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::map::Map;
   8 use crate::ty::query::Providers;
   9 use crate::ty::TyCtxt;
  10
  11 use rustc_errors::struct_span_err;
  12 use rustc_hir as hir;
  13 use rustc_hir::def_id::DefId;
  14 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
  15 use rustc_hir::DUMMY_HIR_ID;
  16 use rustc_hir::{self, HirId, Item, ItemKind, TraitItem, TraitItemKind};
  17 use rustc_session::lint::builtin::UNUSED_ATTRIBUTES;
  18 use rustc_span::symbol::sym;
  19 use rustc_span::Span;
  20 use syntax::ast::Attribute;
  21 use syntax::attr;
  22
  23 use std::fmt::{self, Display};
  24
  25 #[derive(Copy, Clone, PartialEq)]
  26 pub(crate) enum MethodKind {
  27     Trait { body: bool },
  28     Inherent,
  29 }
  30
  31 #[derive(Copy, Clone, PartialEq)]
  32 pub(crate) enum Target {
  33     ExternCrate,
  34     Use,
  35     Static,
  36     Const,
  37     Fn,
  38     Closure,
  39     Mod,
  40     ForeignMod,
  41     GlobalAsm,
  42     TyAlias,
  43     OpaqueTy,
  44     Enum,
  45     Struct,
  46     Union,
  47     Trait,
  48     TraitAlias,
  49     Impl,
  50     Expression,
  51     Statement,
  52     AssocConst,
  53     Method(MethodKind),
  54     AssocTy,
  55     ForeignFn,
  56     ForeignStatic,
  57     ForeignTy,
  58 }
  59
  60 impl Display for Target {
  61     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  62         write!(
  63             f,
  64             "{}",
  65             match *self {
  66                 Target::ExternCrate => "extern crate",
  67                 Target::Use => "use",
  68                 Target::Static => "static item",
  69                 Target::Const => "constant item",
  70                 Target::Fn => "function",
  71                 Target::Closure => "closure",
  72                 Target::Mod => "module",
  73                 Target::ForeignMod => "foreign module",
  74                 Target::GlobalAsm => "global asm",
  75                 Target::TyAlias => "type alias",
  76                 Target::OpaqueTy => "opaque type",
  77                 Target::Enum => "enum",
  78                 Target::Struct => "struct",
  79                 Target::Union => "union",
  80                 Target::Trait => "trait",
  81                 Target::TraitAlias => "trait alias",
  82                 Target::Impl => "item",
  83                 Target::Expression => "expression",
  84                 Target::Statement => "statement",
  85                 Target::AssocConst => "associated const",
  86                 Target::Method(_) => "method",
  87                 Target::AssocTy => "associated type",
  88                 Target::ForeignFn => "foreign function",
  89                 Target::ForeignStatic => "foreign static item",
  90                 Target::ForeignTy => "foreign type",
  91             }
  92         )
  93     }
  94 }
  95
  96 impl Target {
  97     pub(crate) fn from_item(item: &Item<'_>) -> Target {
  98         match item.kind {
  99             ItemKind::ExternCrate(..) => Target::ExternCrate,
 100             ItemKind::Use(..) => Target::Use,
 101             ItemKind::Static(..) => Target::Static,
 102             ItemKind::Const(..) => Target::Const,
 103             ItemKind::Fn(..) => Target::Fn,
 104             ItemKind::Mod(..) => Target::Mod,
 105             ItemKind::ForeignMod(..) => Target::ForeignMod,
 106             ItemKind::GlobalAsm(..) => Target::GlobalAsm,
 107             ItemKind::TyAlias(..) => Target::TyAlias,
 108             ItemKind::OpaqueTy(..) => Target::OpaqueTy,
 109             ItemKind::Enum(..) => Target::Enum,
 110             ItemKind::Struct(..) => Target::Struct,
 111             ItemKind::Union(..) => Target::Union,
 112             ItemKind::Trait(..) => Target::Trait,
 113             ItemKind::TraitAlias(..) => Target::TraitAlias,
 114             ItemKind::Impl { .. } => Target::Impl,
 115         }
 116     }
 117
 118     fn from_trait_item(trait_item: &TraitItem<'_>) -> Target {
 119         match trait_item.kind {
 120             TraitItemKind::Const(..) => Target::AssocConst,
 121             TraitItemKind::Method(_, hir::TraitMethod::Required(_)) => {
 122                 Target::Method(MethodKind::Trait { body: false })
 123             }
