vendor/rustc-ap-rustc_expand/src/config.rs

   1 //! Conditional compilation stripping.
   2
   3 use rustc_ast::attr::HasAttrs;
   4 use rustc_ast::mut_visit::*;
   5 use rustc_ast::ptr::P;
   6 use rustc_ast::token::{DelimToken, Token, TokenKind};
   7 use rustc_ast::tokenstream::{DelimSpan, LazyTokenStreamInner, Spacing, TokenStream, TokenTree};
   8 use rustc_ast::{self as ast, AttrItem, Attribute, MetaItem};
   9 use rustc_attr as attr;
  10 use rustc_data_structures::fx::FxHashMap;
  11 use rustc_data_structures::map_in_place::MapInPlace;
  12 use rustc_data_structures::sync::Lrc;
  13 use rustc_errors::{error_code, struct_span_err, Applicability, Handler};
  14 use rustc_feature::{Feature, Features, State as FeatureState};
  15 use rustc_feature::{
  16     ACCEPTED_FEATURES, ACTIVE_FEATURES, REMOVED_FEATURES, STABLE_REMOVED_FEATURES,
  17 };
  18 use rustc_parse::{parse_in, validate_attr};
  19 use rustc_session::parse::feature_err;
  20 use rustc_session::Session;
  21 use rustc_span::edition::{Edition, ALL_EDITIONS};
  22 use rustc_span::symbol::{sym, Symbol};
  23 use rustc_span::{Span, DUMMY_SP};
  24
  25 use smallvec::SmallVec;
  26
  27 /// A folder that strips out items that do not belong in the current configuration.
  28 pub struct StripUnconfigured<'a> {
  29     pub sess: &'a Session,
  30     pub features: Option<&'a Features>,
  31 }
  32
  33 fn get_features(
  34     sess: &Session,
  35     span_handler: &Handler,
  36     krate_attrs: &[ast::Attribute],
  37 ) -> Features {
  38     fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
  39         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
  40         err.span_label(span, "feature has been removed");
  41         if let Some(reason) = reason {
  42             err.note(reason);
  43         }
  44         err.emit();
  45     }
  46
  47     fn active_features_up_to(edition: Edition) -> impl Iterator<Item = &'static Feature> {
  48         ACTIVE_FEATURES.iter().filter(move |feature| {
  49             if let Some(feature_edition) = feature.edition {
  50                 feature_edition <= edition
  51             } else {
  52                 false
  53             }
  54         })
  55     }
  56
  57     let mut features = Features::default();
  58     let mut edition_enabled_features = FxHashMap::default();
  59     let crate_edition = sess.edition();
  60
  61     for &edition in ALL_EDITIONS {
  62         if edition <= crate_edition {
  63             // The `crate_edition` implies its respective umbrella feature-gate
  64             // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
  65             edition_enabled_features.insert(edition.feature_name(), edition);
  66         }
  67     }
  68
  69     for feature in active_features_up_to(crate_edition) {
  70         feature.set(&mut features, DUMMY_SP);
  71         edition_enabled_features.insert(feature.name, crate_edition);
  72     }
  73
  74     // Process the edition umbrella feature-gates first, to ensure
  75     // `edition_enabled_features` is completed before it's queried.
  76     for attr in krate_attrs {
  77         if !sess.check_name(attr, sym::feature) {
  78             continue;
  79         }
  80
  81         let list = match attr.meta_item_list() {
  82             Some(list) => list,
  83             None => continue,
  84         };
  85
  86         for mi in list {
  87             if !mi.is_word() {
  88                 continue;
  89             }
  90
  91             let name = mi.name_or_empty();
  92
  93             let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
  94             if let Some(edition) = edition {
  95                 if edition <= crate_edition {
  96                     continue;
  97                 }
  98
  99                 for feature in active_features_up_to(edition) {
 100                     // FIXME(Manishearth) there is currently no way to set
 101                     // lib features by edition
 102                     feature.set(&mut features, DUMMY_SP);
 103                     edition_enabled_features.insert(feature.name, edition);
 104                 }
 105             }
 106         }
 107     }
 108
 109     for attr in krate_attrs {
 110         if !sess.check_name(attr, sym::feature) {
 111             continue;
 112         }
 113
 114         let list = match attr.meta_item_list() {
 115             Some(list) => list,
 116             None => continue,
 117         };
 118
 119         let bad_input = |span| {
 120             struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
 121         };
 122
 123         for mi in list {
 124             let name = match mi.ident() {
 125                 Some(ident) if mi.is_word() => ident.name,
 126                 Some(ident) => {
 127                     bad_input(mi.span())
 128                         .span_suggestion(
 129                             mi.span(),
 130                             "expected just one word",
 131                             format!("{}", ident.name),
 132                             Applicability::MaybeIncorrect,
 133                         )
 134                         .emit();
 135                     continue;
 136                 }
 137                 None => {
 138                     bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
 139                     continue;
 140                 }
 141             };
 142
 143             if let Some(edition) = edition_enabled_features.get(&name) {
 144                 let msg =
 145                     &format!("the feature `{}` is included in the Rust {} edition", name, edition);
 146                 span_handler.struct_span_warn_with_code(mi.span(), msg, error_code!(E0705)).emit();
 147                 continue;
 148             }
 149
 150             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
 151                 // Handled in the separate loop above.
