src/librustc_attr/builtin.rs

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