src/librustc/hir/check_attr.rs

   1 //! This module implements some validity checks for attributes.
   2 //! In particular it verifies that `#[inline]` and `#[repr]` attributes are
   3 //! attached to items that actually support them and if there are
   4 //! conflicts between multiple such attributes attached to the same
   5 //! item.
   6
   7 use crate::hir::def_id::DefId;
   8 use crate::hir::intravisit::{self, NestedVisitorMap, Visitor};
   9 use crate::hir::DUMMY_HIR_ID;
  10 use crate::hir::{self, Attribute, HirId, Item, ItemKind, TraitItem, TraitItemKind};
  11 use crate::lint::builtin::UNUSED_ATTRIBUTES;
  12 use crate::ty::query::Providers;
  13 use crate::ty::TyCtxt;
  14
  15 use std::fmt::{self, Display};
  16 use syntax::{attr, symbol::sym};
  17 use syntax_pos::Span;
  18
  19 use rustc_error_codes::*;
  20
  21 #[derive(Copy, Clone, PartialEq)]
  22 pub(crate) enum MethodKind {
  23     Trait { body: bool },
  24     Inherent,
  25 }
  26
  27 #[derive(Copy, Clone, PartialEq)]
  28 pub(crate) enum Target {
  29     ExternCrate,
  30     Use,
  31     Static,
  32     Const,
  33     Fn,
  34     Closure,
  35     Mod,
  36     ForeignMod,
  37     GlobalAsm,
  38     TyAlias,
  39     OpaqueTy,
  40     Enum,
  41     Struct,
  42     Union,
  43     Trait,
  44     TraitAlias,
  45     Impl,
  46     Expression,
  47     Statement,
  48     AssocConst,
  49     Method(MethodKind),
  50     AssocTy,
  51     ForeignFn,
  52     ForeignStatic,
  53     ForeignTy,
  54 }
  55
  56 impl Display for Target {
  57     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  58         write!(
  59             f,
  60             "{}",
  61             match *self {
  62                 Target::ExternCrate => "extern crate",
  63                 Target::Use => "use",
  64                 Target::Static => "static item",
  65                 Target::Const => "constant item",
  66                 Target::Fn => "function",
  67                 Target::Closure => "closure",
  68                 Target::Mod => "module",
  69                 Target::ForeignMod => "foreign module",
  70                 Target::GlobalAsm => "global asm",
  71                 Target::TyAlias => "type alias",
  72                 Target::OpaqueTy => "opaque type",
  73                 Target::Enum => "enum",
  74                 Target::Struct => "struct",
  75                 Target::Union => "union",
  76                 Target::Trait => "trait",
  77                 Target::TraitAlias => "trait alias",
  78                 Target::Impl => "item",
  79                 Target::Expression => "expression",
  80                 Target::Statement => "statement",
  81                 Target::AssocConst => "associated const",
  82                 Target::Method(_) => "method",
  83                 Target::AssocTy => "associated type",
  84                 Target::ForeignFn => "foreign function",
  85                 Target::ForeignStatic => "foreign static item",
  86                 Target::ForeignTy => "foreign type",
  87             }
  88         )
  89     }
  90 }
  91
  92 impl Target {
  93     pub(crate) fn from_item(item: &Item<'_>) -> Target {
  94         match item.kind {
  95             ItemKind::ExternCrate(..) => Target::ExternCrate,
  96             ItemKind::Use(..) => Target::Use,
  97             ItemKind::Static(..) => Target::Static,
  98             ItemKind::Const(..) => Target::Const,
  99             ItemKind::Fn(..) => Target::Fn,
 100             ItemKind::Mod(..) => Target::Mod,
 101             ItemKind::ForeignMod(..) => Target::ForeignMod,
 102             ItemKind::GlobalAsm(..) => Target::GlobalAsm,
 103             ItemKind::TyAlias(..) => Target::TyAlias,
 104             ItemKind::OpaqueTy(..) => Target::OpaqueTy,
 105             ItemKind::Enum(..) => Target::Enum,
 106             ItemKind::Struct(..) => Target::Struct,
 107             ItemKind::Union(..) => Target::Union,
 108             ItemKind::Trait(..) => Target::Trait,
 109             ItemKind::TraitAlias(..) => Target::TraitAlias,
 110             ItemKind::Impl(..) => Target::Impl,
 111         }
 112     }
 113
 114     fn from_trait_item(trait_item: &TraitItem<'_>) -> Target {
 115         match trait_item.kind {
 116             TraitItemKind::Const(..) => Target::AssocConst,
 117             TraitItemKind::Method(_, hir::TraitMethod::Required(_)) => {
