1 //! Process the potential `cfg` attributes on a module.
2 //! Also determine if the module should be included in this configuration.
4 //! This module properly belongs in syntax_expand, but for now it's tied into
5 //! parsing, so we leave it here to avoid complicated out-of-line dependencies.
7 //! A principled solution to this wrong location would be to implement [#64197].
9 //! [#64197]: https://github.com/rust-lang/rust/issues/64197
11 use crate::validate_attr;
12 use syntax::attr::HasAttrs;
13 use syntax::feature_gate::{
15 EXPLAIN_STMT_ATTR_SYNTAX,
22 use syntax::edition::Edition;
23 use syntax::mut_visit::*;
25 use syntax::sess::ParseSess;
26 use syntax::util::map_in_place::MapInPlace;
27 use syntax_pos::symbol::sym;
29 use errors::Applicability;
30 use smallvec::SmallVec;
32 /// A folder that strips out items that do not belong in the current configuration.
33 pub struct StripUnconfigured<'a> {
34 pub sess: &'a ParseSess,
35 pub features: Option<&'a Features>,
38 // `cfg_attr`-process the crate's attributes and compute the crate's features.
39 pub fn features(mut krate: ast::Crate, sess: &ParseSess, edition: Edition,
40 allow_features: &Option<Vec<String>>) -> (ast::Crate, Features) {
43 let mut strip_unconfigured = StripUnconfigured {
48 let unconfigured_attrs = krate.attrs.clone();
49 let err_count = sess.span_diagnostic.err_count();
50 if let Some(attrs) = strip_unconfigured.configure(krate.attrs) {
52 } else { // the entire crate is unconfigured
53 krate.attrs = Vec::new();
54 krate.module.items = Vec::new();
55 return (krate, Features::new());
58 features = get_features(&sess.span_diagnostic, &krate.attrs, edition, allow_features);
60 // Avoid reconfiguring malformed `cfg_attr`s
61 if err_count == sess.span_diagnostic.err_count() {
62 strip_unconfigured.features = Some(&features);
63 strip_unconfigured.configure(unconfigured_attrs);
71 macro_rules! configure {
72 ($this:ident, $node:ident) => {
73 match $this.configure($node) {
75 None => return Default::default(),
80 impl<'a> StripUnconfigured<'a> {
81 pub fn configure<T: HasAttrs>(&mut self, mut node: T) -> Option<T> {
82 self.process_cfg_attrs(&mut node);
83 if self.in_cfg(node.attrs()) { Some(node) } else { None }
86 /// Parse and expand all `cfg_attr` attributes into a list of attributes
87 /// that are within each `cfg_attr` that has a true configuration predicate.
89 /// Gives compiler warnigns if any `cfg_attr` does not contain any
90 /// attributes and is in the original source code. Gives compiler errors if
91 /// the syntax of any `cfg_attr` is incorrect.
92 pub fn process_cfg_attrs<T: HasAttrs>(&mut self, node: &mut T) {
93 node.visit_attrs(|attrs| {
94 attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
98 /// Parse and expand a single `cfg_attr` attribute into a list of attributes
99 /// when the configuration predicate is true, or otherwise expand into an
100 /// empty list of attributes.
102 /// Gives a compiler warning when the `cfg_attr` contains no attributes and
103 /// is in the original source file. Gives a compiler error if the syntax of
104 /// the attribute is incorrect.
105 fn process_cfg_attr(&mut self, attr: ast::Attribute) -> Vec<ast::Attribute> {
106 if !attr.has_name(sym::cfg_attr) {
109 if attr.get_normal_item().tokens.is_empty() {
110 self.sess.span_diagnostic
113 "malformed `cfg_attr` attribute input",
116 "missing condition and attribute",
117 "#[cfg_attr(condition, attribute, other_attribute, ...)]".to_owned(),
118 Applicability::HasPlaceholders,
119 ).note("for more information, visit \
120 <https://doc.rust-lang.org/reference/conditional-compilation.html\
121 #the-cfg_attr-attribute>")
126 let res = crate::parse_in_attr(self.sess, &attr, |p| p.parse_cfg_attr());
127 let (cfg_predicate, expanded_attrs) = match res {
128 Ok(result) => result,
135 // Lint on zero attributes in source.