 152                 continue;
 153             }
 154
 155             let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
 156             let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
 157             if let Some(Feature { state, .. }) = removed.or(stable_removed) {
 158                 if let FeatureState::Removed { reason } | FeatureState::Stabilized { reason } =
 159                     state
 160                 {
 161                     feature_removed(span_handler, mi.span(), *reason);
 162                     continue;
 163                 }
 164             }
 165
 166             if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
 167                 let since = Some(Symbol::intern(since));
 168                 features.declared_lang_features.push((name, mi.span(), since));
 169                 continue;
 170             }
 171
 172             if let Some(allowed) = sess.opts.debugging_opts.allow_features.as_ref() {
 173                 if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
 174                     struct_span_err!(
 175                         span_handler,
 176                         mi.span(),
 177                         E0725,
 178                         "the feature `{}` is not in the list of allowed features",
 179                         name
 180                     )
 181                     .emit();
 182                     continue;
 183                 }
 184             }
 185
 186             if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
 187                 f.set(&mut features, mi.span());
 188                 features.declared_lang_features.push((name, mi.span(), None));
 189                 continue;
 190             }
 191
 192             features.declared_lib_features.push((name, mi.span()));
 193         }
 194     }
 195
 196     features
 197 }
 198
 199 // `cfg_attr`-process the crate's attributes and compute the crate's features.
 200 pub fn features(sess: &Session, mut krate: ast::Crate) -> (ast::Crate, Features) {
 201     let mut strip_unconfigured = StripUnconfigured { sess, features: None };
 202
 203     let unconfigured_attrs = krate.attrs.clone();
 204     let diag = &sess.parse_sess.span_diagnostic;
 205     let err_count = diag.err_count();
 206     let features = match strip_unconfigured.configure(krate.attrs) {
 207         None => {
 208             // The entire crate is unconfigured.
 209             krate.attrs = Vec::new();
 210             krate.module.items = Vec::new();
 211             Features::default()
 212         }
 213         Some(attrs) => {
 214             krate.attrs = attrs;
 215             let features = get_features(sess, diag, &krate.attrs);
 216             if err_count == diag.err_count() {
 217                 // Avoid reconfiguring malformed `cfg_attr`s.
 218                 strip_unconfigured.features = Some(&features);
 219                 strip_unconfigured.configure(unconfigured_attrs);
 220             }
 221             features
 222         }
 223     };
 224     (krate, features)
 225 }
 226
 227 #[macro_export]
 228 macro_rules! configure {
 229     ($this:ident, $node:ident) => {
 230         match $this.configure($node) {
 231             Some(node) => node,
 232             None => return Default::default(),
 233         }
 234     };
 235 }
 236
 237 const CFG_ATTR_GRAMMAR_HELP: &str = "#[cfg_attr(condition, attribute, other_attribute, ...)]";
 238 const CFG_ATTR_NOTE_REF: &str = "for more information, visit \
 239     <https://doc.rust-lang.org/reference/conditional-compilation.html\
 240     #the-cfg_attr-attribute>";
 241
 242 impl<'a> StripUnconfigured<'a> {
 243     pub fn configure<T: HasAttrs>(&mut self, mut node: T) -> Option<T> {
 244         self.process_cfg_attrs(&mut node);
 245         self.in_cfg(node.attrs()).then_some(node)
 246     }
 247
 248     /// Parse and expand all `cfg_attr` attributes into a list of attributes
 249     /// that are within each `cfg_attr` that has a true configuration predicate.
 250     ///
 251     /// Gives compiler warnings if any `cfg_attr` does not contain any
 252     /// attributes and is in the original source code. Gives compiler errors if
 253     /// the syntax of any `cfg_attr` is incorrect.
