1 //! Conditional compilation stripping.
4 use rustc_ast::token::{DelimToken, Token, TokenKind};
5 use rustc_ast::tokenstream::{AttrAnnotatedTokenStream, AttrAnnotatedTokenTree};
6 use rustc_ast::tokenstream::{DelimSpan, Spacing};
7 use rustc_ast::tokenstream::{LazyTokenStream, TokenTree};
8 use rustc_ast::{self as ast, AstLike, AttrItem, AttrStyle, 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_errors::{error_code, struct_span_err, Applicability, Handler};
13 use rustc_feature::{Feature, Features, State as FeatureState};
15 ACCEPTED_FEATURES, ACTIVE_FEATURES, REMOVED_FEATURES, STABLE_REMOVED_FEATURES,
17 use rustc_parse::{parse_in, validate_attr};
18 use rustc_session::parse::feature_err;
19 use rustc_session::Session;
20 use rustc_span::edition::{Edition, ALL_EDITIONS};
21 use rustc_span::symbol::{sym, Symbol};
22 use rustc_span::{Span, DUMMY_SP};
24 /// A folder that strips out items that do not belong in the current configuration.
25 pub struct StripUnconfigured<'a> {
26 pub sess: &'a Session,
27 pub features: Option<&'a Features>,
28 /// If `true`, perform cfg-stripping on attached tokens.
29 /// This is only used for the input to derive macros,
30 /// which needs eager expansion of `cfg` and `cfg_attr`
31 pub config_tokens: bool,
36 span_handler: &Handler,
37 krate_attrs: &[ast::Attribute],
39 fn feature_removed(span_handler: &Handler, span: Span, reason: Option<&str>) {
40 let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
41 err.span_label(span, "feature has been removed");
42 if let Some(reason) = reason {
48 fn active_features_up_to(edition: Edition) -> impl Iterator<Item = &'static Feature> {
49 ACTIVE_FEATURES.iter().filter(move |feature| {
50 if let Some(feature_edition) = feature.edition {
51 feature_edition <= edition
58 let mut features = Features::default();
59 let mut edition_enabled_features = FxHashMap::default();
60 let crate_edition = sess.edition();
62 for &edition in ALL_EDITIONS {
63 if edition <= crate_edition {
64 // The `crate_edition` implies its respective umbrella feature-gate
65 // (i.e., `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
66 edition_enabled_features.insert(edition.feature_name(), edition);
70 for feature in active_features_up_to(crate_edition) {
71 feature.set(&mut features, DUMMY_SP);
72 edition_enabled_features.insert(feature.name, crate_edition);
75 // Process the edition umbrella feature-gates first, to ensure
76 // `edition_enabled_features` is completed before it's queried.
77 for attr in krate_attrs {
78 if !sess.check_name(attr, sym::feature) {
82 let list = match attr.meta_item_list() {
92 let name = mi.name_or_empty();
94 let edition = ALL_EDITIONS.iter().find(|e| name == e.feature_name()).copied();
95 if let Some(edition) = edition {
96 if edition <= crate_edition {
100 for feature in active_features_up_to(edition) {
101 // FIXME(Manishearth) there is currently no way to set
102 // lib features by edition
103 feature.set(&mut features, DUMMY_SP);
104 edition_enabled_features.insert(feature.name, edition);
110 for attr in krate_attrs {
111 if !sess.check_name(attr, sym::feature) {
115 let list = match attr.meta_item_list() {
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));
173 if let Some(allowed) = sess.opts.debugging_opts.allow_features.as_ref() {
174 if allowed.iter().find(|&f| name.as_str() == *f).is_none() {
179 "the feature `{}` is not in the list of allowed features",
187 if let Some(f) = ACTIVE_FEATURES.iter().find(|f| name == f.name) {
188 f.set(&mut features, mi.span());
189 features.declared_lang_features.push((name, mi.span(), None));
193 features.declared_lib_features.push((name, mi.span()));
200 // `cfg_attr`-process the crate's attributes and compute the crate's features.
201 pub fn features(sess: &Session, mut krate: ast::Crate) -> (ast::Crate, Features) {
202 let mut strip_unconfigured = StripUnconfigured { sess, features: None, config_tokens: false };
204 let unconfigured_attrs = krate.attrs.clone();
205 let diag = &sess.parse_sess.span_diagnostic;
206 let err_count = diag.err_count();
207 let features = match strip_unconfigured.configure_krate_attrs(krate.attrs) {
209 // The entire crate is unconfigured.
210 krate.attrs = Vec::new();
211 krate.items = Vec::new();
216 let features = get_features(sess, diag, &krate.attrs);
217 if err_count == diag.err_count() {
218 // Avoid reconfiguring malformed `cfg_attr`s.
