411     ) -> CheckLintNameResult<'_> {
 412         if let Some(tool_name) = tool_name {
 413             if !is_known_lint_tool(tool_name, sess, crate_attrs) {
 414                 return CheckLintNameResult::NoTool;
 415             }
 416         }
 417
 418         let complete_name = if let Some(tool_name) = tool_name {
 419             format!("{}::{}", tool_name, lint_name)
 420         } else {
 421             lint_name.to_string()
 422         };
 423         // If the lint was scoped with `tool::` check if the tool lint exists
 424         if let Some(tool_name) = tool_name {
 425             match self.by_name.get(&complete_name) {
 426                 None => match self.lint_groups.get(&*complete_name) {
 427                     // If the lint isn't registered, there are two possibilities:
 428                     None => {
 429                         // 1. The tool is currently running, so this lint really doesn't exist.
 430                         // FIXME: should this handle tools that never register a lint, like rustfmt?
 431                         tracing::debug!("lints={:?}", self.by_name.keys().collect::<Vec<_>>());
 432                         let tool_prefix = format!("{}::", tool_name);
 433                         return if self.by_name.keys().any(|lint| lint.starts_with(&tool_prefix)) {
 434                             self.no_lint_suggestion(&complete_name)
 435                         } else {
 436                             // 2. The tool isn't currently running, so no lints will be registered.
 437                             // To avoid giving a false positive, ignore all unknown lints.
 438                             CheckLintNameResult::Tool(Err((None, String::new())))
 439                         };
 440                     }
 441                     Some(LintGroup { lint_ids, .. }) => {
 442                         return CheckLintNameResult::Tool(Ok(&lint_ids));
 443                     }
 444                 },
 445                 Some(&Id(ref id)) => return CheckLintNameResult::Tool(Ok(slice::from_ref(id))),
 446                 // If the lint was registered as removed or renamed by the lint tool, we don't need
 447                 // to treat tool_lints and rustc lints different and can use the code below.
 448                 _ => {}
 449             }
 450         }
 451         match self.by_name.get(&complete_name) {
 452             Some(&Renamed(ref new_name, _)) => CheckLintNameResult::Warning(
 453                 format!("lint `{}` has been renamed to `{}`", complete_name, new_name),
 454                 Some(new_name.to_owned()),
 455             ),
 456             Some(&Removed(ref reason)) => CheckLintNameResult::Warning(
 457                 format!("lint `{}` has been removed: {}", complete_name, reason),
 458                 None,
 459             ),
 460             None => match self.lint_groups.get(&*complete_name) {
 461                 // If neither the lint, nor the lint group exists check if there is a `clippy::`
 462                 // variant of this lint
 463                 None => self.check_tool_name_for_backwards_compat(&complete_name, "clippy"),
 464                 Some(LintGroup { lint_ids, depr, .. }) => {
 465                     // Check if the lint group name is deprecated
 466                     if let Some(LintAlias { name, silent }) = depr {
 467                         let LintGroup { lint_ids, .. } = self.lint_groups.get(name).unwrap();
 468                         return if *silent {
 469                             CheckLintNameResult::Ok(&lint_ids)
 470                         } else {
 471                             CheckLintNameResult::Tool(Err((Some(&lint_ids), (*name).to_string())))
 472                         };
 473                     }
 474                     CheckLintNameResult::Ok(&lint_ids)
 475                 }
 476             },
 477             Some(&Id(ref id)) => CheckLintNameResult::Ok(slice::from_ref(id)),
 478             Some(&Ignored) => CheckLintNameResult::Ok(&[]),
 479         }
 480     }
 481
 482     fn no_lint_suggestion(&self, lint_name: &str) -> CheckLintNameResult<'_> {
 483         let name_lower = lint_name.to_lowercase();
 484
 485         if lint_name.chars().any(char::is_uppercase) && self.find_lints(&name_lower).is_ok() {
 486             // First check if the lint name is (partly) in upper case instead of lower case...
