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