src/librustc_attr/builtin.rs

   1 //! Parsing and validation of builtin attributes
   2
   3 use rustc_ast::ast::{self, Attribute, Lit, LitKind, MetaItem, MetaItemKind, NestedMetaItem};
   4 use rustc_ast_pretty::pprust;
   5 use rustc_errors::{struct_span_err, Applicability};
   6 use rustc_feature::{find_gated_cfg, is_builtin_attr_name, Features, GatedCfg};
   7 use rustc_macros::HashStable_Generic;
   8 use rustc_session::parse::{feature_err, ParseSess};
   9 use rustc_session::Session;
  10 use rustc_span::hygiene::Transparency;
  11 use rustc_span::{symbol::sym, symbol::Symbol, Span};
  12 use std::num::NonZeroU32;
  13 use version_check::Version;
  14
  15 pub fn is_builtin_attr(attr: &Attribute) -> bool {
  16     attr.is_doc_comment() || attr.ident().filter(|ident| is_builtin_attr_name(ident.name)).is_some()
  17 }
  18
  19 enum AttrError {
  20     MultipleItem(String),
  21     UnknownMetaItem(String, &'static [&'static str]),
  22     MissingSince,
  23     MissingFeature,
  24     MultipleStabilityLevels,
  25     UnsupportedLiteral(&'static str, /* is_bytestr */ bool),
  26 }
  27
  28 fn handle_errors(sess: &ParseSess, span: Span, error: AttrError) {
  29     let diag = &sess.span_diagnostic;
  30     match error {
  31         AttrError::MultipleItem(item) => {
  32             struct_span_err!(diag, span, E0538, "multiple '{}' items", item).emit();
  33         }
  34         AttrError::UnknownMetaItem(item, expected) => {
  35             let expected = expected.iter().map(|name| format!("`{}`", name)).collect::<Vec<_>>();
  36             struct_span_err!(diag, span, E0541, "unknown meta item '{}'", item)
  37                 .span_label(span, format!("expected one of {}", expected.join(", ")))
  38                 .emit();
  39         }
  40         AttrError::MissingSince => {
  41             struct_span_err!(diag, span, E0542, "missing 'since'").emit();
  42         }
  43         AttrError::MissingFeature => {
  44             struct_span_err!(diag, span, E0546, "missing 'feature'").emit();
  45         }
  46         AttrError::MultipleStabilityLevels => {
  47             struct_span_err!(diag, span, E0544, "multiple stability levels").emit();
  48         }
  49         AttrError::UnsupportedLiteral(msg, is_bytestr) => {
  50             let mut err = struct_span_err!(diag, span, E0565, "{}", msg);
  51             if is_bytestr {
  52                 if let Ok(lint_str) = sess.source_map().span_to_snippet(span) {
  53                     err.span_suggestion(
  54                         span,
  55                         "consider removing the prefix",
  56                         lint_str[1..].to_string(),
  57                         Applicability::MaybeIncorrect,
  58                     );
  59                 }
  60             }
  61             err.emit();
  62         }
  63     }
  64 }
  65
  66 #[derive(Clone, PartialEq, RustcEncodable, RustcDecodable)]
  67 pub enum InlineAttr {
  68     None,
  69     Hint,
  70     Always,
  71     Never,
  72 }
  73
  74 #[derive(Clone, RustcEncodable, RustcDecodable)]
  75 pub enum OptimizeAttr {
  76     None,
  77     Speed,
  78     Size,
  79 }
  80
  81 #[derive(Copy, Clone, PartialEq)]
  82 pub enum UnwindAttr {
  83     Allowed,
  84     Aborts,
  85 }
  86
  87 /// Determine what `#[unwind]` attribute is present in `attrs`, if any.
  88 pub fn find_unwind_attr(sess: &Session, attrs: &[Attribute]) -> Option<UnwindAttr> {
  89     attrs.iter().fold(None, |ia, attr| {
  90         if sess.check_name(attr, sym::unwind) {
  91             if let Some(meta) = attr.meta() {
  92                 if let MetaItemKind::List(items) = meta.kind {
  93                     if items.len() == 1 {
  94                         if items[0].has_name(sym::allowed) {
  95                             return Some(UnwindAttr::Allowed);
  96                         } else if items[0].has_name(sym::aborts) {
  97                             return Some(UnwindAttr::Aborts);
  98                         }
  99                     }
 100
 101                     struct_span_err!(
 102                         sess.diagnostic(),
 103                         attr.span,
 104                         E0633,
 105                         "malformed `unwind` attribute input"
 106                     )
 107                     .span_label(attr.span, "invalid argument")
 108                     .span_suggestions(
 109                         attr.span,
 110                         "the allowed arguments are `allowed` and `aborts`",
 111                         (vec!["allowed", "aborts"])
 112                             .into_iter()
 113                             .map(|s| format!("#[unwind({})]", s)),
 114                         Applicability::MachineApplicable,
 115                     )
 116                     .emit();
 117                 }
 118             }
 119         }
 120
 121         ia
 122     })
 123 }
 124
 125 /// Represents the following attributes:
 126 ///
 127 /// - `#[stable]`
 128 /// - `#[unstable]`
 129 #[derive(RustcEncodable, RustcDecodable, Copy, Clone, Debug, PartialEq, Eq, Hash)]
 130 #[derive(HashStable_Generic)]
 131 pub struct Stability {
 132     pub level: StabilityLevel,
 133     pub feature: Symbol,
 134 }
 135
 136 /// Represents the `#[rustc_const_unstable]` and `#[rustc_const_stable]` attributes.