 487             return CheckLintNameResult::NoLint(Some(Symbol::intern(&name_lower)));
 488         }
 489         // ...if not, search for lints with a similar name
 490         let groups = self.lint_groups.keys().copied().map(Symbol::intern);
 491         let lints = self.lints.iter().map(|l| Symbol::intern(&l.name_lower()));
 492         let names: Vec<Symbol> = groups.chain(lints).collect();
 493         let suggestion = find_best_match_for_name(&names, Symbol::intern(&name_lower), None);
 494         CheckLintNameResult::NoLint(suggestion)
 495     }
 496
 497     fn check_tool_name_for_backwards_compat(
 498         &self,
 499         lint_name: &str,
 500         tool_name: &str,
 501     ) -> CheckLintNameResult<'_> {
 502         let complete_name = format!("{}::{}", tool_name, lint_name);
 503         match self.by_name.get(&complete_name) {
 504             None => match self.lint_groups.get(&*complete_name) {
 505                 // Now we are sure, that this lint exists nowhere
 506                 None => self.no_lint_suggestion(lint_name),
 507                 Some(LintGroup { lint_ids, depr, .. }) => {
 508                     // Reaching this would be weird, but let's cover this case anyway
 509                     if let Some(LintAlias { name, silent }) = depr {
 510                         let LintGroup { lint_ids, .. } = self.lint_groups.get(name).unwrap();
 511                         return if *silent {
 512                             CheckLintNameResult::Tool(Err((Some(&lint_ids), complete_name)))
 513                         } else {
 514                             CheckLintNameResult::Tool(Err((Some(&lint_ids), (*name).to_string())))
 515                         };
 516                     }
 517                     CheckLintNameResult::Tool(Err((Some(&lint_ids), complete_name)))
 518                 }
 519             },
 520             Some(&Id(ref id)) => {
 521                 CheckLintNameResult::Tool(Err((Some(slice::from_ref(id)), complete_name)))
 522             }
 523             Some(other) => {
 524                 tracing::debug!("got renamed lint {:?}", other);
 525                 CheckLintNameResult::NoLint(None)
 526             }
 527         }
 528     }
 529 }
 530
 531 /// Context for lint checking after type checking.
 532 pub struct LateContext<'tcx> {
 533     /// Type context we're checking in.
 534     pub tcx: TyCtxt<'tcx>,
 535
 536     /// Current body, or `None` if outside a body.
 537     pub enclosing_body: Option<hir::BodyId>,
 538
 539     /// Type-checking results for the current body. Access using the `typeck_results`
 540     /// and `maybe_typeck_results` methods, which handle querying the typeck results on demand.
 541     // FIXME(eddyb) move all the code accessing internal fields like this,
 542     // to this module, to avoid exposing it to lint logic.
 543     pub(super) cached_typeck_results: Cell<Option<&'tcx ty::TypeckResults<'tcx>>>,
 544
 545     /// Parameter environment for the item we are in.
 546     pub param_env: ty::ParamEnv<'tcx>,
 547
 548     /// Items accessible from the crate being checked.
 549     pub access_levels: &'tcx AccessLevels,
 550
 551     /// The store of registered lints and the lint levels.
 552     pub lint_store: &'tcx LintStore,
 553
 554     pub last_node_with_lint_attrs: hir::HirId,
 555
 556     /// Generic type parameters in scope for the item we are in.
 557     pub generics: Option<&'tcx hir::Generics<'tcx>>,
 558
 559     /// We are only looking at one module
 560     pub only_module: bool,
 561 }
 562
 563 /// Context for lint checking of the AST, after expansion, before lowering to
 564 /// HIR.
 565 pub struct EarlyContext<'a> {
 566     /// Type context we're checking in.
 567     pub sess: &'a Session,
 568
 569     /// The crate being checked.
 570     pub krate: &'a ast::Crate,
 571
 572     pub builder: LintLevelsBuilder<'a>,
 573
 574     /// The store of registered lints and the lint levels.
