1 //! Conditional compilation stripping.
4 use rustc_ast::token::{Delimiter, Token, TokenKind};
5 use rustc_ast::tokenstream::{AttrAnnotatedTokenStream, AttrAnnotatedTokenTree};
6 use rustc_ast::tokenstream::{DelimSpan, Spacing};
7 use rustc_ast::tokenstream::{LazyTokenStream, TokenTree};
9 use rustc_ast::{self as ast, AttrStyle, Attribute, HasAttrs, HasTokens, MetaItem};
10 use rustc_attr as attr;
11 use rustc_data_structures::fx::FxHashMap;
12 use rustc_data_structures::map_in_place::MapInPlace;
13 use rustc_errors::{error_code, struct_span_err, Applicability, Handler};
14 use rustc_feature::{Feature, Features, State as FeatureState};
16 ACCEPTED_FEATURES, ACTIVE_FEATURES, REMOVED_FEATURES, STABLE_REMOVED_FEATURES,
18 use rustc_parse::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};
25 /// A folder that strips out items that do not belong in the current configuration.
26 pub struct StripUnconfigured<'a> {
27 pub sess: &'a Session,
28 pub features: Option<&'a Features>,
29 /// If `true`, perform cfg-stripping on attached tokens.
30 /// This is only used for the input to derive macros,
31 /// which needs eager expansion of `cfg` and `cfg_attr`
32 pub config_tokens: bool,
33 pub lint_node_id: NodeId,
38 span_handler: &Handler,
39 krate_attrs: &[ast::Attribute],
41 fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
42 let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
43 err.span_label(span, "feature has been removed");
44 if let Some(reason) = reason {
50 fn active_features_up_to(edition: Edition) -> impl Iterator<Item = &'static Feature> {
51 ACTIVE_FEATURES.iter().filter(move |feature| {
52 if let Some(feature_edition) = feature.edition {
53 feature_edition <= edition
60 let mut features = Features::default();
61 let mut edition_enabled_features = FxHashMap::default();
62 let crate_edition = sess.edition();
64 for &edition in ALL_EDITIONS {
65 if edition <= crate_edition {
66 // The `crate_edition` implies its respective umbrella feature-gate
67 // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
68 edition_enabled_features.insert(edition.feature_name(), edition);
72 for feature in active_features_up_to(crate_edition) {
73 feature.set(&mut features, DUMMY_SP);
74 edition_enabled_features.insert(feature.name, crate_edition);
77 // Process the edition umbrella feature-gates first, to ensure
78 // `edition_enabled_features` is completed before it's queried.
79 for attr in krate_attrs {
80 if !attr.has_name(sym::feature) {
84 let Some(list) = attr.meta_item_list() else {
93 let name = mi.name_or_empty();
95 let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
96 if let Some(edition) = edition {
97 if edition <= crate_edition {
101 for feature in active_features_up_to(edition) {
102 // FIXME(Manishearth) there is currently no way to set
103 // lib features by edition
104 feature.set(&mut features, DUMMY_SP);
105 edition_enabled_features.insert(feature.name, edition);
111 for attr in krate_attrs {
112 if !attr.has_name(sym::feature) {
116 let Some(list) = attr.meta_item_list() else {
120 let bad_input = |span| {
121 struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
125 let name = match mi.ident() {
126 Some(ident) if mi.is_word() => ident.name,
131 "expected just one word",
132 format!("{}", ident.name),
133 Applicability::MaybeIncorrect,
139 bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
144 if let Some(edition) = edition_enabled_features.get(&name) {
146 &format!("the feature `{}` is included in the Rust {} edition", name, edition);
147 span_handler.struct_span_warn_with_code(mi.span(), msg, error_code!(E0705)).emit();
151 if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
152 // Handled in the separate loop above.
