1 //! Conditional compilation stripping.
4 FeatureIncludedInEdition, FeatureNotAllowed, FeatureRemoved, FeatureRemovedReason, InvalidCfg,
5 MalformedFeatureAttribute, MalformedFeatureAttributeHelp, RemoveExprNotSupported,
8 use rustc_ast::token::{Delimiter, Token, TokenKind};
9 use rustc_ast::tokenstream::{AttrTokenStream, AttrTokenTree};
10 use rustc_ast::tokenstream::{DelimSpan, Spacing};
11 use rustc_ast::tokenstream::{LazyAttrTokenStream, TokenTree};
12 use rustc_ast::NodeId;
13 use rustc_ast::{self as ast, AttrStyle, Attribute, HasAttrs, HasTokens, MetaItem};
14 use rustc_attr as attr;
15 use rustc_data_structures::fx::FxHashMap;
16 use rustc_data_structures::map_in_place::MapInPlace;
17 use rustc_feature::{Feature, Features, State as FeatureState};
19 ACCEPTED_FEATURES, ACTIVE_FEATURES, REMOVED_FEATURES, STABLE_REMOVED_FEATURES,
21 use rustc_parse::validate_attr;
22 use rustc_session::parse::feature_err;
23 use rustc_session::Session;
24 use rustc_span::edition::{Edition, ALL_EDITIONS};
25 use rustc_span::symbol::{sym, Symbol};
26 use rustc_span::{Span, DUMMY_SP};
28 /// A folder that strips out items that do not belong in the current configuration.
29 pub struct StripUnconfigured<'a> {
30 pub sess: &'a Session,
31 pub features: Option<&'a Features>,
32 /// If `true`, perform cfg-stripping on attached tokens.
33 /// This is only used for the input to derive macros,
34 /// which needs eager expansion of `cfg` and `cfg_attr`
35 pub config_tokens: bool,
36 pub lint_node_id: NodeId,
39 fn get_features(sess: &Session, krate_attrs: &[ast::Attribute]) -> Features {
40 fn feature_removed(sess: &Session, span: Span, reason: Option<&str>) {
41 sess.emit_err(FeatureRemoved {
43 reason: reason.map(|reason| FeatureRemovedReason { reason }),
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
57 let mut features = Features::default();
58 let mut edition_enabled_features = FxHashMap::default();
59 let crate_edition = sess.edition();
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);
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);
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 !attr.has_name(sym::feature) {
81 let Some(list) = attr.meta_item_list() else {
90 let name = mi.name_or_empty();
92 let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
93 if let Some(edition) = edition {
94 if edition <= crate_edition {
98 for feature in active_features_up_to(edition) {
99 // FIXME(Manishearth) there is currently no way to set
100 // lib features by edition
101 feature.set(&mut features, DUMMY_SP);
102 edition_enabled_features.insert(feature.name, edition);
108 for attr in krate_attrs {
109 if !attr.has_name(sym::feature) {
113 let Some(list) = attr.meta_item_list() else {
118 let name = match mi.ident() {
119 Some(ident) if mi.is_word() => ident.name,
121 sess.emit_err(MalformedFeatureAttribute {
123 help: MalformedFeatureAttributeHelp::Suggestion {
125 suggestion: ident.name,
131 sess.emit_err(MalformedFeatureAttribute {
133 help: MalformedFeatureAttributeHelp::Label { span: mi.span() },
139 if let Some(&edition) = edition_enabled_features.get(&name) {
140 sess.emit_warning(FeatureIncludedInEdition {
148 if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
149 // Handled in the separate loop above.
