src/librustc/lint.rs

   1 use std::cmp;
   2
   3 use crate::ich::StableHashingContext;
   4 use crate::lint::context::CheckLintNameResult;
   5 use rustc_data_structures::fx::FxHashMap;
   6 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
   7 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, DiagnosticId};
   8 use rustc_hir::HirId;
   9 pub use rustc_session::lint::{builtin, Level, Lint, LintId, LintPass};
  10 use rustc_session::{DiagnosticMessageId, Session};
  11 use rustc_span::hygiene::MacroKind;
  12 use rustc_span::source_map::{DesugaringKind, ExpnKind, MultiSpan};
  13 use rustc_span::symbol::{sym, Symbol};
  14 use rustc_span::Span;
  15 use syntax::ast;
  16 use syntax::attr;
  17 use syntax::print::pprust;
  18 use syntax::sess::feature_err;
  19
  20 use rustc_error_codes::*;
  21
  22 mod context;
  23 mod passes;
  24
  25 pub use context::add_elided_lifetime_in_path_suggestion;
  26 pub use context::{EarlyContext, LateContext, LintContext, LintStore};
  27 pub use passes::{EarlyLintPass, EarlyLintPassObject, LateLintPass, LateLintPassObject};
  28
  29 /// How a lint level was set.
  30 #[derive(Clone, Copy, PartialEq, Eq, HashStable)]
  31 pub enum LintSource {
  32     /// Lint is at the default level as declared
  33     /// in rustc or a plugin.
  34     Default,
  35
  36     /// Lint level was set by an attribute.
  37     Node(Symbol, Span, Option<Symbol> /* RFC 2383 reason */),
  38
  39     /// Lint level was set by a command-line flag.
  40     CommandLine(Symbol),
  41 }
  42
  43 pub type LevelSource = (Level, LintSource);
  44
  45 pub struct LintLevelSets {
  46     list: Vec<LintSet>,
  47     lint_cap: Level,
  48 }
  49
  50 enum LintSet {
  51     CommandLine {
  52         // -A,-W,-D flags, a `Symbol` for the flag itself and `Level` for which
  53         // flag.
  54         specs: FxHashMap<LintId, LevelSource>,
  55     },
  56
  57     Node {
  58         specs: FxHashMap<LintId, LevelSource>,
  59         parent: u32,
  60     },
  61 }
  62
  63 impl LintLevelSets {
  64     pub fn new() -> Self {
  65         LintLevelSets { list: Vec::new(), lint_cap: Level::Forbid }
  66     }
  67
  68     pub fn get_lint_level(
  69         &self,
  70         lint: &'static Lint,
  71         idx: u32,
  72         aux: Option<&FxHashMap<LintId, LevelSource>>,
  73         sess: &Session,
  74     ) -> LevelSource {
  75         let (level, mut src) = self.get_lint_id_level(LintId::of(lint), idx, aux);
  76
  77         // If `level` is none then we actually assume the default level for this
  78         // lint.
  79         let mut level = level.unwrap_or_else(|| lint.default_level(sess.edition()));
  80
  81         // If we're about to issue a warning, check at the last minute for any
  82         // directives against the warnings "lint". If, for example, there's an
  83         // `allow(warnings)` in scope then we want to respect that instead.
  84         if level == Level::Warn {
  85             let (warnings_level, warnings_src) =
  86                 self.get_lint_id_level(LintId::of(builtin::WARNINGS), idx, aux);
  87             if let Some(configured_warning_level) = warnings_level {
  88                 if configured_warning_level != Level::Warn {
  89                     level = configured_warning_level;
  90                     src = warnings_src;
  91                 }
  92             }
  93         }
  94
  95         // Ensure that we never exceed the `--cap-lints` argument.
  96         level = cmp::min(level, self.lint_cap);
  97
  98         if let Some(driver_level) = sess.driver_lint_caps.get(&LintId::of(lint)) {
  99             // Ensure that we never exceed driver level.
