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 ast::util::unicode::TEXT_FLOW_CONTROL_CHARS;
  22 use rustc_ast as ast;
  23 use rustc_data_structures::fx::FxHashMap;
  24 use rustc_data_structures::sync;
  25 use rustc_errors::{struct_span_err, Applicability, SuggestionStyle};
  26 use rustc_hir as hir;
  27 use rustc_hir::def::Res;
  28 use rustc_hir::def_id::{CrateNum, DefId};
  29 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
  30 use rustc_middle::lint::LintDiagnosticBuilder;
  31 use rustc_middle::middle::privacy::AccessLevels;
  32 use rustc_middle::middle::stability;
  33 use rustc_middle::ty::layout::{LayoutError, LayoutOfHelpers, TyAndLayout};
  34 use rustc_middle::ty::print::with_no_trimmed_paths;
  35 use rustc_middle::ty::{self, print::Printer, subst::GenericArg, Ty, TyCtxt};
  36 use rustc_serialize::json::Json;
  37 use rustc_session::lint::{BuiltinLintDiagnostics, ExternDepSpec};
  38 use rustc_session::lint::{FutureIncompatibleInfo, Level, Lint, LintBuffer, LintId};
  39 use rustc_session::Session;
  40 use rustc_span::lev_distance::find_best_match_for_name;
  41 use rustc_span::{symbol::Symbol, BytePos, MultiSpan, Span, DUMMY_SP};
  42 use rustc_target::abi;
  43 use tracing::debug;
  44
  45 use std::cell::Cell;
  46 use std::iter;
  47 use std::slice;
  48
  49 /// Information about the registered lints.
  50 ///
  51 /// This is basically the subset of `Context` that we can
  52 /// build early in the compile pipeline.
  53 pub struct LintStore {
  54     /// Registered lints.
  55     lints: Vec<&'static Lint>,
  56
  57     /// Constructor functions for each variety of lint pass.
  58     ///
  59     /// These should only be called once, but since we want to avoid locks or
  60     /// interior mutability, we don't enforce this (and lints should, in theory,
  61     /// be compatible with being constructed more than once, though not
  62     /// necessarily in a sane manner. This is safe though.)
  63     pub pre_expansion_passes: Vec<Box<dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync>>,
  64     pub early_passes: Vec<Box<dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync>>,
  65     pub late_passes: Vec<Box<dyn Fn() -> LateLintPassObject + sync::Send + sync::Sync>>,
  66     /// This is unique in that we construct them per-module, so not once.
  67     pub late_module_passes: Vec<Box<dyn Fn() -> LateLintPassObject + sync::Send + sync::Sync>>,
  68
  69     /// Lints indexed by name.
  70     by_name: FxHashMap<String, TargetLint>,
  71
  72     /// Map of registered lint groups to what lints they expand to.
  73     lint_groups: FxHashMap<&'static str, LintGroup>,
  74 }
  75
  76 /// The target of the `by_name` map, which accounts for renaming/deprecation.
  77 #[derive(Debug)]
  78 enum TargetLint {
  79     /// A direct lint target
  80     Id(LintId),
  81
  82     /// Temporary renaming, used for easing migration pain; see #16545
  83     Renamed(String, LintId),
  84
  85     /// Lint with this name existed previously, but has been removed/deprecated.
  86     /// The string argument is the reason for removal.
  87     Removed(String),
  88
  89     /// A lint name that should give no warnings and have no effect.
  90     ///
  91     /// This is used by rustc to avoid warning about old rustdoc lints before rustdoc registers them as tool lints.
  92     Ignored,
  93 }
  94
  95 pub enum FindLintError {
  96     NotFound,
  97     Removed,
  98 }
  99
 100 struct LintAlias {
 101     name: &'static str,
 102     /// Whether deprecation warnings should be suppressed for this alias.
 103     silent: bool,
 104 }
 105
 106 struct LintGroup {
 107     lint_ids: Vec<LintId>,
 108     from_plugin: bool,
 109     depr: Option<LintAlias>,
 110 }
 111
 112 pub enum CheckLintNameResult<'a> {
 113     Ok(&'a [LintId]),
 114     /// Lint doesn't exist. Potentially contains a suggestion for a correct lint name.
 115     NoLint(Option<Symbol>),
 116     /// The lint refers to a tool that has not been registered.
 117     NoTool,
 118     /// The lint is either renamed or removed. This is the warning
 119     /// message, and an optional new name (`None` if removed).
 120     Warning(String, Option<String>),
 121     /// The lint is from a tool. If the Option is None, then either
 122     /// the lint does not exist in the tool or the code was not
 123     /// compiled with the tool and therefore the lint was never
 124     /// added to the `LintStore`. Otherwise the `LintId` will be
 125     /// returned as if it where a rustc lint.
 126     Tool(Result<&'a [LintId], (Option<&'a [LintId]>, String)>),
 127 }
 128
 129 impl LintStore {
 130     pub fn new() -> LintStore {
 131         LintStore {
 132             lints: vec![],
 133             pre_expansion_passes: vec![],
 134             early_passes: vec![],
 135             late_passes: vec![],
 136             late_module_passes: vec![],
 137             by_name: Default::default(),
 138             lint_groups: Default::default(),
 139         }
 140     }
 141
 142     pub fn get_lints<'t>(&'t self) -> &'t [&'static Lint] {
 143         &self.lints
 144     }
 145
 146     pub fn get_lint_groups<'t>(&'t self) -> Vec<(&'static str, Vec<LintId>, bool)> {
 147         self.lint_groups
 148             .iter()
 149             .filter(|(_, LintGroup { depr, .. })| {
 150                 // Don't display deprecated lint groups.
