compiler/rustc_middle/src/lint.rs

   1 use std::cmp;
   2
   3 use rustc_data_structures::fx::FxHashMap;
   4 use rustc_data_structures::sorted_map::SortedMap;
   5 use rustc_errors::{Diagnostic, DiagnosticBuilder, DiagnosticId, DiagnosticMessage, MultiSpan};
   6 use rustc_hir::{HirId, ItemLocalId};
   7 use rustc_session::lint::{
   8     builtin::{self, FORBIDDEN_LINT_GROUPS},
   9     FutureIncompatibilityReason, Level, Lint, LintId,
  10 };
  11 use rustc_session::Session;
  12 use rustc_span::hygiene::MacroKind;
  13 use rustc_span::source_map::{DesugaringKind, ExpnKind};
  14 use rustc_span::{symbol, Span, Symbol, DUMMY_SP};
  15
  16 use crate::ty::TyCtxt;
  17
  18 /// How a lint level was set.
  19 #[derive(Clone, Copy, PartialEq, Eq, HashStable, Debug)]
  20 pub enum LintLevelSource {
  21     /// Lint is at the default level as declared
  22     /// in rustc or a plugin.
  23     Default,
  24
  25     /// Lint level was set by an attribute.
  26     Node {
  27         name: Symbol,
  28         span: Span,
  29         /// RFC 2383 reason
  30         reason: Option<Symbol>,
  31     },
  32
  33     /// Lint level was set by a command-line flag.
  34     /// The provided `Level` is the level specified on the command line.
  35     /// (The actual level may be lower due to `--cap-lints`.)
  36     CommandLine(Symbol, Level),
  37 }
  38
  39 impl LintLevelSource {
  40     pub fn name(&self) -> Symbol {
  41         match *self {
  42             LintLevelSource::Default => symbol::kw::Default,
  43             LintLevelSource::Node { name, .. } => name,
  44             LintLevelSource::CommandLine(name, _) => name,
  45         }
  46     }
  47
  48     pub fn span(&self) -> Span {
  49         match *self {
  50             LintLevelSource::Default => DUMMY_SP,
  51             LintLevelSource::Node { span, .. } => span,
  52             LintLevelSource::CommandLine(_, _) => DUMMY_SP,
  53         }
  54     }
  55 }
  56
  57 /// A tuple of a lint level and its source.
  58 pub type LevelAndSource = (Level, LintLevelSource);
  59
  60 /// Return type for the `shallow_lint_levels_on` query.
  61 ///
  62 /// This map represents the set of allowed lints and allowance levels given
  63 /// by the attributes for *a single HirId*.
  64 #[derive(Default, Debug, HashStable)]
  65 pub struct ShallowLintLevelMap {
  66     pub specs: SortedMap<ItemLocalId, FxHashMap<LintId, LevelAndSource>>,
  67 }
  68
  69 /// From an initial level and source, verify the effect of special annotations:
  70 /// `warnings` lint level and lint caps.
  71 ///
  72 /// The return of this function is suitable for diagnostics.
  73 pub fn reveal_actual_level(
  74     level: Option<Level>,
  75     src: &mut LintLevelSource,
  76     sess: &Session,
  77     lint: LintId,
  78     probe_for_lint_level: impl FnOnce(LintId) -> (Option<Level>, LintLevelSource),
  79 ) -> Level {
  80     // If `level` is none then we actually assume the default level for this lint.
  81     let mut level = level.unwrap_or_else(|| lint.lint.default_level(sess.edition()));
  82
  83     // If we're about to issue a warning, check at the last minute for any
  84     // directives against the warnings "lint". If, for example, there's an
  85     // `allow(warnings)` in scope then we want to respect that instead.
  86     //
  87     // We exempt `FORBIDDEN_LINT_GROUPS` from this because it specifically
  88     // triggers in cases (like #80988) where you have `forbid(warnings)`,
  89     // and so if we turned that into an error, it'd defeat the purpose of the
  90     // future compatibility warning.