 100             level = cmp::min(*driver_level, level);
 101         }
 102
 103         return (level, src);
 104     }
 105
 106     pub fn get_lint_id_level(
 107         &self,
 108         id: LintId,
 109         mut idx: u32,
 110         aux: Option<&FxHashMap<LintId, LevelSource>>,
 111     ) -> (Option<Level>, LintSource) {
 112         if let Some(specs) = aux {
 113             if let Some(&(level, src)) = specs.get(&id) {
 114                 return (Some(level), src);
 115             }
 116         }
 117         loop {
 118             match self.list[idx as usize] {
 119                 LintSet::CommandLine { ref specs } => {
 120                     if let Some(&(level, src)) = specs.get(&id) {
 121                         return (Some(level), src);
 122                     }
 123                     return (None, LintSource::Default);
 124                 }
 125                 LintSet::Node { ref specs, parent } => {
 126                     if let Some(&(level, src)) = specs.get(&id) {
 127                         return (Some(level), src);
 128                     }
 129                     idx = parent;
 130                 }
 131             }
 132         }
 133     }
 134 }
 135
 136 pub struct LintLevelsBuilder<'a> {
 137     sess: &'a Session,
 138     sets: LintLevelSets,
 139     id_to_set: FxHashMap<HirId, u32>,
 140     cur: u32,
 141     warn_about_weird_lints: bool,
 142 }
 143
 144 pub struct BuilderPush {
 145     prev: u32,
 146     pub changed: bool,
 147 }
 148
 149 impl<'a> LintLevelsBuilder<'a> {
 150     pub fn new(sess: &'a Session, warn_about_weird_lints: bool, store: &LintStore) -> Self {
 151         let mut builder = LintLevelsBuilder {
 152             sess,
 153             sets: LintLevelSets::new(),
 154             cur: 0,
 155             id_to_set: Default::default(),
 156             warn_about_weird_lints,
 157         };
 158         builder.process_command_line(sess, store);
 159         assert_eq!(builder.sets.list.len(), 1);
 160         builder
 161     }
 162
 163     fn process_command_line(&mut self, sess: &Session, store: &LintStore) {
 164         let mut specs = FxHashMap::default();
 165         self.sets.lint_cap = sess.opts.lint_cap.unwrap_or(Level::Forbid);
 166
 167         for &(ref lint_name, level) in &sess.opts.lint_opts {
 168             store.check_lint_name_cmdline(sess, &lint_name, level);
 169
 170             // If the cap is less than this specified level, e.g., if we've got
 171             // `--cap-lints allow` but we've also got `-D foo` then we ignore
 172             // this specification as the lint cap will set it to allow anyway.
 173             let level = cmp::min(level, self.sets.lint_cap);
 174
 175             let lint_flag_val = Symbol::intern(lint_name);
 176             let ids = match store.find_lints(&lint_name) {
 177                 Ok(ids) => ids,
 178                 Err(_) => continue, // errors handled in check_lint_name_cmdline above
 179             };
 180             for id in ids {
 181                 let src = LintSource::CommandLine(lint_flag_val);
 182                 specs.insert(id, (level, src));
 183             }
 184         }
 185
 186         self.sets.list.push(LintSet::CommandLine { specs });
 187     }
 188
 189     /// Pushes a list of AST lint attributes onto this context.
 190     ///
 191     /// This function will return a `BuilderPush` object which should be passed
 192     /// to `pop` when this scope for the attributes provided is exited.
 193     ///
 194     /// This function will perform a number of tasks:
 195     ///
 196     /// * It'll validate all lint-related attributes in `attrs`
 197     /// * It'll mark all lint-related attributes as used
 198     /// * Lint levels will be updated based on the attributes provided
 199     /// * Lint attributes are validated, e.g., a #[forbid] can't be switched to
 200     ///   #[allow]
 201     ///
 202     /// Don't forget to call `pop`!
