4 EXPLAIN_STMT_ATTR_SYNTAX,
12 use errors::Applicability;
14 use parse::{token, ParseSess};
16 use smallvec::SmallVec;
17 use util::map_in_place::MapInPlace;
19 /// A folder that strips out items that do not belong in the current configuration.
20 pub struct StripUnconfigured<'a> {
21 pub sess: &'a ParseSess,
22 pub features: Option<&'a Features>,
25 // `cfg_attr`-process the crate's attributes and compute the crate's features.
26 pub fn features(mut krate: ast::Crate, sess: &ParseSess, edition: Edition)
27 -> (ast::Crate, Features) {
30 let mut strip_unconfigured = StripUnconfigured {
35 let unconfigured_attrs = krate.attrs.clone();
36 let err_count = sess.span_diagnostic.err_count();
37 if let Some(attrs) = strip_unconfigured.configure(krate.attrs) {
39 } else { // the entire crate is unconfigured
40 krate.attrs = Vec::new();
41 krate.module.items = Vec::new();
42 return (krate, Features::new());
45 features = get_features(&sess.span_diagnostic, &krate.attrs, edition);
47 // Avoid reconfiguring malformed `cfg_attr`s
48 if err_count == sess.span_diagnostic.err_count() {
49 strip_unconfigured.features = Some(&features);
50 strip_unconfigured.configure(unconfigured_attrs);
57 macro_rules! configure {
58 ($this:ident, $node:ident) => {
59 match $this.configure($node) {
61 None => return Default::default(),
66 impl<'a> StripUnconfigured<'a> {
67 pub fn configure<T: HasAttrs>(&mut self, mut node: T) -> Option<T> {
68 self.process_cfg_attrs(&mut node);
69 if self.in_cfg(node.attrs()) { Some(node) } else { None }
72 /// Parse and expand all `cfg_attr` attributes into a list of attributes
73 /// that are within each `cfg_attr` that has a true configuration predicate.
75 /// Gives compiler warnigns if any `cfg_attr` does not contain any
76 /// attributes and is in the original source code. Gives compiler errors if
77 /// the syntax of any `cfg_attr` is incorrect.
78 pub fn process_cfg_attrs<T: HasAttrs>(&mut self, node: &mut T) {
79 node.visit_attrs(|attrs| {
80 attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
84 /// Parse and expand a single `cfg_attr` attribute into a list of attributes
85 /// when the configuration predicate is true, or otherwise expand into an
86 /// empty list of attributes.
88 /// Gives a compiler warning when the `cfg_attr` contains no attributes and
89 /// is in the original source file. Gives a compiler error if the syntax of
90 /// the attribute is incorrect
91 fn process_cfg_attr(&mut self, attr: ast::Attribute) -> Vec<ast::Attribute> {
92 if !attr.check_name("cfg_attr") {
96 let (cfg_predicate, expanded_attrs) = match attr.parse(self.sess, |parser| {
97 parser.expect(&token::OpenDelim(token::Paren))?;
99 let cfg_predicate = parser.parse_meta_item()?;
100 parser.expect(&token::Comma)?;
102 // Presumably, the majority of the time there will only be one attr.
103 let mut expanded_attrs = Vec::with_capacity(1);
105 while !parser.check(&token::CloseDelim(token::Paren)) {
106 let lo = parser.span.lo();
107 let (path, tokens) = parser.parse_meta_item_unrestricted()?;
108 expanded_attrs.push((path, tokens, parser.prev_span.with_lo(lo)));
109 parser.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Paren)])?;
112 parser.expect(&token::CloseDelim(token::Paren))?;
113 Ok((cfg_predicate, expanded_attrs))
115 Ok(result) => result,
122 // Check feature gate and lint on zero attributes in source. Even if the feature is gated,
123 // we still compute as if it wasn't, since the emitted error will stop compilation further
124 // along the compilation.
125 if expanded_attrs.len() == 0 {
126 // FIXME: Emit unused attribute lint here.
129 if attr::cfg_matches(&cfg_predicate, self.sess, self.features) {
130 // We call `process_cfg_attr` recursively in case there's a
131 // `cfg_attr` inside of another `cfg_attr`. E.g.
132 // `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
133 expanded_attrs.into_iter()
134 .flat_map(|(path, tokens, span)| self.process_cfg_attr(ast::Attribute {
135 id: attr::mk_attr_id(),
139 is_sugared_doc: false,
148 /// Determine if a node with the given attributes should be included in this configuration.
149 pub fn in_cfg(&mut self, attrs: &[ast::Attribute]) -> bool {
150 attrs.iter().all(|attr| {
155 let error = |span, msg, suggestion: &str| {
156 let mut err = self.sess.span_diagnostic.struct_span_err(span, msg);
157 if !suggestion.is_empty() {
160 "expected syntax is",
162 Applicability::MaybeIncorrect,
169 let meta_item = match attr.parse_meta(self.sess) {
170 Ok(meta_item) => meta_item,
171 Err(mut err) => { err.emit(); return true; }
173 let nested_meta_items = if let Some(nested_meta_items) = meta_item.meta_item_list() {
176 return error(meta_item.span, "`cfg` is not followed by parentheses",
177 "cfg(/* predicate */)");
180 if nested_meta_items.is_empty() {
181 return error(meta_item.span, "`cfg` predicate is not specified", "");
182 } else if nested_meta_items.len() > 1 {
183 return error(nested_meta_items.last().unwrap().span,
184 "multiple `cfg` predicates are specified", "");
187 match nested_meta_items[0].meta_item() {
188 Some(meta_item) => attr::cfg_matches(meta_item, self.sess, self.features),
189 None => error(nested_meta_items[0].span,
190 "`cfg` predicate key cannot be a literal", ""),
195 /// Visit attributes on expression and statements (but not attributes on items in blocks).