136 if expanded_attrs.is_empty() {
140 // At this point we know the attribute is considered used.
141 attr::mark_used(&attr);
143 if attr::cfg_matches(&cfg_predicate, self.sess, self.features) {
144 // We call `process_cfg_attr` recursively in case there's a
145 // `cfg_attr` inside of another `cfg_attr`. E.g.
146 // `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
147 expanded_attrs.into_iter()
148 .flat_map(|(item, span)| self.process_cfg_attr(attr::mk_attr_from_item(
159 /// Determines if a node with the given attributes should be included in this configuration.
160 pub fn in_cfg(&self, attrs: &[ast::Attribute]) -> bool {
161 attrs.iter().all(|attr| {
166 let error = |span, msg, suggestion: &str| {
167 let mut err = self.sess.span_diagnostic.struct_span_err(span, msg);
168 if !suggestion.is_empty() {
171 "expected syntax is",
173 Applicability::MaybeIncorrect,
180 let meta_item = match validate_attr::parse_meta(self.sess, attr) {
181 Ok(meta_item) => meta_item,
182 Err(mut err) => { err.emit(); return true; }
184 let nested_meta_items = if let Some(nested_meta_items) = meta_item.meta_item_list() {
187 return error(meta_item.span, "`cfg` is not followed by parentheses",
188 "cfg(/* predicate */)");
191 if nested_meta_items.is_empty() {
192 return error(meta_item.span, "`cfg` predicate is not specified", "");
193 } else if nested_meta_items.len() > 1 {
194 return error(nested_meta_items.last().unwrap().span(),
195 "multiple `cfg` predicates are specified", "");
198 match nested_meta_items[0].meta_item() {
199 Some(meta_item) => attr::cfg_matches(meta_item, self.sess, self.features),
200 None => error(nested_meta_items[0].span(),
201 "`cfg` predicate key cannot be a literal", ""),
206 /// Visit attributes on expression and statements (but not attributes on items in blocks).
207 fn visit_expr_attrs(&mut self, attrs: &[ast::Attribute]) {
208 // flag the offending attributes
209 for attr in attrs.iter() {
210 self.maybe_emit_expr_attr_err(attr);
214 /// If attributes are not allowed on expressions, emit an error for `attr`
215 pub fn maybe_emit_expr_attr_err(&self, attr: &ast::Attribute) {
216 if !self.features.map(|features| features.stmt_expr_attributes).unwrap_or(true) {
217 let mut err = feature_err(self.sess,
218 sym::stmt_expr_attributes,
221 EXPLAIN_STMT_ATTR_SYNTAX);
223 if attr.is_doc_comment() {
224 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
231 pub fn configure_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
232 let ast::ForeignMod { abi: _, items } = foreign_mod;
233 items.flat_map_in_place(|item| self.configure(item));
236 pub fn configure_generic_params(&mut self, params: &mut Vec<ast::GenericParam>) {
237 params.flat_map_in_place(|param| self.configure(param));
240 fn configure_variant_data(&mut self, vdata: &mut ast::VariantData) {
242 ast::VariantData::Struct(fields, ..) | ast::VariantData::Tuple(fields, _) =>
243 fields.flat_map_in_place(|field| self.configure(field)),
244 ast::VariantData::Unit(_) => {}
248 pub fn configure_item_kind(&mut self, item: &mut ast::ItemKind) {
250 ast::ItemKind::Struct(def, _generics) |
251 ast::ItemKind::Union(def, _generics) => self.configure_variant_data(def),
252 ast::ItemKind::Enum(ast::EnumDef { variants }, _generics) => {
253 variants.flat_map_in_place(|variant| self.configure(variant));
254 for variant in variants {
255 self.configure_variant_data(&mut variant.data);
262 pub fn configure_expr_kind(&mut self, expr_kind: &mut ast::ExprKind) {
264 ast::ExprKind::Match(_m, arms) => {
265 arms.flat_map_in_place(|arm| self.configure(arm));
267 ast::ExprKind::Struct(_path, fields, _base) => {
268 fields.flat_map_in_place(|field| self.configure(field));
274 pub fn configure_expr(&mut self, expr: &mut P<ast::Expr>) {
275 self.visit_expr_attrs(expr.attrs());
277 // If an expr is valid to cfg away it will have been removed by the
278 // outer stmt or expression folder before descending in here.