 203     pub fn push(&mut self, attrs: &[ast::Attribute], store: &LintStore) -> BuilderPush {
 204         let mut specs = FxHashMap::default();
 205         let sess = self.sess;
 206         let bad_attr = |span| struct_span_err!(sess, span, E0452, "malformed lint attribute input");
 207         for attr in attrs {
 208             let level = match Level::from_symbol(attr.name_or_empty()) {
 209                 None => continue,
 210                 Some(lvl) => lvl,
 211             };
 212
 213             let meta = unwrap_or!(attr.meta(), continue);
 214             attr::mark_used(attr);
 215
 216             let mut metas = unwrap_or!(meta.meta_item_list(), continue);
 217
 218             if metas.is_empty() {
 219                 // FIXME (#55112): issue unused-attributes lint for `#[level()]`
 220                 continue;
 221             }
 222
 223             // Before processing the lint names, look for a reason (RFC 2383)
 224             // at the end.
 225             let mut reason = None;
 226             let tail_li = &metas[metas.len() - 1];
 227             if let Some(item) = tail_li.meta_item() {
 228                 match item.kind {
 229                     ast::MetaItemKind::Word => {} // actual lint names handled later
 230                     ast::MetaItemKind::NameValue(ref name_value) => {
 231                         if item.path == sym::reason {
 232                             // found reason, reslice meta list to exclude it
 233                             metas = &metas[0..metas.len() - 1];
 234                             // FIXME (#55112): issue unused-attributes lint if we thereby
 235                             // don't have any lint names (`#[level(reason = "foo")]`)
 236                             if let ast::LitKind::Str(rationale, _) = name_value.kind {
 237                                 if !self.sess.features_untracked().lint_reasons {
 238                                     feature_err(
 239                                         &self.sess.parse_sess,
 240                                         sym::lint_reasons,
 241                                         item.span,
 242                                         "lint reasons are experimental",
 243                                     )
 244                                     .emit();
 245                                 }
 246                                 reason = Some(rationale);
 247                             } else {
 248                                 bad_attr(name_value.span)
 249                                     .span_label(name_value.span, "reason must be a string literal")
 250                                     .emit();
 251                             }
 252                         } else {
 253                             bad_attr(item.span)
 254                                 .span_label(item.span, "bad attribute argument")
 255                                 .emit();
 256                         }
 257                     }
 258                     ast::MetaItemKind::List(_) => {
 259                         bad_attr(item.span).span_label(item.span, "bad attribute argument").emit();
 260                     }
 261                 }
 262             }
 263
 264             for li in metas {
 265                 let meta_item = match li.meta_item() {
 266                     Some(meta_item) if meta_item.is_word() => meta_item,
 267                     _ => {
 268                         let sp = li.span();
 269                         let mut err = bad_attr(sp);
 270                         let mut add_label = true;
 271                         if let Some(item) = li.meta_item() {
 272                             if let ast::MetaItemKind::NameValue(_) = item.kind {
 273                                 if item.path == sym::reason {
 274                                     err.span_label(sp, "reason in lint attribute must come last");
 275                                     add_label = false;
 276                                 }
 277                             }
 278                         }
 279                         if add_label {
 280                             err.span_label(sp, "bad attribute argument");
 281                         }
 282                         err.emit();
 283                         continue;
 284                     }
 285                 };
 286                 let tool_name = if meta_item.path.segments.len() > 1 {
 287                     let tool_ident = meta_item.path.segments[0].ident;
 288                     if !attr::is_known_lint_tool(tool_ident) {
 289                         struct_span_err!(
 290                             sess,
 291                             tool_ident.span,
 292                             E0710,
 293                             "an unknown tool name found in scoped lint: `{}`",
 294                             pprust::path_to_string(&meta_item.path),
 295                         )
 296                         .emit();
 297                         continue;
 298                     }
 299
 300                     Some(tool_ident.name)
 301                 } else {