 575     pub lint_store: &'a LintStore,
 576
 577     pub buffered: LintBuffer,
 578 }
 579
 580 pub trait LintPassObject: Sized {}
 581
 582 impl LintPassObject for EarlyLintPassObject {}
 583
 584 impl LintPassObject for LateLintPassObject {}
 585
 586 pub trait LintContext: Sized {
 587     type PassObject: LintPassObject;
 588
 589     fn sess(&self) -> &Session;
 590     fn lints(&self) -> &LintStore;
 591
 592     fn lookup_with_diagnostics(
 593         &self,
 594         lint: &'static Lint,
 595         span: Option<impl Into<MultiSpan>>,
 596         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 597         diagnostic: BuiltinLintDiagnostics,
 598     ) {
 599         self.lookup(lint, span, |lint| {
 600             // We first generate a blank diagnostic.
 601             let mut db = lint.build("");
 602
 603             // Now, set up surrounding context.
 604             let sess = self.sess();
 605             match diagnostic {
 606                 BuiltinLintDiagnostics::Normal => (),
 607                 BuiltinLintDiagnostics::BareTraitObject(span, is_global) => {
 608                     let (sugg, app) = match sess.source_map().span_to_snippet(span) {
 609                         Ok(s) if is_global => {
 610                             (format!("dyn ({})", s), Applicability::MachineApplicable)
 611                         }
 612                         Ok(s) => (format!("dyn {}", s), Applicability::MachineApplicable),
 613                         Err(_) => ("dyn <type>".to_string(), Applicability::HasPlaceholders),
 614                     };
 615                     db.span_suggestion(span, "use `dyn`", sugg, app);
 616                 }
 617                 BuiltinLintDiagnostics::AbsPathWithModule(span) => {
 618                     let (sugg, app) = match sess.source_map().span_to_snippet(span) {
 619                         Ok(ref s) => {
 620                             // FIXME(Manishearth) ideally the emitting code
 621                             // can tell us whether or not this is global
 622                             let opt_colon =
 623                                 if s.trim_start().starts_with("::") { "" } else { "::" };
 624
 625                             (format!("crate{}{}", opt_colon, s), Applicability::MachineApplicable)
 626                         }
 627                         Err(_) => ("crate::<path>".to_string(), Applicability::HasPlaceholders),
 628                     };
 629                     db.span_suggestion(span, "use `crate`", sugg, app);
 630                 }
 631                 BuiltinLintDiagnostics::ProcMacroDeriveResolutionFallback(span) => {
 632                     db.span_label(
 633                         span,
 634                         "names from parent modules are not accessible without an explicit import",
 635                     );
 636                 }
 637                 BuiltinLintDiagnostics::MacroExpandedMacroExportsAccessedByAbsolutePaths(
 638                     span_def,
 639                 ) => {
 640                     db.span_note(span_def, "the macro is defined here");
 641                 }
 642                 BuiltinLintDiagnostics::ElidedLifetimesInPaths(
 643                     n,
 644                     path_span,
 645                     incl_angl_brckt,
 646                     insertion_span,
 647                     anon_lts,
 648                 ) => {
 649                     add_elided_lifetime_in_path_suggestion(
 650                         sess.source_map(),
 651                         &mut db,
 652                         n,
 653                         path_span,
 654                         incl_angl_brckt,
 655                         insertion_span,
 656                         anon_lts,
 657                     );
 658                 }
 659                 BuiltinLintDiagnostics::UnknownCrateTypes(span, note, sugg) => {
 660                     db.span_suggestion(span, &note, sugg, Applicability::MaybeIncorrect);
 661                 }
 662                 BuiltinLintDiagnostics::UnusedImports(message, replaces) => {
 663                     if !replaces.is_empty() {
 664                         db.tool_only_multipart_suggestion(
 665                             &message,
 666                             replaces,
 667                             Applicability::MachineApplicable,
 668                         );
 669                     }
 670                 }
 671                 BuiltinLintDiagnostics::RedundantImport(spans, ident) => {
 672                     for (span, is_imported) in spans {
 673                         let introduced = if is_imported { "imported" } else { "defined" };
 674                         db.span_label(
 675                             span,
 676                             format!("the item `{}` is already {} here", ident, introduced),
 677                         );
 678                     }
 679                 }
 680                 BuiltinLintDiagnostics::DeprecatedMacro(suggestion, span) => {