  91     if level == Level::Warn && lint != LintId::of(FORBIDDEN_LINT_GROUPS) {
  92         let (warnings_level, warnings_src) = probe_for_lint_level(LintId::of(builtin::WARNINGS));
  93         if let Some(configured_warning_level) = warnings_level {
  94             if configured_warning_level != Level::Warn {
  95                 level = configured_warning_level;
  96                 *src = warnings_src;
  97             }
  98         }
  99     }
 100
 101     // Ensure that we never exceed the `--cap-lints` argument unless the source is a --force-warn
 102     level = if let LintLevelSource::CommandLine(_, Level::ForceWarn(_)) = src {
 103         level
 104     } else {
 105         cmp::min(level, sess.opts.lint_cap.unwrap_or(Level::Forbid))
 106     };
 107
 108     if let Some(driver_level) = sess.driver_lint_caps.get(&lint) {
 109         // Ensure that we never exceed driver level.
 110         level = cmp::min(*driver_level, level);
 111     }
 112
 113     level
 114 }
 115
 116 impl ShallowLintLevelMap {
 117     /// Perform a deep probe in the HIR tree looking for the actual level for the lint.
 118     /// This lint level is not usable for diagnostics, it needs to be corrected by
 119     /// `reveal_actual_level` beforehand.
 120     #[instrument(level = "trace", skip(self, tcx), ret)]
 121     fn probe_for_lint_level(
 122         &self,
 123         tcx: TyCtxt<'_>,
 124         id: LintId,
 125         start: HirId,
 126     ) -> (Option<Level>, LintLevelSource) {
 127         if let Some(map) = self.specs.get(&start.local_id)
 128             && let Some(&(level, src)) = map.get(&id)
 129         {
 130             return (Some(level), src);
 131         }
 132
 133         let mut owner = start.owner;
 134         let mut specs = &self.specs;
 135
 136         for parent in tcx.hir().parent_id_iter(start) {
 137             if parent.owner != owner {
 138                 owner = parent.owner;
 139                 specs = &tcx.shallow_lint_levels_on(owner).specs;
 140             }
 141             if let Some(map) = specs.get(&parent.local_id)
 142                 && let Some(&(level, src)) = map.get(&id)
 143             {
 144                 return (Some(level), src);
 145             }
 146         }
 147
 148         (None, LintLevelSource::Default)
 149     }
 150
 151     /// Fetch and return the user-visible lint level for the given lint at the given HirId.
 152     #[instrument(level = "trace", skip(self, tcx), ret)]
 153     pub fn lint_level_id_at_node(
 154         &self,
 155         tcx: TyCtxt<'_>,
 156         lint: LintId,
 157         cur: HirId,
 158     ) -> (Level, LintLevelSource) {
 159         let (level, mut src) = self.probe_for_lint_level(tcx, lint, cur);
 160         let level = reveal_actual_level(level, &mut src, tcx.sess, lint, |lint| {
 161             self.probe_for_lint_level(tcx, lint, cur)
 162         });
 163         (level, src)
 164     }
 165 }
 166
 167 impl TyCtxt<'_> {
 168     /// Fetch and return the user-visible lint level for the given lint at the given HirId.
 169     pub fn lint_level_at_node(self, lint: &'static Lint, id: HirId) -> (Level, LintLevelSource) {
 170         self.shallow_lint_levels_on(id.owner).lint_level_id_at_node(self, LintId::of(lint), id)
 171     }
 172
 173     /// Walks upwards from `id` to find a node which might change lint levels with attributes.
 174     /// It stops at `bound` and just returns it if reached.
 175     pub fn maybe_lint_level_root_bounded(self, mut id: HirId, bound: HirId) -> HirId {
 176         let hir = self.hir();
 177         loop {
 178             if id == bound {
 179                 return bound;
 180             }
 181
 182             if hir.attrs(id).iter().any(|attr| Level::from_attr(attr).is_some()) {
 183                 return id;
 184             }
 185             let next = hir.parent_id(id);
 186             if next == id {
 187                 bug!("lint traversal reached the root of the crate");
 188             }
 189             id = next;
 190         }
 191     }
 192 }
 193
 194 /// This struct represents a lint expectation and holds all required information
 195 /// to emit the `unfulfilled_lint_expectations` lint if it is unfulfilled after
 196 /// the `LateLintPass` has completed.
 197 #[derive(Clone, Debug, HashStable)]
 198 pub struct LintExpectation {
 199     /// The reason for this expectation that can optionally be added as part of
 200     /// the attribute. It will be displayed as part of the lint message.
