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         if target == Target::Fn || target == Target::Const {
  97             self.tcx.codegen_fn_attrs(self.tcx.hir().local_def_id(item.hir_id));
  98         } else if let Some(a) = item.attrs.iter().find(|a| a.check_name(sym::target_feature)) {
  99             self.tcx.sess.struct_span_err(a.span, "attribute should be applied to a function")
 100                 .span_label(item.span, "not a function")
 101                 .emit();
 102         }
 103
 104         for attr in &item.attrs {
 105             if attr.check_name(sym::inline) {
 106                 self.check_inline(attr, &item.span, target)
 107             } else if attr.check_name(sym::non_exhaustive) {
 108                 self.check_non_exhaustive(attr, item, target)
 109             } else if attr.check_name(sym::marker) {
 110                 self.check_marker(attr, item, target)
 111             }
 112         }
 113
 114         self.check_repr(item, target);
 115         self.check_used(item, target);
 116     }
 117
 118     /// Checks if an `#[inline]` is applied to a function or a closure.
 119     fn check_inline(&self, attr: &hir::Attribute, span: &Span, target: Target) {
 120         if target != Target::Fn && target != Target::Closure {
 121             struct_span_err!(self.tcx.sess,
 122                              attr.span,
 123                              E0518,
 124                              "attribute should be applied to function or closure")
 125                 .span_label(*span, "not a function or closure")
 126                 .emit();
 127         }
 128     }
 129
 130     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid.
 131     fn check_non_exhaustive(&self, attr: &hir::Attribute, item: &hir::Item, target: Target) {
 132         match target {
 133             Target::Struct | Target::Enum => { /* Valid */ },
 134             _ => {
 135                 struct_span_err!(self.tcx.sess,
 136                                  attr.span,
 137                                  E0701,
 138                                  "attribute can only be applied to a struct or enum")
 139                     .span_label(item.span, "not a struct or enum")
 140                     .emit();
 141                 return;
 142             }
 143         }
 144     }
 145
 146     /// Checks if the `#[marker]` attribute on an `item` is valid.
 147     fn check_marker(&self, attr: &hir::Attribute, item: &hir::Item, target: Target) {
 148         match target {
 149             Target::Trait => { /* Valid */ },
 150             _ => {
 151                 self.tcx.sess
 152                     .struct_span_err(attr.span, "attribute can only be applied to a trait")
 153                     .span_label(item.span, "not a trait")
 154                     .emit();
 155                 return;
 156             }
 157         }
 158     }
 159
 160     /// Checks if the `#[repr]` attributes on `item` are valid.
 161     fn check_repr(&self, item: &hir::Item, target: Target) {
 162         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
 163         // ```
 164         // #[repr(foo)]
 165         // #[repr(bar, align(8))]
 166         // ```
 167         let hints: Vec<_> = item.attrs
 168             .iter()
 169             .filter(|attr| attr.check_name(sym::repr))
 170             .filter_map(|attr| attr.meta_item_list())
 171             .flatten()
 172             .collect();
 173
 174         let mut int_reprs = 0;
 175         let mut is_c = false;
 176         let mut is_simd = false;
 177         let mut is_transparent = false;
 178
 179         for hint in &hints {
 180             let (article, allowed_targets) = match hint.name_or_empty() {
 181                 name @ sym::C | name @ sym::align => {
 182                     is_c |= name == sym::C;
 183                     match target {
 184                         Target::Struct | Target::Union | Target::Enum => continue,
 185                         _ => ("a", "struct, enum, or union"),
 186                     }
 187                 }
 188                 sym::packed => {
 189                     if target != Target::Struct &&
 190                             target != Target::Union {
 191                                 ("a", "struct or union")
 192                     } else {
 193                         continue
 194                     }
 195                 }
 196                 sym::simd => {
 197                     is_simd = true;
 198                     if target != Target::Struct {
 199                         ("a", "struct")
 200                     } else {
 201                         continue
 202                     }
 203                 }
 204                 sym::transparent => {
 205                     is_transparent = true;
 206                     match target {
 207                         Target::Struct | Target::Union | Target::Enum => continue,
 208                         _ => ("a", "struct, enum, or union"),
 209                     }
 210                 }
 211                 sym::i8  | sym::u8  | sym::i16 | sym::u16 |
 212                 sym::i32 | sym::u32 | sym::i64 | sym::u64 |
 213                 sym::isize | sym::usize => {
 214                     int_reprs += 1;
 215                     if target != Target::Enum {
 216                         ("an", "enum")
 217                     } else {
 218                         continue
 219                     }
 220                 }
 221                 _ => continue,
 222             };
 223             self.emit_repr_error(
 224                 hint.span(),
 225                 item.span,
 226                 &format!("attribute should be applied to {}", allowed_targets),
 227                 &format!("not {} {}", article, allowed_targets),
 228             )
 229         }
 230
 231         // Just point at all repr hints if there are any incompatibilities.