 302                     None
 303                 };
 304                 let name = meta_item.path.segments.last().expect("empty lint name").ident.name;
 305                 match store.check_lint_name(&name.as_str(), tool_name) {
 306                     CheckLintNameResult::Ok(ids) => {
 307                         let src = LintSource::Node(name, li.span(), reason);
 308                         for id in ids {
 309                             specs.insert(*id, (level, src));
 310                         }
 311                     }
 312
 313                     CheckLintNameResult::Tool(result) => {
 314                         match result {
 315                             Ok(ids) => {
 316                                 let complete_name = &format!("{}::{}", tool_name.unwrap(), name);
 317                                 let src = LintSource::Node(
 318                                     Symbol::intern(complete_name),
 319                                     li.span(),
 320                                     reason,
 321                                 );
 322                                 for id in ids {
 323                                     specs.insert(*id, (level, src));
 324                                 }
 325                             }
 326                             Err((Some(ids), new_lint_name)) => {
 327                                 let lint = builtin::RENAMED_AND_REMOVED_LINTS;
 328                                 let (lvl, src) =
 329                                     self.sets.get_lint_level(lint, self.cur, Some(&specs), &sess);
 330                                 let msg = format!(
 331                                     "lint name `{}` is deprecated \
 332                                      and may not have an effect in the future. \
 333                                      Also `cfg_attr(cargo-clippy)` won't be necessary anymore",
 334                                     name
 335                                 );
 336                                 struct_lint_level(
 337                                     self.sess,
 338                                     lint,
 339                                     lvl,
 340                                     src,
 341                                     Some(li.span().into()),
 342                                     &msg,
 343                                 )
 344                                 .span_suggestion(
 345                                     li.span(),
 346                                     "change it to",
 347                                     new_lint_name.to_string(),
 348                                     Applicability::MachineApplicable,
 349                                 )
 350                                 .emit();
 351
 352                                 let src = LintSource::Node(
 353                                     Symbol::intern(&new_lint_name),
 354                                     li.span(),
 355                                     reason,
 356                                 );
 357                                 for id in ids {
 358                                     specs.insert(*id, (level, src));
 359                                 }
 360                             }
 361                             Err((None, _)) => {
 362                                 // If Tool(Err(None, _)) is returned, then either the lint does not
 363                                 // exist in the tool or the code was not compiled with the tool and
 364                                 // therefore the lint was never added to the `LintStore`. To detect
 365                                 // this is the responsibility of the lint tool.
 366                             }
 367                         }
 368                     }
 369
 370                     _ if !self.warn_about_weird_lints => {}
 371
 372                     CheckLintNameResult::Warning(msg, renamed) => {
 373                         let lint = builtin::RENAMED_AND_REMOVED_LINTS;
 374                         let (level, src) =
 375                             self.sets.get_lint_level(lint, self.cur, Some(&specs), &sess);
 376                         let mut err = struct_lint_level(
 377                             self.sess,
 378                             lint,
 379                             level,
 380                             src,
 381                             Some(li.span().into()),
 382                             &msg,
 383                         );
 384                         if let Some(new_name) = renamed {
 385                             err.span_suggestion(
 386                                 li.span(),
 387                                 "use the new name",
 388                                 new_name,
 389                                 Applicability::MachineApplicable,
 390                             );
 391                         }
 392                         err.emit();
 393                     }
 394                     CheckLintNameResult::NoLint(suggestion) => {
 395                         let lint = builtin::UNKNOWN_LINTS;
 396                         let (level, src) =