153 let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
154 let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
155 if let Some(Feature { state, .. }) = removed.or(stable_removed) {
156 if let FeatureState::Removed { reason } | FeatureState::Stabilized { reason } =
159 feature_removed(sess, mi.span(), *reason);
164 if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
165 let since = Some(Symbol::intern(since));
166 features.declared_lang_features.push((name, mi.span(), since));
167 features.active_features.insert(name);
171 if let Some(allowed) = sess.opts.unstable_opts.allow_features.as_ref() {
172 if allowed.iter().all(|f| name.as_str() != f) {
173 sess.emit_err(FeatureNotAllowed { span: mi.span(), name });
178 if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
179 f.set(&mut features, mi.span());
180 features.declared_lang_features.push((name, mi.span(), None));
181 features.active_features.insert(name);
185 features.declared_lib_features.push((name, mi.span()));
186 features.active_features.insert(name);
193 /// `cfg_attr`-process the crate's attributes and compute the crate's features.
196 mut krate: ast::Crate,
197 lint_node_id: NodeId,
198 ) -> (ast::Crate, Features) {
199 let mut strip_unconfigured =
200 StripUnconfigured { sess, features: None, config_tokens: false, lint_node_id };
202 let unconfigured_attrs = krate.attrs.clone();
203 let diag = &sess.parse_sess.span_diagnostic;
204 let err_count = diag.err_count();
205 let features = match strip_unconfigured.configure_krate_attrs(krate.attrs) {
207 // The entire crate is unconfigured.
208 krate.attrs = ast::AttrVec::new();
209 krate.items = Vec::new();
214 let features = get_features(sess, &krate.attrs);
215 if err_count == diag.err_count() {
216 // Avoid reconfiguring malformed `cfg_attr`s.
217 strip_unconfigured.features = Some(&features);
218 // Run configuration again, this time with features available
219 // so that we can perform feature-gating.
220 strip_unconfigured.configure_krate_attrs(unconfigured_attrs);
229 macro_rules! configure {
230 ($this:ident, $node:ident) => {
231 match $this.configure($node) {
233 None => return Default::default(),
238 impl<'a> StripUnconfigured<'a> {
239 pub fn configure<T: HasAttrs + HasTokens>(&self, mut node: T) -> Option<T> {
240 self.process_cfg_attrs(&mut node);
241 if self.in_cfg(node.attrs()) {
242 self.try_configure_tokens(&mut node);
249 fn try_configure_tokens<T: HasTokens>(&self, node: &mut T) {
250 if self.config_tokens {
251 if let Some(Some(tokens)) = node.tokens_mut() {
252 let attr_stream = tokens.to_attr_token_stream();
253 *tokens = LazyAttrTokenStream::new(self.configure_tokens(&attr_stream));
258 fn configure_krate_attrs(&self, mut attrs: ast::AttrVec) -> Option<ast::AttrVec> {
259 attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
260 if self.in_cfg(&attrs) { Some(attrs) } else { None }
263 /// Performs cfg-expansion on `stream`, producing a new `AttrTokenStream`.
264 /// This is only used during the invocation of `derive` proc-macros,
265 /// which require that we cfg-expand their entire input.
266 /// Normal cfg-expansion operates on parsed AST nodes via the `configure` method
267 fn configure_tokens(&self, stream: &AttrTokenStream) -> AttrTokenStream {
268 fn can_skip(stream: &AttrTokenStream) -> bool {
269 stream.0.iter().all(|tree| match tree {
270 AttrTokenTree::Attributes(_) => false,
271 AttrTokenTree::Token(..) => true,
272 AttrTokenTree::Delimited(_, _, inner) => can_skip(inner),
276 if can_skip(stream) {
277 return stream.clone();
280 let trees: Vec<_> = stream
283 .flat_map(|tree| match tree.clone() {
284 AttrTokenTree::Attributes(mut data) => {
285 data.attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
287 if self.in_cfg(&data.attrs) {
288 data.tokens = LazyAttrTokenStream::new(
289 self.configure_tokens(&data.tokens.to_attr_token_stream()),
291 Some(AttrTokenTree::Attributes(data)).into_iter()
296 AttrTokenTree::Delimited(sp, delim, mut inner) => {
297 inner = self.configure_tokens(&inner);
298 Some(AttrTokenTree::Delimited(sp, delim, inner))
301 AttrTokenTree::Token(ref token, _) if let TokenKind::Interpolated(ref nt) = token.kind => {
303 "Nonterminal should have been flattened at {:?}: {:?}",
307 AttrTokenTree::Token(token, spacing) => {
308 Some(AttrTokenTree::Token(token, spacing)).into_iter()
312 AttrTokenStream::new(trees)
315 /// Parse and expand all `cfg_attr` attributes into a list of attributes
316 /// that are within each `cfg_attr` that has a true configuration predicate.