 681                     stability::deprecation_suggestion(&mut db, "macro", suggestion, span)
 682                 }
 683                 BuiltinLintDiagnostics::UnusedDocComment(span) => {
 684                     db.span_label(span, "rustdoc does not generate documentation for macro invocations");
 685                     db.help("to document an item produced by a macro, \
 686                                   the macro must produce the documentation as part of its expansion");
 687                 }
 688                 BuiltinLintDiagnostics::PatternsInFnsWithoutBody(span, ident) => {
 689                     db.span_suggestion(span, "remove `mut` from the parameter", ident.to_string(), Applicability::MachineApplicable);
 690                 }
 691                 BuiltinLintDiagnostics::MissingAbi(span, default_abi) => {
 692                     db.span_label(span, "ABI should be specified here");
 693                     db.help(&format!("the default ABI is {}", default_abi.name()));
 694                 }
 695                 BuiltinLintDiagnostics::LegacyDeriveHelpers(span) => {
 696                     db.span_label(span, "the attribute is introduced here");
 697                 }
 698                 BuiltinLintDiagnostics::ExternDepSpec(krate, loc) => {
 699                     let json = match loc {
 700                         ExternDepSpec::Json(json) => {
 701                             db.help(&format!("remove unnecessary dependency `{}`", krate));
 702                             json
 703                         }
 704                         ExternDepSpec::Raw(raw) => {
 705                             db.help(&format!("remove unnecessary dependency `{}` at `{}`", krate, raw));
 706                             db.span_suggestion_with_style(
 707                                 DUMMY_SP,
 708                                 "raw extern location",
 709                                 raw.clone(),
 710                                 Applicability::Unspecified,
 711                                 SuggestionStyle::CompletelyHidden,
 712                             );
 713                             Json::String(raw)
 714                         }
 715                     };
 716                     db.tool_only_suggestion_with_metadata(
 717                         "json extern location",
 718                         Applicability::Unspecified,
 719                         json
 720                     );
 721                 }
 722                 BuiltinLintDiagnostics::ProcMacroBackCompat(note) => {
 723                     db.note(&note);
 724                 }
 725                 BuiltinLintDiagnostics::OrPatternsBackCompat(span,suggestion) => {
 726                     db.span_suggestion(span, "use pat_param to preserve semantics", suggestion, Applicability::MachineApplicable);
 727                 }
 728                 BuiltinLintDiagnostics::ReservedPrefix(span) => {
 729                     db.span_label(span, "unknown prefix");
 730                     db.span_suggestion_verbose(
 731                         span.shrink_to_hi(),
 732                         "insert whitespace here to avoid this being parsed as a prefix in Rust 2021",
 733                         " ".into(),
 734                         Applicability::MachineApplicable,
 735                     );
 736                 }
 737                 BuiltinLintDiagnostics::UnusedBuiltinAttribute {
 738                     attr_name,
 739                     macro_name,
 740                     invoc_span
 741                 } => {
 742                     db.span_note(
 743                         invoc_span,
 744                         &format!("the built-in attribute `{attr_name}` will be ignored, since it's applied to the macro invocation `{macro_name}`")
 745                     );
 746                 }
 747                 BuiltinLintDiagnostics::TrailingMacro(is_trailing, name) => {
 748                     if is_trailing {
 749                         db.note("macro invocations at the end of a block are treated as expressions");
 750                         db.note(&format!("to ignore the value produced by the macro, add a semicolon after the invocation of `{name}`"));
 751                     }
 752                 }
 753                 BuiltinLintDiagnostics::BreakWithLabelAndLoop(span) => {
 754                     db.multipart_suggestion(
 755                         "wrap this expression in parentheses",
 756                         vec![(span.shrink_to_lo(), "(".to_string()),
 757                              (span.shrink_to_hi(), ")".to_string())],
 758                         Applicability::MachineApplicable
 759                     );
 760                 }
 761                 BuiltinLintDiagnostics::NamedAsmLabel(help) => {
 762                     db.help(&help);
 763                     db.note("see the asm section of the unstable book <https://doc.rust-lang.org/nightly/unstable-book/library-features/asm.html#labels> for more information");
 764                 }
 765             }
 766             // Rewrap `db`, and pass control to the user.