 397                             self.sets.get_lint_level(lint, self.cur, Some(&specs), self.sess);
 398                         let msg = format!("unknown lint: `{}`", name);
 399                         let mut db = struct_lint_level(
 400                             self.sess,
 401                             lint,
 402                             level,
 403                             src,
 404                             Some(li.span().into()),
 405                             &msg,
 406                         );
 407
 408                         if let Some(suggestion) = suggestion {
 409                             db.span_suggestion(
 410                                 li.span(),
 411                                 "did you mean",
 412                                 suggestion.to_string(),
 413                                 Applicability::MachineApplicable,
 414                             );
 415                         }
 416
 417                         db.emit();
 418                     }
 419                 }
 420             }
 421         }
 422
 423         for (id, &(level, ref src)) in specs.iter() {
 424             if level == Level::Forbid {
 425                 continue;
 426             }
 427             let forbid_src = match self.sets.get_lint_id_level(*id, self.cur, None) {
 428                 (Some(Level::Forbid), src) => src,
 429                 _ => continue,
 430             };
 431             let forbidden_lint_name = match forbid_src {
 432                 LintSource::Default => id.to_string(),
 433                 LintSource::Node(name, _, _) => name.to_string(),
 434                 LintSource::CommandLine(name) => name.to_string(),
 435             };
 436             let (lint_attr_name, lint_attr_span) = match *src {
 437                 LintSource::Node(name, span, _) => (name, span),
 438                 _ => continue,
 439             };
 440             let mut diag_builder = struct_span_err!(
 441                 self.sess,
 442                 lint_attr_span,
 443                 E0453,
 444                 "{}({}) overruled by outer forbid({})",
 445                 level.as_str(),
 446                 lint_attr_name,
 447                 forbidden_lint_name
 448             );
 449             diag_builder.span_label(lint_attr_span, "overruled by previous forbid");
 450             match forbid_src {
 451                 LintSource::Default => {}
 452                 LintSource::Node(_, forbid_source_span, reason) => {
 453                     diag_builder.span_label(forbid_source_span, "`forbid` level set here");
 454                     if let Some(rationale) = reason {
 455                         diag_builder.note(&rationale.as_str());
 456                     }
 457                 }
 458                 LintSource::CommandLine(_) => {
 459                     diag_builder.note("`forbid` lint level was set on command line");
 460                 }
 461             }
 462             diag_builder.emit();
 463             // don't set a separate error for every lint in the group
 464             break;
 465         }
 466
 467         let prev = self.cur;
 468         if specs.len() > 0 {
 469             self.cur = self.sets.list.len() as u32;
 470             self.sets.list.push(LintSet::Node { specs: specs, parent: prev });
 471         }
 472
 473         BuilderPush { prev: prev, changed: prev != self.cur }
 474     }
 475
 476     /// Called after `push` when the scope of a set of attributes are exited.
 477     pub fn pop(&mut self, push: BuilderPush) {
 478         self.cur = push.prev;
 479     }
 480
 481     /// Used to emit a lint-related diagnostic based on the current state of
 482     /// this lint context.
 483     pub fn struct_lint(
 484         &self,
 485         lint: &'static Lint,
 486         span: Option<MultiSpan>,
 487         msg: &str,
 488     ) -> DiagnosticBuilder<'a> {
 489         let (level, src) = self.sets.get_lint_level(lint, self.cur, None, self.sess);
 490         struct_lint_level(self.sess, lint, level, src, span, msg)
 491     }
 492
 493     /// Registers the ID provided with the current set of lints stored in
 494     /// this context.
 495     pub fn register_id(&mut self, id: HirId) {
 496         self.id_to_set.insert(id, self.cur);
 497     }
 498
 499     pub fn build(self) -> LintLevelSets {
 500         self.sets
 501     }
 502
 503     pub fn build_map(self) -> LintLevelMap {
 504         LintLevelMap { sets: self.sets, id_to_set: self.id_to_set }
 505     }
 506 }
 507
 508 pub struct LintLevelMap {
 509     sets: LintLevelSets,
 510     id_to_set: FxHashMap<HirId, u32>,
 511 }
 512
 513 impl LintLevelMap {
 514     /// If the `id` was previously registered with `register_id` when building
 515     /// this `LintLevelMap` this returns the corresponding lint level and source
 516     /// of the lint level for the lint provided.
 517     ///
 518     /// If the `id` was not previously registered, returns `None`. If `None` is
 519     /// returned then the parent of `id` should be acquired and this function
 520     /// should be called again.