 151                 depr.is_none()
 152             })
 153             .map(|(k, LintGroup { lint_ids, from_plugin, .. })| {
 154                 (*k, lint_ids.clone(), *from_plugin)
 155             })
 156             .collect()
 157     }
 158
 159     pub fn register_early_pass(
 160         &mut self,
 161         pass: impl Fn() -> EarlyLintPassObject + 'static + sync::Send + sync::Sync,
 162     ) {
 163         self.early_passes.push(Box::new(pass));
 164     }
 165
 166     /// Used by clippy.
 167     pub fn register_pre_expansion_pass(
 168         &mut self,
 169         pass: impl Fn() -> EarlyLintPassObject + 'static + sync::Send + sync::Sync,
 170     ) {
 171         self.pre_expansion_passes.push(Box::new(pass));
 172     }
 173
 174     pub fn register_late_pass(
 175         &mut self,
 176         pass: impl Fn() -> LateLintPassObject + 'static + sync::Send + sync::Sync,
 177     ) {
 178         self.late_passes.push(Box::new(pass));
 179     }
 180
 181     pub fn register_late_mod_pass(
 182         &mut self,
 183         pass: impl Fn() -> LateLintPassObject + 'static + sync::Send + sync::Sync,
 184     ) {
 185         self.late_module_passes.push(Box::new(pass));
 186     }
 187
 188     // Helper method for register_early/late_pass
 189     pub fn register_lints(&mut self, lints: &[&'static Lint]) {
 190         for lint in lints {
 191             self.lints.push(lint);
 192
 193             let id = LintId::of(lint);
 194             if self.by_name.insert(lint.name_lower(), Id(id)).is_some() {
 195                 bug!("duplicate specification of lint {}", lint.name_lower())
 196             }
 197
 198             if let Some(FutureIncompatibleInfo { reason, .. }) = lint.future_incompatible {
 199                 if let Some(edition) = reason.edition() {
 200                     self.lint_groups
 201                         .entry(edition.lint_name())
 202                         .or_insert(LintGroup {
 203                             lint_ids: vec![],
 204                             from_plugin: lint.is_plugin,
 205                             depr: None,
 206                         })
 207                         .lint_ids
 208                         .push(id);
 209                 } else {
 210                     // Lints belonging to the `future_incompatible` lint group are lints where a
 211                     // future version of rustc will cause existing code to stop compiling.
 212                     // Lints tied to an edition don't count because they are opt-in.
 213                     self.lint_groups
 214                         .entry("future_incompatible")
 215                         .or_insert(LintGroup {
 216                             lint_ids: vec![],
 217                             from_plugin: lint.is_plugin,
 218                             depr: None,
 219                         })
 220                         .lint_ids
 221                         .push(id);
 222                 }
 223             }
 224         }
 225     }
 226
 227     pub fn register_group_alias(&mut self, lint_name: &'static str, alias: &'static str) {
 228         self.lint_groups.insert(
 229             alias,
 230             LintGroup {
 231                 lint_ids: vec![],
 232                 from_plugin: false,
 233                 depr: Some(LintAlias { name: lint_name, silent: true }),
 234             },
 235         );
 236     }
 237
 238     pub fn register_group(
 239         &mut self,
 240         from_plugin: bool,
 241         name: &'static str,
 242         deprecated_name: Option<&'static str>,
 243         to: Vec<LintId>,
 244     ) {
 245         let new = self
 246             .lint_groups
 247             .insert(name, LintGroup { lint_ids: to, from_plugin, depr: None })
 248             .is_none();
 249         if let Some(deprecated) = deprecated_name {
 250             self.lint_groups.insert(
 251                 deprecated,
 252                 LintGroup {
 253                     lint_ids: vec![],
 254                     from_plugin,
 255                     depr: Some(LintAlias { name, silent: false }),
 256                 },
 257             );
 258         }
 259
 260         if !new {
 261             bug!("duplicate specification of lint group {}", name);
 262         }
 263     }
 264
 265     /// This lint should give no warning and have no effect.
 266     ///
 267     /// This is used by rustc to avoid warning about old rustdoc lints before rustdoc registers them as tool lints.
 268     #[track_caller]
 269     pub fn register_ignored(&mut self, name: &str) {
 270         if self.by_name.insert(name.to_string(), Ignored).is_some() {
 271             bug!("duplicate specification of lint {}", name);
 272         }
 273     }
 274
 275     /// This lint has been renamed; warn about using the new name and apply the lint.
 276     #[track_caller]
 277     pub fn register_renamed(&mut self, old_name: &str, new_name: &str) {
 278         let target = match self.by_name.get(new_name) {
 279             Some(&Id(lint_id)) => lint_id,
 280             _ => bug!("invalid lint renaming of {} to {}", old_name, new_name),
 281         };
 282         self.by_name.insert(old_name.to_string(), Renamed(new_name.to_string(), target));
 283     }
 284
 285     pub fn register_removed(&mut self, name: &str, reason: &str) {
 286         self.by_name.insert(name.into(), Removed(reason.into()));
 287     }
 288
 289     pub fn find_lints(&self, mut lint_name: &str) -> Result<Vec<LintId>, FindLintError> {
 290         match self.by_name.get(lint_name) {
 291             Some(&Id(lint_id)) => Ok(vec![lint_id]),
 292             Some(&Renamed(_, lint_id)) => Ok(vec![lint_id]),
 293             Some(&Removed(_)) => Err(FindLintError::Removed),
 294             Some(&Ignored) => Ok(vec![]),
 295             None => loop {
 296                 return match self.lint_groups.get(lint_name) {
 297                     Some(LintGroup { lint_ids, depr, .. }) => {
 298                         if let Some(LintAlias { name, .. }) = depr {
 299                             lint_name = name;
 300                             continue;
 301                         }
 302                         Ok(lint_ids.clone())
 303                     }
 304                     None => Err(FindLintError::Removed),
 305                 };
 306             },
 307         }
 308     }
 309
 310     /// Checks the validity of lint names derived from the command line.
