src/librustc_parse/config.rs

   1 //! Process the potential `cfg` attributes on a module.
   2 //! Also determine if the module should be included in this configuration.
   3 //!
   4 //! This module properly belongs in rustc_expand, but for now it's tied into
   5 //! parsing, so we leave it here to avoid complicated out-of-line dependencies.
   6 //!
   7 //! A principled solution to this wrong location would be to implement [#64197].
   8 //!
   9 //! [#64197]: https://github.com/rust-lang/rust/issues/64197
  10
  11 use crate::{parse_in, validate_attr};
  12 use rustc_ast::ast::{self, AttrItem, Attribute, MetaItem};
  13 use rustc_ast::attr::HasAttrs;
  14 use rustc_ast::mut_visit::*;
  15 use rustc_ast::ptr::P;
  16 use rustc_ast::util::map_in_place::MapInPlace;
  17 use rustc_attr as attr;
  18 use rustc_data_structures::fx::FxHashMap;
  19 use rustc_errors::{error_code, struct_span_err, Applicability, Handler};
  20 use rustc_feature::{Feature, Features, State as FeatureState};
  21 use rustc_feature::{
  22     ACCEPTED_FEATURES, ACTIVE_FEATURES, REMOVED_FEATURES, STABLE_REMOVED_FEATURES,
  23 };
  24 use rustc_session::parse::{feature_err, ParseSess};
  25 use rustc_span::edition::{Edition, ALL_EDITIONS};
  26 use rustc_span::symbol::{sym, Symbol};
  27 use rustc_span::{Span, DUMMY_SP};
  28
  29 use smallvec::SmallVec;
  30
  31 /// A folder that strips out items that do not belong in the current configuration.
  32 pub struct StripUnconfigured<'a> {
  33     pub sess: &'a ParseSess,
  34     pub features: Option<&'a Features>,
  35 }
  36
  37 fn get_features(
  38     span_handler: &Handler,
  39     krate_attrs: &[ast::Attribute],
  40     crate_edition: Edition,
  41     allow_features: &Option<Vec<String>>,
  42 ) -> Features {
  43     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
  44         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
  45         err.span_label(span, "feature has been removed");
  46         if let Some(reason) = reason {
  47             err.note(reason);
  48         }
  49         err.emit();
  50     }
  51
  52     fn active_features_up_to(edition: Edition) -> impl Iterator<Item = &'static Feature> {
  53         ACTIVE_FEATURES.iter().filter(move |feature| {
  54             if let Some(feature_edition) = feature.edition {
  55                 feature_edition <= edition
  56             } else {
  57                 false
  58             }
  59         })
  60     }
  61
  62     let mut features = Features::default();
  63     let mut edition_enabled_features = FxHashMap::default();
  64
  65     for &edition in ALL_EDITIONS {
  66         if edition <= crate_edition {
  67             // The `crate_edition` implies its respective umbrella feature-gate
  68             // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
  69             edition_enabled_features.insert(edition.feature_name(), edition);
  70         }
  71     }
  72
  73     for feature in active_features_up_to(crate_edition) {
  74         feature.set(&mut features, DUMMY_SP);
  75         edition_enabled_features.insert(feature.name, crate_edition);
  76     }
  77
  78     // Process the edition umbrella feature-gates first, to ensure
  79     // `edition_enabled_features` is completed before it's queried.