 137 #[derive(RustcEncodable, RustcDecodable, Copy, Clone, Debug, PartialEq, Eq, Hash)]
 138 #[derive(HashStable_Generic)]
 139 pub struct ConstStability {
 140     pub level: StabilityLevel,
 141     pub feature: Symbol,
 142     /// whether the function has a `#[rustc_promotable]` attribute
 143     pub promotable: bool,
 144     /// whether the function has a `#[rustc_allow_const_fn_ptr]` attribute
 145     pub allow_const_fn_ptr: bool,
 146 }
 147
 148 /// The available stability levels.
 149 #[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Copy, Clone, Debug, Eq, Hash)]
 150 #[derive(HashStable_Generic)]
 151 pub enum StabilityLevel {
 152     // Reason for the current stability level and the relevant rust-lang issue
 153     Unstable { reason: Option<Symbol>, issue: Option<NonZeroU32>, is_soft: bool },
 154     Stable { since: Symbol },
 155 }
 156
 157 impl StabilityLevel {
 158     pub fn is_unstable(&self) -> bool {
 159         if let StabilityLevel::Unstable { .. } = *self { true } else { false }
 160     }
 161     pub fn is_stable(&self) -> bool {
 162         if let StabilityLevel::Stable { .. } = *self { true } else { false }
 163     }
 164 }
 165
 166 /// Collects stability info from all stability attributes in `attrs`.
 167 /// Returns `None` if no stability attributes are found.
 168 pub fn find_stability(
 169     sess: &Session,
 170     attrs: &[Attribute],
 171     item_sp: Span,
 172 ) -> (Option<Stability>, Option<ConstStability>) {
 173     find_stability_generic(sess, attrs.iter(), item_sp)
 174 }
 175
 176 fn find_stability_generic<'a, I>(
 177     sess: &Session,
 178     attrs_iter: I,
 179     item_sp: Span,
 180 ) -> (Option<Stability>, Option<ConstStability>)
 181 where
 182     I: Iterator<Item = &'a Attribute>,
 183 {
 184     use StabilityLevel::*;
 185
 186     let mut stab: Option<Stability> = None;
 187     let mut const_stab: Option<ConstStability> = None;
 188     let mut promotable = false;
 189     let mut allow_const_fn_ptr = false;
 190     let diagnostic = &sess.parse_sess.span_diagnostic;
 191
 192     'outer: for attr in attrs_iter {
 193         if ![
 194             sym::rustc_const_unstable,
 195             sym::rustc_const_stable,
 196             sym::unstable,
 197             sym::stable,
 198             sym::rustc_promotable,
 199             sym::rustc_allow_const_fn_ptr,
 200         ]
 201         .iter()
 202         .any(|&s| attr.has_name(s))
 203         {
 204             continue; // not a stability level
 205         }
 206
 207         sess.mark_attr_used(attr);
 208
 209         let meta = attr.meta();
 210
 211         if attr.has_name(sym::rustc_promotable) {
 212             promotable = true;
 213         }
 214         if attr.has_name(sym::rustc_allow_const_fn_ptr) {
 215             allow_const_fn_ptr = true;
 216         }
 217         // attributes with data
 218         else if let Some(MetaItem { kind: MetaItemKind::List(ref metas), .. }) = meta {
 219             let meta = meta.as_ref().unwrap();
 220             let get = |meta: &MetaItem, item: &mut Option<Symbol>| {
 221                 if item.is_some() {
 222                     handle_errors(
 223                         &sess.parse_sess,
 224                         meta.span,
 225                         AttrError::MultipleItem(pprust::path_to_string(&meta.path)),
 226                     );
 227                     return false;
 228                 }
 229                 if let Some(v) = meta.value_str() {
 230                     *item = Some(v);
 231                     true
 232                 } else {
 233                     struct_span_err!(diagnostic, meta.span, E0539, "incorrect meta item").emit();
 234                     false
 235                 }
 236             };
 237
 238             let meta_name = meta.name_or_empty();
 239             match meta_name {
 240                 sym::rustc_const_unstable | sym::unstable => {
 241                     if meta_name == sym::unstable && stab.is_some() {
 242                         handle_errors(
 243                             &sess.parse_sess,
 244                             attr.span,
 245                             AttrError::MultipleStabilityLevels,
 246                         );
 247                         break;
 248                     } else if meta_name == sym::rustc_const_unstable && const_stab.is_some() {
 249                         handle_errors(
 250                             &sess.parse_sess,
 251                             attr.span,
 252                             AttrError::MultipleStabilityLevels,
 253                         );
 254                         break;
 255                     }
 256
 257                     let mut feature = None;
 258                     let mut reason = None;
 259                     let mut issue = None;
 260                     let mut issue_num = None;
 261                     let mut is_soft = false;
 262                     for meta in metas {
 263                         if let Some(mi) = meta.meta_item() {
 264                             match mi.name_or_empty() {
 265                                 sym::feature => {
 266                                     if !get(mi, &mut feature) {
 267                                         continue 'outer;
 268                                     }
 269                                 }
 270                                 sym::reason => {
 271                                     if !get(mi, &mut reason) {
 272                                         continue 'outer;
 273                                     }
 274                                 }
 275                                 sym::issue => {
 276                                     if !get(mi, &mut issue) {
 277                                         continue 'outer;
 278                                     }
 279
 280                                     // These unwraps are safe because `get` ensures the meta item
 281                                     // is a name/value pair string literal.