 201     pub reason: Option<Symbol>,
 202     /// The [`Span`] of the attribute that this expectation originated from.
 203     pub emission_span: Span,
 204     /// Lint messages for the `unfulfilled_lint_expectations` lint will be
 205     /// adjusted to include an additional note. Therefore, we have to track if
 206     /// the expectation is for the lint.
 207     pub is_unfulfilled_lint_expectations: bool,
 208     /// This will hold the name of the tool that this lint belongs to. For
 209     /// the lint `clippy::some_lint` the tool would be `clippy`, the same
 210     /// goes for `rustdoc`. This will be `None` for rustc lints
 211     pub lint_tool: Option<Symbol>,
 212 }
 213
 214 impl LintExpectation {
 215     pub fn new(
 216         reason: Option<Symbol>,
 217         emission_span: Span,
 218         is_unfulfilled_lint_expectations: bool,
 219         lint_tool: Option<Symbol>,
 220     ) -> Self {
 221         Self { reason, emission_span, is_unfulfilled_lint_expectations, lint_tool }
 222     }
 223 }
 224
 225 pub fn explain_lint_level_source(
 226     lint: &'static Lint,
 227     level: Level,
 228     src: LintLevelSource,
 229     err: &mut Diagnostic,
 230 ) {
 231     let name = lint.name_lower();
 232     match src {
 233         LintLevelSource::Default => {
 234             err.note_once(&format!("`#[{}({})]` on by default", level.as_str(), name));
 235         }
 236         LintLevelSource::CommandLine(lint_flag_val, orig_level) => {
 237             let flag = orig_level.to_cmd_flag();
 238             let hyphen_case_lint_name = name.replace('_', "-");
 239             if lint_flag_val.as_str() == name {
 240                 err.note_once(&format!(
 241                     "requested on the command line with `{} {}`",
 242                     flag, hyphen_case_lint_name
 243                 ));
 244             } else {
 245                 let hyphen_case_flag_val = lint_flag_val.as_str().replace('_', "-");
 246                 err.note_once(&format!(
 247                     "`{} {}` implied by `{} {}`",
 248                     flag, hyphen_case_lint_name, flag, hyphen_case_flag_val
 249                 ));
 250             }
 251         }
 252         LintLevelSource::Node { name: lint_attr_name, span, reason, .. } => {
 253             if let Some(rationale) = reason {
 254                 err.note(rationale.as_str());
 255             }
 256             err.span_note_once(span, "the lint level is defined here");
 257             if lint_attr_name.as_str() != name {
 258                 let level_str = level.as_str();
 259                 err.note_once(&format!(
 260                     "`#[{}({})]` implied by `#[{}({})]`",
 261                     level_str, name, level_str, lint_attr_name
 262                 ));
 263             }
 264         }
 265     }
 266 }
 267
 268 /// The innermost function for emitting lints.
 269 ///
 270 /// If you are looking to implement a lint, look for higher level functions,
 271 /// for example:
 272 /// - [`TyCtxt::emit_spanned_lint`]
 273 /// - [`TyCtxt::struct_span_lint_hir`]
 274 /// - [`TyCtxt::emit_lint`]
 275 /// - [`TyCtxt::struct_lint_node`]
 276 /// - `LintContext::lookup`
 277 ///
 278 /// ## `decorate` signature
 279 ///
 280 /// The return value of `decorate` is ignored by this function. So what is the
 281 /// point of returning `&'b mut DiagnosticBuilder<'a, ()>`?
 282 ///
 283 /// There are 2 reasons for this signature.
 284 ///
 285 /// First of all, it prevents accidental use of `.emit()` -- it's clear that the
 286 /// builder will be later used and shouldn't be emitted right away (this is
 287 /// especially important because the old API expected you to call `.emit()` in
 288 /// the closure).