 124             TraitItemKind::Method(_, hir::TraitMethod::Provided(_)) => {
 125                 Target::Method(MethodKind::Trait { body: true })
 126             }
 127             TraitItemKind::Type(..) => Target::AssocTy,
 128         }
 129     }
 130
 131     fn from_foreign_item(foreign_item: &hir::ForeignItem<'_>) -> Target {
 132         match foreign_item.kind {
 133             hir::ForeignItemKind::Fn(..) => Target::ForeignFn,
 134             hir::ForeignItemKind::Static(..) => Target::ForeignStatic,
 135             hir::ForeignItemKind::Type => Target::ForeignTy,
 136         }
 137     }
 138
 139     fn from_impl_item<'tcx>(tcx: TyCtxt<'tcx>, impl_item: &hir::ImplItem<'_>) -> Target {
 140         match impl_item.kind {
 141             hir::ImplItemKind::Const(..) => Target::AssocConst,
 142             hir::ImplItemKind::Method(..) => {
 143                 let parent_hir_id = tcx.hir().get_parent_item(impl_item.hir_id);
 144                 let containing_item = tcx.hir().expect_item(parent_hir_id);
 145                 let containing_impl_is_for_trait = match &containing_item.kind {
 146                     hir::ItemKind::Impl { ref of_trait, .. } => of_trait.is_some(),
 147                     _ => bug!("parent of an ImplItem must be an Impl"),
 148                 };
 149                 if containing_impl_is_for_trait {
 150                     Target::Method(MethodKind::Trait { body: true })
 151                 } else {
 152                     Target::Method(MethodKind::Inherent)
 153                 }
 154             }
 155             hir::ImplItemKind::TyAlias(..) | hir::ImplItemKind::OpaqueTy(..) => Target::AssocTy,
 156         }
 157     }
 158 }
 159
 160 struct CheckAttrVisitor<'tcx> {
 161     tcx: TyCtxt<'tcx>,
 162 }
 163
 164 impl CheckAttrVisitor<'tcx> {
 165     /// Checks any attribute.
 166     fn check_attributes(
 167         &self,
 168         hir_id: HirId,
 169         attrs: &'hir [Attribute],
 170         span: &Span,
 171         target: Target,
 172         item: Option<&Item<'_>>,
 173     ) {
 174         let mut is_valid = true;
 175         for attr in attrs {
 176             is_valid &= if attr.check_name(sym::inline) {
 177                 self.check_inline(hir_id, attr, span, target)
 178             } else if attr.check_name(sym::non_exhaustive) {
 179                 self.check_non_exhaustive(attr, span, target)
 180             } else if attr.check_name(sym::marker) {
 181                 self.check_marker(attr, span, target)
 182             } else if attr.check_name(sym::target_feature) {
 183                 self.check_target_feature(attr, span, target)
 184             } else if attr.check_name(sym::track_caller) {
 185                 self.check_track_caller(&attr.span, attrs, span, target)
 186             } else {
 187                 true
 188             };
 189         }
 190
 191         if !is_valid {
 192             return;
 193         }
 194
 195         if target == Target::Fn {
 196             self.tcx.codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
 197         }
 198
 199         self.check_repr(attrs, span, target, item);
 200         self.check_used(attrs, target);
 201     }
 202
 203     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
 204     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) -> bool {
 205         match target {
 206             Target::Fn
 207             | Target::Closure
 208             | Target::Method(MethodKind::Trait { body: true })
 209             | Target::Method(MethodKind::Inherent) => true,
 210             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
 211                 self.tcx
 212                     .struct_span_lint_hir(
 213                         UNUSED_ATTRIBUTES,
 214                         hir_id,
 215                         attr.span,
 216                         "`#[inline]` is ignored on function prototypes",
 217                     )
 218                     .emit();
 219                 true
 220             }
 221             // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
 222             // just a lint, because we previously erroneously allowed it and some crates used it
 223             // accidentally, to to be compatible with crates depending on them, we can't throw an
 224             // error here.