 254     pub fn process_cfg_attrs<T: HasAttrs>(&mut self, node: &mut T) {
 255         node.visit_attrs(|attrs| {
 256             attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
 257         });
 258     }
 259
 260     /// Parse and expand a single `cfg_attr` attribute into a list of attributes
 261     /// when the configuration predicate is true, or otherwise expand into an
 262     /// empty list of attributes.
 263     ///
 264     /// Gives a compiler warning when the `cfg_attr` contains no attributes and
 265     /// is in the original source file. Gives a compiler error if the syntax of
 266     /// the attribute is incorrect.
 267     fn process_cfg_attr(&mut self, attr: Attribute) -> Vec<Attribute> {
 268         if !attr.has_name(sym::cfg_attr) {
 269             return vec![attr];
 270         }
 271
 272         let (cfg_predicate, expanded_attrs) = match self.parse_cfg_attr(&attr) {
 273             None => return vec![],
 274             Some(r) => r,
 275         };
 276
 277         // Lint on zero attributes in source.
 278         if expanded_attrs.is_empty() {
 279             return vec![attr];
 280         }
 281
 282         // At this point we know the attribute is considered used.
 283         self.sess.mark_attr_used(&attr);
 284
 285         if !attr::cfg_matches(&cfg_predicate, &self.sess.parse_sess, self.features) {
 286             return vec![];
 287         }
 288
 289         // We call `process_cfg_attr` recursively in case there's a
 290         // `cfg_attr` inside of another `cfg_attr`. E.g.
 291         //  `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
 292         expanded_attrs
 293             .into_iter()
 294             .flat_map(|(item, span)| {
 295                 let orig_tokens =
 296                     attr.tokens.as_ref().unwrap_or_else(|| panic!("Missing tokens for {:?}", attr));
 297
 298                 // We are taking an attribute of the form `#[cfg_attr(pred, attr)]`
 299                 // and producing an attribute of the form `#[attr]`. We
 300                 // have captured tokens for `attr` itself, but we need to
 301                 // synthesize tokens for the wrapper `#` and `[]`, which
 302                 // we do below.
 303
 304                 // Use the `#` in `#[cfg_attr(pred, attr)]` as the `#` token
 305                 // for `attr` when we expand it to `#[attr]`
 306                 let pound_token = orig_tokens.into_token_stream().trees().next().unwrap();
 307                 if !matches!(pound_token, TokenTree::Token(Token { kind: TokenKind::Pound, .. })) {
 308                     panic!("Bad tokens for attribute {:?}", attr);
 309                 }
 310                 // We don't really have a good span to use for the syntheized `[]`
 311                 // in `#[attr]`, so just use the span of the `#` token.
 312                 let bracket_group = TokenTree::Delimited(
 313                     DelimSpan::from_single(pound_token.span()),
 314                     DelimToken::Bracket,
 315                     item.tokens
 316                         .clone()
 317                         .unwrap_or_else(|| panic!("Missing tokens for {:?}", item))
 318                         .into_token_stream(),
 319                 );
 320
 321                 let mut attr = attr::mk_attr_from_item(attr.style, item, span);
 322                 attr.tokens = Some(Lrc::new(LazyTokenStreamInner::Ready(TokenStream::new(vec![
 323                     (pound_token, Spacing::Alone),
 324                     (bracket_group, Spacing::Alone),
 325                 ]))));
 326                 self.process_cfg_attr(attr)
 327             })
 328             .collect()
 329     }
 330
 331     fn parse_cfg_attr(&self, attr: &Attribute) -> Option<(MetaItem, Vec<(AttrItem, Span)>)> {
 332         match attr.get_normal_item().args {
 333             ast::MacArgs::Delimited(dspan, delim, ref tts) if !tts.is_empty() => {
 334                 let msg = "wrong `cfg_attr` delimiters";
 335                 validate_attr::check_meta_bad_delim(&self.sess.parse_sess, dspan, delim, msg);
 336                 match parse_in(&self.sess.parse_sess, tts.clone(), "`cfg_attr` input", |p| {
 337                     p.parse_cfg_attr()
 338                 }) {
 339                     Ok(r) => return Some(r),
 340                     Err(mut e) => {
 341                         e.help(&format!("the valid syntax is `{}`", CFG_ATTR_GRAMMAR_HELP))
 342                             .note(CFG_ATTR_NOTE_REF)
 343                             .emit();
 344                     }
 345                 }
 346             }
 347             _ => self.error_malformed_cfg_attr_missing(attr.span),
 348         }
 349         None
 350     }
 351
 352     fn error_malformed_cfg_attr_missing(&self, span: Span) {
 353         self.sess
 354             .parse_sess
 355             .span_diagnostic
 356             .struct_span_err(span, "malformed `cfg_attr` attribute input")
 357             .span_suggestion(
 358                 span,
 359                 "missing condition and attribute",
 360                 CFG_ATTR_GRAMMAR_HELP.to_string(),
 361                 Applicability::HasPlaceholders,
 362             )
 363             .note(CFG_ATTR_NOTE_REF)
 364             .emit();
 365     }
 366
 367     /// Determines if a node with the given attributes should be included in this configuration.