 118                 Target::Method(MethodKind::Trait { body: false })
 119             }
 120             TraitItemKind::Method(_, hir::TraitMethod::Provided(_)) => {
 121                 Target::Method(MethodKind::Trait { body: true })
 122             }
 123             TraitItemKind::Type(..) => Target::AssocTy,
 124         }
 125     }
 126
 127     fn from_foreign_item(foreign_item: &hir::ForeignItem<'_>) -> Target {
 128         match foreign_item.kind {
 129             hir::ForeignItemKind::Fn(..) => Target::ForeignFn,
 130             hir::ForeignItemKind::Static(..) => Target::ForeignStatic,
 131             hir::ForeignItemKind::Type => Target::ForeignTy,
 132         }
 133     }
 134
 135     fn from_impl_item<'tcx>(tcx: TyCtxt<'tcx>, impl_item: &hir::ImplItem<'_>) -> Target {
 136         match impl_item.kind {
 137             hir::ImplItemKind::Const(..) => Target::AssocConst,
 138             hir::ImplItemKind::Method(..) => {
 139                 let parent_hir_id = tcx.hir().get_parent_item(impl_item.hir_id);
 140                 let containing_item = tcx.hir().expect_item(parent_hir_id);
 141                 let containing_impl_is_for_trait = match &containing_item.kind {
 142                     hir::ItemKind::Impl(_, _, _, _, tr, _, _) => tr.is_some(),
 143                     _ => bug!("parent of an ImplItem must be an Impl"),
 144                 };
 145                 if containing_impl_is_for_trait {
 146                     Target::Method(MethodKind::Trait { body: true })
 147                 } else {
 148                     Target::Method(MethodKind::Inherent)
 149                 }
 150             }
 151             hir::ImplItemKind::TyAlias(..) | hir::ImplItemKind::OpaqueTy(..) => Target::AssocTy,
 152         }
 153     }
 154 }
 155
 156 struct CheckAttrVisitor<'tcx> {
 157     tcx: TyCtxt<'tcx>,
 158 }
 159
 160 impl CheckAttrVisitor<'tcx> {
 161     /// Checks any attribute.
 162     fn check_attributes(
 163         &self,
 164         hir_id: HirId,
 165         attrs: &'hir [Attribute],
 166         span: &Span,
 167         target: Target,
 168         item: Option<&Item<'_>>,
 169     ) {
 170         let mut is_valid = true;
 171         for attr in attrs {
 172             is_valid &= if attr.check_name(sym::inline) {
 173                 self.check_inline(hir_id, attr, span, target)
 174             } else if attr.check_name(sym::non_exhaustive) {
 175                 self.check_non_exhaustive(attr, span, target)
 176             } else if attr.check_name(sym::marker) {
 177                 self.check_marker(attr, span, target)
 178             } else if attr.check_name(sym::target_feature) {
 179                 self.check_target_feature(attr, span, target)
 180             } else if attr.check_name(sym::track_caller) {
 181                 self.check_track_caller(&attr.span, attrs, span, target)
 182             } else {
 183                 true
 184             };
 185         }
 186
 187         if !is_valid {
 188             return;
 189         }
 190
 191         if target == Target::Fn {
 192             self.tcx.codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
 193         }
 194
 195         self.check_repr(attrs, span, target, item);
 196         self.check_used(attrs, target);
 197     }
 198
 199     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
 200     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) -> bool {
 201         match target {
 202             Target::Fn
 203             | Target::Closure
 204             | Target::Method(MethodKind::Trait { body: true })
 205             | Target::Method(MethodKind::Inherent) => true,
 206             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
 207                 self.tcx
 208                     .struct_span_lint_hir(
 209                         UNUSED_ATTRIBUTES,
 210                         hir_id,
 211                         attr.span,
 212                         "`#[inline]` is ignored on function prototypes",
 213                     )
 214                     .emit();
 215                 true
 216             }
 217             // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
 218             // just a lint, because we previously erroneously allowed it and some crates used it
 219             // accidentally, to to be compatible with crates depending on them, we can't throw an
 220             // error here.