 521     pub fn level_and_source(
 522         &self,
 523         lint: &'static Lint,
 524         id: HirId,
 525         session: &Session,
 526     ) -> Option<LevelSource> {
 527         self.id_to_set.get(&id).map(|idx| self.sets.get_lint_level(lint, *idx, None, session))
 528     }
 529 }
 530
 531 impl<'a> HashStable<StableHashingContext<'a>> for LintLevelMap {
 532     #[inline]
 533     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
 534         let LintLevelMap { ref sets, ref id_to_set } = *self;
 535
 536         id_to_set.hash_stable(hcx, hasher);
 537
 538         let LintLevelSets { ref list, lint_cap } = *sets;
 539
 540         lint_cap.hash_stable(hcx, hasher);
 541
 542         hcx.while_hashing_spans(true, |hcx| {
 543             list.len().hash_stable(hcx, hasher);
 544
 545             // We are working under the assumption here that the list of
 546             // lint-sets is built in a deterministic order.
 547             for lint_set in list {
 548                 ::std::mem::discriminant(lint_set).hash_stable(hcx, hasher);
 549
 550                 match *lint_set {
 551                     LintSet::CommandLine { ref specs } => {
 552                         specs.hash_stable(hcx, hasher);
 553                     }
 554                     LintSet::Node { ref specs, parent } => {
 555                         specs.hash_stable(hcx, hasher);
 556                         parent.hash_stable(hcx, hasher);
 557                     }
 558                 }
 559             }
 560         })
 561     }
 562 }
 563
 564 pub fn struct_lint_level<'a>(
 565     sess: &'a Session,
 566     lint: &'static Lint,
 567     level: Level,
 568     src: LintSource,
 569     span: Option<MultiSpan>,
 570     msg: &str,
 571 ) -> DiagnosticBuilder<'a> {
 572     let mut err = match (level, span) {
 573         (Level::Allow, _) => return sess.diagnostic().struct_dummy(),
 574         (Level::Warn, Some(span)) => sess.struct_span_warn(span, msg),
 575         (Level::Warn, None) => sess.struct_warn(msg),
 576         (Level::Deny, Some(span)) | (Level::Forbid, Some(span)) => sess.struct_span_err(span, msg),
 577         (Level::Deny, None) | (Level::Forbid, None) => sess.struct_err(msg),
 578     };
 579
 580     // Check for future incompatibility lints and issue a stronger warning.
 581     let lint_id = LintId::of(lint);
 582     let future_incompatible = lint.future_incompatible;
 583
 584     // If this code originates in a foreign macro, aka something that this crate
 585     // did not itself author, then it's likely that there's nothing this crate
 586     // can do about it. We probably want to skip the lint entirely.
 587     if err.span.primary_spans().iter().any(|s| in_external_macro(sess, *s)) {
 588         // Any suggestions made here are likely to be incorrect, so anything we
 589         // emit shouldn't be automatically fixed by rustfix.
 590         err.allow_suggestions(false);
 591
 592         // If this is a future incompatible lint it'll become a hard error, so
 593         // we have to emit *something*. Also allow lints to whitelist themselves
 594         // on a case-by-case basis for emission in a foreign macro.
 595         if future_incompatible.is_none() && !lint.report_in_external_macro {
 596             err.cancel();
 597             // Don't continue further, since we don't want to have
 598             // `diag_span_note_once` called for a diagnostic that isn't emitted.