 282                                     issue_num = match &*issue.unwrap().as_str() {
 283                                         "none" => None,
 284                                         issue => {
 285                                             let emit_diag = |msg: &str| {
 286                                                 struct_span_err!(
 287                                                     diagnostic,
 288                                                     mi.span,
 289                                                     E0545,
 290                                                     "`issue` must be a non-zero numeric string \
 291                                                     or \"none\"",
 292                                                 )
 293                                                 .span_label(
 294                                                     mi.name_value_literal().unwrap().span,
 295                                                     msg,
 296                                                 )
 297                                                 .emit();
 298                                             };
 299                                             match issue.parse() {
 300                                                 Ok(num) if num == 0 => {
 301                                                     emit_diag(
 302                                                         "`issue` must not be \"0\", \
 303                                                         use \"none\" instead",
 304                                                     );
 305                                                     continue 'outer;
 306                                                 }
 307                                                 Ok(num) => NonZeroU32::new(num),
 308                                                 Err(err) => {
 309                                                     emit_diag(&err.to_string());
 310                                                     continue 'outer;
 311                                                 }
 312                                             }
 313                                         }
 314                                     };
 315                                 }
 316                                 sym::soft => {
 317                                     if !mi.is_word() {
 318                                         let msg = "`soft` should not have any arguments";
 319                                         sess.parse_sess.span_diagnostic.span_err(mi.span, msg);
 320                                     }
 321                                     is_soft = true;
 322                                 }
 323                                 _ => {
 324                                     handle_errors(
 325                                         &sess.parse_sess,
 326                                         meta.span(),
 327                                         AttrError::UnknownMetaItem(
 328                                             pprust::path_to_string(&mi.path),
 329                                             &["feature", "reason", "issue", "soft"],
 330                                         ),
 331                                     );
 332                                     continue 'outer;
 333                                 }
 334                             }
 335                         } else {
 336                             handle_errors(
 337                                 &sess.parse_sess,
 338                                 meta.span(),
 339                                 AttrError::UnsupportedLiteral("unsupported literal", false),
 340                             );
 341                             continue 'outer;
 342                         }
 343                     }
 344
 345                     match (feature, reason, issue) {
 346                         (Some(feature), reason, Some(_)) => {
 347                             let level = Unstable { reason, issue: issue_num, is_soft };
 348                             if sym::unstable == meta_name {
 349                                 stab = Some(Stability { level, feature });
 350                             } else {
 351                                 const_stab = Some(ConstStability {
 352                                     level,
 353                                     feature,
 354                                     promotable: false,
 355                                     allow_const_fn_ptr: false,
 356                                 });
 357                             }
 358                         }
 359                         (None, _, _) => {
 360                             handle_errors(&sess.parse_sess, attr.span, AttrError::MissingFeature);
 361                             continue;
 362                         }
 363                         _ => {
 364                             struct_span_err!(diagnostic, attr.span, E0547, "missing 'issue'")
 365                                 .emit();
 366                             continue;
 367                         }
 368                     }
 369                 }
 370                 sym::rustc_const_stable | sym::stable => {
 371                     if meta_name == sym::stable && stab.is_some() {
 372                         handle_errors(
 373                             &sess.parse_sess,
 374                             attr.span,
 375                             AttrError::MultipleStabilityLevels,
 376                         );
 377                         break;
 378                     } else if meta_name == sym::rustc_const_stable && const_stab.is_some() {
 379                         handle_errors(
 380                             &sess.parse_sess,
 381                             attr.span,
 382                             AttrError::MultipleStabilityLevels,
 383                         );
 384                         break;
 385                     }
 386
 387                     let mut feature = None;
 388                     let mut since = None;
 389                     for meta in metas {
 390                         match meta {
 391                             NestedMetaItem::MetaItem(mi) => match mi.name_or_empty() {