 221             Target::AssocConst => {
 222                 self.tcx
 223                     .struct_span_lint_hir(
 224                         UNUSED_ATTRIBUTES,
 225                         hir_id,
 226                         attr.span,
 227                         "`#[inline]` is ignored on constants",
 228                     )
 229                     .warn(
 230                         "this was previously accepted by the compiler but is \
 231                        being phased out; it will become a hard error in \
 232                        a future release!",
 233                     )
 234                     .note(
 235                         "for more information, see issue #65833 \
 236                        <https://github.com/rust-lang/rust/issues/65833>",
 237                     )
 238                     .emit();
 239                 true
 240             }
 241             _ => {
 242                 struct_span_err!(
 243                     self.tcx.sess,
 244                     attr.span,
 245                     E0518,
 246                     "attribute should be applied to function or closure",
 247                 )
 248                 .span_label(*span, "not a function or closure")
 249                 .emit();
 250                 false
 251             }
 252         }
 253     }
 254
 255     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 256     fn check_track_caller(
 257         &self,
 258         attr_span: &Span,
 259         attrs: &'hir [Attribute],
 260         span: &Span,
 261         target: Target,
 262     ) -> bool {
 263         match target {
 264             Target::Fn if attr::contains_name(attrs, sym::naked) => {
 265                 struct_span_err!(
 266                     self.tcx.sess,
 267                     *attr_span,
 268                     E0736,
 269                     "cannot use `#[track_caller]` with `#[naked]`",
 270                 )
 271                 .emit();
 272                 false
 273             }
 274             Target::Fn | Target::Method(MethodKind::Inherent) => true,
 275             Target::Method(_) => {
 276                 struct_span_err!(
 277                     self.tcx.sess,
 278                     *attr_span,
 279                     E0738,
 280                     "`#[track_caller]` may not be used on trait methods",
 281                 )
 282                 .emit();
 283                 false
 284             }
 285             _ => {
 286                 struct_span_err!(
 287                     self.tcx.sess,
 288                     *attr_span,
 289                     E0739,
 290                     "attribute should be applied to function"
 291                 )
 292                 .span_label(*span, "not a function")
 293                 .emit();
 294                 false
 295             }
 296         }
 297     }
 298
 299     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 300     fn check_non_exhaustive(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 301         match target {
 302             Target::Struct | Target::Enum => true,
 303             _ => {
 304                 struct_span_err!(
 305                     self.tcx.sess,
 306                     attr.span,
 307                     E0701,
 308                     "attribute can only be applied to a struct or enum"
 309                 )
 310                 .span_label(*span, "not a struct or enum")
 311                 .emit();
 312                 false
 313             }
 314         }
 315     }
 316
 317     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 318     fn check_marker(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 319         match target {
 320             Target::Trait => true,
 321             _ => {
 322                 self.tcx
 323                     .sess
 324                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 325                     .span_label(*span, "not a trait")
 326                     .emit();
 327                 false
 328             }
 329         }
 330     }
 331
 332     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 333     fn check_target_feature(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 334         match target {
 335             Target::Fn
 336             | Target::Method(MethodKind::Trait { body: true })
 337             | Target::Method(MethodKind::Inherent) => true,
 338             _ => {
 339                 self.tcx
 340                     .sess
 341                     .struct_span_err(attr.span, "attribute should be applied to a function")
 342                     .span_label(*span, "not a function")
 343                     .emit();
 344                 false
 345             }
 346         }
 347     }
 348
 349     /// Checks if the `#[repr]` attributes on `item` are valid.