196 fn visit_expr_attrs(&mut self, attrs: &[ast::Attribute]) {
197 // flag the offending attributes
198 for attr in attrs.iter() {
199 self.maybe_emit_expr_attr_err(attr);
203 /// If attributes are not allowed on expressions, emit an error for `attr`
204 pub fn maybe_emit_expr_attr_err(&self, attr: &ast::Attribute) {
205 if !self.features.map(|features| features.stmt_expr_attributes).unwrap_or(true) {
206 let mut err = feature_err(self.sess,
207 "stmt_expr_attributes",
210 EXPLAIN_STMT_ATTR_SYNTAX);
212 if attr.is_sugared_doc {
213 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
220 pub fn configure_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
221 let ast::ForeignMod { abi: _, items } = foreign_mod;
222 items.flat_map_in_place(|item| self.configure(item));
225 fn configure_variant_data(&mut self, vdata: &mut ast::VariantData) {
227 ast::VariantData::Struct(fields, _id) |
228 ast::VariantData::Tuple(fields, _id) =>
229 fields.flat_map_in_place(|field| self.configure(field)),
230 ast::VariantData::Unit(_id) => {}
234 pub fn configure_item_kind(&mut self, item: &mut ast::ItemKind) {
236 ast::ItemKind::Struct(def, _generics) |
237 ast::ItemKind::Union(def, _generics) => self.configure_variant_data(def),
238 ast::ItemKind::Enum(ast::EnumDef { variants }, _generics) => {
239 variants.flat_map_in_place(|variant| self.configure(variant));
240 for variant in variants {
241 self.configure_variant_data(&mut variant.node.data);
248 pub fn configure_expr_kind(&mut self, expr_kind: &mut ast::ExprKind) {
250 ast::ExprKind::Match(_m, arms) => {
251 arms.flat_map_in_place(|arm| self.configure(arm));
253 ast::ExprKind::Struct(_path, fields, _base) => {
254 fields.flat_map_in_place(|field| self.configure(field));
260 pub fn configure_expr(&mut self, expr: &mut P<ast::Expr>) {
261 self.visit_expr_attrs(expr.attrs());
263 // If an expr is valid to cfg away it will have been removed by the
264 // outer stmt or expression folder before descending in here.
265 // Anything else is always required, and thus has to error out
266 // in case of a cfg attr.
268 // N.B., this is intentionally not part of the visit_expr() function
269 // in order for filter_map_expr() to be able to avoid this check
270 if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(a)) {
271 let msg = "removing an expression is not supported in this position";
272 self.sess.span_diagnostic.span_err(attr.span, msg);
275 self.process_cfg_attrs(expr)
278 pub fn configure_pat(&mut self, pat: &mut P<ast::Pat>) {
279 if let ast::PatKind::Struct(_path, fields, _etc) = &mut pat.node {
280 fields.flat_map_in_place(|field| self.configure(field));
284 // deny #[cfg] on generic parameters until we decide what to do with it.
286 pub fn disallow_cfg_on_generic_param(&mut self, param: &ast::GenericParam) {
287 for attr in param.attrs() {
288 let offending_attr = if attr.check_name("cfg") {
290 } else if attr.check_name("cfg_attr") {
295 let msg = format!("#[{}] cannot be applied on a generic parameter", offending_attr);
296 self.sess.span_diagnostic.span_err(attr.span, &msg);
301 impl<'a> MutVisitor for StripUnconfigured<'a> {
302 fn visit_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
303 self.configure_foreign_mod(foreign_mod);
304 noop_visit_foreign_mod(foreign_mod, self);
307 fn visit_item_kind(&mut self, item: &mut ast::ItemKind) {
308 self.configure_item_kind(item);
309 noop_visit_item_kind(item, self);
312 fn visit_expr(&mut self, expr: &mut P<ast::Expr>) {
313 self.configure_expr(expr);
314 self.configure_expr_kind(&mut expr.node);
315 noop_visit_expr(expr, self);
318 fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
319 let mut expr = configure!(self, expr);
320 self.configure_expr_kind(&mut expr.node);
321 noop_visit_expr(&mut expr, self);
325 fn flat_map_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
326 noop_flat_map_stmt(configure!(self, stmt), self)
329 fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
330 noop_flat_map_item(configure!(self, item), self)
333 fn flat_map_impl_item(&mut self, item: ast::ImplItem) -> SmallVec<[ast::ImplItem; 1]> {
334 noop_flat_map_impl_item(configure!(self, item), self)
337 fn flat_map_trait_item(&mut self, item: ast::TraitItem) -> SmallVec<[ast::TraitItem; 1]> {
338 noop_flat_map_trait_item(configure!(self, item), self)
341 fn visit_mac(&mut self, _mac: &mut ast::Mac) {
342 // Don't configure interpolated AST (cf. issue #34171).
343 // Interpolated AST will get configured once the surrounding tokens are parsed.
346 fn visit_pat(&mut self, pat: &mut P<ast::Pat>) {
347 self.configure_pat(pat);
348 noop_visit_pat(pat, self)
352 fn is_cfg(attr: &ast::Attribute) -> bool {
353 attr.check_name("cfg")