 225             Target::AssocConst => {
 226                 self.tcx
 227                     .struct_span_lint_hir(
 228                         UNUSED_ATTRIBUTES,
 229                         hir_id,
 230                         attr.span,
 231                         "`#[inline]` is ignored on constants",
 232                     )
 233                     .warn(
 234                         "this was previously accepted by the compiler but is \
 235                        being phased out; it will become a hard error in \
 236                        a future release!",
 237                     )
 238                     .note(
 239                         "for more information, see issue #65833 \
 240                        <https://github.com/rust-lang/rust/issues/65833>",
 241                     )
 242                     .emit();
 243                 true
 244             }
 245             _ => {
 246                 struct_span_err!(
 247                     self.tcx.sess,
 248                     attr.span,
 249                     E0518,
 250                     "attribute should be applied to function or closure",
 251                 )
 252                 .span_label(*span, "not a function or closure")
 253                 .emit();
 254                 false
 255             }
 256         }
 257     }
 258
 259     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 260     fn check_track_caller(
 261         &self,
 262         attr_span: &Span,
 263         attrs: &'hir [Attribute],
 264         span: &Span,
 265         target: Target,
 266     ) -> bool {
 267         match target {
 268             Target::Fn if attr::contains_name(attrs, sym::naked) => {
 269                 struct_span_err!(
 270                     self.tcx.sess,
 271                     *attr_span,
 272                     E0736,
 273                     "cannot use `#[track_caller]` with `#[naked]`",
 274                 )
 275                 .emit();
 276                 false
 277             }
 278             Target::Fn | Target::Method(MethodKind::Inherent) => true,
 279             Target::Method(_) => {
 280                 struct_span_err!(
 281                     self.tcx.sess,
 282                     *attr_span,
 283                     E0738,
 284                     "`#[track_caller]` may not be used on trait methods",
 285                 )
 286                 .emit();
 287                 false
 288             }
 289             _ => {
 290                 struct_span_err!(
 291                     self.tcx.sess,
 292                     *attr_span,
 293                     E0739,
 294                     "attribute should be applied to function"
 295                 )
 296                 .span_label(*span, "not a function")
 297                 .emit();
 298                 false
 299             }
 300         }
 301     }
 302
 303     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 304     fn check_non_exhaustive(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 305         match target {
 306             Target::Struct | Target::Enum => true,
 307             _ => {
 308                 struct_span_err!(
 309                     self.tcx.sess,
 310                     attr.span,
 311                     E0701,
 312                     "attribute can only be applied to a struct or enum"
 313                 )
 314                 .span_label(*span, "not a struct or enum")
 315                 .emit();
 316                 false
 317             }
 318         }
 319     }
 320
 321     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 322     fn check_marker(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 323         match target {
 324             Target::Trait => true,
 325             _ => {
 326                 self.tcx
 327                     .sess
 328                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 329                     .span_label(*span, "not a trait")
 330                     .emit();
 331                 false
 332             }
 333         }
 334     }
 335
 336     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 337     fn check_target_feature(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 338         match target {
 339             Target::Fn
 340             | Target::Method(MethodKind::Trait { body: true })
 341             | Target::Method(MethodKind::Inherent) => true,
 342             _ => {
 343                 self.tcx
 344                     .sess
 345                     .struct_span_err(attr.span, "attribute should be applied to a function")
 346                     .span_label(*span, "not a function")
 347                     .emit();
 348                 false
 349             }
 350         }
 351     }
 352
 353     /// Checks if the `#[repr]` attributes on `item` are valid.
