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::Const,
 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(..) => Target::TyAlias,
 146             hir::ImplItemKind::OpaqueTy(..) => Target::OpaqueTy,
 147         }
 148     }
 149 }
 150
 151 struct CheckAttrVisitor<'tcx> {
 152     tcx: TyCtxt<'tcx>,
 153 }
 154
 155 impl CheckAttrVisitor<'tcx> {
 156     /// Checks any attribute.
 157     fn check_attributes(
 158         &self,
 159         hir_id: HirId,
 160         attrs: &HirVec<Attribute>,
 161         span: &Span,
 162         target: Target,
 163         item: Option<&Item>,
 164     ) {
 165         let mut is_valid = true;
 166         for attr in attrs {
 167             is_valid &= if attr.check_name(sym::inline) {
 168                 self.check_inline(hir_id, attr, span, target)
 169             } else if attr.check_name(sym::non_exhaustive) {
 170                 self.check_non_exhaustive(attr, span, target)
 171             } else if attr.check_name(sym::marker) {
 172                 self.check_marker(attr, span, target)
 173             } else if attr.check_name(sym::target_feature) {
 174                 self.check_target_feature(attr, span, target)
 175             } else if attr.check_name(sym::track_caller) {
 176                 self.check_track_caller(&attr.span, attrs, span, target)
 177             } else {
 178                 true
 179             };
 180         }
 181
 182         if !is_valid {
 183             return;
 184         }
 185
 186         if target == Target::Fn {
 187             self.tcx.codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
 188         }
 189
 190         self.check_repr(attrs, span, target, item);
 191         self.check_used(attrs, target);
 192     }
 193
 194     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
 195     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: &Span, target: Target) -> bool {
 196         match target {
 197             Target::Fn | Target::Closure | Target::Method(MethodKind::Trait { body: true })
 198             | Target::Method(MethodKind::Inherent) => true,
 199             Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
 200                 self.tcx.struct_span_lint_hir(
 201                     UNUSED_ATTRIBUTES,
 202                     hir_id,
 203                     attr.span,
 204                     "`#[inline]` is ignored on function prototypes",
 205                 ).emit();
 206                 true
 207             }
 208             _ => {
 209                 struct_span_err!(self.tcx.sess,
 210                                  attr.span,
 211                                  E0518,
 212                                  "attribute should be applied to function or closure")
 213                     .span_label(*span, "not a function or closure")
 214                     .emit();
 215                 false
 216             }
 217         }
 218     }
 219
 220     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 221     fn check_track_caller(
 222         &self,
 223         attr_span: &Span,
 224         attrs: &HirVec<Attribute>,
 225         span: &Span,
 226         target: Target,
 227     ) -> bool {
 228         match target {
 229             Target::Fn if attr::contains_name(attrs, sym::naked) => {
 230                 struct_span_err!(
 231                     self.tcx.sess,
 232                     *attr_span,
 233                     E0736,
 234                     "cannot use `#[track_caller]` with `#[naked]`",
 235                 ).emit();
 236                 false
 237             }
 238             Target::Fn | Target::Method(MethodKind::Inherent) => true,
 239             Target::Method(_) => {
 240                 struct_span_err!(
 241                     self.tcx.sess,
 242                     *attr_span,
 243                     E0738,
 244                     "`#[track_caller]` may not be used on trait methods",
 245                 ).emit();
 246                 false
 247             }
 248             _ => {
 249                 struct_span_err!(
 250                     self.tcx.sess,
 251                     *attr_span,
 252                     E0739,
 253                     "attribute should be applied to function"
 254                 )
 255                 .span_label(*span, "not a function")
 256                 .emit();
 257                 false
 258             }
 259         }
 260     }
 261
 262     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 263     fn check_non_exhaustive(
 264         &self,
 265         attr: &Attribute,
 266         span: &Span,
 267         target: Target,
 268     ) -> bool {
 269         match target {
 270             Target::Struct | Target::Enum => true,
 271             _ => {
 272                 struct_span_err!(self.tcx.sess,
 273                                  attr.span,
 274                                  E0701,
 275                                  "attribute can only be applied to a struct or enum")
 276                     .span_label(*span, "not a struct or enum")
 277                     .emit();
 278                 false
 279             }
 280         }
 281     }
 282
 283     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 284     fn check_marker(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 285         match target {
 286             Target::Trait => true,
 287             _ => {
 288                 self.tcx.sess
 289                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 290                     .span_label(*span, "not a trait")
 291                     .emit();
 292                 false
 293             }
 294         }
 295     }
 296
 297     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 298     fn check_target_feature(&self, attr: &Attribute, span: &Span, target: Target) -> bool {
 299         match target {
 300             Target::Fn | Target::Method(MethodKind::Trait { body: true })
 301             | Target::Method(MethodKind::Inherent) => true,
 302             _ => {
 303                 self.tcx.sess
 304                     .struct_span_err(attr.span, "attribute should be applied to a function")
 305                     .span_label(*span, "not a function")
 306                     .emit();
 307                 false
 308             },
 309         }
 310     }
 311
 312     /// Checks if the `#[repr]` attributes on `item` are valid.