  80     for attr in krate_attrs {
  81         if !attr.check_name(sym::feature) {
  82             continue;
  83         }
  84
  85         let list = match attr.meta_item_list() {
  86             Some(list) => list,
  87             None => continue,
  88         };
  89
  90         for mi in list {
  91             if !mi.is_word() {
  92                 continue;
  93             }
  94
  95             let name = mi.name_or_empty();
  96
  97             let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
  98             if let Some(edition) = edition {
  99                 if edition <= crate_edition {
 100                     continue;
 101                 }
 102
 103                 for feature in active_features_up_to(edition) {
 104                     // FIXME(Manishearth) there is currently no way to set
 105                     // lib features by edition
 106                     feature.set(&mut features, DUMMY_SP);
 107                     edition_enabled_features.insert(feature.name, edition);
 108                 }
 109             }
 110         }
 111     }
 112
 113     for attr in krate_attrs {
 114         if !attr.check_name(sym::feature) {
 115             continue;
 116         }
 117
 118         let list = match attr.meta_item_list() {
 119             Some(list) => list,
 120             None => continue,
 121         };
 122
 123         let bad_input = |span| {
 124             struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
 125         };
 126
 127         for mi in list {
 128             let name = match mi.ident() {
 129                 Some(ident) if mi.is_word() => ident.name,
 130                 Some(ident) => {
 131                     bad_input(mi.span())
 132                         .span_suggestion(
 133                             mi.span(),
 134                             "expected just one word",
 135                             format!("{}", ident.name),
 136                             Applicability::MaybeIncorrect,
 137                         )
 138                         .emit();
 139                     continue;
 140                 }
 141                 None => {
 142                     bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
 143                     continue;
 144                 }
 145             };
 146
 147             if let Some(edition) = edition_enabled_features.get(&name) {
 148                 let msg =
 149                     &format!("the feature `{}` is included in the Rust {} edition", name, edition);
 150                 span_handler.struct_span_warn_with_code(mi.span(), msg, error_code!(E0705)).emit();
 151                 continue;
 152             }
 153
 154             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
 155                 // Handled in the separate loop above.
 156                 continue;
 157             }
 158
 159             let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
 160             let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
 161             if let Some(Feature { state, .. }) = removed.or(stable_removed) {
 162                 if let FeatureState::Removed { reason } | FeatureState::Stabilized { reason } =
 163                     state
 164                 {
 165                     feature_removed(span_handler, mi.span(), *reason);
 166                     continue;
 167                 }
 168             }
 169
 170             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
 171                 let since = Some(Symbol::intern(since));
 172                 features.declared_lang_features.push((name, mi.span(), since));
 173                 continue;
 174             }
 175
 176             if let Some(allowed) = allow_features.as_ref() {
 177                 if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
 178                     struct_span_err!(
 179                         span_handler,
 180                         mi.span(),
 181                         E0725,
 182                         "the feature `{}` is not in the list of allowed features",
 183                         name
 184                     )
 185                     .emit();
 186                     continue;
 187                 }
 188             }
 189
 190             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
 191                 f.set(&mut features, mi.span());
 192                 features.declared_lang_features.push((name, mi.span(), None));
 193                 continue;
 194             }
 195
 196             features.declared_lib_features.push((name, mi.span()));
 197         }
 198     }
 199
 200     features
 201 }
 202
 203 // `cfg_attr`-process the crate's attributes and compute the crate's features.
 204 pub fn features(
 205     mut krate: ast::Crate,
 206     sess: &ParseSess,
 207     edition: Edition,
 208     allow_features: &Option<Vec<String>>,
 209 ) -> (ast::Crate, Features) {
 210     let mut strip_unconfigured = StripUnconfigured { sess, features: None };
 211
 212     let unconfigured_attrs = krate.attrs.clone();
 213     let diag = &sess.span_diagnostic;
 214     let err_count = diag.err_count();
 215     let features = match strip_unconfigured.configure(krate.attrs) {
 216         None => {
 217             // The entire crate is unconfigured.
 218             krate.attrs = Vec::new();
 219             krate.module.items = Vec::new();
 220             Features::default()
 221         }
 222         Some(attrs) => {
 223             krate.attrs = attrs;
 224             let features = get_features(diag, &krate.attrs, edition, allow_features);
 225             if err_count == diag.err_count() {
 226                 // Avoid reconfiguring malformed `cfg_attr`s.
 227                 strip_unconfigured.features = Some(&features);
 228                 strip_unconfigured.configure(unconfigured_attrs);
 229             }
 230             features
 231         }
 232     };
 233     (krate, features)
 234 }
 235
 236 #[macro_export]
 237 macro_rules! configure {
 238     ($this:ident, $node:ident) => {
 239         match $this.configure($node) {
 240             Some(node) => node,
 241             None => return Default::default(),
 242         }
 243     };
 244 }
 245
 246 const CFG_ATTR_GRAMMAR_HELP: &str = "#[cfg_attr(condition, attribute, other_attribute, ...)]";
 247 const CFG_ATTR_NOTE_REF: &str = "for more information, visit \
 248     <https://doc.rust-lang.org/reference/conditional-compilation.html\
 249     #the-cfg_attr-attribute>";
 250
 251 impl<'a> StripUnconfigured<'a> {
 252     pub fn configure<T: HasAttrs>(&mut self, mut node: T) -> Option<T> {
 253         self.process_cfg_attrs(&mut node);
 254         self.in_cfg(node.attrs()).then_some(node)
 255     }
 256
 257     /// Parse and expand all `cfg_attr` attributes into a list of attributes
 258     /// that are within each `cfg_attr` that has a true configuration predicate.