 354     fn check_repr(
 355         &self,
 356         attrs: &'hir [Attribute],
 357         span: &Span,
 358         target: Target,
 359         item: Option<&Item<'_>>,
 360     ) {
 361         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 362         // ```
 363         // #[repr(foo)]
 364         // #[repr(bar, align(8))]
 365         // ```
 366         let hints: Vec<_> = attrs
 367             .iter()
 368             .filter(|attr| attr.check_name(sym::repr))
 369             .filter_map(|attr| attr.meta_item_list())
 370             .flatten()
 371             .collect();
 372
 373         let mut int_reprs = 0;
 374         let mut is_c = false;
 375         let mut is_simd = false;
 376         let mut is_transparent = false;
 377
 378         for hint in &hints {
 379             let (article, allowed_targets) = match hint.name_or_empty() {
 380                 name @ sym::C | name @ sym::align => {
 381                     is_c |= name == sym::C;
 382                     match target {
 383                         Target::Struct | Target::Union | Target::Enum => continue,
 384                         _ => ("a", "struct, enum, or union"),
 385                     }
 386                 }
 387                 sym::packed => {
 388                     if target != Target::Struct && target != Target::Union {
 389                         ("a", "struct or union")
 390                     } else {
 391                         continue;
 392                     }
 393                 }
 394                 sym::simd => {
 395                     is_simd = true;
 396                     if target != Target::Struct { ("a", "struct") } else { continue }
 397                 }
 398                 sym::transparent => {
 399                     is_transparent = true;
 400                     match target {
 401                         Target::Struct | Target::Union | Target::Enum => continue,
 402                         _ => ("a", "struct, enum, or union"),
 403                     }
 404                 }
 405                 sym::i8
 406                 | sym::u8
 407                 | sym::i16
 408                 | sym::u16
 409                 | sym::i32
 410                 | sym::u32
 411                 | sym::i64
 412                 | sym::u64
 413                 | sym::isize
 414                 | sym::usize => {
 415                     int_reprs += 1;
 416                     if target != Target::Enum { ("an", "enum") } else { continue }
 417                 }
 418                 _ => continue,
 419             };
 420             self.emit_repr_error(
 421                 hint.span(),
 422                 *span,
 423                 &format!("attribute should be applied to {}", allowed_targets),
 424                 &format!("not {} {}", article, allowed_targets),
 425             )
 426         }
 427
 428         // Just point at all repr hints if there are any incompatibilities.
 429         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 430         let hint_spans = hints.iter().map(|hint| hint.span());
 431
 432         // Error on repr(transparent, <anything else>).
