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::{attr, 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 if attr.check_name(sym::track_caller) {
 107                 self.check_track_caller(attr, &item, target)
 108             } else {
 109                 true
 110             };
 111         }
 112
 113         if !is_valid {
 114             return;
 115         }
 116
 117         if target == Target::Fn {
 118             self.tcx.codegen_fn_attrs(self.tcx.hir().local_def_id(item.hir_id));
 119         }
 120
 121         self.check_repr(item, target);
 122         self.check_used(item, target);
 123     }
 124
 125     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
 126     fn check_inline(&self, attr: &hir::Attribute, span: &Span, target: Target) -> bool {
 127         if target != Target::Fn && target != Target::Closure {
 128             struct_span_err!(self.tcx.sess,
 129                              attr.span,
 130                              E0518,
 131                              "attribute should be applied to function or closure")
 132                 .span_label(*span, "not a function or closure")
 133                 .emit();
 134             false
 135         } else {
 136             true
 137         }
 138     }
 139
 140     /// Checks if a `#[track_caller]` is applied to a non-naked function. Returns `true` if valid.
 141     fn check_track_caller(&self, attr: &hir::Attribute, item: &hir::Item, target: Target) -> bool {
 142         if target != Target::Fn {
 143             struct_span_err!(
 144                 self.tcx.sess,
 145                 attr.span,
 146                 E0739,
 147                 "attribute should be applied to function"
 148             )
 149             .span_label(item.span, "not a function")
 150             .emit();
 151             false
 152         } else if attr::contains_name(&item.attrs, sym::naked) {
 153             struct_span_err!(
 154                 self.tcx.sess,
 155                 attr.span,
 156                 E0736,
 157                 "cannot use `#[track_caller]` with `#[naked]`",
 158             )
 159             .emit();
 160             false
 161         } else {
 162             true
 163         }
 164     }
 165
 166     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid. Returns `true` if valid.
 167     fn check_non_exhaustive(
 168         &self,
 169         attr: &hir::Attribute,
 170         item: &hir::Item,
 171         target: Target,
 172     ) -> bool {
 173         match target {
 174             Target::Struct | Target::Enum => true,
 175             _ => {
 176                 struct_span_err!(self.tcx.sess,
 177                                  attr.span,
 178                                  E0701,
 179                                  "attribute can only be applied to a struct or enum")
 180                     .span_label(item.span, "not a struct or enum")
 181                     .emit();
 182                 false
 183             }
 184         }
 185     }
 186
 187     /// Checks if the `#[marker]` attribute on an `item` is valid. Returns `true` if valid.
 188     fn check_marker(&self, attr: &hir::Attribute, item: &hir::Item, target: Target) -> bool {
 189         match target {
 190             Target::Trait => true,
 191             _ => {
 192                 self.tcx.sess
 193                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 194                     .span_label(item.span, "not a trait")
 195                     .emit();
 196                 false
 197             }
 198         }
 199     }
 200
 201     /// Checks if the `#[target_feature]` attribute on `item` is valid. Returns `true` if valid.
 202     fn check_target_feature(
 203         &self,
 204         attr: &hir::Attribute,
 205         item: &hir::Item,
 206         target: Target,
 207     ) -> bool {
 208         match target {
 209             Target::Fn => true,
 210             _ => {
 211                 self.tcx.sess
 212                     .struct_span_err(attr.span, "attribute should be applied to a function")
 213                     .span_label(item.span, "not a function")
 214                     .emit();
 215                 false
 216             },
 217         }
 218     }
 219
 220     /// Checks if the `#[repr]` attributes on `item` are valid.
 221     fn check_repr(&self, item: &hir::Item, target: Target) {
 222         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 223         // ```
 224         // #[repr(foo)]
 225         // #[repr(bar, align(8))]
 226         // ```
 227         let hints: Vec<_> = item.attrs
 228             .iter()
 229             .filter(|attr| attr.check_name(sym::repr))
 230             .filter_map(|attr| attr.meta_item_list())
 231             .flatten()
 232             .collect();
 233
 234         let mut int_reprs = 0;
 235         let mut is_c = false;
 236         let mut is_simd = false;
 237         let mut is_transparent = false;
 238
 239         for hint in &hints {
 240             let (article, allowed_targets) = match hint.name_or_empty() {
 241                 name @ sym::C | name @ sym::align => {
 242                     is_c |= name == sym::C;
 243                     match target {
 244                         Target::Struct | Target::Union | Target::Enum => continue,
 245                         _ => ("a", "struct, enum, or union"),
 246                     }
 247                 }
 248                 sym::packed => {
 249                     if target != Target::Struct &&
 250                             target != Target::Union {
 251                                 ("a", "struct or union")
 252                     } else {
 253                         continue
 254                     }
 255                 }
 256                 sym::simd => {
 257                     is_simd = true;
 258                     if target != Target::Struct {
 259                         ("a", "struct")
 260                     } else {
 261                         continue
 262                     }
 263                 }
 264                 sym::transparent => {
 265                     is_transparent = true;
 266                     match target {
 267                         Target::Struct | Target::Union | Target::Enum => continue,
 268                         _ => ("a", "struct, enum, or union"),
 269                     }
 270                 }
 271                 sym::i8  | sym::u8  | sym::i16 | sym::u16 |
 272                 sym::i32 | sym::u32 | sym::i64 | sym::u64 |
 273                 sym::isize | sym::usize => {
 274                     int_reprs += 1;
 275                     if target != Target::Enum {
 276                         ("an", "enum")
 277                     } else {
 278                         continue
 279                     }
 280                 }
 281                 _ => continue,
 282             };
 283             self.emit_repr_error(
 284                 hint.span(),
 285                 item.span,
 286                 &format!("attribute should be applied to {}", allowed_targets),
 287                 &format!("not {} {}", article, allowed_targets),
 288             )
 289         }
 290
 291         // Just point at all repr hints if there are any incompatibilities.