 311     pub fn check_lint_name_cmdline(
 312         &self,
 313         sess: &Session,
 314         lint_name: &str,
 315         level: Level,
 316         crate_attrs: &[ast::Attribute],
 317     ) {
 318         let (tool_name, lint_name_only) = parse_lint_and_tool_name(lint_name);
 319         if lint_name_only == crate::WARNINGS.name_lower() && level == Level::ForceWarn {
 320             return struct_span_err!(
 321                 sess,
 322                 DUMMY_SP,
 323                 E0602,
 324                 "`{}` lint group is not supported with ´--force-warn´",
 325                 crate::WARNINGS.name_lower()
 326             )
 327             .emit();
 328         }
 329         let db = match self.check_lint_name(sess, lint_name_only, tool_name, crate_attrs) {
 330             CheckLintNameResult::Ok(_) => None,
 331             CheckLintNameResult::Warning(ref msg, _) => Some(sess.struct_warn(msg)),
 332             CheckLintNameResult::NoLint(suggestion) => {
 333                 let mut err =
 334                     struct_span_err!(sess, DUMMY_SP, E0602, "unknown lint: `{}`", lint_name);
 335
 336                 if let Some(suggestion) = suggestion {
 337                     err.help(&format!("did you mean: `{}`", suggestion));
 338                 }
 339
 340                 Some(err)
 341             }
 342             CheckLintNameResult::Tool(result) => match result {
 343                 Err((Some(_), new_name)) => Some(sess.struct_warn(&format!(
 344                     "lint name `{}` is deprecated \
 345                      and does not have an effect anymore. \
 346                      Use: {}",
 347                     lint_name, new_name
 348                 ))),
 349                 _ => None,
 350             },
 351             CheckLintNameResult::NoTool => Some(struct_span_err!(
 352                 sess,
 353                 DUMMY_SP,
 354                 E0602,
 355                 "unknown lint tool: `{}`",
 356                 tool_name.unwrap()
 357             )),
 358         };
 359
 360         if let Some(mut db) = db {
 361             let msg = format!(
 362                 "requested on the command line with `{} {}`",
 363                 match level {
 364                     Level::Allow => "-A",
 365                     Level::Warn => "-W",
 366                     Level::ForceWarn => "--force-warn",
 367                     Level::Deny => "-D",
 368                     Level::Forbid => "-F",
 369                 },
 370                 lint_name
 371             );
 372             db.note(&msg);
 373             db.emit();
 374         }
 375     }
 376
 377     /// True if this symbol represents a lint group name.
 378     pub fn is_lint_group(&self, lint_name: Symbol) -> bool {
 379         debug!(
 380             "is_lint_group(lint_name={:?}, lint_groups={:?})",
 381             lint_name,
 382             self.lint_groups.keys().collect::<Vec<_>>()
 383         );
 384         let lint_name_str = &*lint_name.as_str();
 385         self.lint_groups.contains_key(&lint_name_str) || {
 386             let warnings_name_str = crate::WARNINGS.name_lower();
 387             lint_name_str == &*warnings_name_str
 388         }
 389     }
 390
 391     /// Checks the name of a lint for its existence, and whether it was
 392     /// renamed or removed. Generates a DiagnosticBuilder containing a
 393     /// warning for renamed and removed lints. This is over both lint
 394     /// names from attributes and those passed on the command line. Since
 395     /// it emits non-fatal warnings and there are *two* lint passes that
 396     /// inspect attributes, this is only run from the late pass to avoid
 397     /// printing duplicate warnings.
 398     pub fn check_lint_name(
 399         &self,
 400         sess: &Session,
 401         lint_name: &str,
 402         tool_name: Option<Symbol>,
 403         crate_attrs: &[ast::Attribute],
 404     ) -> CheckLintNameResult<'_> {
 405         if let Some(tool_name) = tool_name {
 406             if !is_known_lint_tool(tool_name, sess, crate_attrs) {
 407                 return CheckLintNameResult::NoTool;
 408             }
 409         }
 410
 411         let complete_name = if let Some(tool_name) = tool_name {
 412             format!("{}::{}", tool_name, lint_name)
 413         } else {
 414             lint_name.to_string()
 415         };
 416         // If the lint was scoped with `tool::` check if the tool lint exists
 417         if let Some(tool_name) = tool_name {
 418             match self.by_name.get(&complete_name) {
 419                 None => match self.lint_groups.get(&*complete_name) {
 420                     // If the lint isn't registered, there are two possibilities:
 421                     None => {
 422                         // 1. The tool is currently running, so this lint really doesn't exist.
 423                         // FIXME: should this handle tools that never register a lint, like rustfmt?
 424                         tracing::debug!("lints={:?}", self.by_name.keys().collect::<Vec<_>>());
 425                         let tool_prefix = format!("{}::", tool_name);
 426                         return if self.by_name.keys().any(|lint| lint.starts_with(&tool_prefix)) {
 427                             self.no_lint_suggestion(&complete_name)
 428                         } else {
 429                             // 2. The tool isn't currently running, so no lints will be registered.
 430                             // To avoid giving a false positive, ignore all unknown lints.