 392                                 sym::feature => {
 393                                     if !get(mi, &mut feature) {
 394                                         continue 'outer;
 395                                     }
 396                                 }
 397                                 sym::since => {
 398                                     if !get(mi, &mut since) {
 399                                         continue 'outer;
 400                                     }
 401                                 }
 402                                 _ => {
 403                                     handle_errors(
 404                                         &sess.parse_sess,
 405                                         meta.span(),
 406                                         AttrError::UnknownMetaItem(
 407                                             pprust::path_to_string(&mi.path),
 408                                             &["since", "note"],
 409                                         ),
 410                                     );
 411                                     continue 'outer;
 412                                 }
 413                             },
 414                             NestedMetaItem::Literal(lit) => {
 415                                 handle_errors(
 416                                     &sess.parse_sess,
 417                                     lit.span,
 418                                     AttrError::UnsupportedLiteral("unsupported literal", false),
 419                                 );
 420                                 continue 'outer;
 421                             }
 422                         }
 423                     }
 424
 425                     match (feature, since) {
 426                         (Some(feature), Some(since)) => {
 427                             let level = Stable { since };
 428                             if sym::stable == meta_name {
 429                                 stab = Some(Stability { level, feature });
 430                             } else {
 431                                 const_stab = Some(ConstStability {
 432                                     level,
 433                                     feature,
 434                                     promotable: false,
 435                                     allow_const_fn_ptr: false,
 436                                 });
 437                             }
 438                         }
 439                         (None, _) => {
 440                             handle_errors(&sess.parse_sess, attr.span, AttrError::MissingFeature);
 441                             continue;
 442                         }
 443                         _ => {
 444                             handle_errors(&sess.parse_sess, attr.span, AttrError::MissingSince);
 445                             continue;
 446                         }
 447                     }
 448                 }
 449                 _ => unreachable!(),
 450             }
 451         }
 452     }
 453
 454     // Merge the const-unstable info into the stability info
 455     if promotable || allow_const_fn_ptr {
 456         if let Some(ref mut stab) = const_stab {
 457             stab.promotable = promotable;
 458             stab.allow_const_fn_ptr = allow_const_fn_ptr;
 459         } else {
 460             struct_span_err!(
 461                 diagnostic,
 462                 item_sp,
 463                 E0717,
 464                 "rustc_promotable and rustc_allow_const_fn_ptr attributes \
 465                       must be paired with either a rustc_const_unstable or a rustc_const_stable \
 466                       attribute"
 467             )
 468             .emit();
 469         }
 470     }
 471
 472     (stab, const_stab)
 473 }
 474
 475 pub fn find_crate_name(sess: &Session, attrs: &[Attribute]) -> Option<Symbol> {
 476     sess.first_attr_value_str_by_name(attrs, sym::crate_name)
 477 }
 478
 479 /// Tests if a cfg-pattern matches the cfg set
 480 pub fn cfg_matches(cfg: &ast::MetaItem, sess: &ParseSess, features: Option<&Features>) -> bool {
 481     eval_condition(cfg, sess, features, &mut |cfg| {
 482         try_gate_cfg(cfg, sess, features);
 483         let error = |span, msg| {
 484             sess.span_diagnostic.span_err(span, msg);
 485             true
 486         };
 487         if cfg.path.segments.len() != 1 {
 488             return error(cfg.path.span, "`cfg` predicate key must be an identifier");
 489         }
 490         match &cfg.kind {
 491             MetaItemKind::List(..) => {
 492                 error(cfg.span, "unexpected parentheses after `cfg` predicate key")
 493             }
 494             MetaItemKind::NameValue(lit) if !lit.kind.is_str() => {
 495                 handle_errors(
 496                     sess,
 497                     lit.span,
 498                     AttrError::UnsupportedLiteral(
 499                         "literal in `cfg` predicate value must be a string",
 500                         lit.kind.is_bytestr(),
 501                     ),
 502                 );
 503                 true
 504             }
 505             MetaItemKind::NameValue(..) | MetaItemKind::Word => {
 506                 let ident = cfg.ident().expect("multi-segment cfg predicate");
 507                 sess.config.contains(&(ident.name, cfg.value_str()))
 508             }
 509         }
 510     })
 511 }
 512
 513 fn try_gate_cfg(cfg: &ast::MetaItem, sess: &ParseSess, features: Option<&Features>) {
 514     let gate = find_gated_cfg(|sym| cfg.has_name(sym));
 515     if let (Some(feats), Some(gated_cfg)) = (features, gate) {
 516         gate_cfg(&gated_cfg, cfg.span, sess, feats);
 517     }
 518 }
 519
 520 fn gate_cfg(gated_cfg: &GatedCfg, cfg_span: Span, sess: &ParseSess, features: &Features) {
 521     let (cfg, feature, has_feature) = gated_cfg;
 522     if !has_feature(features) && !cfg_span.allows_unstable(*feature) {
 523         let explain = format!("`cfg({})` is experimental and subject to change", cfg);
 524         feature_err(sess, *feature, cfg_span, &explain).emit();
 525     }
 526 }
 527
 528 /// Evaluate a cfg-like condition (with `any` and `all`), using `eval` to
 529 /// evaluate individual items.