 599             return err;
 600         }
 601     }
 602
 603     let name = lint.name_lower();
 604     match src {
 605         LintSource::Default => {
 606             sess.diag_note_once(
 607                 &mut err,
 608                 DiagnosticMessageId::from(lint),
 609                 &format!("`#[{}({})]` on by default", level.as_str(), name),
 610             );
 611         }
 612         LintSource::CommandLine(lint_flag_val) => {
 613             let flag = match level {
 614                 Level::Warn => "-W",
 615                 Level::Deny => "-D",
 616                 Level::Forbid => "-F",
 617                 Level::Allow => panic!(),
 618             };
 619             let hyphen_case_lint_name = name.replace("_", "-");
 620             if lint_flag_val.as_str() == name {
 621                 sess.diag_note_once(
 622                     &mut err,
 623                     DiagnosticMessageId::from(lint),
 624                     &format!(
 625                         "requested on the command line with `{} {}`",
 626                         flag, hyphen_case_lint_name
 627                     ),
 628                 );
 629             } else {
 630                 let hyphen_case_flag_val = lint_flag_val.as_str().replace("_", "-");
 631                 sess.diag_note_once(
 632                     &mut err,
 633                     DiagnosticMessageId::from(lint),
 634                     &format!(
 635                         "`{} {}` implied by `{} {}`",
 636                         flag, hyphen_case_lint_name, flag, hyphen_case_flag_val
 637                     ),
 638                 );
 639             }
 640         }
 641         LintSource::Node(lint_attr_name, src, reason) => {
 642             if let Some(rationale) = reason {
 643                 err.note(&rationale.as_str());
 644             }
 645             sess.diag_span_note_once(
 646                 &mut err,
 647                 DiagnosticMessageId::from(lint),
 648                 src,
 649                 "lint level defined here",
 650             );
 651             if lint_attr_name.as_str() != name {
 652                 let level_str = level.as_str();
 653                 sess.diag_note_once(
 654                     &mut err,
 655                     DiagnosticMessageId::from(lint),
 656                     &format!(
 657                         "`#[{}({})]` implied by `#[{}({})]`",
 658                         level_str, name, level_str, lint_attr_name
 659                     ),
 660                 );
 661             }
 662         }
 663     }
 664
 665     err.code(DiagnosticId::Lint(name));
 666
 667     if let Some(future_incompatible) = future_incompatible {
 668         const STANDARD_MESSAGE: &str = "this was previously accepted by the compiler but is being phased out; \
 669              it will become a hard error";
 670
 671         let explanation = if lint_id == LintId::of(builtin::UNSTABLE_NAME_COLLISIONS) {
 672             "once this method is added to the standard library, \
 673              the ambiguity may cause an error or change in behavior!"
 674                 .to_owned()
 675         } else if lint_id == LintId::of(builtin::MUTABLE_BORROW_RESERVATION_CONFLICT) {
 676             "this borrowing pattern was not meant to be accepted, \
 677              and may become a hard error in the future"
 678                 .to_owned()
 679         } else if let Some(edition) = future_incompatible.edition {
 680             format!("{} in the {} edition!", STANDARD_MESSAGE, edition)
 681         } else {
 682             format!("{} in a future release!", STANDARD_MESSAGE)
 683         };
 684         let citation = format!("for more information, see {}", future_incompatible.reference);
 685         err.warn(&explanation);
 686         err.note(&citation);
 687     }
 688
 689     return err;
 690 }
 691
 692 /// Returns whether `span` originates in a foreign crate's external macro.
 693 ///
 694 /// This is used to test whether a lint should not even begin to figure out whether it should
 695 /// be reported on the current node.
 696 pub fn in_external_macro(sess: &Session, span: Span) -> bool {
 697     let expn_data = span.ctxt().outer_expn_data();
 698     match expn_data.kind {
 699         ExpnKind::Root | ExpnKind::Desugaring(DesugaringKind::ForLoop) => false,
 700         ExpnKind::AstPass(_) | ExpnKind::Desugaring(_) => true, // well, it's "external"
 701         ExpnKind::Macro(MacroKind::Bang, _) => {
 702             if expn_data.def_site.is_dummy() {
 703                 // Dummy span for the `def_site` means it's an external macro.
 704                 return true;
 705             }
 706             match sess.source_map().span_to_snippet(expn_data.def_site) {
 707                 Ok(code) => !code.starts_with("macro_rules"),
 708                 // No snippet means external macro or compiler-builtin expansion.
 709                 Err(_) => true,
 710             }
 711         }
 712         ExpnKind::Macro(..) => true, // definitely a plugin
 713     }
 714 }