 232         // This is not ideal, but tracking precisely which ones are at fault is a huge hassle.
 233         let hint_spans = hints.iter().map(|hint| hint.span());
 234
 235         // Error on repr(transparent, <anything else>).
 236         if is_transparent && hints.len() > 1 {
 237             let hint_spans: Vec<_> = hint_spans.clone().collect();
 238             span_err!(self.tcx.sess, hint_spans, E0692,
 239                       "transparent {} cannot have other repr hints", target);
 240         }
 241         // Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
 242         if (int_reprs > 1)
 243            || (is_simd && is_c)
 244            || (int_reprs == 1 && is_c && is_c_like_enum(item)) {
 245             let hint_spans: Vec<_> = hint_spans.collect();
 246             span_warn!(self.tcx.sess, hint_spans, E0566,
 247                        "conflicting representation hints");
 248         }
 249     }
 250
 251     fn emit_repr_error(
 252         &self,
 253         hint_span: Span,
 254         label_span: Span,
 255         hint_message: &str,
 256         label_message: &str,
 257     ) {
 258         struct_span_err!(self.tcx.sess, hint_span, E0517, "{}", hint_message)
 259             .span_label(label_span, label_message)
 260             .emit();
 261     }
 262
 263     fn check_stmt_attributes(&self, stmt: &hir::Stmt) {
 264         // When checking statements ignore expressions, they will be checked later
 265         if let hir::StmtKind::Local(ref l) = stmt.kind {
 266             for attr in l.attrs.iter() {
 267                 if attr.check_name(sym::inline) {
 268                     self.check_inline(attr, &stmt.span, Target::Statement);
 269                 }
 270                 if attr.check_name(sym::repr) {
 271                     self.emit_repr_error(
 272                         attr.span,
 273                         stmt.span,
 274                         "attribute should not be applied to a statement",
 275                         "not a struct, enum, or union",
 276                     );
 277                 }
 278             }
 279         }
 280     }
 281
 282     fn check_expr_attributes(&self, expr: &hir::Expr) {
 283         let target = match expr.kind {
 284             hir::ExprKind::Closure(..) => Target::Closure,
 285             _ => Target::Expression,
 286         };
 287         for attr in expr.attrs.iter() {
 288             if attr.check_name(sym::inline) {
 289                 self.check_inline(attr, &expr.span, target);
 290             }
 291             if attr.check_name(sym::repr) {
 292                 self.emit_repr_error(
 293                     attr.span,
 294                     expr.span,
 295                     "attribute should not be applied to an expression",
 296                     "not defining a struct, enum, or union",
 297                 );
 298             }
 299         }
 300     }
 301
 302     fn check_used(&self, item: &hir::Item, target: Target) {
 303         for attr in &item.attrs {
 304             if attr.check_name(sym::used) && target != Target::Static {
 305                 self.tcx.sess
 306                     .span_err(attr.span, "attribute must be applied to a `static` variable");
 307             }
 308         }
 309     }
 310 }
 311
 312 impl Visitor<'tcx> for CheckAttrVisitor<'tcx> {
 313     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 314         NestedVisitorMap::OnlyBodies(&self.tcx.hir())
 315     }
 316
 317     fn visit_item(&mut self, item: &'tcx hir::Item) {
 318         let target = Target::from_item(item);
 319         self.check_attributes(item, target);
 320         intravisit::walk_item(self, item)
 321     }
 322
 323
 324     fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt) {
 325         self.check_stmt_attributes(stmt);
 326         intravisit::walk_stmt(self, stmt)
 327     }
 328
 329     fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
 330         self.check_expr_attributes(expr);
 331         intravisit::walk_expr(self, expr)
 332     }
 333 }
 334
 335 fn is_c_like_enum(item: &hir::Item) -> bool {
 336     if let hir::ItemKind::Enum(ref def, _) = item.kind {
 337         for variant in &def.variants {
 338             match variant.data {
 339                 hir::VariantData::Unit(..) => { /* continue */ }
 340                 _ => { return false; }
 341             }
 342         }
 343         true
 344     } else {
 345         false
 346     }
 347 }
 348
 349 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: DefId) {
 350     tcx.hir().visit_item_likes_in_module(
 351         module_def_id,
 352         &mut CheckAttrVisitor { tcx }.as_deep_visitor()
 353     );
 354 }
 355
 356 pub(crate) fn provide(providers: &mut Providers<'_>) {
 357     *providers = Providers {
 358         check_mod_attrs,
 359         ..*providers
 360     };
 361 }