318 /// Gives compiler warnings if any `cfg_attr` does not contain any
319 /// attributes and is in the original source code. Gives compiler errors if
320 /// the syntax of any `cfg_attr` is incorrect.
321 fn process_cfg_attrs<T: HasAttrs>(&self, node: &mut T) {
322 node.visit_attrs(|attrs| {
323 attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
327 fn process_cfg_attr(&self, attr: Attribute) -> Vec<Attribute> {
328 if attr.has_name(sym::cfg_attr) { self.expand_cfg_attr(attr, true) } else { vec![attr] }
331 /// Parse and expand a single `cfg_attr` attribute into a list of attributes
332 /// when the configuration predicate is true, or otherwise expand into an
333 /// empty list of attributes.
335 /// Gives a compiler warning when the `cfg_attr` contains no attributes and
336 /// is in the original source file. Gives a compiler error if the syntax of
337 /// the attribute is incorrect.
338 pub(crate) fn expand_cfg_attr(&self, attr: Attribute, recursive: bool) -> Vec<Attribute> {
339 let Some((cfg_predicate, expanded_attrs)) =
340 rustc_parse::parse_cfg_attr(&attr, &self.sess.parse_sess) else {
344 // Lint on zero attributes in source.
345 if expanded_attrs.is_empty() {
346 self.sess.parse_sess.buffer_lint(
347 rustc_lint_defs::builtin::UNUSED_ATTRIBUTES,
350 "`#[cfg_attr]` does not expand to any attributes",
354 if !attr::cfg_matches(
356 &self.sess.parse_sess,
364 // We call `process_cfg_attr` recursively in case there's a
365 // `cfg_attr` inside of another `cfg_attr`. E.g.
366 // `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
369 .flat_map(|item| self.process_cfg_attr(self.expand_cfg_attr_item(&attr, item)))
372 expanded_attrs.into_iter().map(|item| self.expand_cfg_attr_item(&attr, item)).collect()
376 fn expand_cfg_attr_item(
379 (item, item_span): (ast::AttrItem, Span),
381 let orig_tokens = attr.tokens();
383 // We are taking an attribute of the form `#[cfg_attr(pred, attr)]`
384 // and producing an attribute of the form `#[attr]`. We
385 // have captured tokens for `attr` itself, but we need to
386 // synthesize tokens for the wrapper `#` and `[]`, which
389 // Use the `#` in `#[cfg_attr(pred, attr)]` as the `#` token
390 // for `attr` when we expand it to `#[attr]`
391 let mut orig_trees = orig_tokens.into_trees();
392 let TokenTree::Token(pound_token @ Token { kind: TokenKind::Pound, .. }, _) = orig_trees.next().unwrap() else {
393 panic!("Bad tokens for attribute {:?}", attr);
395 let pound_span = pound_token.span;
397 let mut trees = vec![AttrTokenTree::Token(pound_token, Spacing::Alone)];
398 if attr.style == AttrStyle::Inner {
399 // For inner attributes, we do the same thing for the `!` in `#![some_attr]`
400 let TokenTree::Token(bang_token @ Token { kind: TokenKind::Not, .. }, _) = orig_trees.next().unwrap() else {
401 panic!("Bad tokens for attribute {:?}", attr);
403 trees.push(AttrTokenTree::Token(bang_token, Spacing::Alone));
405 // We don't really have a good span to use for the synthesized `[]`
406 // in `#[attr]`, so just use the span of the `#` token.