 368     pub fn in_cfg(&self, attrs: &[Attribute]) -> bool {
 369         attrs.iter().all(|attr| {
 370             if !is_cfg(self.sess, attr) {
 371                 return true;
 372             }
 373             let meta_item = match validate_attr::parse_meta(&self.sess.parse_sess, attr) {
 374                 Ok(meta_item) => meta_item,
 375                 Err(mut err) => {
 376                     err.emit();
 377                     return true;
 378                 }
 379             };
 380             let error = |span, msg, suggestion: &str| {
 381                 let mut err = self.sess.parse_sess.span_diagnostic.struct_span_err(span, msg);
 382                 if !suggestion.is_empty() {
 383                     err.span_suggestion(
 384                         span,
 385                         "expected syntax is",
 386                         suggestion.into(),
 387                         Applicability::MaybeIncorrect,
 388                     );
 389                 }
 390                 err.emit();
 391                 true
 392             };
 393             let span = meta_item.span;
 394             match meta_item.meta_item_list() {
 395                 None => error(span, "`cfg` is not followed by parentheses", "cfg(/* predicate */)"),
 396                 Some([]) => error(span, "`cfg` predicate is not specified", ""),
 397                 Some([_, .., l]) => error(l.span(), "multiple `cfg` predicates are specified", ""),
 398                 Some([single]) => match single.meta_item() {
 399                     Some(meta_item) => {
 400                         attr::cfg_matches(meta_item, &self.sess.parse_sess, self.features)
 401                     }
 402                     None => error(single.span(), "`cfg` predicate key cannot be a literal", ""),
 403                 },
 404             }
 405         })
 406     }
 407
 408     /// Visit attributes on expression and statements (but not attributes on items in blocks).
 409     fn visit_expr_attrs(&mut self, attrs: &[Attribute]) {
 410         // flag the offending attributes
 411         for attr in attrs.iter() {
 412             self.maybe_emit_expr_attr_err(attr);
 413         }
 414     }
 415
 416     /// If attributes are not allowed on expressions, emit an error for `attr`
 417     pub fn maybe_emit_expr_attr_err(&self, attr: &Attribute) {
 418         if !self.features.map(|features| features.stmt_expr_attributes).unwrap_or(true) {
 419             let mut err = feature_err(
 420                 &self.sess.parse_sess,
 421                 sym::stmt_expr_attributes,
 422                 attr.span,
 423                 "attributes on expressions are experimental",
 424             );
 425
 426             if attr.is_doc_comment() {
 427                 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
 428             }
 429
 430             err.emit();
 431         }
 432     }
 433
 434     pub fn configure_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
 435         let ast::ForeignMod { unsafety: _, abi: _, items } = foreign_mod;
 436         items.flat_map_in_place(|item| self.configure(item));
 437     }
 438
 439     fn configure_variant_data(&mut self, vdata: &mut ast::VariantData) {
 440         match vdata {
 441             ast::VariantData::Struct(fields, ..) | ast::VariantData::Tuple(fields, _) => {
 442                 fields.flat_map_in_place(|field| self.configure(field))
 443             }
 444             ast::VariantData::Unit(_) => {}
 445         }
 446     }
 447
 448     pub fn configure_item_kind(&mut self, item: &mut ast::ItemKind) {
 449         match item {
 450             ast::ItemKind::Struct(def, _generics) | ast::ItemKind::Union(def, _generics) => {
 451                 self.configure_variant_data(def)
 452             }
 453             ast::ItemKind::Enum(ast::EnumDef { variants }, _generics) => {
 454                 variants.flat_map_in_place(|variant| self.configure(variant));
 455                 for variant in variants {
 456                     self.configure_variant_data(&mut variant.data);
 457                 }
 458             }
 459             _ => {}
 460         }
 461     }
 462
 463     pub fn configure_expr_kind(&mut self, expr_kind: &mut ast::ExprKind) {
 464         match expr_kind {
 465             ast::ExprKind::Match(_m, arms) => {
 466                 arms.flat_map_in_place(|arm| self.configure(arm));
 467             }
 468             ast::ExprKind::Struct(_path, fields, _base) => {
 469                 fields.flat_map_in_place(|field| self.configure(field));
 470             }
 471             _ => {}
 472         }
 473     }
 474
 475     pub fn configure_expr(&mut self, expr: &mut P<ast::Expr>) {
 476         self.visit_expr_attrs(expr.attrs());
 477
 478         // If an expr is valid to cfg away it will have been removed by the
 479         // outer stmt or expression folder before descending in here.
