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;
   8 use crate::hir::def_id::DefId;
   9 use crate::hir::intravisit::{self, Visitor, NestedVisitorMap};
  10 use crate::ty::TyCtxt;
  11 use crate::ty::query::Providers;
  12
  13 use std::fmt::{self, Display};
  14 use syntax::symbol::sym;
  15 use syntax_pos::Span;
  16
  17 #[derive(Copy, Clone, PartialEq)]
  18 pub(crate) enum Target {
  19     ExternCrate,
  20     Use,
  21     Static,
  22     Const,
  23     Fn,
  24     Closure,
  25     Mod,
  26     ForeignMod,
  27     GlobalAsm,
  28     TyAlias,
  29     OpaqueTy,
  30     Enum,
  31     Struct,
  32     Union,
  33     Trait,
  34     TraitAlias,
  35     Impl,
  36     Expression,
  37     Statement,
  38 }
  39
  40 impl Display for Target {
  41     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  42         write!(f, "{}", match *self {
  43             Target::ExternCrate => "extern crate",
  44             Target::Use => "use",
  45             Target::Static => "static item",
  46             Target::Const => "constant item",
  47             Target::Fn => "function",
  48             Target::Closure => "closure",
  49             Target::Mod => "module",
  50             Target::ForeignMod => "foreign module",
  51             Target::GlobalAsm => "global asm",
  52             Target::TyAlias => "type alias",
  53             Target::OpaqueTy => "opaque type",
  54             Target::Enum => "enum",
  55             Target::Struct => "struct",
  56             Target::Union => "union",
  57             Target::Trait => "trait",
  58             Target::TraitAlias => "trait alias",
  59             Target::Impl => "item",
  60             Target::Expression => "expression",
  61             Target::Statement => "statement",
  62         })
  63     }
  64 }
  65
  66 impl Target {
  67     pub(crate) fn from_item(item: &hir::Item) -> Target {
  68         match item.kind {
  69             hir::ItemKind::ExternCrate(..) => Target::ExternCrate,
  70             hir::ItemKind::Use(..) => Target::Use,
  71             hir::ItemKind::Static(..) => Target::Static,
  72             hir::ItemKind::Const(..) => Target::Const,
  73             hir::ItemKind::Fn(..) => Target::Fn,
  74             hir::ItemKind::Mod(..) => Target::Mod,
  75             hir::ItemKind::ForeignMod(..) => Target::ForeignMod,
  76             hir::ItemKind::GlobalAsm(..) => Target::GlobalAsm,
  77             hir::ItemKind::TyAlias(..) => Target::TyAlias,
  78             hir::ItemKind::OpaqueTy(..) => Target::OpaqueTy,
  79             hir::ItemKind::Enum(..) => Target::Enum,
  80             hir::ItemKind::Struct(..) => Target::Struct,
  81             hir::ItemKind::Union(..) => Target::Union,
  82             hir::ItemKind::Trait(..) => Target::Trait,
  83             hir::ItemKind::TraitAlias(..) => Target::TraitAlias,
  84             hir::ItemKind::Impl(..) => Target::Impl,
  85         }
  86     }
  87 }
  88
  89 struct CheckAttrVisitor<'tcx> {
  90     tcx: TyCtxt<'tcx>,
  91 }
  92
  93 impl CheckAttrVisitor<'tcx> {
  94     /// Checks any attribute.