 289 ///
 290 /// Second of all, it makes the most common case of adding just a single label
 291 /// /suggestion much nicer, since [`DiagnosticBuilder`] methods return
 292 /// `&mut DiagnosticBuilder`, you can just chain methods, without needed
 293 /// awkward `{ ...; }`:
 294 /// ```ignore pseudo-code
 295 /// struct_lint_level(
 296 ///     ...,
 297 ///     |lint| lint.span_label(sp, "lbl")
 298 ///     //          ^^^^^^^^^^^^^^^^^^^^^ returns `&mut DiagnosticBuilder` by default
 299 /// )
 300 /// ```
 301 pub fn struct_lint_level(
 302     sess: &Session,
 303     lint: &'static Lint,
 304     level: Level,
 305     src: LintLevelSource,
 306     span: Option<MultiSpan>,
 307     msg: impl Into<DiagnosticMessage>,
 308     decorate: impl for<'a, 'b> FnOnce(
 309         &'b mut DiagnosticBuilder<'a, ()>,
 310     ) -> &'b mut DiagnosticBuilder<'a, ()>,
 311 ) {
 312     // Avoid codegen bloat from monomorphization by immediately doing dyn dispatch of `decorate` to
 313     // the "real" work.
 314     fn struct_lint_level_impl(
 315         sess: &Session,
 316         lint: &'static Lint,
 317         level: Level,
 318         src: LintLevelSource,
 319         span: Option<MultiSpan>,
 320         msg: impl Into<DiagnosticMessage>,
 321         decorate: Box<
 322             dyn '_
 323                 + for<'a, 'b> FnOnce(
 324                     &'b mut DiagnosticBuilder<'a, ()>,
 325                 ) -> &'b mut DiagnosticBuilder<'a, ()>,
 326         >,
 327     ) {
 328         // Check for future incompatibility lints and issue a stronger warning.
 329         let future_incompatible = lint.future_incompatible;
 330
 331         let has_future_breakage = future_incompatible.map_or(
 332             // Default allow lints trigger too often for testing.
 333             sess.opts.unstable_opts.future_incompat_test && lint.default_level != Level::Allow,
 334             |incompat| {
 335                 matches!(incompat.reason, FutureIncompatibilityReason::FutureReleaseErrorReportNow)
 336             },
 337         );
 338
 339         let mut err = match (level, span) {
 340             (Level::Allow, span) => {
 341                 if has_future_breakage {
 342                     if let Some(span) = span {
 343                         sess.struct_span_allow(span, "")
 344                     } else {
 345                         sess.struct_allow("")
 346                     }
 347                 } else {
 348                     return;
 349                 }
 350             }
 351             (Level::Expect(expect_id), _) => {
 352                 // This case is special as we actually allow the lint itself in this context, but
 353                 // we can't return early like in the case for `Level::Allow` because we still
 354                 // need the lint diagnostic to be emitted to `rustc_error::HandlerInner`.
 355                 //
 356                 // We can also not mark the lint expectation as fulfilled here right away, as it
 357                 // can still be cancelled in the decorate function. All of this means that we simply
 358                 // create a `DiagnosticBuilder` and continue as we would for warnings.
 359                 sess.struct_expect("", expect_id)
 360             }
 361             (Level::ForceWarn(Some(expect_id)), Some(span)) => {
 362                 sess.struct_span_warn_with_expectation(span, "", expect_id)
 363             }
 364             (Level::ForceWarn(Some(expect_id)), None) => {
 365                 sess.struct_warn_with_expectation("", expect_id)
 366             }
 367             (Level::Warn | Level::ForceWarn(None), Some(span)) => sess.struct_span_warn(span, ""),
 368             (Level::Warn | Level::ForceWarn(None), None) => sess.struct_warn(""),
 369             (Level::Deny | Level::Forbid, Some(span)) => {
 370                 let mut builder = sess.diagnostic().struct_err_lint("");
 371                 builder.set_span(span);
 372                 builder
 373             }
 374             (Level::Deny | Level::Forbid, None) => sess.diagnostic().struct_err_lint(""),
 375         };
 376
 377         err.set_is_lint();
 378
 379         // If this code originates in a foreign macro, aka something that this crate
 380         // did not itself author, then it's likely that there's nothing this crate
 381         // can do about it. We probably want to skip the lint entirely.
 382         if err.span.primary_spans().iter().any(|s| in_external_macro(sess, *s)) {
 383             // Any suggestions made here are likely to be incorrect, so anything we
 384             // emit shouldn't be automatically fixed by rustfix.
 385             err.disable_suggestions();
 386
 387             // If this is a future incompatible that is not an edition fixing lint
 388             // it'll become a hard error, so we have to emit *something*. Also,
 389             // if this lint occurs in the expansion of a macro from an external crate,
 390             // allow individual lints to opt-out from being reported.