 431                             CheckLintNameResult::Tool(Err((None, String::new())))
 432                         };
 433                     }
 434                     Some(LintGroup { lint_ids, .. }) => {
 435                         return CheckLintNameResult::Tool(Ok(&lint_ids));
 436                     }
 437                 },
 438                 Some(&Id(ref id)) => return CheckLintNameResult::Tool(Ok(slice::from_ref(id))),
 439                 // If the lint was registered as removed or renamed by the lint tool, we don't need
 440                 // to treat tool_lints and rustc lints different and can use the code below.
 441                 _ => {}
 442             }
 443         }
 444         match self.by_name.get(&complete_name) {
 445             Some(&Renamed(ref new_name, _)) => CheckLintNameResult::Warning(
 446                 format!("lint `{}` has been renamed to `{}`", complete_name, new_name),
 447                 Some(new_name.to_owned()),
 448             ),
 449             Some(&Removed(ref reason)) => CheckLintNameResult::Warning(
 450                 format!("lint `{}` has been removed: {}", complete_name, reason),
 451                 None,
 452             ),
 453             None => match self.lint_groups.get(&*complete_name) {
 454                 // If neither the lint, nor the lint group exists check if there is a `clippy::`
 455                 // variant of this lint
 456                 None => self.check_tool_name_for_backwards_compat(&complete_name, "clippy"),
 457                 Some(LintGroup { lint_ids, depr, .. }) => {
 458                     // Check if the lint group name is deprecated
 459                     if let Some(LintAlias { name, silent }) = depr {
 460                         let LintGroup { lint_ids, .. } = self.lint_groups.get(name).unwrap();
 461                         return if *silent {
 462                             CheckLintNameResult::Ok(&lint_ids)
 463                         } else {
 464                             CheckLintNameResult::Tool(Err((Some(&lint_ids), (*name).to_string())))
 465                         };
 466                     }
 467                     CheckLintNameResult::Ok(&lint_ids)
 468                 }
 469             },
 470             Some(&Id(ref id)) => CheckLintNameResult::Ok(slice::from_ref(id)),
 471             Some(&Ignored) => CheckLintNameResult::Ok(&[]),
 472         }
 473     }
 474
 475     fn no_lint_suggestion(&self, lint_name: &str) -> CheckLintNameResult<'_> {
 476         let name_lower = lint_name.to_lowercase();
 477
 478         if lint_name.chars().any(char::is_uppercase) && self.find_lints(&name_lower).is_ok() {
 479             // First check if the lint name is (partly) in upper case instead of lower case...
 480             return CheckLintNameResult::NoLint(Some(Symbol::intern(&name_lower)));
 481         }
 482         // ...if not, search for lints with a similar name
 483         let groups = self.lint_groups.keys().copied().map(Symbol::intern);
 484         let lints = self.lints.iter().map(|l| Symbol::intern(&l.name_lower()));
 485         let names: Vec<Symbol> = groups.chain(lints).collect();
 486         let suggestion = find_best_match_for_name(&names, Symbol::intern(&name_lower), None);
 487         CheckLintNameResult::NoLint(suggestion)
 488     }
 489
 490     fn check_tool_name_for_backwards_compat(
 491         &self,
 492         lint_name: &str,
 493         tool_name: &str,
 494     ) -> CheckLintNameResult<'_> {
 495         let complete_name = format!("{}::{}", tool_name, lint_name);
 496         match self.by_name.get(&complete_name) {
 497             None => match self.lint_groups.get(&*complete_name) {
 498                 // Now we are sure, that this lint exists nowhere
 499                 None => self.no_lint_suggestion(lint_name),
 500                 Some(LintGroup { lint_ids, depr, .. }) => {
 501                     // Reaching this would be weird, but let's cover this case anyway
 502                     if let Some(LintAlias { name, silent }) = depr {
 503                         let LintGroup { lint_ids, .. } = self.lint_groups.get(name).unwrap();
 504                         return if *silent {
 505                             CheckLintNameResult::Tool(Err((Some(&lint_ids), complete_name)))
 506                         } else {
 507                             CheckLintNameResult::Tool(Err((Some(&lint_ids), (*name).to_string())))
 508                         };
 509                     }
 510                     CheckLintNameResult::Tool(Err((Some(&lint_ids), complete_name)))
 511                 }
 512             },
 513             Some(&Id(ref id)) => {
 514                 CheckLintNameResult::Tool(Err((Some(slice::from_ref(id)), complete_name)))
 515             }
 516             Some(other) => {
 517                 tracing::debug!("got renamed lint {:?}", other);
 518                 CheckLintNameResult::NoLint(None)
 519             }
 520         }
 521     }
 522 }
 523
 524 /// Context for lint checking after type checking.
 525 pub struct LateContext<'tcx> {
 526     /// Type context we're checking in.
 527     pub tcx: TyCtxt<'tcx>,
 528
 529     /// Current body, or `None` if outside a body.
 530     pub enclosing_body: Option<hir::BodyId>,
 531
 532     /// Type-checking results for the current body. Access using the `typeck_results`
 533     /// and `maybe_typeck_results` methods, which handle querying the typeck results on demand.
 534     // FIXME(eddyb) move all the code accessing internal fields like this,
 535     // to this module, to avoid exposing it to lint logic.
 536     pub(super) cached_typeck_results: Cell<Option<&'tcx ty::TypeckResults<'tcx>>>,
 537
 538     /// Parameter environment for the item we are in.
 539     pub param_env: ty::ParamEnv<'tcx>,
 540
 541     /// Items accessible from the crate being checked.
 542     pub access_levels: &'tcx AccessLevels,
 543
 544     /// The store of registered lints and the lint levels.