 313     fn check_repr(
 314         &self,
 315         attrs: &HirVec<Attribute>,
 316         span: &Span,
 317         target: Target,
 318         item: Option<&Item>,
 319     ) {
 320         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 321         // ```
 322         // #[repr(foo)]
 323         // #[repr(bar, align(8))]
 324         // ```
 325         let hints: Vec<_> = attrs
 326             .iter()
 327             .filter(|attr| attr.check_name(sym::repr))
 328             .filter_map(|attr| attr.meta_item_list())
 329             .flatten()
 330             .collect();
 331
 332         let mut int_reprs = 0;
 333         let mut is_c = false;
 334         let mut is_simd = false;
 335         let mut is_transparent = false;
 336
 337         for hint in &hints {
 338             let (article, allowed_targets) = match hint.name_or_empty() {
 339                 name @ sym::C | name @ sym::align => {
 340                     is_c |= name == sym::C;
 341                     match target {
 342                         Target::Struct | Target::Union | Target::Enum => continue,
 343                         _ => ("a", "struct, enum, or union"),
 344                     }
 345                 }
 346                 sym::packed => {
 347                     if target != Target::Struct &&
 348                             target != Target::Union {
 349                                 ("a", "struct or union")
 350                     } else {
 351                         continue
 352                     }
 353                 }
 354                 sym::simd => {
 355                     is_simd = true;
 356                     if target != Target::Struct {
 357                         ("a", "struct")
 358                     } else {
 359                         continue
 360                     }
 361                 }
 362                 sym::transparent => {
 363                     is_transparent = true;
 364                     match target {
 365                         Target::Struct | Target::Union | Target::Enum => continue,
 366                         _ => ("a", "struct, enum, or union"),
 367                     }
 368                 }
 369                 sym::i8  | sym::u8  | sym::i16 | sym::u16 |
 370                 sym::i32 | sym::u32 | sym::i64 | sym::u64 |
 371                 sym::isize | sym::usize => {
 372                     int_reprs += 1;
 373                     if target != Target::Enum {
 374                         ("an", "enum")
 375                     } else {
 376                         continue
 377                     }
 378                 }
 379                 _ => continue,
 380             };
 381             self.emit_repr_error(
 382                 hint.span(),
 383                 *span,
 384                 &format!("attribute should be applied to {}", allowed_targets),
 385                 &format!("not {} {}", article, allowed_targets),
 386             )
 387         }
 388
 389         // Just point at all repr hints if there are any incompatibilities.
 390         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 391         let hint_spans = hints.iter().map(|hint| hint.span());
 392
 393         // Error on repr(transparent, <anything else>).