 350     fn check_repr(
 351         &self,
 352         attrs: &'hir [Attribute],
 353         span: &Span,
 354         target: Target,
 355         item: Option<&Item<'_>>,
 356     ) {
 357         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 358         // ```
 359         // #[repr(foo)]
 360         // #[repr(bar, align(8))]
 361         // ```
 362         let hints: Vec<_> = attrs
 363             .iter()
 364             .filter(|attr| attr.check_name(sym::repr))
 365             .filter_map(|attr| attr.meta_item_list())
 366             .flatten()
 367             .collect();
 368
 369         let mut int_reprs = 0;
 370         let mut is_c = false;
 371         let mut is_simd = false;
 372         let mut is_transparent = false;
 373
 374         for hint in &hints {
 375             let (article, allowed_targets) = match hint.name_or_empty() {
 376                 name @ sym::C | name @ sym::align => {
 377                     is_c |= name == sym::C;
 378                     match target {
 379                         Target::Struct | Target::Union | Target::Enum => continue,
 380                         _ => ("a", "struct, enum, or union"),
 381                     }
 382                 }
 383                 sym::packed => {
 384                     if target != Target::Struct && target != Target::Union {
 385                         ("a", "struct or union")
 386                     } else {
 387                         continue;
 388                     }
 389                 }
 390                 sym::simd => {
 391                     is_simd = true;
 392                     if target != Target::Struct { ("a", "struct") } else { continue }
 393                 }
 394                 sym::transparent => {
 395                     is_transparent = true;
 396                     match target {
 397                         Target::Struct | Target::Union | Target::Enum => continue,
 398                         _ => ("a", "struct, enum, or union"),
 399                     }
 400                 }
 401                 sym::i8
 402                 | sym::u8
 403                 | sym::i16
 404                 | sym::u16
 405                 | sym::i32
 406                 | sym::u32
 407                 | sym::i64
 408                 | sym::u64
 409                 | sym::isize
 410                 | sym::usize => {
 411                     int_reprs += 1;
 412                     if target != Target::Enum { ("an", "enum") } else { continue }
 413                 }
 414                 _ => continue,
 415             };
 416             self.emit_repr_error(
 417                 hint.span(),
 418                 *span,
 419                 &format!("attribute should be applied to {}", allowed_targets),
 420                 &format!("not {} {}", article, allowed_targets),
 421             )
 422         }
 423
 424         // Just point at all repr hints if there are any incompatibilities.
 425         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 426         let hint_spans = hints.iter().map(|hint| hint.span());
 427
 428         // Error on repr(transparent, <anything else>).
