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