 394         if is_transparent && hints.len() > 1 {
 395             let hint_spans: Vec<_> = hint_spans.clone().collect();
 396             span_err!(self.tcx.sess, hint_spans, E0692,
 397                       "transparent {} cannot have other repr hints", target);
 398         }
 399         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 400         if (int_reprs > 1)
 401            || (is_simd && is_c)
 402            || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item))) {
 403             let hint_spans: Vec<_> = hint_spans.collect();
 404             span_warn!(self.tcx.sess, hint_spans, E0566,
 405                        "conflicting representation hints");
 406         }
 407     }
 408
 409     fn emit_repr_error(
 410         &self,
 411         hint_span: Span,
 412         label_span: Span,
 413         hint_message: &str,
 414         label_message: &str,
 415     ) {
 416         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 417             .span_label(label_span, label_message)
 418             .emit();
 419     }
 420
 421     fn check_stmt_attributes(&self, stmt: &hir::Stmt) {
 422         // When checking statements ignore expressions, they will be checked later
 423         if let hir::StmtKind::Local(ref l) = stmt.kind {
 424             for attr in l.attrs.iter() {
 425                 if attr.check_name(sym::inline) {
 426                     self.check_inline(DUMMY_HIR_ID, attr, &stmt.span, Target::Statement);
 427                 }
 428                 if attr.check_name(sym::repr) {
 429                     self.emit_repr_error(
 430                         attr.span,
 431                         stmt.span,
 432                         "attribute should not be applied to a statement",
 433                         "not a struct, enum, or union",
 434                     );
 435                 }
 436             }
 437         }
 438     }
 439
 440     fn check_expr_attributes(&self, expr: &hir::Expr) {
 441         let target = match expr.kind {
 442             hir::ExprKind::Closure(..) => Target::Closure,
 443             _ => Target::Expression,
 444         };
 445         for attr in expr.attrs.iter() {
 446             if attr.check_name(sym::inline) {
 447                 self.check_inline(DUMMY_HIR_ID, attr, &expr.span, target);
 448             }
 449             if attr.check_name(sym::repr) {
 450                 self.emit_repr_error(
 451                     attr.span,
 452                     expr.span,
 453                     "attribute should not be applied to an expression",
 454                     "not defining a struct, enum, or union",
 455                 );
 456             }
 457         }
 458     }
 459
 460     fn check_used(&self, attrs: &HirVec<Attribute>, target: Target) {
 461         for attr in attrs {
 462             if attr.check_name(sym::used) && target != Target::Static {
 463                 self.tcx.sess
 464                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 465             }
 466         }
 467     }
 468 }
 469
 470 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 471     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 472         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 473     }
 474
 475     fn visit_item(&mut self, item: &'tcx Item) {
 476         let target = Target::from_item(item);
 477         self.check_attributes(item.hir_id, &item.attrs, &item.span, target, Some(item));
 478         intravisit::walk_item(self, item)
 479     }
 480
 481     fn visit_trait_item(&mut self, trait_item: &'tcx TraitItem) {
 482         let target = Target::from_trait_item(trait_item);
 483         self.check_attributes(trait_item.hir_id, &trait_item.attrs, &trait_item.span, target, None);
 484         intravisit::walk_trait_item(self, trait_item)
 485     }
 486
 487     fn visit_foreign_item(&mut self, f_item: &'tcx hir::ForeignItem) {
 488         let target = Target::from_foreign_item(f_item);
 489         self.check_attributes(f_item.hir_id, &f_item.attrs, &f_item.span, target, None);
 490         intravisit::walk_foreign_item(self, f_item)
 491     }
 492
 493     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
 494         let target = Target::from_impl_item(self.tcx, impl_item);
 495         self.check_attributes(impl_item.hir_id, &impl_item.attrs, &impl_item.span, target, None);
 496         intravisit::walk_impl_item(self, impl_item)
 497     }
 498
 499     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt) {
 500         self.check_stmt_attributes(stmt);
 501         intravisit::walk_stmt(self, stmt)
 502     }
 503
 504     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
 505         self.check_expr_attributes(expr);
 506         intravisit::walk_expr(self, expr)
 507     }
 508 }
 509
 510 fn is_c_like_enum(item: &Item) -> bool {
 511     if let ItemKind::Enum(ref def, _) = item.kind {
 512         for variant in &def.variants {
 513             match variant.data {
 514                 hir::VariantData::Unit(..) => { /* continue */ }
 515                 _ => return false,
 516             }
 517         }
 518         true
 519     } else {
 520         false
 521     }
 522 }
 523
 524 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: DefId) {
 525     tcx.hir().visit_item_likes_in_module(
 526         module_def_id,
 527         &mut CheckAttrVisitor { tcx }.as_deep_visitor()
 528     );
 529 }
 530
 531 pub(crate) fn provide(providers: &mut Providers<'_>) {
 532     *providers = Providers {
 533         check_mod_attrs,
 534         ..*providers
 535     };
 536 }