 429         if is_transparent && hints.len() > 1 {
 430             let hint_spans: Vec<_> = hint_spans.clone().collect();
 431             span_err!(
 432                 self.tcx.sess,
 433                 hint_spans,
 434                 E0692,
 435                 "transparent {} cannot have other repr hints",
 436                 target
 437             );
 438         }
 439         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 440         if (int_reprs > 1)
 441             || (is_simd && is_c)
 442             || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item)))
 443         {
 444             let hint_spans: Vec<_> = hint_spans.collect();
 445             span_warn!(self.tcx.sess, hint_spans, E0566, "conflicting representation hints");
 446         }
 447     }
 448
 449     fn emit_repr_error(
 450         &self,
 451         hint_span: Span,
 452         label_span: Span,
 453         hint_message: &str,
 454         label_message: &str,
 455     ) {
 456         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 457             .span_label(label_span, label_message)
 458             .emit();
 459     }
 460
 461     fn check_stmt_attributes(&self, stmt: &hir::Stmt) {
 462         // When checking statements ignore expressions, they will be checked later
 463         if let hir::StmtKind::Local(ref l) = stmt.kind {
 464             for attr in l.attrs.iter() {
 465                 if attr.check_name(sym::inline) {
 466                     self.check_inline(DUMMY_HIR_ID, attr, &stmt.span, Target::Statement);
 467                 }
 468                 if attr.check_name(sym::repr) {
 469                     self.emit_repr_error(
 470                         attr.span,
 471                         stmt.span,
 472                         "attribute should not be applied to a statement",
 473                         "not a struct, enum, or union",
 474                     );
 475                 }
 476             }
 477         }
 478     }
 479
 480     fn check_expr_attributes(&self, expr: &hir::Expr) {
 481         let target = match expr.kind {
 482             hir::ExprKind::Closure(..) => Target::Closure,
 483             _ => Target::Expression,
 484         };
 485         for attr in expr.attrs.iter() {
 486             if attr.check_name(sym::inline) {
 487                 self.check_inline(DUMMY_HIR_ID, attr, &expr.span, target);
 488             }
 489             if attr.check_name(sym::repr) {
 490                 self.emit_repr_error(
 491                     attr.span,
 492                     expr.span,
 493                     "attribute should not be applied to an expression",
 494                     "not defining a struct, enum, or union",
 495                 );
 496             }
 497         }
 498     }
 499
 500     fn check_used(&self, attrs: &'hir [Attribute], target: Target) {
 501         for attr in attrs {
 502             if attr.check_name(sym::used) && target != Target::Static {
 503                 self.tcx
 504                     .sess
 505                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 506             }
 507         }
 508     }
 509 }
 510
 511 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 512     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 513         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 514     }
 515
 516     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
 517         let target = Target::from_item(item);
 518         self.check_attributes(item.hir_id, item.attrs, &item.span, target, Some(item));
 519         intravisit::walk_item(self, item)
 520     }
 521
 522     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
 523         let target = Target::from_trait_item(trait_item);
 524         self.check_attributes(trait_item.hir_id, &trait_item.attrs, &trait_item.span, target, None);
 525         intravisit::walk_trait_item(self, trait_item)
 526     }
 527
 528     fn visit_foreign_item(&mut self, f_item: &'tcx hir::ForeignItem<'tcx>) {
 529         let target = Target::from_foreign_item(f_item);
 530         self.check_attributes(f_item.hir_id, &f_item.attrs, &f_item.span, target, None);
 531         intravisit::walk_foreign_item(self, f_item)
 532     }
 533
 534     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 535         let target = Target::from_impl_item(self.tcx, impl_item);
 536         self.check_attributes(impl_item.hir_id, &impl_item.attrs, &impl_item.span, target, None);
 537         intravisit::walk_impl_item(self, impl_item)
 538     }
 539
 540     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt) {
 541         self.check_stmt_attributes(stmt);
 542         intravisit::walk_stmt(self, stmt)
 543     }
 544
 545     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
 546         self.check_expr_attributes(expr);
 547         intravisit::walk_expr(self, expr)
 548     }
 549 }
 550
 551 fn is_c_like_enum(item: &Item<'_>) -> bool {
 552     if let ItemKind::Enum(ref def, _) = item.kind {
 553         for variant in def.variants {
 554             match variant.data {
 555                 hir::VariantData::Unit(..) => { /* continue */ }
 556                 _ => return false,
 557             }
 558         }
 559         true
 560     } else {
 561         false
 562     }
 563 }
 564
 565 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: DefId) {
 566     tcx.hir()
 567         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
 568 }
 569
 570 pub(crate) fn provide(providers: &mut Providers<'_>) {
 571     *providers = Providers { check_mod_attrs, ..*providers };
 572 }