 545     pub lint_store: &'tcx LintStore,
 546
 547     pub last_node_with_lint_attrs: hir::HirId,
 548
 549     /// Generic type parameters in scope for the item we are in.
 550     pub generics: Option<&'tcx hir::Generics<'tcx>>,
 551
 552     /// We are only looking at one module
 553     pub only_module: bool,
 554 }
 555
 556 /// Context for lint checking of the AST, after expansion, before lowering to
 557 /// HIR.
 558 pub struct EarlyContext<'a> {
 559     /// Type context we're checking in.
 560     pub sess: &'a Session,
 561
 562     /// The crate being checked.
 563     pub krate: &'a ast::Crate,
 564
 565     pub builder: LintLevelsBuilder<'a>,
 566
 567     /// The store of registered lints and the lint levels.
 568     pub lint_store: &'a LintStore,
 569
 570     pub buffered: LintBuffer,
 571 }
 572
 573 pub trait LintPassObject: Sized {}
 574
 575 impl LintPassObject for EarlyLintPassObject {}
 576
 577 impl LintPassObject for LateLintPassObject {}
 578
 579 pub trait LintContext: Sized {
 580     type PassObject: LintPassObject;
 581
 582     fn sess(&self) -> &Session;
 583     fn lints(&self) -> &LintStore;
 584
 585     fn lookup_with_diagnostics(
 586         &self,
 587         lint: &'static Lint,
 588         span: Option<impl Into<MultiSpan>>,
 589         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 590         diagnostic: BuiltinLintDiagnostics,
 591     ) {
 592         self.lookup(lint, span, |lint| {
 593             // We first generate a blank diagnostic.
 594             let mut db = lint.build("");
 595
 596             // Now, set up surrounding context.
 597             let sess = self.sess();
 598             match diagnostic {
 599                 BuiltinLintDiagnostics::UnicodeTextFlow(span, content) => {
 600                     let spans: Vec<_> = content
 601                         .char_indices()
 602                         .filter_map(|(i, c)| {
 603                             TEXT_FLOW_CONTROL_CHARS.contains(&c).then(|| {
 604                                 let lo = span.lo() + BytePos(2 + i as u32);
 605                                 (c, span.with_lo(lo).with_hi(lo + BytePos(c.len_utf8() as u32)))
 606                             })
 607                         })
 608                         .collect();
 609                     let (an, s) = match spans.len() {
 610                         1 => ("an ", ""),
 611                         _ => ("", "s"),
 612                     };
 613                     db.span_label(span, &format!(
 614                         "this comment contains {}invisible unicode text flow control codepoint{}",
 615                         an,
 616                         s,
 617                     ));
 618                     for (c, span) in &spans {
 619                         db.span_label(*span, format!("{:?}", c));
 620                     }
 621                     db.note(
 622                         "these kind of unicode codepoints change the way text flows on \
 623                          applications that support them, but can cause confusion because they \
 624                          change the order of characters on the screen",
 625                     );
 626                     if !spans.is_empty() {
 627                         db.multipart_suggestion_with_style(
 628                             "if their presence wasn't intentional, you can remove them",
 629                             spans.into_iter().map(|(_, span)| (span, "".to_string())).collect(),
 630                             Applicability::MachineApplicable,
 631                             SuggestionStyle::HideCodeAlways,
 632                         );
 633                     }
 634                 },
 635                 BuiltinLintDiagnostics::Normal => (),
 636                 BuiltinLintDiagnostics::BareTraitObject(span, is_global) => {
 637                     let (sugg, app) = match sess.source_map().span_to_snippet(span) {
 638                         Ok(s) if is_global => {
 639                             (format!("dyn ({})", s), Applicability::MachineApplicable)
 640                         }
 641                         Ok(s) => (format!("dyn {}", s), Applicability::MachineApplicable),
 642                         Err(_) => ("dyn <type>".to_string(), Applicability::HasPlaceholders),
 643                     };
 644                     db.span_suggestion(span, "use `dyn`", sugg, app);
 645                 }
 646                 BuiltinLintDiagnostics::AbsPathWithModule(span) => {
 647                     let (sugg, app) = match sess.source_map().span_to_snippet(span) {
 648                         Ok(ref s) => {
 649                             // FIXME(Manishearth) ideally the emitting code
 650                             // can tell us whether or not this is global
 651                             let opt_colon =
 652                                 if s.trim_start().starts_with("::") { "" } else { "::" };
 653
 654                             (format!("crate{}{}", opt_colon, s), Applicability::MachineApplicable)
 655                         }
 656                         Err(_) => ("crate::<path>".to_string(), Applicability::HasPlaceholders),
 657                     };
 658                     db.span_suggestion(span, "use `crate`", sugg, app);
 659                 }
 660                 BuiltinLintDiagnostics::ProcMacroDeriveResolutionFallback(span) => {
 661                     db.span_label(
 662                         span,
 663                         "names from parent modules are not accessible without an explicit import",
 664                     );
 665                 }
 666                 BuiltinLintDiagnostics::MacroExpandedMacroExportsAccessedByAbsolutePaths(
 667                     span_def,
 668                 ) => {
 669                     db.span_note(span_def, "the macro is defined here");
 670                 }
 671                 BuiltinLintDiagnostics::UnknownCrateTypes(span, note, sugg) => {
 672                     db.span_suggestion(span, &note, sugg, Applicability::MaybeIncorrect);
 673                 }
 674                 BuiltinLintDiagnostics::UnusedImports(message, replaces) => {
 675                     if !replaces.is_empty() {
 676                         db.tool_only_multipart_suggestion(
 677                             &message,
 678                             replaces,
 679                             Applicability::MachineApplicable,
 680                         );