 530 pub fn eval_condition(
 531     cfg: &ast::MetaItem,
 532     sess: &ParseSess,
 533     features: Option<&Features>,
 534     eval: &mut impl FnMut(&ast::MetaItem) -> bool,
 535 ) -> bool {
 536     match cfg.kind {
 537         ast::MetaItemKind::List(ref mis) if cfg.name_or_empty() == sym::version => {
 538             try_gate_cfg(cfg, sess, features);
 539             let (min_version, span) = match &mis[..] {
 540                 [NestedMetaItem::Literal(Lit { kind: LitKind::Str(sym, ..), span, .. })] => {
 541                     (sym, span)
 542                 }
 543                 [NestedMetaItem::Literal(Lit { span, .. })
 544                 | NestedMetaItem::MetaItem(MetaItem { span, .. })] => {
 545                     sess.span_diagnostic
 546                         .struct_span_err(*span, "expected a version literal")
 547                         .emit();
 548                     return false;
 549                 }
 550                 [..] => {
 551                     sess.span_diagnostic
 552                         .struct_span_err(cfg.span, "expected single version literal")
 553                         .emit();
 554                     return false;
 555                 }
 556             };
 557             let min_version = match Version::parse(&min_version.as_str()) {
 558                 Some(ver) => ver,
 559                 None => {
 560                     sess.span_diagnostic.struct_span_err(*span, "invalid version literal").emit();
 561                     return false;
 562                 }
 563             };
 564             let channel = env!("CFG_RELEASE_CHANNEL");
 565             let nightly = channel == "nightly" || channel == "dev";
 566             let rustc_version = Version::parse(env!("CFG_RELEASE")).unwrap();
 567
 568             // See https://github.com/rust-lang/rust/issues/64796#issuecomment-625474439 for details
 569             if nightly { rustc_version > min_version } else { rustc_version >= min_version }
 570         }
 571         ast::MetaItemKind::List(ref mis) => {
 572             for mi in mis.iter() {
 573                 if !mi.is_meta_item() {
 574                     handle_errors(
 575                         sess,
 576                         mi.span(),
 577                         AttrError::UnsupportedLiteral("unsupported literal", false),
 578                     );
 579                     return false;
 580                 }
 581             }
 582
 583             // The unwraps below may look dangerous, but we've already asserted
 584             // that they won't fail with the loop above.
 585             match cfg.name_or_empty() {
 586                 sym::any => mis
 587                     .iter()
 588                     .any(|mi| eval_condition(mi.meta_item().unwrap(), sess, features, eval)),
 589                 sym::all => mis
 590                     .iter()
 591                     .all(|mi| eval_condition(mi.meta_item().unwrap(), sess, features, eval)),
 592                 sym::not => {
 593                     if mis.len() != 1 {
 594                         struct_span_err!(
 595                             sess.span_diagnostic,
 596                             cfg.span,
 597                             E0536,
 598                             "expected 1 cfg-pattern"
 599                         )
 600                         .emit();
 601                         return false;
 602                     }
 603
 604                     !eval_condition(mis[0].meta_item().unwrap(), sess, features, eval)
 605                 }
 606                 _ => {
 607                     struct_span_err!(
 608                         sess.span_diagnostic,
 609                         cfg.span,
 610                         E0537,
 611                         "invalid predicate `{}`",
 612                         pprust::path_to_string(&cfg.path)
 613                     )
 614                     .emit();
 615                     false
 616                 }
 617             }
 618         }
 619         ast::MetaItemKind::Word | ast::MetaItemKind::NameValue(..) => eval(cfg),
 620     }
 621 }
 622
 623 #[derive(RustcEncodable, RustcDecodable, Clone, HashStable_Generic)]
 624 pub struct Deprecation {
 625     pub since: Option<Symbol>,
 626     /// The note to issue a reason.
 627     pub note: Option<Symbol>,
 628     /// A text snippet used to completely replace any use of the deprecated item in an expression.
 629     ///
 630     /// This is currently unstable.
 631     pub suggestion: Option<Symbol>,
 632
 633     /// Whether to treat the since attribute as being a Rust version identifier
 634     /// (rather than an opaque string).