219 strip_unconfigured.features = Some(&features);
220 // Run configuration again, this time with features available
221 // so that we can perform feature-gating.
222 strip_unconfigured.configure_krate_attrs(unconfigured_attrs);
231 macro_rules! configure {
232 ($this:ident, $node:ident) => {
233 match $this.configure($node) {
235 None => return Default::default(),
240 const CFG_ATTR_GRAMMAR_HELP: &str = "#[cfg_attr(condition, attribute, other_attribute, ...)]";
241 const CFG_ATTR_NOTE_REF: &str = "for more information, visit \
242 <https://doc.rust-lang.org/reference/conditional-compilation.html\
243 #the-cfg_attr-attribute>";
245 impl<'a> StripUnconfigured<'a> {
246 pub fn configure<T: AstLike>(&mut self, mut node: T) -> Option<T> {
247 self.process_cfg_attrs(&mut node);
248 if self.in_cfg(node.attrs()) {
249 self.try_configure_tokens(&mut node);
256 fn try_configure_tokens<T: AstLike>(&mut self, node: &mut T) {
257 if self.config_tokens {
258 if let Some(Some(tokens)) = node.tokens_mut() {
259 let attr_annotated_tokens = tokens.create_token_stream();
260 *tokens = LazyTokenStream::new(self.configure_tokens(&attr_annotated_tokens));
265 fn configure_krate_attrs(
267 mut attrs: Vec<ast::Attribute>,
268 ) -> 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(&mut 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(token) => {
314 if let TokenKind::Interpolated(nt) = token.kind {
316 "Nonterminal should have been flattened at {:?}: {:?}",
320 Some((AttrAnnotatedTokenTree::Token(token), *spacing)).into_iter()
325 AttrAnnotatedTokenStream::new(trees)
328 /// Parse and expand all `cfg_attr` attributes into a list of attributes
329 /// that are within each `cfg_attr` that has a true configuration predicate.
331 /// Gives compiler warnings if any `cfg_attr` does not contain any
332 /// attributes and is in the original source code. Gives compiler errors if
333 /// the syntax of any `cfg_attr` is incorrect.
334 fn process_cfg_attrs<T: AstLike>(&mut self, node: &mut T) {
335 node.visit_attrs(|attrs| {
336 attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
340 /// Parse and expand a single `cfg_attr` attribute into a list of attributes
341 /// when the configuration predicate is true, or otherwise expand into an
342 /// empty list of attributes.
344 /// Gives a compiler warning when the `cfg_attr` contains no attributes and
345 /// is in the original source file. Gives a compiler error if the syntax of
346 /// the attribute is incorrect.
347 fn process_cfg_attr(&mut self, attr: Attribute) -> Vec<Attribute> {
348 if !attr.has_name(sym::cfg_attr) {
352 let (cfg_predicate, expanded_attrs) = match self.parse_cfg_attr(&attr) {
353 None => return vec![],
357 // Lint on zero attributes in source.
358 if expanded_attrs.is_empty() {
362 // At this point we know the attribute is considered used.
363 self.sess.mark_attr_used(&attr);
365 if !attr::cfg_matches(&cfg_predicate, &self.sess.parse_sess, self.features) {
369 // We call `process_cfg_attr` recursively in case there's a
370 // `cfg_attr` inside of another `cfg_attr`. E.g.
371 // `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
374 .flat_map(|(item, span)| {
375 let orig_tokens = attr.tokens().to_tokenstream();
377 // We are taking an attribute of the form `#[cfg_attr(pred, attr)]`
378 // and producing an attribute of the form `#[attr]`. We
379 // have captured tokens for `attr` itself, but we need to
380 // synthesize tokens for the wrapper `#` and `[]`, which
383 // Use the `#` in `#[cfg_attr(pred, attr)]` as the `#` token
384 // for `attr` when we expand it to `#[attr]`
385 let mut orig_trees = orig_tokens.trees();
386 let pound_token = match orig_trees.next().unwrap() {
387 TokenTree::Token(token @ Token { kind: TokenKind::Pound, .. }) => token,
388 _ => panic!("Bad tokens for attribute {:?}", attr),
390 let pound_span = pound_token.span;
392 let mut trees = vec![(AttrAnnotatedTokenTree::Token(pound_token), Spacing::Alone)];
393 if attr.style == AttrStyle::Inner {
394 // For inner attributes, we do the same thing for the `!` in `#![some_attr]`
395 let bang_token = match orig_trees.next().unwrap() {
396 TokenTree::Token(token @ Token { kind: TokenKind::Not, .. }) => token,
397 _ => panic!("Bad tokens for attribute {:?}", attr),
399 trees.push((AttrAnnotatedTokenTree::Token(bang_token), Spacing::Alone));
401 // We don't really have a good span to use for the syntheized `[]`
402 // in `#[attr]`, so just use the span of the `#` token.