156 let removed = REMOVED_FEATURES.iter().find(|f| name == f.name);
157 let stable_removed = STABLE_REMOVED_FEATURES.iter().find(|f| name == f.name);
158 if let Some(Feature { state, .. }) = removed.or(stable_removed) {
159 if let FeatureState::Removed { reason } | FeatureState::Stabilized { reason } =
162 feature_removed(span_handler, mi.span(), *reason);
167 if let Some(Feature { since, .. }) = ACCEPTED_FEATURES.iter().find(|f| name == f.name) {
168 let since = Some(Symbol::intern(since));
169 features.declared_lang_features.push((name, mi.span(), since));
170 features.active_features.insert(name);
174 if let Some(allowed) = sess.opts.unstable_opts.allow_features.as_ref() {
175 if allowed.iter().all(|f| name.as_str() != f) {
180 "the feature `{}` is not in the list of allowed features",
188 if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
189 f.set(&mut features, mi.span());
190 features.declared_lang_features.push((name, mi.span(), None));
191 features.active_features.insert(name);
195 features.declared_lib_features.push((name, mi.span()));
196 features.active_features.insert(name);
203 // `cfg_attr`-process the crate's attributes and compute the crate's features.
206 mut krate: ast::Crate,
207 lint_node_id: NodeId,
208 ) -> (ast::Crate, Features) {
209 let mut strip_unconfigured =
210 StripUnconfigured { sess, features: None, config_tokens: false, lint_node_id };
212 let unconfigured_attrs = krate.attrs.clone();
213 let diag = &sess.parse_sess.span_diagnostic;
214 let err_count = diag.err_count();
215 let features = match strip_unconfigured.configure_krate_attrs(krate.attrs) {
217 // The entire crate is unconfigured.
218 krate.attrs = Vec::new();
219 krate.items = Vec::new();
224 let features = get_features(sess, diag, &krate.attrs);
225 if err_count == diag.err_count() {
226 // Avoid reconfiguring malformed `cfg_attr`s.
227 strip_unconfigured.features = Some(&features);
228 // Run configuration again, this time with features available
229 // so that we can perform feature-gating.
230 strip_unconfigured.configure_krate_attrs(unconfigured_attrs);
239 macro_rules! configure {
240 ($this:ident, $node:ident) => {
241 match $this.configure($node) {
243 None => return Default::default(),
248 impl<'a> StripUnconfigured<'a> {
249 pub fn configure<T: HasAttrs + HasTokens>(&self, mut node: T) -> Option<T> {
250 self.process_cfg_attrs(&mut node);
251 if self.in_cfg(node.attrs()) {
252 self.try_configure_tokens(&mut node);
259 fn try_configure_tokens<T: HasTokens>(&self, node: &mut T) {
260 if self.config_tokens {
261 if let Some(Some(tokens)) = node.tokens_mut() {
262 let attr_annotated_tokens = tokens.create_token_stream();
263 *tokens = LazyTokenStream::new(self.configure_tokens(&attr_annotated_tokens));
268 fn configure_krate_attrs(&self, mut attrs: Vec<ast::Attribute>) -> Option<Vec<ast::Attribute>> {
269 attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
270 if self.in_cfg(&attrs) { Some(attrs) } else { None }
273 /// Performs cfg-expansion on `stream`, producing a new `AttrAnnotatedTokenStream`.
274 /// This is only used during the invocation of `derive` proc-macros,
275 /// which require that we cfg-expand their entire input.
276 /// Normal cfg-expansion operates on parsed AST nodes via the `configure` method
277 fn configure_tokens(&self, stream: &AttrAnnotatedTokenStream) -> AttrAnnotatedTokenStream {
278 fn can_skip(stream: &AttrAnnotatedTokenStream) -> bool {
279 stream.0.iter().all(|(tree, _spacing)| match tree {
280 AttrAnnotatedTokenTree::Attributes(_) => false,
281 AttrAnnotatedTokenTree::Token(_) => true,
282 AttrAnnotatedTokenTree::Delimited(_, _, inner) => can_skip(inner),
286 if can_skip(stream) {
287 return stream.clone();
290 let trees: Vec<_> = stream
293 .flat_map(|(tree, spacing)| match tree.clone() {
294 AttrAnnotatedTokenTree::Attributes(mut data) => {
295 let mut attrs: Vec<_> = std::mem::take(&mut data.attrs).into();
296 attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
297 data.attrs = attrs.into();
299 if self.in_cfg(&data.attrs) {
300 data.tokens = LazyTokenStream::new(
301 self.configure_tokens(&data.tokens.create_token_stream()),
303 Some((AttrAnnotatedTokenTree::Attributes(data), *spacing)).into_iter()
308 AttrAnnotatedTokenTree::Delimited(sp, delim, mut inner) => {
309 inner = self.configure_tokens(&inner);
310 Some((AttrAnnotatedTokenTree::Delimited(sp, delim, inner), *spacing))
313 AttrAnnotatedTokenTree::Token(ref token) if let TokenKind::Interpolated(ref nt) = token.kind => {
315 "Nonterminal should have been flattened at {:?}: {:?}",
319 AttrAnnotatedTokenTree::Token(token) => {
320 Some((AttrAnnotatedTokenTree::Token(token), *spacing)).into_iter()
324 AttrAnnotatedTokenStream::new(trees)
327 /// Parse and expand all `cfg_attr` attributes into a list of attributes
328 /// that are within each `cfg_attr` that has a true configuration predicate.