 635     pub is_since_rustc_version: bool,
 636 }
 637
 638 /// Finds the deprecation attribute. `None` if none exists.
 639 pub fn find_deprecation(sess: &Session, attrs: &[Attribute], item_sp: Span) -> Option<Deprecation> {
 640     find_deprecation_generic(sess, attrs.iter(), item_sp)
 641 }
 642
 643 fn find_deprecation_generic<'a, I>(
 644     sess: &Session,
 645     attrs_iter: I,
 646     item_sp: Span,
 647 ) -> Option<Deprecation>
 648 where
 649     I: Iterator<Item = &'a Attribute>,
 650 {
 651     let mut depr: Option<Deprecation> = None;
 652     let diagnostic = &sess.parse_sess.span_diagnostic;
 653
 654     'outer: for attr in attrs_iter {
 655         if !(sess.check_name(attr, sym::deprecated) || sess.check_name(attr, sym::rustc_deprecated))
 656         {
 657             continue;
 658         }
 659
 660         if depr.is_some() {
 661             struct_span_err!(diagnostic, item_sp, E0550, "multiple deprecated attributes").emit();
 662             break;
 663         }
 664
 665         let meta = match attr.meta() {
 666             Some(meta) => meta,
 667             None => continue,
 668         };
 669         let mut since = None;
 670         let mut note = None;
 671         let mut suggestion = None;
 672         match &meta.kind {
 673             MetaItemKind::Word => {}
 674             MetaItemKind::NameValue(..) => note = meta.value_str(),
 675             MetaItemKind::List(list) => {
 676                 let get = |meta: &MetaItem, item: &mut Option<Symbol>| {
 677                     if item.is_some() {
 678                         handle_errors(
 679                             &sess.parse_sess,
 680                             meta.span,
 681                             AttrError::MultipleItem(pprust::path_to_string(&meta.path)),
 682                         );
 683                         return false;
 684                     }
 685                     if let Some(v) = meta.value_str() {
 686                         *item = Some(v);
 687                         true
 688                     } else {
 689                         if let Some(lit) = meta.name_value_literal() {
 690                             handle_errors(
 691                                 &sess.parse_sess,
 692                                 lit.span,
 693                                 AttrError::UnsupportedLiteral(
 694                                     "literal in `deprecated` \
 695                                     value must be a string",
 696                                     lit.kind.is_bytestr(),
 697                                 ),
 698                             );
 699                         } else {
 700                             struct_span_err!(diagnostic, meta.span, E0551, "incorrect meta item")
 701                                 .emit();
 702                         }
 703
 704                         false
 705                     }
 706                 };
 707
 708                 for meta in list {
 709                     match meta {
 710                         NestedMetaItem::MetaItem(mi) => match mi.name_or_empty() {
 711                             sym::since => {
 712                                 if !get(mi, &mut since) {
 713                                     continue 'outer;
 714                                 }
 715                             }
 716                             sym::note if sess.check_name(attr, sym::deprecated) => {
 717                                 if !get(mi, &mut note) {
 718                                     continue 'outer;
 719                                 }
 720                             }
 721                             sym::reason if sess.check_name(attr, sym::rustc_deprecated) => {
 722                                 if !get(mi, &mut note) {
 723                                     continue 'outer;
 724                                 }
 725                             }
 726                             sym::suggestion if sess.check_name(attr, sym::rustc_deprecated) => {
 727                                 if !get(mi, &mut suggestion) {
 728                                     continue 'outer;
 729                                 }
 730                             }
 731                             _ => {
 732                                 handle_errors(
 733                                     &sess.parse_sess,
 734                                     meta.span(),
 735                                     AttrError::UnknownMetaItem(
 736                                         pprust::path_to_string(&mi.path),
 737                                         if sess.check_name(attr, sym::deprecated) {
 738                                             &["since", "note"]
 739                                         } else {
 740                                             &["since", "reason", "suggestion"]
 741                                         },
 742                                     ),
 743                                 );
 744                                 continue 'outer;
 745                             }
 746                         },
 747                         NestedMetaItem::Literal(lit) => {
 748                             handle_errors(
 749                                 &sess.parse_sess,
 750                                 lit.span,
 751                                 AttrError::UnsupportedLiteral(
 752                                     "item in `deprecated` must be a key/value pair",
 753                                     false,
 754                                 ),
 755                             );
 756                             continue 'outer;
 757                         }
 758                     }
 759                 }
 760             }
 761         }
 762
 763         if suggestion.is_some() && sess.check_name(attr, sym::deprecated) {
 764             unreachable!("only allowed on rustc_deprecated")
 765         }
 766
 767         if sess.check_name(attr, sym::rustc_deprecated) {
 768             if since.is_none() {
 769                 handle_errors(&sess.parse_sess, attr.span, AttrError::MissingSince);
 770                 continue;
 771             }
 772
 773             if note.is_none() {
 774                 struct_span_err!(diagnostic, attr.span, E0543, "missing 'reason'").emit();
 775                 continue;
 776             }
 777         }
 778
 779         sess.mark_attr_used(&attr);
 780
 781         let is_since_rustc_version = sess.check_name(attr, sym::rustc_deprecated);
 782         depr = Some(Deprecation { since, note, suggestion, is_since_rustc_version });
 783     }
 784
 785     depr
 786 }
 787
 788 #[derive(PartialEq, Debug, RustcEncodable, RustcDecodable, Copy, Clone)]
 789 pub enum ReprAttr {
 790     ReprInt(IntType),
 791     ReprC,
 792     ReprPacked(u32),
 793     ReprSimd,
 794     ReprTransparent,
 795     ReprAlign(u32),
 796     ReprNoNiche,
 797 }
 798
 799 #[derive(Eq, PartialEq, Debug, RustcEncodable, RustcDecodable, Copy, Clone, HashStable_Generic)]
 800 pub enum IntType {
 801     SignedInt(ast::IntTy),
 802     UnsignedInt(ast::UintTy),
 803 }
 804
 805 impl IntType {
 806     #[inline]
 807     pub fn is_signed(self) -> bool {
 808         use IntType::*;
 809
 810         match self {
 811             SignedInt(..) => true,
 812             UnsignedInt(..) => false,
 813         }
 814     }
 815 }
 816
 817 /// Parse #[repr(...)] forms.