 681                     }
 682                 }
 683                 BuiltinLintDiagnostics::RedundantImport(spans, ident) => {
 684                     for (span, is_imported) in spans {
 685                         let introduced = if is_imported { "imported" } else { "defined" };
 686                         db.span_label(
 687                             span,
 688                             format!("the item `{}` is already {} here", ident, introduced),
 689                         );
 690                     }
 691                 }
 692                 BuiltinLintDiagnostics::DeprecatedMacro(suggestion, span) => {
 693                     stability::deprecation_suggestion(&mut db, "macro", suggestion, span)
 694                 }
 695                 BuiltinLintDiagnostics::UnusedDocComment(span) => {
 696                     db.span_label(span, "rustdoc does not generate documentation for macro invocations");
 697                     db.help("to document an item produced by a macro, \
 698                                   the macro must produce the documentation as part of its expansion");
 699                 }
 700                 BuiltinLintDiagnostics::PatternsInFnsWithoutBody(span, ident) => {
 701                     db.span_suggestion(span, "remove `mut` from the parameter", ident.to_string(), Applicability::MachineApplicable);
 702                 }
 703                 BuiltinLintDiagnostics::MissingAbi(span, default_abi) => {
 704                     db.span_label(span, "ABI should be specified here");
 705                     db.help(&format!("the default ABI is {}", default_abi.name()));
 706                 }
 707                 BuiltinLintDiagnostics::LegacyDeriveHelpers(span) => {
 708                     db.span_label(span, "the attribute is introduced here");
 709                 }
 710                 BuiltinLintDiagnostics::ExternDepSpec(krate, loc) => {
 711                     let json = match loc {
 712                         ExternDepSpec::Json(json) => {
 713                             db.help(&format!("remove unnecessary dependency `{}`", krate));
 714                             json
 715                         }
 716                         ExternDepSpec::Raw(raw) => {
 717                             db.help(&format!("remove unnecessary dependency `{}` at `{}`", krate, raw));
 718                             db.span_suggestion_with_style(
 719                                 DUMMY_SP,
 720                                 "raw extern location",
 721                                 raw.clone(),
 722                                 Applicability::Unspecified,
 723                                 SuggestionStyle::CompletelyHidden,
 724                             );
 725                             Json::String(raw)
 726                         }
 727                     };
 728                     db.tool_only_suggestion_with_metadata(
 729                         "json extern location",
 730                         Applicability::Unspecified,
 731                         json
 732                     );
 733                 }
 734                 BuiltinLintDiagnostics::ProcMacroBackCompat(note) => {
 735                     db.note(&note);
 736                 }
 737                 BuiltinLintDiagnostics::OrPatternsBackCompat(span,suggestion) => {
 738                     db.span_suggestion(span, "use pat_param to preserve semantics", suggestion, Applicability::MachineApplicable);
 739                 }
 740                 BuiltinLintDiagnostics::ReservedPrefix(span) => {
 741                     db.span_label(span, "unknown prefix");
 742                     db.span_suggestion_verbose(
 743                         span.shrink_to_hi(),
 744                         "insert whitespace here to avoid this being parsed as a prefix in Rust 2021",
 745                         " ".into(),
 746                         Applicability::MachineApplicable,
 747                     );
 748                 }
 749                 BuiltinLintDiagnostics::UnusedBuiltinAttribute {
 750                     attr_name,
 751                     macro_name,
 752                     invoc_span
 753                 } => {
 754                     db.span_note(
 755                         invoc_span,
 756                         &format!("the built-in attribute `{attr_name}` will be ignored, since it's applied to the macro invocation `{macro_name}`")
 757                     );
 758                 }
 759                 BuiltinLintDiagnostics::TrailingMacro(is_trailing, name) => {
 760                     if is_trailing {
 761                         db.note("macro invocations at the end of a block are treated as expressions");
 762                         db.note(&format!("to ignore the value produced by the macro, add a semicolon after the invocation of `{name}`"));
 763                     }
 764                 }
 765                 BuiltinLintDiagnostics::BreakWithLabelAndLoop(span) => {
 766                     db.multipart_suggestion(
 767                         "wrap this expression in parentheses",
 768                         vec![(span.shrink_to_lo(), "(".to_string()),
 769                              (span.shrink_to_hi(), ")".to_string())],
 770                         Applicability::MachineApplicable
 771                     );
 772                 }
 773                 BuiltinLintDiagnostics::NamedAsmLabel(help) => {
 774                     db.help(&help);
 775                     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");
 776                 }
 777             }
 778             // Rewrap `db`, and pass control to the user.
 779             decorate(LintDiagnosticBuilder::new(db));
 780         });
 781     }
 782
 783     // FIXME: These methods should not take an Into<MultiSpan> -- instead, callers should need to
 784     // set the span in their `decorate` function (preferably using set_span).
 785     fn lookup<S: Into<MultiSpan>>(
 786         &self,
 787         lint: &'static Lint,
 788         span: Option<S>,
 789         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 790     );
 791
 792     fn struct_span_lint<S: Into<MultiSpan>>(
 793         &self,
 794         lint: &'static Lint,
 795         span: S,
 796         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 797     ) {
 798         self.lookup(lint, Some(span), decorate);
 799     }
 800     /// Emit a lint at the appropriate level, with no associated span.