 433         if is_transparent && hints.len() > 1 {
 434             let hint_spans: Vec<_> = hint_spans.clone().collect();
 435             struct_span_err!(
 436                 self.tcx.sess,
 437                 hint_spans,
 438                 E0692,
 439                 "transparent {} cannot have other repr hints",
 440                 target
 441             )
 442             .emit();
 443         }
 444         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 445         if (int_reprs > 1)
 446             || (is_simd && is_c)
 447             || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item)))
 448         {
 449             struct_span_err!(
 450                 self.tcx.sess,
 451                 hint_spans.collect::<Vec<Span>>(),
 452                 E0566,
 453                 "conflicting representation hints",
 454             )
 455             .emit();
 456         }
 457     }
 458
 459     fn emit_repr_error(
 460         &self,
 461         hint_span: Span,
 462         label_span: Span,
 463         hint_message: &str,
 464         label_message: &str,
 465     ) {
 466         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 467             .span_label(label_span, label_message)
 468             .emit();
 469     }
 470
 471     fn check_stmt_attributes(&self, stmt: &hir::Stmt<'_>) {
 472         // When checking statements ignore expressions, they will be checked later
 473         if let hir::StmtKind::Local(ref l) = stmt.kind {
 474             for attr in l.attrs.iter() {
 475                 if attr.check_name(sym::inline) {
 476                     self.check_inline(DUMMY_HIR_ID, attr, &stmt.span, Target::Statement);
 477                 }
 478                 if attr.check_name(sym::repr) {
 479                     self.emit_repr_error(
 480                         attr.span,
 481                         stmt.span,
 482                         "attribute should not be applied to a statement",
 483                         "not a struct, enum, or union",
 484                     );
 485                 }
 486             }
 487         }
 488     }
 489
 490     fn check_expr_attributes(&self, expr: &hir::Expr<'_>) {
 491         let target = match expr.kind {
 492             hir::ExprKind::Closure(..) => Target::Closure,
 493             _ => Target::Expression,
 494         };
 495         for attr in expr.attrs.iter() {
 496             if attr.check_name(sym::inline) {
 497                 self.check_inline(DUMMY_HIR_ID, attr, &expr.span, target);
 498             }
 499             if attr.check_name(sym::repr) {
 500                 self.emit_repr_error(
 501                     attr.span,
 502                     expr.span,
 503                     "attribute should not be applied to an expression",
 504                     "not defining a struct, enum, or union",
 505                 );
 506             }
 507         }
 508     }
 509
 510     fn check_used(&self, attrs: &'hir [Attribute], target: Target) {
 511         for attr in attrs {
 512             if attr.check_name(sym::used) && target != Target::Static {
 513                 self.tcx
 514                     .sess
 515                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 516             }
 517         }
 518     }
 519 }
 520
 521 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 522     type Map = Map<'tcx>;
 523
 524     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, Self::Map> {
 525         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 526     }
 527
 528     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
 529         let target = Target::from_item(item);
 530         self.check_attributes(item.hir_id, item.attrs, &item.span, target, Some(item));
 531         intravisit::walk_item(self, item)
 532     }
 533
 534     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem<'tcx>) {
 535         let target = Target::from_trait_item(trait_item);
 536         self.check_attributes(trait_item.hir_id, &trait_item.attrs, &trait_item.span, target, None);
 537         intravisit::walk_trait_item(self, trait_item)
 538     }
 539
 540     fn visit_foreign_item(&mut self, f_item: &'tcx hir::ForeignItem<'tcx>) {
 541         let target = Target::from_foreign_item(f_item);
 542         self.check_attributes(f_item.hir_id, &f_item.attrs, &f_item.span, target, None);
 543         intravisit::walk_foreign_item(self, f_item)
 544     }
 545
 546     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
 547         let target = Target::from_impl_item(self.tcx, impl_item);
 548         self.check_attributes(impl_item.hir_id, &impl_item.attrs, &impl_item.span, target, None);
 549         intravisit::walk_impl_item(self, impl_item)
 550     }
 551
 552     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt<'tcx>) {
 553         self.check_stmt_attributes(stmt);
 554         intravisit::walk_stmt(self, stmt)
 555     }
 556
 557     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
 558         self.check_expr_attributes(expr);
 559         intravisit::walk_expr(self, expr)
 560     }
 561 }
 562
 563 fn is_c_like_enum(item: &Item<'_>) -> bool {
 564     if let ItemKind::Enum(ref def, _) = item.kind {
 565         for variant in def.variants {
 566             match variant.data {
 567                 hir::VariantData::Unit(..) => { /* continue */ }
 568                 _ => return false,
 569             }
 570         }
 571         true
 572     } else {
 573         false
 574     }
 575 }
 576
 577 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: DefId) {
 578     tcx.hir()
 579         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
 580 }
 581
 582 pub(crate) fn provide(providers: &mut Providers<'_>) {
 583     *providers = Providers { check_mod_attrs, ..*providers };
 584 }