407 let bracket_group = AttrTokenTree::Delimited(
408 DelimSpan::from_single(pound_span),
412 .unwrap_or_else(|| panic!("Missing tokens for {:?}", item))
413 .to_attr_token_stream(),
415 trees.push(bracket_group);
416 let tokens = Some(LazyAttrTokenStream::new(AttrTokenStream::new(trees)));
417 let attr = attr::mk_attr_from_item(
418 &self.sess.parse_sess.attr_id_generator,
424 if attr.has_name(sym::crate_type) {
425 self.sess.parse_sess.buffer_lint(
426 rustc_lint_defs::builtin::DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
429 "`crate_type` within an `#![cfg_attr] attribute is deprecated`",
432 if attr.has_name(sym::crate_name) {
433 self.sess.parse_sess.buffer_lint(
434 rustc_lint_defs::builtin::DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
437 "`crate_name` within an `#![cfg_attr] attribute is deprecated`",
443 /// Determines if a node with the given attributes should be included in this configuration.
444 fn in_cfg(&self, attrs: &[Attribute]) -> bool {
445 attrs.iter().all(|attr| !is_cfg(attr) || self.cfg_true(attr))
448 pub(crate) fn cfg_true(&self, attr: &Attribute) -> bool {
449 let meta_item = match validate_attr::parse_meta(&self.sess.parse_sess, attr) {
450 Ok(meta_item) => meta_item,
456 parse_cfg(&meta_item, &self.sess).map_or(true, |meta_item| {
457 attr::cfg_matches(&meta_item, &self.sess.parse_sess, self.lint_node_id, self.features)
461 /// If attributes are not allowed on expressions, emit an error for `attr`
462 #[instrument(level = "trace", skip(self))]
463 pub(crate) fn maybe_emit_expr_attr_err(&self, attr: &Attribute) {
464 if !self.features.map_or(true, |features| features.stmt_expr_attributes) {
465 let mut err = feature_err(
466 &self.sess.parse_sess,
467 sym::stmt_expr_attributes,
469 "attributes on expressions are experimental",
472 if attr.is_doc_comment() {
473 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
480 #[instrument(level = "trace", skip(self))]
481 pub fn configure_expr(&self, expr: &mut P<ast::Expr>, method_receiver: bool) {
482 if !method_receiver {
483 for attr in expr.attrs.iter() {
484 self.maybe_emit_expr_attr_err(attr);
488 // If an expr is valid to cfg away it will have been removed by the
489 // outer stmt or expression folder before descending in here.
490 // Anything else is always required, and thus has to error out
491 // in case of a cfg attr.
493 // N.B., this is intentionally not part of the visit_expr() function
494 // in order for filter_map_expr() to be able to avoid this check
495 if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(*a)) {
496 self.sess.emit_err(RemoveExprNotSupported { span: attr.span });
499 self.process_cfg_attrs(expr);
500 self.try_configure_tokens(&mut *expr);
504 pub fn parse_cfg<'a>(meta_item: &'a MetaItem, sess: &Session) -> Option<&'a MetaItem> {
505 let span = meta_item.span;
506 match meta_item.meta_item_list() {
508 sess.emit_err(InvalidCfg::NotFollowedByParens { span });
512 sess.emit_err(InvalidCfg::NoPredicate { span });
515 Some([_, .., l]) => {
516 sess.emit_err(InvalidCfg::MultiplePredicates { span: l.span() });
519 Some([single]) => match single.meta_item() {
520 Some(meta_item) => Some(meta_item),
522 sess.emit_err(InvalidCfg::PredicateLiteral { span: single.span() });
529 fn is_cfg(attr: &Attribute) -> bool {
530 attr.has_name(sym::cfg)