 292         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 293         let hint_spans = hints.iter().map(|hint| hint.span());
 294
 295         // Error on repr(transparent, <anything else>).
 296         if is_transparent && hints.len() > 1 {
 297             let hint_spans: Vec<_> = hint_spans.clone().collect();
 298             span_err!(self.tcx.sess, hint_spans, E0692,
 299                       "transparent {} cannot have other repr hints", target);
 300         }
 301         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 302         if (int_reprs > 1)
 303            || (is_simd && is_c)
 304            || (int_reprs == 1 && is_c && is_c_like_enum(item)) {
 305             let hint_spans: Vec<_> = hint_spans.collect();
 306             span_warn!(self.tcx.sess, hint_spans, E0566,
 307                        "conflicting representation hints");
 308         }
 309     }
 310
 311     fn emit_repr_error(
 312         &self,
 313         hint_span: Span,
 314         label_span: Span,
 315         hint_message: &str,
 316         label_message: &str,
 317     ) {
 318         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 319             .span_label(label_span, label_message)
 320             .emit();
 321     }
 322
 323     fn check_stmt_attributes(&self, stmt: &hir::Stmt) {
 324         // When checking statements ignore expressions, they will be checked later
 325         if let hir::StmtKind::Local(ref l) = stmt.kind {
 326             for attr in l.attrs.iter() {
 327                 if attr.check_name(sym::inline) {
 328                     self.check_inline(attr, &stmt.span, Target::Statement);
 329                 }
 330                 if attr.check_name(sym::repr) {
 331                     self.emit_repr_error(
 332                         attr.span,
 333                         stmt.span,
 334                         "attribute should not be applied to a statement",
 335                         "not a struct, enum, or union",
 336                     );
 337                 }
 338             }
 339         }
 340     }
 341
 342     fn check_expr_attributes(&self, expr: &hir::Expr) {
 343         let target = match expr.kind {
 344             hir::ExprKind::Closure(..) => Target::Closure,
 345             _ => Target::Expression,
 346         };
 347         for attr in expr.attrs.iter() {
 348             if attr.check_name(sym::inline) {
 349                 self.check_inline(attr, &expr.span, target);
 350             }
 351             if attr.check_name(sym::repr) {
 352                 self.emit_repr_error(
 353                     attr.span,
 354                     expr.span,
 355                     "attribute should not be applied to an expression",
 356                     "not defining a struct, enum, or union",
 357                 );
 358             }
 359         }
 360     }
 361
 362     fn check_used(&self, item: &hir::Item, target: Target) {
 363         for attr in &item.attrs {
 364             if attr.check_name(sym::used) && target != Target::Static {
 365                 self.tcx.sess
 366                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 367             }
 368         }
 369     }
 370 }
 371
 372 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 373     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 374         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 375     }
 376
 377     fn visit_item(&mut self, item: &'tcx hir::Item) {
 378         let target = Target::from_item(item);
 379         self.check_attributes(item, target);
 380         intravisit::walk_item(self, item)
 381     }
 382
 383
 384     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt) {
 385         self.check_stmt_attributes(stmt);
 386         intravisit::walk_stmt(self, stmt)
 387     }
 388
 389     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
 390         self.check_expr_attributes(expr);
 391         intravisit::walk_expr(self, expr)
 392     }
 393 }
 394
 395 fn is_c_like_enum(item: &hir::Item) -> bool {
 396     if let hir::ItemKind::Enum(ref def, _) = item.kind {
 397         for variant in &def.variants {
 398             match variant.data {
 399                 hir::VariantData::Unit(..) => { /* continue */ }
 400                 _ => { return false; }
 401             }
 402         }
 403         true
 404     } else {
 405         false
 406     }
 407 }
 408
 409 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: DefId) {
 410     tcx.hir().visit_item_likes_in_module(
 411         module_def_id,
 412         &mut CheckAttrVisitor { tcx }.as_deep_visitor()
 413     );
 414 }
 415
 416 pub(crate) fn provide(providers: &mut Providers<'_>) {
 417     *providers = Providers {
 418         check_mod_attrs,
 419         ..*providers
 420     };
 421 }