 767             decorate(LintDiagnosticBuilder::new(db));
 768         });
 769     }
 770
 771     // FIXME: These methods should not take an Into<MultiSpan> -- instead, callers should need to
 772     // set the span in their `decorate` function (preferably using set_span).
 773     fn lookup<S: Into<MultiSpan>>(
 774         &self,
 775         lint: &'static Lint,
 776         span: Option<S>,
 777         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 778     );
 779
 780     fn struct_span_lint<S: Into<MultiSpan>>(
 781         &self,
 782         lint: &'static Lint,
 783         span: S,
 784         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 785     ) {
 786         self.lookup(lint, Some(span), decorate);
 787     }
 788     /// Emit a lint at the appropriate level, with no associated span.
 789     fn lint(&self, lint: &'static Lint, decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>)) {
 790         self.lookup(lint, None as Option<Span>, decorate);
 791     }
 792 }
 793
 794 impl<'a> EarlyContext<'a> {
 795     pub fn new(
 796         sess: &'a Session,
 797         lint_store: &'a LintStore,
 798         krate: &'a ast::Crate,
 799         buffered: LintBuffer,
 800         warn_about_weird_lints: bool,
 801     ) -> EarlyContext<'a> {
 802         EarlyContext {
 803             sess,
 804             krate,
 805             lint_store,
 806             builder: LintLevelsBuilder::new(sess, warn_about_weird_lints, lint_store, &krate.attrs),
 807             buffered,
 808         }
 809     }
 810 }
 811
 812 impl LintContext for LateContext<'_> {
 813     type PassObject = LateLintPassObject;
 814
 815     /// Gets the overall compiler `Session` object.
 816     fn sess(&self) -> &Session {
 817         &self.tcx.sess
 818     }
 819
 820     fn lints(&self) -> &LintStore {
 821         &*self.lint_store
 822     }
 823
 824     fn lookup<S: Into<MultiSpan>>(
 825         &self,
 826         lint: &'static Lint,
 827         span: Option<S>,
 828         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 829     ) {
 830         let hir_id = self.last_node_with_lint_attrs;
 831
 832         match span {
 833             Some(s) => self.tcx.struct_span_lint_hir(lint, hir_id, s, decorate),
 834             None => self.tcx.struct_lint_node(lint, hir_id, decorate),
 835         }
 836     }
 837 }
 838
 839 impl LintContext for EarlyContext<'_> {
 840     type PassObject = EarlyLintPassObject;
 841
 842     /// Gets the overall compiler `Session` object.
 843     fn sess(&self) -> &Session {
 844         &self.sess
 845     }
 846
 847     fn lints(&self) -> &LintStore {
 848         &*self.lint_store
 849     }
 850
 851     fn lookup<S: Into<MultiSpan>>(
 852         &self,
 853         lint: &'static Lint,
 854         span: Option<S>,
 855         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 856     ) {
 857         self.builder.struct_lint(lint, span.map(|s| s.into()), decorate)
 858     }
 859 }
 860
 861 impl<'tcx> LateContext<'tcx> {
 862     /// Gets the type-checking results for the current body,
 863     /// or `None` if outside a body.
 864     pub fn maybe_typeck_results(&self) -> Option<&'tcx ty::TypeckResults<'tcx>> {
 865         self.cached_typeck_results.get().or_else(|| {
 866             self.enclosing_body.map(|body| {
 867                 let typeck_results = self.tcx.typeck_body(body);
 868                 self.cached_typeck_results.set(Some(typeck_results));
 869                 typeck_results
 870             })
 871         })
 872     }
 873
 874     /// Gets the type-checking results for the current body.