 259     ///
 260     /// Gives compiler warnings if any `cfg_attr` does not contain any
 261     /// attributes and is in the original source code. Gives compiler errors if
 262     /// the syntax of any `cfg_attr` is incorrect.
 263     pub fn process_cfg_attrs<T: HasAttrs>(&mut self, node: &mut T) {
 264         node.visit_attrs(|attrs| {
 265             attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
 266         });
 267     }
 268
 269     /// Parse and expand a single `cfg_attr` attribute into a list of attributes
 270     /// when the configuration predicate is true, or otherwise expand into an
 271     /// empty list of attributes.
 272     ///
 273     /// Gives a compiler warning when the `cfg_attr` contains no attributes and
 274     /// is in the original source file. Gives a compiler error if the syntax of
 275     /// the attribute is incorrect.
 276     fn process_cfg_attr(&mut self, attr: Attribute) -> Vec<Attribute> {
 277         if !attr.has_name(sym::cfg_attr) {
 278             return vec![attr];
 279         }
 280
 281         let (cfg_predicate, expanded_attrs) = match self.parse_cfg_attr(&attr) {
 282             None => return vec![],
 283             Some(r) => r,
 284         };
 285
 286         // Lint on zero attributes in source.
 287         if expanded_attrs.is_empty() {
 288             return vec![attr];
 289         }
 290
 291         // At this point we know the attribute is considered used.
 292         attr::mark_used(&attr);
 293
 294         if !attr::cfg_matches(&cfg_predicate, self.sess, self.features) {
 295             return vec![];
 296         }
 297
 298         // We call `process_cfg_attr` recursively in case there's a
 299         // `cfg_attr` inside of another `cfg_attr`. E.g.
 300         //  `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
 301         expanded_attrs
 302             .into_iter()
 303             .flat_map(|(item, span)| {
 304                 let attr = attr::mk_attr_from_item(attr.style, item, span);
 305                 self.process_cfg_attr(attr)
 306             })
 307             .collect()
 308     }
 309
 310     fn parse_cfg_attr(&self, attr: &Attribute) -> Option<(MetaItem, Vec<(AttrItem, Span)>)> {
 311         match attr.get_normal_item().args {
 312             ast::MacArgs::Delimited(dspan, delim, ref tts) if !tts.is_empty() => {
 313                 let msg = "wrong `cfg_attr` delimiters";
 314                 validate_attr::check_meta_bad_delim(self.sess, dspan, delim, msg);
 315                 match parse_in(self.sess, tts.clone(), "`cfg_attr` input", |p| p.parse_cfg_attr()) {
 316                     Ok(r) => return Some(r),
 317                     Err(mut e) => {
 318                         e.help(&format!("the valid syntax is `{}`", CFG_ATTR_GRAMMAR_HELP))
 319                             .note(CFG_ATTR_NOTE_REF)
 320                             .emit();
 321                     }
 322                 }
 323             }
 324             _ => self.error_malformed_cfg_attr_missing(attr.span),
 325         }
 326         None
 327     }
 328
 329     fn error_malformed_cfg_attr_missing(&self, span: Span) {
 330         self.sess
 331             .span_diagnostic
 332             .struct_span_err(span, "malformed `cfg_attr` attribute input")
 333             .span_suggestion(
 334                 span,
 335                 "missing condition and attribute",
 336                 CFG_ATTR_GRAMMAR_HELP.to_string(),
 337                 Applicability::HasPlaceholders,
 338             )
 339             .note(CFG_ATTR_NOTE_REF)
 340             .emit();
 341     }
 342
 343     /// Determines if a node with the given attributes should be included in this configuration.