 480         // Anything else is always required, and thus has to error out
 481         // in case of a cfg attr.
 482         //
 483         // N.B., this is intentionally not part of the visit_expr() function
 484         //     in order for filter_map_expr() to be able to avoid this check
 485         if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(self.sess, a)) {
 486             let msg = "removing an expression is not supported in this position";
 487             self.sess.parse_sess.span_diagnostic.span_err(attr.span, msg);
 488         }
 489
 490         self.process_cfg_attrs(expr)
 491     }
 492
 493     pub fn configure_pat(&mut self, pat: &mut P<ast::Pat>) {
 494         if let ast::PatKind::Struct(_path, fields, _etc) = &mut pat.kind {
 495             fields.flat_map_in_place(|field| self.configure(field));
 496         }
 497     }
 498
 499     pub fn configure_fn_decl(&mut self, fn_decl: &mut ast::FnDecl) {
 500         fn_decl.inputs.flat_map_in_place(|arg| self.configure(arg));
 501     }
 502 }
 503
 504 impl<'a> MutVisitor for StripUnconfigured<'a> {
 505     fn visit_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
 506         self.configure_foreign_mod(foreign_mod);
 507         noop_visit_foreign_mod(foreign_mod, self);
 508     }
 509
 510     fn visit_item_kind(&mut self, item: &mut ast::ItemKind) {
 511         self.configure_item_kind(item);
 512         noop_visit_item_kind(item, self);
 513     }
 514
 515     fn visit_expr(&mut self, expr: &mut P<ast::Expr>) {
 516         self.configure_expr(expr);
 517         self.configure_expr_kind(&mut expr.kind);
 518         noop_visit_expr(expr, self);
 519     }
 520
 521     fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
 522         let mut expr = configure!(self, expr);
 523         self.configure_expr_kind(&mut expr.kind);
 524         noop_visit_expr(&mut expr, self);
 525         Some(expr)
 526     }
 527
 528     fn flat_map_generic_param(
 529         &mut self,
 530         param: ast::GenericParam,
 531     ) -> SmallVec<[ast::GenericParam; 1]> {
 532         noop_flat_map_generic_param(configure!(self, param), self)
 533     }
 534
 535     fn flat_map_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
 536         noop_flat_map_stmt(configure!(self, stmt), self)
 537     }
 538
 539     fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
 540         noop_flat_map_item(configure!(self, item), self)
 541     }
 542
 543     fn flat_map_impl_item(&mut self, item: P<ast::AssocItem>) -> SmallVec<[P<ast::AssocItem>; 1]> {
 544         noop_flat_map_assoc_item(configure!(self, item), self)
 545     }
 546
 547     fn flat_map_trait_item(&mut self, item: P<ast::AssocItem>) -> SmallVec<[P<ast::AssocItem>; 1]> {
 548         noop_flat_map_assoc_item(configure!(self, item), self)
 549     }
 550
 551     fn visit_mac(&mut self, _mac: &mut ast::MacCall) {
 552         // Don't configure interpolated AST (cf. issue #34171).
 553         // Interpolated AST will get configured once the surrounding tokens are parsed.
 554     }
 555
 556     fn visit_pat(&mut self, pat: &mut P<ast::Pat>) {
 557         self.configure_pat(pat);
 558         noop_visit_pat(pat, self)
 559     }
 560
 561     fn visit_fn_decl(&mut self, mut fn_decl: &mut P<ast::FnDecl>) {
 562         self.configure_fn_decl(&mut fn_decl);
 563         noop_visit_fn_decl(fn_decl, self);
 564     }
 565 }
 566
 567 fn is_cfg(sess: &Session, attr: &Attribute) -> bool {
 568     sess.check_name(attr, sym::cfg)
 569 }