 875     /// As this will ICE if called outside bodies, only call when working with
 876     /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
 877     #[track_caller]
 878     pub fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
 879         self.maybe_typeck_results().expect("`LateContext::typeck_results` called outside of body")
 880     }
 881
 882     /// Returns the final resolution of a `QPath`, or `Res::Err` if unavailable.
 883     /// Unlike `.typeck_results().qpath_res(qpath, id)`, this can be used even outside
 884     /// bodies (e.g. for paths in `hir::Ty`), without any risk of ICE-ing.
 885     pub fn qpath_res(&self, qpath: &hir::QPath<'_>, id: hir::HirId) -> Res {
 886         match *qpath {
 887             hir::QPath::Resolved(_, ref path) => path.res,
 888             hir::QPath::TypeRelative(..) | hir::QPath::LangItem(..) => self
 889                 .maybe_typeck_results()
 890                 .filter(|typeck_results| typeck_results.hir_owner == id.owner)
 891                 .or_else(|| {
 892                     if self.tcx.has_typeck_results(id.owner.to_def_id()) {
 893                         Some(self.tcx.typeck(id.owner))
 894                     } else {
 895                         None
 896                     }
 897                 })
 898                 .and_then(|typeck_results| typeck_results.type_dependent_def(id))
 899                 .map_or(Res::Err, |(kind, def_id)| Res::Def(kind, def_id)),
 900         }
 901     }
 902
 903     /// Check if a `DefId`'s path matches the given absolute type path usage.
 904     ///
 905     /// Anonymous scopes such as `extern` imports are matched with `kw::Empty`;
 906     /// inherent `impl` blocks are matched with the name of the type.
 907     ///
 908     /// Instead of using this method, it is often preferable to instead use
 909     /// `rustc_diagnostic_item` or a `lang_item`. This is less prone to errors
 910     /// as paths get invalidated if the target definition moves.
 911     ///
 912     /// # Examples
 913     ///
 914     /// ```rust,ignore (no context or def id available)
 915     /// if cx.match_def_path(def_id, &[sym::core, sym::option, sym::Option]) {
 916     ///     // The given `def_id` is that of an `Option` type
 917     /// }
 918     /// ```
 919     ///
 920     /// Used by clippy, but should be replaced by diagnostic items eventually.
 921     pub fn match_def_path(&self, def_id: DefId, path: &[Symbol]) -> bool {
 922         let names = self.get_def_path(def_id);
 923
 924         names.len() == path.len() && iter::zip(names, path).all(|(a, &b)| a == b)
 925     }
 926
 927     /// Gets the absolute path of `def_id` as a vector of `Symbol`.
 928     ///
 929     /// # Examples
 930     ///
 931     /// ```rust,ignore (no context or def id available)
 932     /// let def_path = cx.get_def_path(def_id);
 933     /// if let &[sym::core, sym::option, sym::Option] = &def_path[..] {
 934     ///     // The given `def_id` is that of an `Option` type
 935     /// }
 936     /// ```
 937     pub fn get_def_path(&self, def_id: DefId) -> Vec<Symbol> {
 938         pub struct AbsolutePathPrinter<'tcx> {
 939             pub tcx: TyCtxt<'tcx>,
 940         }
 941
 942         impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
 943             type Error = !;
 944
 945             type Path = Vec<Symbol>;
 946             type Region = ();
 947             type Type = ();
 948             type DynExistential = ();
 949             type Const = ();
 950
 951             fn tcx(&self) -> TyCtxt<'tcx> {
 952                 self.tcx
 953             }
 954
 955             fn print_region(self, _region: ty::Region<'_>) -> Result<Self::Region, Self::Error> {
 956                 Ok(())
 957             }
 958
 959             fn print_type(self, _ty: Ty<'tcx>) -> Result<Self::Type, Self::Error> {
 960                 Ok(())
 961             }
 962
 963             fn print_dyn_existential(
 964                 self,
 965                 _predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
 966             ) -> Result<Self::DynExistential, Self::Error> {
 967                 Ok(())