 818 ///
 819 /// Valid repr contents: any of the primitive integral type names (see
 820 /// `int_type_of_word`, below) to specify enum discriminant type; `C`, to use
 821 /// the same discriminant size that the corresponding C enum would or C
 822 /// structure layout, `packed` to remove padding, and `transparent` to elegate representation
 823 /// concerns to the only non-ZST field.
 824 pub fn find_repr_attrs(sess: &Session, attr: &Attribute) -> Vec<ReprAttr> {
 825     use ReprAttr::*;
 826
 827     let mut acc = Vec::new();
 828     let diagnostic = &sess.parse_sess.span_diagnostic;
 829     if attr.has_name(sym::repr) {
 830         if let Some(items) = attr.meta_item_list() {
 831             sess.mark_attr_used(attr);
 832             for item in items {
 833                 if !item.is_meta_item() {
 834                     handle_errors(
 835                         &sess.parse_sess,
 836                         item.span(),
 837                         AttrError::UnsupportedLiteral(
 838                             "meta item in `repr` must be an identifier",
 839                             false,
 840                         ),
 841                     );
 842                     continue;
 843                 }
 844
 845                 let mut recognised = false;
 846                 if item.is_word() {
 847                     let hint = match item.name_or_empty() {
 848                         sym::C => Some(ReprC),
 849                         sym::packed => Some(ReprPacked(1)),
 850                         sym::simd => Some(ReprSimd),
 851                         sym::transparent => Some(ReprTransparent),
 852                         sym::no_niche => Some(ReprNoNiche),
 853                         name => int_type_of_word(name).map(ReprInt),
 854                     };
 855
 856                     if let Some(h) = hint {
 857                         recognised = true;
 858                         acc.push(h);
 859                     }
 860                 } else if let Some((name, value)) = item.name_value_literal() {
 861                     let parse_alignment = |node: &ast::LitKind| -> Result<u32, &'static str> {
 862                         if let ast::LitKind::Int(literal, ast::LitIntType::Unsuffixed) = node {
 863                             if literal.is_power_of_two() {
 864                                 // rustc_middle::ty::layout::Align restricts align to <= 2^29
 865                                 if *literal <= 1 << 29 {
 866                                     Ok(*literal as u32)
 867                                 } else {
 868                                     Err("larger than 2^29")
 869                                 }
 870                             } else {
 871                                 Err("not a power of two")
 872                             }
 873                         } else {
 874                             Err("not an unsuffixed integer")
 875                         }
 876                     };
 877
 878                     let mut literal_error = None;
 879                     if name == sym::align {
 880                         recognised = true;
 881                         match parse_alignment(&value.kind) {
 882                             Ok(literal) => acc.push(ReprAlign(literal)),
 883                             Err(message) => literal_error = Some(message),
 884                         };
 885                     } else if name == sym::packed {
 886                         recognised = true;
 887                         match parse_alignment(&value.kind) {
 888                             Ok(literal) => acc.push(ReprPacked(literal)),
 889                             Err(message) => literal_error = Some(message),
 890                         };
 891                     }
 892                     if let Some(literal_error) = literal_error {
 893                         struct_span_err!(
 894                             diagnostic,
 895                             item.span(),
 896                             E0589,
 897                             "invalid `repr(align)` attribute: {}",
 898                             literal_error
 899                         )
 900                         .emit();
 901                     }
 902                 } else {
 903                     if let Some(meta_item) = item.meta_item() {
 904                         if meta_item.has_name(sym::align) {
 905                             if let MetaItemKind::NameValue(ref value) = meta_item.kind {
 906                                 recognised = true;
 907                                 let mut err = struct_span_err!(
 908                                     diagnostic,
 909                                     item.span(),
 910                                     E0693,
 911                                     "incorrect `repr(align)` attribute format"
 912                                 );
 913                                 match value.kind {