 344     pub fn in_cfg(&self, attrs: &[Attribute]) -> bool {
 345         attrs.iter().all(|attr| {
 346             if !is_cfg(attr) {
 347                 return true;
 348             }
 349             let meta_item = match validate_attr::parse_meta(self.sess, attr) {
 350                 Ok(meta_item) => meta_item,
 351                 Err(mut err) => {
 352                     err.emit();
 353                     return true;
 354                 }
 355             };
 356             let error = |span, msg, suggestion: &str| {
 357                 let mut err = self.sess.span_diagnostic.struct_span_err(span, msg);
 358                 if !suggestion.is_empty() {
 359                     err.span_suggestion(
 360                         span,
 361                         "expected syntax is",
 362                         suggestion.into(),
 363                         Applicability::MaybeIncorrect,
 364                     );
 365                 }
 366                 err.emit();
 367                 true
 368             };
 369             let span = meta_item.span;
 370             match meta_item.meta_item_list() {
 371                 None => error(span, "`cfg` is not followed by parentheses", "cfg(/* predicate */)"),
 372                 Some([]) => error(span, "`cfg` predicate is not specified", ""),
 373                 Some([_, .., l]) => error(l.span(), "multiple `cfg` predicates are specified", ""),
 374                 Some([single]) => match single.meta_item() {
 375                     Some(meta_item) => attr::cfg_matches(meta_item, self.sess, self.features),
 376                     None => error(single.span(), "`cfg` predicate key cannot be a literal", ""),
 377                 },
 378             }
 379         })
 380     }
 381
 382     /// Visit attributes on expression and statements (but not attributes on items in blocks).
 383     fn visit_expr_attrs(&mut self, attrs: &[Attribute]) {
 384         // flag the offending attributes
 385         for attr in attrs.iter() {
 386             self.maybe_emit_expr_attr_err(attr);
 387         }
 388     }
 389
 390     /// If attributes are not allowed on expressions, emit an error for `attr`
 391     pub fn maybe_emit_expr_attr_err(&self, attr: &Attribute) {
 392         if !self.features.map(|features| features.stmt_expr_attributes).unwrap_or(true) {
 393             let mut err = feature_err(
 394                 self.sess,
 395                 sym::stmt_expr_attributes,
 396                 attr.span,
 397                 "attributes on expressions are experimental",
 398             );
 399
 400             if attr.is_doc_comment() {
 401                 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
 402             }
 403
 404             err.emit();
 405         }
 406     }
 407
 408     pub fn configure_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
 409         let ast::ForeignMod { abi: _, items } = foreign_mod;
 410         items.flat_map_in_place(|item| self.configure(item));
 411     }
 412
 413     pub fn configure_generic_params(&mut self, params: &mut Vec<ast::GenericParam>) {
 414         params.flat_map_in_place(|param| self.configure(param));
 415     }
 416
 417     fn configure_variant_data(&mut self, vdata: &mut ast::VariantData) {
 418         match vdata {
 419             ast::VariantData::Struct(fields, ..) | ast::VariantData::Tuple(fields, _) => {
 420                 fields.flat_map_in_place(|field| self.configure(field))
 421             }
 422             ast::VariantData::Unit(_) => {}
 423         }
 424     }
 425
 426     pub fn configure_item_kind(&mut self, item: &mut ast::ItemKind) {
 427         match item {
 428             ast::ItemKind::Struct(def, _generics) | ast::ItemKind::Union(def, _generics) => {
 429                 self.configure_variant_data(def)
 430             }
 431             ast::ItemKind::Enum(ast::EnumDef { variants }, _generics) => {
 432                 variants.flat_map_in_place(|variant| self.configure(variant));
 433                 for variant in variants {
 434                     self.configure_variant_data(&mut variant.data);
 435                 }
 436             }
 437             _ => {}
 438         }
 439     }
 440
 441     pub fn configure_expr_kind(&mut self, expr_kind: &mut ast::ExprKind) {
 442         match expr_kind {
 443             ast::ExprKind::Match(_m, arms) => {
 444                 arms.flat_map_in_place(|arm| self.configure(arm));
 445             }
 446             ast::ExprKind::Struct(_path, fields, _base) => {
 447                 fields.flat_map_in_place(|field| self.configure(field));
 448             }
 449             _ => {}
 450         }
 451     }
 452
 453     pub fn configure_expr(&mut self, expr: &mut P<ast::Expr>) {
 454         self.visit_expr_attrs(expr.attrs());
 455
 456         // If an expr is valid to cfg away it will have been removed by the
 457         // outer stmt or expression folder before descending in here.