 391             let not_future_incompatible =
 392                 future_incompatible.map(|f| f.reason.edition().is_some()).unwrap_or(true);
 393             if not_future_incompatible && !lint.report_in_external_macro {
 394                 err.cancel();
 395                 // Don't continue further, since we don't want to have
 396                 // `diag_span_note_once` called for a diagnostic that isn't emitted.
 397                 return;
 398             }
 399         }
 400
 401         // Delay evaluating and setting the primary message until after we've
 402         // suppressed the lint due to macros.
 403         err.set_primary_message(msg);
 404
 405         // Lint diagnostics that are covered by the expect level will not be emitted outside
 406         // the compiler. It is therefore not necessary to add any information for the user.
 407         // This will therefore directly call the decorate function which will in turn emit
 408         // the `Diagnostic`.
 409         if let Level::Expect(_) = level {
 410             let name = lint.name_lower();
 411             err.code(DiagnosticId::Lint { name, has_future_breakage, is_force_warn: false });
 412
 413             decorate(&mut err);
 414             err.emit();
 415             return;
 416         }
 417
 418         let name = lint.name_lower();
 419         let is_force_warn = matches!(level, Level::ForceWarn(_));
 420         err.code(DiagnosticId::Lint { name, has_future_breakage, is_force_warn });
 421
 422         if let Some(future_incompatible) = future_incompatible {
 423             let explanation = match future_incompatible.reason {
 424                 FutureIncompatibilityReason::FutureReleaseError
 425                 | FutureIncompatibilityReason::FutureReleaseErrorReportNow => {
 426                     "this was previously accepted by the compiler but is being phased out; \
 427                          it will become a hard error in a future release!"
 428                         .to_owned()
 429                 }
 430                 FutureIncompatibilityReason::FutureReleaseSemanticsChange => {
 431                     "this will change its meaning in a future release!".to_owned()
 432                 }
 433                 FutureIncompatibilityReason::EditionError(edition) => {
 434                     let current_edition = sess.edition();
 435                     format!(
 436                         "this is accepted in the current edition (Rust {}) but is a hard error in Rust {}!",
 437                         current_edition, edition
 438                     )
 439                 }
 440                 FutureIncompatibilityReason::EditionSemanticsChange(edition) => {
 441                     format!("this changes meaning in Rust {}", edition)
 442                 }
 443                 FutureIncompatibilityReason::Custom(reason) => reason.to_owned(),
 444             };
 445
 446             if future_incompatible.explain_reason {
 447                 err.warn(&explanation);
 448             }
 449             if !future_incompatible.reference.is_empty() {
 450                 let citation =
 451                     format!("for more information, see {}", future_incompatible.reference);
 452                 err.note(&citation);
 453             }
 454         }
 455
 456         // Finally, run `decorate`.
 457         decorate(&mut err);
 458         explain_lint_level_source(lint, level, src, &mut *err);
 459         err.emit()
 460     }
 461     struct_lint_level_impl(sess, lint, level, src, span, msg, Box::new(decorate))
 462 }
 463
 464 /// Returns whether `span` originates in a foreign crate's external macro.
 465 ///
 466 /// This is used to test whether a lint should not even begin to figure out whether it should
 467 /// be reported on the current node.
 468 pub fn in_external_macro(sess: &Session, span: Span) -> bool {
 469     let expn_data = span.ctxt().outer_expn_data();
 470     match expn_data.kind {
 471         ExpnKind::Inlined
 472         | ExpnKind::Root
 473         | ExpnKind::Desugaring(
 474             DesugaringKind::ForLoop | DesugaringKind::WhileLoop | DesugaringKind::OpaqueTy,
 475         ) => false,
 476         ExpnKind::AstPass(_) | ExpnKind::Desugaring(_) => true, // well, it's "external"
 477         ExpnKind::Macro(MacroKind::Bang, _) => {
 478             // Dummy span for the `def_site` means it's an external macro.
 479             expn_data.def_site.is_dummy() || sess.source_map().is_imported(expn_data.def_site)
 480         }
 481         ExpnKind::Macro { .. } => true, // definitely a plugin
 482     }
 483 }