 801     fn lint(&self, lint: &'static Lint, decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>)) {
 802         self.lookup(lint, None as Option<Span>, decorate);
 803     }
 804 }
 805
 806 impl<'a> EarlyContext<'a> {
 807     pub fn new(
 808         sess: &'a Session,
 809         lint_store: &'a LintStore,
 810         krate: &'a ast::Crate,
 811         crate_attrs: &'a [ast::Attribute],
 812         buffered: LintBuffer,
 813         warn_about_weird_lints: bool,
 814     ) -> EarlyContext<'a> {
 815         EarlyContext {
 816             sess,
 817             krate,
 818             lint_store,
 819             builder: LintLevelsBuilder::new(sess, warn_about_weird_lints, lint_store, crate_attrs),
 820             buffered,
 821         }
 822     }
 823 }
 824
 825 impl LintContext for LateContext<'_> {
 826     type PassObject = LateLintPassObject;
 827
 828     /// Gets the overall compiler `Session` object.
 829     fn sess(&self) -> &Session {
 830         &self.tcx.sess
 831     }
 832
 833     fn lints(&self) -> &LintStore {
 834         &*self.lint_store
 835     }
 836
 837     fn lookup<S: Into<MultiSpan>>(
 838         &self,
 839         lint: &'static Lint,
 840         span: Option<S>,
 841         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 842     ) {
 843         let hir_id = self.last_node_with_lint_attrs;
 844
 845         match span {
 846             Some(s) => self.tcx.struct_span_lint_hir(lint, hir_id, s, decorate),
 847             None => self.tcx.struct_lint_node(lint, hir_id, decorate),
 848         }
 849     }
 850 }
 851
 852 impl LintContext for EarlyContext<'_> {
 853     type PassObject = EarlyLintPassObject;
 854
 855     /// Gets the overall compiler `Session` object.
 856     fn sess(&self) -> &Session {
 857         &self.sess
 858     }
 859
 860     fn lints(&self) -> &LintStore {
 861         &*self.lint_store
 862     }
 863
 864     fn lookup<S: Into<MultiSpan>>(
 865         &self,
 866         lint: &'static Lint,
 867         span: Option<S>,
 868         decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
 869     ) {
 870         self.builder.struct_lint(lint, span.map(|s| s.into()), decorate)
 871     }
 872 }
 873
 874 impl<'tcx> LateContext<'tcx> {
 875     /// Gets the type-checking results for the current body,
 876     /// or `None` if outside a body.
 877     pub fn maybe_typeck_results(&self) -> Option<&'tcx ty::TypeckResults<'tcx>> {
 878         self.cached_typeck_results.get().or_else(|| {
 879             self.enclosing_body.map(|body| {
 880                 let typeck_results = self.tcx.typeck_body(body);
 881                 self.cached_typeck_results.set(Some(typeck_results));
 882                 typeck_results
 883             })
 884         })
 885     }
 886
 887     /// Gets the type-checking results for the current body.
 888     /// As this will ICE if called outside bodies, only call when working with
 889     /// `Expr` or `Pat` nodes (they are guaranteed to be found only in bodies).
 890     #[track_caller]
 891     pub fn typeck_results(&self) -> &'tcx ty::TypeckResults<'tcx> {
 892         self.maybe_typeck_results().expect("`LateContext::typeck_results` called outside of body")
 893     }
 894
 895     /// Returns the final resolution of a `QPath`, or `Res::Err` if unavailable.
 896     /// Unlike `.typeck_results().qpath_res(qpath, id)`, this can be used even outside
 897     /// bodies (e.g. for paths in `hir::Ty`), without any risk of ICE-ing.
 898     pub fn qpath_res(&self, qpath: &hir::QPath<'_>, id: hir::HirId) -> Res {
 899         match *qpath {
 900             hir::QPath::Resolved(_, ref path) => path.res,
 901             hir::QPath::TypeRelative(..) | hir::QPath::LangItem(..) => self
 902                 .maybe_typeck_results()
 903                 .filter(|typeck_results| typeck_results.hir_owner == id.owner)
 904                 .or_else(|| {
 905                     if self.tcx.has_typeck_results(id.owner.to_def_id()) {
 906                         Some(self.tcx.typeck(id.owner))
 907                     } else {
 908                         None
 909                     }
 910                 })
 911                 .and_then(|typeck_results| typeck_results.type_dependent_def(id))
 912                 .map_or(Res::Err, |(kind, def_id)| Res::Def(kind, def_id)),
 913         }
 914     }
 915
 916     /// Check if a `DefId`'s path matches the given absolute type path usage.
 917     ///
 918     /// Anonymous scopes such as `extern` imports are matched with `kw::Empty`;
 919     /// inherent `impl` blocks are matched with the name of the type.
 920     ///
 921     /// Instead of using this method, it is often preferable to instead use
 922     /// `rustc_diagnostic_item` or a `lang_item`. This is less prone to errors
 923     /// as paths get invalidated if the target definition moves.
 924     ///
 925     /// # Examples
 926     ///
 927     /// ```rust,ignore (no context or def id available)
 928     /// if cx.match_def_path(def_id, &[sym::core, sym::option, sym::Option]) {
 929     ///     // The given `def_id` is that of an `Option` type
 930     /// }
 931     /// ```
 932     ///
 933     /// Used by clippy, but should be replaced by diagnostic items eventually.
 934     pub fn match_def_path(&self, def_id: DefId, path: &[Symbol]) -> bool {
 935         let names = self.get_def_path(def_id);
 936
 937         names.len() == path.len() && iter::zip(names, path).all(|(a, &b)| a == b)
 938     }
 939
 940     /// Gets the absolute path of `def_id` as a vector of `Symbol`.