330 /// Gives compiler warnings if any `cfg_attr` does not contain any
331 /// attributes and is in the original source code. Gives compiler errors if
332 /// the syntax of any `cfg_attr` is incorrect.
333 fn process_cfg_attrs<T: HasAttrs>(&self, node: &mut T) {
334 node.visit_attrs(|attrs| {
335 attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
339 fn process_cfg_attr(&self, attr: Attribute) -> Vec<Attribute> {
340 if attr.has_name(sym::cfg_attr) { self.expand_cfg_attr(attr, true) } else { vec![attr] }
343 /// Parse and expand a single `cfg_attr` attribute into a list of attributes
344 /// when the configuration predicate is true, or otherwise expand into an
345 /// empty list of attributes.
347 /// Gives a compiler warning when the `cfg_attr` contains no attributes and
348 /// is in the original source file. Gives a compiler error if the syntax of
349 /// the attribute is incorrect.
350 pub(crate) fn expand_cfg_attr(&self, attr: Attribute, recursive: bool) -> Vec<Attribute> {
351 let Some((cfg_predicate, expanded_attrs)) =
352 rustc_parse::parse_cfg_attr(&attr, &self.sess.parse_sess) else {
356 // Lint on zero attributes in source.
357 if expanded_attrs.is_empty() {
358 self.sess.parse_sess.buffer_lint(
359 rustc_lint_defs::builtin::UNUSED_ATTRIBUTES,
362 "`#[cfg_attr]` does not expand to any attributes",
366 if !attr::cfg_matches(
368 &self.sess.parse_sess,
376 // We call `process_cfg_attr` recursively in case there's a
377 // `cfg_attr` inside of another `cfg_attr`. E.g.
378 // `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
381 .flat_map(|item| self.process_cfg_attr(self.expand_cfg_attr_item(&attr, item)))
384 expanded_attrs.into_iter().map(|item| self.expand_cfg_attr_item(&attr, item)).collect()
388 fn expand_cfg_attr_item(
391 (item, item_span): (ast::AttrItem, Span),
393 let orig_tokens = attr.tokens().to_tokenstream();
395 // We are taking an attribute of the form `#[cfg_attr(pred, attr)]`
396 // and producing an attribute of the form `#[attr]`. We
397 // have captured tokens for `attr` itself, but we need to
398 // synthesize tokens for the wrapper `#` and `[]`, which
401 // Use the `#` in `#[cfg_attr(pred, attr)]` as the `#` token
402 // for `attr` when we expand it to `#[attr]`
403 let mut orig_trees = orig_tokens.into_trees();
404 let TokenTree::Token(pound_token @ Token { kind: TokenKind::Pound, .. }, _) = orig_trees.next().unwrap() else {
405 panic!("Bad tokens for attribute {:?}", attr);
407 let pound_span = pound_token.span;
409 let mut trees = vec![(AttrAnnotatedTokenTree::Token(pound_token), Spacing::Alone)];
410 if attr.style == AttrStyle::Inner {
411 // For inner attributes, we do the same thing for the `!` in `#![some_attr]`
412 let TokenTree::Token(bang_token @ Token { kind: TokenKind::Not, .. }, _) = orig_trees.next().unwrap() else {
413 panic!("Bad tokens for attribute {:?}", attr);
415 trees.push((AttrAnnotatedTokenTree::Token(bang_token), Spacing::Alone));
417 // We don't really have a good span to use for the synthesized `[]`
418 // in `#[attr]`, so just use the span of the `#` token.