279 // Anything else is always required, and thus has to error out
280 // in case of a cfg attr.
282 // N.B., this is intentionally not part of the visit_expr() function
283 // in order for filter_map_expr() to be able to avoid this check
284 if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(a)) {
285 let msg = "removing an expression is not supported in this position";
286 self.sess.span_diagnostic.span_err(attr.span, msg);
289 self.process_cfg_attrs(expr)
292 pub fn configure_pat(&mut self, pat: &mut P<ast::Pat>) {
293 if let ast::PatKind::Struct(_path, fields, _etc) = &mut pat.kind {
294 fields.flat_map_in_place(|field| self.configure(field));
298 pub fn configure_fn_decl(&mut self, fn_decl: &mut ast::FnDecl) {
299 fn_decl.inputs.flat_map_in_place(|arg| self.configure(arg));
303 impl<'a> MutVisitor for StripUnconfigured<'a> {
304 fn visit_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
305 self.configure_foreign_mod(foreign_mod);
306 noop_visit_foreign_mod(foreign_mod, self);
309 fn visit_item_kind(&mut self, item: &mut ast::ItemKind) {
310 self.configure_item_kind(item);
311 noop_visit_item_kind(item, self);
314 fn visit_expr(&mut self, expr: &mut P<ast::Expr>) {
315 self.configure_expr(expr);
316 self.configure_expr_kind(&mut expr.kind);
317 noop_visit_expr(expr, self);
320 fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
321 let mut expr = configure!(self, expr);
322 self.configure_expr_kind(&mut expr.kind);
323 noop_visit_expr(&mut expr, self);
327 fn flat_map_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
328 noop_flat_map_stmt(configure!(self, stmt), self)
331 fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
332 noop_flat_map_item(configure!(self, item), self)
335 fn flat_map_impl_item(&mut self, item: ast::ImplItem) -> SmallVec<[ast::ImplItem; 1]> {
336 noop_flat_map_impl_item(configure!(self, item), self)
339 fn flat_map_trait_item(&mut self, item: ast::TraitItem) -> SmallVec<[ast::TraitItem; 1]> {
340 noop_flat_map_trait_item(configure!(self, item), self)
343 fn visit_mac(&mut self, _mac: &mut ast::Mac) {
344 // Don't configure interpolated AST (cf. issue #34171).
345 // Interpolated AST will get configured once the surrounding tokens are parsed.
348 fn visit_pat(&mut self, pat: &mut P<ast::Pat>) {
349 self.configure_pat(pat);
350 noop_visit_pat(pat, self)
353 fn visit_fn_decl(&mut self, mut fn_decl: &mut P<ast::FnDecl>) {
354 self.configure_fn_decl(&mut fn_decl);
355 noop_visit_fn_decl(fn_decl, self);
359 fn is_cfg(attr: &ast::Attribute) -> bool {
360 attr.check_name(sym::cfg)
363 /// Process the potential `cfg` attributes on a module.
364 /// Also determine if the module should be included in this configuration.
365 pub fn process_configure_mod(
368 attrs: &[ast::Attribute],
369 ) -> (bool, Vec<ast::Attribute>) {
370 // Don't perform gated feature checking.
371 let mut strip_unconfigured = StripUnconfigured { sess, features: None };
372 let mut attrs = attrs.to_owned();
373 strip_unconfigured.process_cfg_attrs(&mut attrs);
374 (!cfg_mods || strip_unconfigured.in_cfg(&attrs), attrs)