 941     ///
 942     /// # Examples
 943     ///
 944     /// ```rust,ignore (no context or def id available)
 945     /// let def_path = cx.get_def_path(def_id);
 946     /// if let &[sym::core, sym::option, sym::Option] = &def_path[..] {
 947     ///     // The given `def_id` is that of an `Option` type
 948     /// }
 949     /// ```
 950     pub fn get_def_path(&self, def_id: DefId) -> Vec<Symbol> {
 951         pub struct AbsolutePathPrinter<'tcx> {
 952             pub tcx: TyCtxt<'tcx>,
 953         }
 954
 955         impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
 956             type Error = !;
 957
 958             type Path = Vec<Symbol>;
 959             type Region = ();
 960             type Type = ();
 961             type DynExistential = ();
 962             type Const = ();
 963
 964             fn tcx(&self) -> TyCtxt<'tcx> {
 965                 self.tcx
 966             }
 967
 968             fn print_region(self, _region: ty::Region<'_>) -> Result<Self::Region, Self::Error> {
 969                 Ok(())
 970             }
 971
 972             fn print_type(self, _ty: Ty<'tcx>) -> Result<Self::Type, Self::Error> {
 973                 Ok(())
 974             }
 975
 976             fn print_dyn_existential(
 977                 self,
 978                 _predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
 979             ) -> Result<Self::DynExistential, Self::Error> {
 980                 Ok(())
 981             }
 982
 983             fn print_const(self, _ct: &'tcx ty::Const<'tcx>) -> Result<Self::Const, Self::Error> {
 984                 Ok(())
 985             }
 986
 987             fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
 988                 Ok(vec![self.tcx.crate_name(cnum)])
 989             }
 990
 991             fn path_qualified(
 992                 self,
 993                 self_ty: Ty<'tcx>,
 994                 trait_ref: Option<ty::TraitRef<'tcx>>,
 995             ) -> Result<Self::Path, Self::Error> {
 996                 if trait_ref.is_none() {
 997                     if let ty::Adt(def, substs) = self_ty.kind() {
 998                         return self.print_def_path(def.did, substs);
 999                     }
1000                 }
1001
1002                 // This shouldn't ever be needed, but just in case:
1003                 with_no_trimmed_paths(|| {
1004                     Ok(vec![match trait_ref {
1005                         Some(trait_ref) => Symbol::intern(&format!("{:?}", trait_ref)),
1006                         None => Symbol::intern(&format!("<{}>", self_ty)),
1007                     }])
1008                 })
1009             }
1010
1011             fn path_append_impl(
1012                 self,
1013                 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
1014                 _disambiguated_data: &DisambiguatedDefPathData,
1015                 self_ty: Ty<'tcx>,
1016                 trait_ref: Option<ty::TraitRef<'tcx>>,
1017             ) -> Result<Self::Path, Self::Error> {
1018                 let mut path = print_prefix(self)?;
1019
1020                 // This shouldn't ever be needed, but just in case:
1021                 path.push(match trait_ref {
1022                     Some(trait_ref) => with_no_trimmed_paths(|| {
1023                         Symbol::intern(&format!(
1024                             "<impl {} for {}>",
1025                             trait_ref.print_only_trait_path(),
1026                             self_ty
1027                         ))
1028                     }),
1029                     None => {
1030                         with_no_trimmed_paths(|| Symbol::intern(&format!("<impl {}>", self_ty)))
1031                     }
1032                 });
1033
1034                 Ok(path)
1035             }
1036
1037             fn path_append(
1038                 self,
1039                 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
1040                 disambiguated_data: &DisambiguatedDefPathData,
1041             ) -> Result<Self::Path, Self::Error> {
1042                 let mut path = print_prefix(self)?;
1043
1044                 // Skip `::{{constructor}}` on tuple/unit structs.
1045                 if let DefPathData::Ctor = disambiguated_data.data {
1046                     return Ok(path);
1047                 }
1048
1049                 path.push(Symbol::intern(&disambiguated_data.data.to_string()));
1050                 Ok(path)
1051             }
1052
1053             fn path_generic_args(
1054                 self,
1055                 print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
1056                 _args: &[GenericArg<'tcx>],
1057             ) -> Result<Self::Path, Self::Error> {
1058                 print_prefix(self)
1059             }
1060         }
1061
1062         AbsolutePathPrinter { tcx: self.tcx }.print_def_path(def_id, &[]).unwrap()
1063     }
1064 }
1065
1066 impl<'tcx> abi::HasDataLayout for LateContext<'tcx> {
1067     #[inline]
1068     fn data_layout(&self) -> &abi::TargetDataLayout {
1069         &self.tcx.data_layout
1070     }
1071 }
1072
1073 impl<'tcx> ty::layout::HasTyCtxt<'tcx> for LateContext<'tcx> {
1074     #[inline]
1075     fn tcx(&self) -> TyCtxt<'tcx> {
1076         self.tcx
1077     }
1078 }
1079
1080 impl<'tcx> ty::layout::HasParamEnv<'tcx> for LateContext<'tcx> {
1081     #[inline]
1082     fn param_env(&self) -> ty::ParamEnv<'tcx> {
1083         self.param_env
1084     }
1085 }
1086
1087 impl<'tcx> LayoutOfHelpers<'tcx> for LateContext<'tcx> {
1088     type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
1089
1090     #[inline]
1091     fn handle_layout_err(&self, err: LayoutError<'tcx>, _: Span, _: Ty<'tcx>) -> LayoutError<'tcx> {
1092         err
1093     }
1094 }
1095
1096 pub fn parse_lint_and_tool_name(lint_name: &str) -> (Option<Symbol>, &str) {
1097     match lint_name.split_once("::") {
1098         Some((tool_name, lint_name)) => {
1099             let tool_name = Symbol::intern(tool_name);
1100
1101             (Some(tool_name), lint_name)
1102         }
1103         None => (None, lint_name),
1104     }
1105 }