403 let bracket_group = AttrAnnotatedTokenTree::Delimited(
404 DelimSpan::from_single(pound_span),
408 .unwrap_or_else(|| panic!("Missing tokens for {:?}", item))
409 .create_token_stream(),
411 trees.push((bracket_group, Spacing::Alone));
412 let tokens = Some(LazyTokenStream::new(AttrAnnotatedTokenStream::new(trees)));
413 self.process_cfg_attr(attr::mk_attr_from_item(item, tokens, attr.style, span))
418 fn parse_cfg_attr(&self, attr: &Attribute) -> Option<(MetaItem, Vec<(AttrItem, Span)>)> {
419 match attr.get_normal_item().args {
420 ast::MacArgs::Delimited(dspan, delim, ref tts) if !tts.is_empty() => {
421 let msg = "wrong `cfg_attr` delimiters";
422 validate_attr::check_meta_bad_delim(&self.sess.parse_sess, dspan, delim, msg);
423 match parse_in(&self.sess.parse_sess, tts.clone(), "`cfg_attr` input", |p| {
426 Ok(r) => return Some(r),
428 e.help(&format!("the valid syntax is `{}`", CFG_ATTR_GRAMMAR_HELP))
429 .note(CFG_ATTR_NOTE_REF)
434 _ => self.error_malformed_cfg_attr_missing(attr.span),
439 fn error_malformed_cfg_attr_missing(&self, span: Span) {
443 .struct_span_err(span, "malformed `cfg_attr` attribute input")
446 "missing condition and attribute",
447 CFG_ATTR_GRAMMAR_HELP.to_string(),
448 Applicability::HasPlaceholders,
450 .note(CFG_ATTR_NOTE_REF)
454 /// Determines if a node with the given attributes should be included in this configuration.
455 fn in_cfg(&self, attrs: &[Attribute]) -> bool {
456 attrs.iter().all(|attr| {
457 if !is_cfg(self.sess, attr) {
460 let meta_item = match validate_attr::parse_meta(&self.sess.parse_sess, attr) {
461 Ok(meta_item) => meta_item,
467 parse_cfg(&meta_item, &self.sess).map_or(true, |meta_item| {
468 attr::cfg_matches(&meta_item, &self.sess.parse_sess, self.features)
473 /// If attributes are not allowed on expressions, emit an error for `attr`
474 crate fn maybe_emit_expr_attr_err(&self, attr: &Attribute) {
475 if !self.features.map_or(true, |features| features.stmt_expr_attributes) {
476 let mut err = feature_err(
477 &self.sess.parse_sess,
478 sym::stmt_expr_attributes,
480 "attributes on expressions are experimental",
483 if attr.is_doc_comment() {
484 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
491 pub fn configure_expr(&mut self, expr: &mut P<ast::Expr>) {
492 for attr in expr.attrs.iter() {
493 self.maybe_emit_expr_attr_err(attr);
496 // If an expr is valid to cfg away it will have been removed by the
497 // outer stmt or expression folder before descending in here.
498 // Anything else is always required, and thus has to error out
499 // in case of a cfg attr.
501 // N.B., this is intentionally not part of the visit_expr() function
502 // in order for filter_map_expr() to be able to avoid this check
503 if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(self.sess, a)) {
504 let msg = "removing an expression is not supported in this position";
505 self.sess.parse_sess.span_diagnostic.span_err(attr.span, msg);
508 self.process_cfg_attrs(expr);
509 self.try_configure_tokens(&mut *expr);
513 pub fn parse_cfg<'a>(meta_item: &'a MetaItem, sess: &Session) -> Option<&'a MetaItem> {
514 let error = |span, msg, suggestion: &str| {
515 let mut err = sess.parse_sess.span_diagnostic.struct_span_err(span, msg);
516 if !suggestion.is_empty() {
519 "expected syntax is",
521 Applicability::HasPlaceholders,
527 let span = meta_item.span;
528 match meta_item.meta_item_list() {
529 None => error(span, "`cfg` is not followed by parentheses", "cfg(/* predicate */)"),
530 Some([]) => error(span, "`cfg` predicate is not specified", ""),
531 Some([_, .., l]) => error(l.span(), "multiple `cfg` predicates are specified", ""),
532 Some([single]) => match single.meta_item() {
533 Some(meta_item) => Some(meta_item),
534 None => error(single.span(), "`cfg` predicate key cannot be a literal", ""),
539 fn is_cfg(sess: &Session, attr: &Attribute) -> bool {
540 sess.check_name(attr, sym::cfg)