 968             }
 969
 970             fn print_const(self, _ct: &'tcx ty::Const<'tcx>) -> Result<Self::Const, Self::Error> {
 971                 Ok(())
 972             }
 973
 974             fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
 975                 Ok(vec![self.tcx.crate_name(cnum)])
 976             }
 977
 978             fn path_qualified(
 979                 self,
 980                 self_ty: Ty<'tcx>,
 981                 trait_ref: Option<ty::TraitRef<'tcx>>,
 982             ) -> Result<Self::Path, Self::Error> {
 983                 if trait_ref.is_none() {
 984                     if let ty::Adt(def, substs) = self_ty.kind() {
 985                         return self.print_def_path(def.did, substs);
 986                     }
 987                 }
 988
 989                 // This shouldn't ever be needed, but just in case:
 990                 with_no_trimmed_paths(|| {
 991                     Ok(vec![match trait_ref {
 992                         Some(trait_ref) => Symbol::intern(&format!("{:?}", trait_ref)),
 993                         None => Symbol::intern(&format!("<{}>", self_ty)),
 994                     }])
 995                 })
 996             }
 997
 998             fn path_append_impl(
 999                 self,
1000                 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
1001                 _disambiguated_data: &DisambiguatedDefPathData,
1002                 self_ty: Ty<'tcx>,
1003                 trait_ref: Option<ty::TraitRef<'tcx>>,
1004             ) -> Result<Self::Path, Self::Error> {
1005                 let mut path = print_prefix(self)?;
1006
1007                 // This shouldn't ever be needed, but just in case:
1008                 path.push(match trait_ref {
1009                     Some(trait_ref) => with_no_trimmed_paths(|| {
1010                         Symbol::intern(&format!(
1011                             "<impl {} for {}>",
1012                             trait_ref.print_only_trait_path(),
1013                             self_ty
1014                         ))
1015                     }),
1016                     None => {
1017                         with_no_trimmed_paths(|| Symbol::intern(&format!("<impl {}>", self_ty)))
1018                     }
1019                 });
1020
1021                 Ok(path)
1022             }
1023
1024             fn path_append(
1025                 self,
1026                 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
1027                 disambiguated_data: &DisambiguatedDefPathData,
1028             ) -> Result<Self::Path, Self::Error> {
1029                 let mut path = print_prefix(self)?;
1030
1031                 // Skip `::{{constructor}}` on tuple/unit structs.
1032                 if let DefPathData::Ctor = disambiguated_data.data {
1033                     return Ok(path);
1034                 }
1035
1036                 path.push(Symbol::intern(&disambiguated_data.data.to_string()));
1037                 Ok(path)
1038             }
1039
1040             fn path_generic_args(
1041                 self,
1042                 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
1043                 _args: &[GenericArg<'tcx>],
1044             ) -> Result<Self::Path, Self::Error> {
1045                 print_prefix(self)
1046             }
1047         }
1048
1049         AbsolutePathPrinter { tcx: self.tcx }.print_def_path(def_id, &[]).unwrap()
1050     }
1051 }
1052
1053 impl<'tcx> LayoutOf for LateContext<'tcx> {
1054     type Ty = Ty<'tcx>;
1055     type TyAndLayout = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
1056
1057     fn layout_of(&self, ty: Ty<'tcx>) -> Self::TyAndLayout {
1058         self.tcx.layout_of(self.param_env.and(ty))
1059     }
1060 }
1061
1062 pub fn parse_lint_and_tool_name(lint_name: &str) -> (Option<Symbol>, &str) {
1063     match lint_name.split_once("::") {
1064         Some((tool_name, lint_name)) => {
1065             let tool_name = Symbol::intern(tool_name);
1066
1067             (Some(tool_name), lint_name)
1068         }
1069         None => (None, lint_name),
1070     }
1071 }