  95     fn check_attributes(&self, item: &hir::Item, target: Target) {
  96         let mut is_valid = true;
  97         for attr in &item.attrs {
  98             is_valid &= if attr.check_name(sym::inline) {
  99                 self.check_inline(attr, &item.span, target)
 100             } else if attr.check_name(sym::non_exhaustive) {
 101                 self.check_non_exhaustive(attr, item, target)
 102             } else if attr.check_name(sym::marker) {
 103                 self.check_marker(attr, item, target)
 104             } else if attr.check_name(sym::target_feature) {
 105                 self.check_target_feature(attr, item, target)
 106             } else {
 107                 true
 108             };
 109         }
 110
 111         if !is_valid {
 112             return;
 113         }
 114
 115         if target == Target::Fn {
 116             self.tcx.codegen_fn_attrs(self.tcx.hir().local_def_id(item.hir_id));
 117         }
 118
 119         self.check_repr(item, target);
 120         self.check_used(item, target);
 121     }
 122
 123     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
 124     fn check_inline(&self, attr: &hir::Attribute, span: &Span, target: Target) -> bool {
 125         if target != Target::Fn && target != Target::Closure {
 126             struct_span_err!(self.tcx.sess,
 127                              attr.span,
 128                              E0518,
 129                              "attribute should be applied to function or closure")
 130                 .span_label(*span, "not a function or closure")
 131                 .emit();
 132             false
 133         } else {
 134             true
 135         }
 136     }
 137
 138     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 139     fn check_non_exhaustive(
 140         &self,
 141         attr: &hir::Attribute,
 142         item: &hir::Item,
 143         target: Target,
 144     ) -> bool {
 145         match target {
 146             Target::Struct | Target::Enum => true,
 147             _ => {
 148                 struct_span_err!(self.tcx.sess,
 149                                  attr.span,
 150                                  E0701,
 151                                  "attribute can only be applied to a struct or enum")
 152                     .span_label(item.span, "not a struct or enum")
 153                     .emit();
 154                 false
 155             }
 156         }
 157     }
 158
 159     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 160     fn check_marker(&self, attr: &hir::Attribute, item: &hir::Item, target: Target) -> bool {
 161         match target {
 162             Target::Trait => true,
 163             _ => {
 164                 self.tcx.sess
 165                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 166                     .span_label(item.span, "not a trait")
 167                     .emit();
 168                 false
 169             }
 170         }
 171     }
 172
 173     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 174     fn check_target_feature(
 175         &self,
 176         attr: &hir::Attribute,
 177         item: &hir::Item,
 178         target: Target,
 179     ) -> bool {
 180         match target {
 181             Target::Fn => true,
 182             _ => {
 183                 self.tcx.sess
 184                     .struct_span_err(attr.span, "attribute should be applied to a function")
 185                     .span_label(item.span, "not a function")
 186                     .emit();
 187                 false
 188             },
 189         }
 190     }
 191
 192     /// Checks if the `#[repr]` attributes on `item` are valid.
 193     fn check_repr(&self, item: &hir::Item, target: Target) {
 194         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 195         // ```
 196         // #[repr(foo)]
 197         // #[repr(bar, align(8))]
 198         // ```
 199         let hints: Vec<_> = item.attrs
 200             .iter()
 201             .filter(|attr| attr.check_name(sym::repr))
 202             .filter_map(|attr| attr.meta_item_list())
 203             .flatten()
 204             .collect();
 205
 206         let mut int_reprs = 0;
 207         let mut is_c = false;
 208         let mut is_simd = false;
 209         let mut is_transparent = false;
 210
 211         for hint in &hints {
 212             let (article, allowed_targets) = match hint.name_or_empty() {
 213                 name @ sym::C | name @ sym::align => {
 214                     is_c |= name == sym::C;
 215                     match target {
 216                         Target::Struct | Target::Union | Target::Enum => continue,
 217                         _ => ("a", "struct, enum, or union"),
 218                     }
 219                 }
 220                 sym::packed => {
 221                     if target != Target::Struct &&
 222                             target != Target::Union {
 223                                 ("a", "struct or union")
 224                     } else {
 225                         continue
 226                     }
 227                 }
 228                 sym::simd => {
 229                     is_simd = true;
 230                     if target != Target::Struct {
 231                         ("a", "struct")
 232                     } else {
 233                         continue
 234                     }
 235                 }
 236                 sym::transparent => {
 237                     is_transparent = true;
 238                     match target {
 239                         Target::Struct | Target::Union | Target::Enum => continue,
 240                         _ => ("a", "struct, enum, or union"),
 241                     }
 242                 }
 243                 sym::i8  | sym::u8  | sym::i16 | sym::u16 |
 244                 sym::i32 | sym::u32 | sym::i64 | sym::u64 |
 245                 sym::isize | sym::usize => {
 246                     int_reprs += 1;
 247                     if target != Target::Enum {
 248                         ("an", "enum")
 249                     } else {
 250                         continue
 251                     }
 252                 }
 253                 _ => continue,
 254             };
 255             self.emit_repr_error(
 256                 hint.span(),
 257                 item.span,
 258                 &format!("attribute should be applied to {}", allowed_targets),
 259                 &format!("not {} {}", article, allowed_targets),
 260             )
 261         }
 262
 263         // Just point at all repr hints if there are any incompatibilities.