 458         // Anything else is always required, and thus has to error out
 459         // in case of a cfg attr.
 460         //
 461         // N.B., this is intentionally not part of the visit_expr() function
 462         //     in order for filter_map_expr() to be able to avoid this check
 463         if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(a)) {
 464             let msg = "removing an expression is not supported in this position";
 465             self.sess.span_diagnostic.span_err(attr.span, msg);
 466         }
 467
 468         self.process_cfg_attrs(expr)
 469     }
 470
 471     pub fn configure_pat(&mut self, pat: &mut P<ast::Pat>) {
 472         if let ast::PatKind::Struct(_path, fields, _etc) = &mut pat.kind {
 473             fields.flat_map_in_place(|field| self.configure(field));
 474         }
 475     }
 476
 477     pub fn configure_fn_decl(&mut self, fn_decl: &mut ast::FnDecl) {
 478         fn_decl.inputs.flat_map_in_place(|arg| self.configure(arg));
 479     }
 480 }
 481
 482 impl<'a> MutVisitor for StripUnconfigured<'a> {
 483     fn visit_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
 484         self.configure_foreign_mod(foreign_mod);
 485         noop_visit_foreign_mod(foreign_mod, self);
 486     }
 487
 488     fn visit_item_kind(&mut self, item: &mut ast::ItemKind) {
 489         self.configure_item_kind(item);
 490         noop_visit_item_kind(item, self);
 491     }
 492
 493     fn visit_expr(&mut self, expr: &mut P<ast::Expr>) {
 494         self.configure_expr(expr);
 495         self.configure_expr_kind(&mut expr.kind);
 496         noop_visit_expr(expr, self);
 497     }
 498
 499     fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
 500         let mut expr = configure!(self, expr);
 501         self.configure_expr_kind(&mut expr.kind);
 502         noop_visit_expr(&mut expr, self);
 503         Some(expr)
 504     }
 505
 506     fn flat_map_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
 507         noop_flat_map_stmt(configure!(self, stmt), self)
 508     }
 509
 510     fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
 511         noop_flat_map_item(configure!(self, item), self)
 512     }
 513
 514     fn flat_map_impl_item(&mut self, item: P<ast::AssocItem>) -> SmallVec<[P<ast::AssocItem>; 1]> {
 515         noop_flat_map_assoc_item(configure!(self, item), self)
 516     }
 517
 518     fn flat_map_trait_item(&mut self, item: P<ast::AssocItem>) -> SmallVec<[P<ast::AssocItem>; 1]> {
 519         noop_flat_map_assoc_item(configure!(self, item), self)
 520     }
 521
 522     fn visit_mac(&mut self, _mac: &mut ast::Mac) {
 523         // Don't configure interpolated AST (cf. issue #34171).
 524         // Interpolated AST will get configured once the surrounding tokens are parsed.
 525     }
 526
 527     fn visit_pat(&mut self, pat: &mut P<ast::Pat>) {
 528         self.configure_pat(pat);
 529         noop_visit_pat(pat, self)
 530     }
 531
 532     fn visit_fn_decl(&mut self, mut fn_decl: &mut P<ast::FnDecl>) {
 533         self.configure_fn_decl(&mut fn_decl);
 534         noop_visit_fn_decl(fn_decl, self);
 535     }
 536 }
 537
 538 fn is_cfg(attr: &Attribute) -> bool {
 539     attr.check_name(sym::cfg)
 540 }
 541
 542 /// Process the potential `cfg` attributes on a module.
 543 /// Also determine if the module should be included in this configuration.
 544 pub fn process_configure_mod(sess: &ParseSess, cfg_mods: bool, attrs: &mut Vec<Attribute>) -> bool {
 545     // Don't perform gated feature checking.
 546     let mut strip_unconfigured = StripUnconfigured { sess, features: None };
 547     strip_unconfigured.process_cfg_attrs(attrs);
 548     !cfg_mods || strip_unconfigured.in_cfg(&attrs)
 549 }