 914                                     ast::LitKind::Int(int, ast::LitIntType::Unsuffixed) => {
 915                                         err.span_suggestion(
 916                                             item.span(),
 917                                             "use parentheses instead",
 918                                             format!("align({})", int),
 919                                             Applicability::MachineApplicable,
 920                                         );
 921                                     }
 922                                     ast::LitKind::Str(s, _) => {
 923                                         err.span_suggestion(
 924                                             item.span(),
 925                                             "use parentheses instead",
 926                                             format!("align({})", s),
 927                                             Applicability::MachineApplicable,
 928                                         );
 929                                     }
 930                                     _ => {}
 931                                 }
 932                                 err.emit();
 933                             }
 934                         }
 935                     }
 936                 }
 937                 if !recognised {
 938                     // Not a word we recognize
 939                     struct_span_err!(
 940                         diagnostic,
 941                         item.span(),
 942                         E0552,
 943                         "unrecognized representation hint"
 944                     )
 945                     .emit();
 946                 }
 947             }
 948         }
 949     }
 950     acc
 951 }
 952
 953 fn int_type_of_word(s: Symbol) -> Option<IntType> {
 954     use IntType::*;
 955
 956     match s {
 957         sym::i8 => Some(SignedInt(ast::IntTy::I8)),
 958         sym::u8 => Some(UnsignedInt(ast::UintTy::U8)),
 959         sym::i16 => Some(SignedInt(ast::IntTy::I16)),
 960         sym::u16 => Some(UnsignedInt(ast::UintTy::U16)),
 961         sym::i32 => Some(SignedInt(ast::IntTy::I32)),
 962         sym::u32 => Some(UnsignedInt(ast::UintTy::U32)),
 963         sym::i64 => Some(SignedInt(ast::IntTy::I64)),
 964         sym::u64 => Some(UnsignedInt(ast::UintTy::U64)),
 965         sym::i128 => Some(SignedInt(ast::IntTy::I128)),
 966         sym::u128 => Some(UnsignedInt(ast::UintTy::U128)),
 967         sym::isize => Some(SignedInt(ast::IntTy::Isize)),
 968         sym::usize => Some(UnsignedInt(ast::UintTy::Usize)),
 969         _ => None,
 970     }
 971 }
 972
 973 pub enum TransparencyError {
 974     UnknownTransparency(Symbol, Span),
 975     MultipleTransparencyAttrs(Span, Span),
 976 }
 977
 978 pub fn find_transparency(
 979     sess: &Session,
 980     attrs: &[Attribute],
 981     macro_rules: bool,
 982 ) -> (Transparency, Option<TransparencyError>) {
 983     let mut transparency = None;
 984     let mut error = None;
 985     for attr in attrs {
 986         if sess.check_name(attr, sym::rustc_macro_transparency) {
 987             if let Some((_, old_span)) = transparency {
 988                 error = Some(TransparencyError::MultipleTransparencyAttrs(old_span, attr.span));
 989                 break;
 990             } else if let Some(value) = attr.value_str() {
 991                 transparency = Some((
 992                     match value {
 993                         sym::transparent => Transparency::Transparent,
 994                         sym::semitransparent => Transparency::SemiTransparent,
 995                         sym::opaque => Transparency::Opaque,
 996                         _ => {
 997                             error = Some(TransparencyError::UnknownTransparency(value, attr.span));
 998                             continue;
 999                         }
1000                     },
1001                     attr.span,
1002                 ));
1003             }
1004         }
1005     }
1006     let fallback = if macro_rules { Transparency::SemiTransparent } else { Transparency::Opaque };
1007     (transparency.map_or(fallback, |t| t.0), error)
1008 }
1009
1010 pub fn allow_internal_unstable<'a>(
1011     sess: &'a Session,
1012     attrs: &[Attribute],
1013 ) -> Option<impl Iterator<Item = Symbol> + 'a> {
1014     let attr = sess.find_by_name(attrs, sym::allow_internal_unstable)?;
1015     let list = attr.meta_item_list().or_else(|| {
1016         sess.diagnostic()
1017             .span_err(attr.span, "allow_internal_unstable expects list of feature names");
1018         None
1019     })?;
1020     Some(list.into_iter().filter_map(move |it| {
1021         let name = it.ident().map(|ident| ident.name);
1022         if name.is_none() {
1023             sess.diagnostic()
1024                 .span_err(it.span(), "`allow_internal_unstable` expects feature names");
1025         }
1026         name
1027     }))
1028 }