 264         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 265         let hint_spans = hints.iter().map(|hint| hint.span());
 266
 267         // Error on repr(transparent, <anything else>).
 268         if is_transparent && hints.len() > 1 {
 269             let hint_spans: Vec<_> = hint_spans.clone().collect();
 270             span_err!(self.tcx.sess, hint_spans, E0692,
 271                       "transparent {} cannot have other repr hints", target);
 272         }
 273         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 274         if (int_reprs > 1)
 275            || (is_simd && is_c)
 276            || (int_reprs == 1 && is_c && is_c_like_enum(item)) {
 277             let hint_spans: Vec<_> = hint_spans.collect();
 278             span_warn!(self.tcx.sess, hint_spans, E0566,
 279                        "conflicting representation hints");
 280         }
 281     }
 282
 283     fn emit_repr_error(
 284         &self,
 285         hint_span: Span,
 286         label_span: Span,
 287         hint_message: &str,
 288         label_message: &str,
 289     ) {
 290         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 291             .span_label(label_span, label_message)
 292             .emit();
 293     }
 294
 295     fn check_stmt_attributes(&self, stmt: &hir::Stmt) {
 296         // When checking statements ignore expressions, they will be checked later
 297         if let hir::StmtKind::Local(ref l) = stmt.kind {
 298             for attr in l.attrs.iter() {
 299                 if attr.check_name(sym::inline) {
 300                     self.check_inline(attr, &stmt.span, Target::Statement);
 301                 }
 302                 if attr.check_name(sym::repr) {
 303                     self.emit_repr_error(
 304                         attr.span,
 305                         stmt.span,
 306                         "attribute should not be applied to a statement",
 307                         "not a struct, enum, or union",
 308                     );
 309                 }
 310             }
 311         }
 312     }
 313
 314     fn check_expr_attributes(&self, expr: &hir::Expr) {
 315         let target = match expr.kind {
 316             hir::ExprKind::Closure(..) => Target::Closure,
 317             _ => Target::Expression,
 318         };
 319         for attr in expr.attrs.iter() {
 320             if attr.check_name(sym::inline) {
 321                 self.check_inline(attr, &expr.span, target);
 322             }
 323             if attr.check_name(sym::repr) {
 324                 self.emit_repr_error(
 325                     attr.span,
 326                     expr.span,
 327                     "attribute should not be applied to an expression",
 328                     "not defining a struct, enum, or union",
 329                 );
 330             }
 331         }
 332     }
 333
 334     fn check_used(&self, item: &hir::Item, target: Target) {
 335         for attr in &item.attrs {
 336             if attr.check_name(sym::used) && target != Target::Static {
 337                 self.tcx.sess
 338                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 339             }
 340         }
 341     }
 342 }
 343
 344 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 345     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 346         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 347     }
 348
 349     fn visit_item(&mut self, item: &'tcx hir::Item) {
 350         let target = Target::from_item(item);
 351         self.check_attributes(item, target);
 352         intravisit::walk_item(self, item)
 353     }
 354
 355
 356     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt) {
 357         self.check_stmt_attributes(stmt);
 358         intravisit::walk_stmt(self, stmt)
 359     }
 360
 361     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
 362         self.check_expr_attributes(expr);
 363         intravisit::walk_expr(self, expr)
 364     }
 365 }
 366
 367 fn is_c_like_enum(item: &hir::Item) -> bool {
 368     if let hir::ItemKind::Enum(ref def, _) = item.kind {
 369         for variant in &def.variants {
 370             match variant.data {
 371                 hir::VariantData::Unit(..) => { /* continue */ }
 372                 _ => { return false; }
 373             }
 374         }
 375         true
 376     } else {
 377         false
 378     }
 379 }
 380
 381 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: DefId) {
 382     tcx.hir().visit_item_likes_in_module(
 383         module_def_id,
 384         &mut CheckAttrVisitor { tcx }.as_deep_visitor()
 385     );
 386 }
 387
 388 pub(crate) fn provide(providers: &mut Providers<'_>) {
 389     *providers = Providers {
 390         check_mod_attrs,
 391         ..*providers
 392     };
 393 }