419 let bracket_group = AttrAnnotatedTokenTree::Delimited(
420 DelimSpan::from_single(pound_span),
424 .unwrap_or_else(|| panic!("Missing tokens for {:?}", item))
425 .create_token_stream(),
427 trees.push((bracket_group, Spacing::Alone));
428 let tokens = Some(LazyTokenStream::new(AttrAnnotatedTokenStream::new(trees)));
429 let attr = attr::mk_attr_from_item(item, tokens, attr.style, item_span);
430 if attr.has_name(sym::crate_type) {
431 self.sess.parse_sess.buffer_lint(
432 rustc_lint_defs::builtin::DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
435 "`crate_type` within an `#![cfg_attr] attribute is deprecated`",
438 if attr.has_name(sym::crate_name) {
439 self.sess.parse_sess.buffer_lint(
440 rustc_lint_defs::builtin::DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
443 "`crate_name` within an `#![cfg_attr] attribute is deprecated`",
449 /// Determines if a node with the given attributes should be included in this configuration.
450 fn in_cfg(&self, attrs: &[Attribute]) -> bool {
451 attrs.iter().all(|attr| !is_cfg(attr) || self.cfg_true(attr))
454 pub(crate) fn cfg_true(&self, attr: &Attribute) -> bool {
455 let meta_item = match validate_attr::parse_meta(&self.sess.parse_sess, attr) {
456 Ok(meta_item) => meta_item,
462 parse_cfg(&meta_item, &self.sess).map_or(true, |meta_item| {
463 attr::cfg_matches(&meta_item, &self.sess.parse_sess, self.lint_node_id, self.features)
467 /// If attributes are not allowed on expressions, emit an error for `attr`
468 pub(crate) fn maybe_emit_expr_attr_err(&self, attr: &Attribute) {
469 if !self.features.map_or(true, |features| features.stmt_expr_attributes) {
470 let mut err = feature_err(
471 &self.sess.parse_sess,
472 sym::stmt_expr_attributes,
474 "attributes on expressions are experimental",
477 if attr.is_doc_comment() {
478 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
485 pub fn configure_expr(&self, expr: &mut P<ast::Expr>) {
486 for attr in expr.attrs.iter() {
487 self.maybe_emit_expr_attr_err(attr);
490 // If an expr is valid to cfg away it will have been removed by the
491 // outer stmt or expression folder before descending in here.
492 // Anything else is always required, and thus has to error out
493 // in case of a cfg attr.
495 // N.B., this is intentionally not part of the visit_expr() function
496 // in order for filter_map_expr() to be able to avoid this check
497 if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(*a)) {
498 let msg = "removing an expression is not supported in this position";
499 self.sess.parse_sess.span_diagnostic.span_err(attr.span, msg);
502 self.process_cfg_attrs(expr);
503 self.try_configure_tokens(&mut *expr);
507 pub fn parse_cfg<'a>(meta_item: &'a MetaItem, sess: &Session) -> Option<&'a MetaItem> {
508 let error = |span, msg, suggestion: &str| {
509 let mut err = sess.parse_sess.span_diagnostic.struct_span_err(span, msg);
510 if !suggestion.is_empty() {
513 "expected syntax is",
515 Applicability::HasPlaceholders,
521 let span = meta_item.span;
522 match meta_item.meta_item_list() {
523 None => error(span, "`cfg` is not followed by parentheses", "cfg(/* predicate */)"),
524 Some([]) => error(span, "`cfg` predicate is not specified", ""),
525 Some([_, .., l]) => error(l.span(), "multiple `cfg` predicates are specified", ""),
526 Some([single]) => match single.meta_item() {
527 Some(meta_item) => Some(meta_item),
528 None => error(single.span(), "`cfg` predicate key cannot be a literal", ""),
533 fn is_cfg(attr: &Attribute) -> bool {
534 attr.has_name(sym::cfg)