1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
14 EXPLAIN_STMT_ATTR_SYNTAX,
22 use source_map::Spanned;
24 use parse::{token, ParseSess};
25 use smallvec::SmallVec;
26 use errors::Applicability;
30 /// A folder that strips out items that do not belong in the current configuration.
31 pub struct StripUnconfigured<'a> {
32 pub sess: &'a ParseSess,
33 pub features: Option<&'a Features>,
36 // `cfg_attr`-process the crate's attributes and compute the crate's features.
37 pub fn features(mut krate: ast::Crate, sess: &ParseSess, edition: Edition)
38 -> (ast::Crate, Features) {
41 let mut strip_unconfigured = StripUnconfigured {
46 let unconfigured_attrs = krate.attrs.clone();
47 let err_count = sess.span_diagnostic.err_count();
48 if let Some(attrs) = strip_unconfigured.configure(krate.attrs) {
50 } else { // the entire crate is unconfigured
51 krate.attrs = Vec::new();
52 krate.module.items = Vec::new();
53 return (krate, Features::new());
56 features = get_features(&sess.span_diagnostic, &krate.attrs, edition);
58 // Avoid reconfiguring malformed `cfg_attr`s
59 if err_count == sess.span_diagnostic.err_count() {
60 strip_unconfigured.features = Some(&features);
61 strip_unconfigured.configure(unconfigured_attrs);
68 macro_rules! configure {
69 ($this:ident, $node:ident) => {
70 match $this.configure($node) {
72 None => return Default::default(),
77 impl<'a> StripUnconfigured<'a> {
78 pub fn configure<T: HasAttrs>(&mut self, node: T) -> Option<T> {
79 let node = self.process_cfg_attrs(node);
80 if self.in_cfg(node.attrs()) { Some(node) } else { None }
83 /// Parse and expand all `cfg_attr` attributes into a list of attributes
84 /// that are within each `cfg_attr` that has a true configuration predicate.
86 /// Gives compiler warnigns if any `cfg_attr` does not contain any
87 /// attributes and is in the original source code. Gives compiler errors if
88 /// the syntax of any `cfg_attr` is incorrect.
89 pub fn process_cfg_attrs<T: HasAttrs>(&mut self, node: T) -> T {
90 node.map_attrs(|attrs| {
91 attrs.into_iter().flat_map(|attr| self.process_cfg_attr(attr)).collect()
95 /// Parse and expand a single `cfg_attr` attribute into a list of attributes
96 /// when the configuration predicate is true, or otherwise expand into an
97 /// empty list of attributes.
99 /// Gives a compiler warning when the `cfg_attr` contains no attributes and
100 /// is in the original source file. Gives a compiler error if the syntax of
101 /// the attribute is incorrect
102 fn process_cfg_attr(&mut self, attr: ast::Attribute) -> Vec<ast::Attribute> {
103 if !attr.check_name("cfg_attr") {
107 let gate_cfg_attr_multi = if let Some(ref features) = self.features {
108 !features.cfg_attr_multi
112 let cfg_attr_span = attr.span;
114 let (cfg_predicate, expanded_attrs) = match attr.parse(self.sess, |parser| {
115 parser.expect(&token::OpenDelim(token::Paren))?;
117 let cfg_predicate = parser.parse_meta_item()?;
118 parser.expect(&token::Comma)?;
120 // Presumably, the majority of the time there will only be one attr.
121 let mut expanded_attrs = Vec::with_capacity(1);
123 while !parser.check(&token::CloseDelim(token::Paren)) {
124 let lo = parser.span.lo();
125 let (path, tokens) = parser.parse_meta_item_unrestricted()?;
126 expanded_attrs.push((path, tokens, parser.prev_span.with_lo(lo)));
127 parser.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Paren)])?;
130 parser.expect(&token::CloseDelim(token::Paren))?;
131 Ok((cfg_predicate, expanded_attrs))
133 Ok(result) => result,
140 // Check feature gate and lint on zero attributes in source. Even if the feature is gated,
141 // we still compute as if it wasn't, since the emitted error will stop compilation further
142 // along the compilation.
143 match (expanded_attrs.len(), gate_cfg_attr_multi) {
145 // FIXME: Emit unused attribute lint here.
154 "cfg_attr with zero or more than one attributes is experimental",
160 if attr::cfg_matches(&cfg_predicate, self.sess, self.features) {
161 // We call `process_cfg_attr` recursively in case there's a
162 // `cfg_attr` inside of another `cfg_attr`. E.g.
163 // `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
164 expanded_attrs.into_iter()
165 .flat_map(|(path, tokens, span)| self.process_cfg_attr(ast::Attribute {
166 id: attr::mk_attr_id(),
170 is_sugared_doc: false,
179 /// Determine if a node with the given attributes should be included in this configuration.
180 pub fn in_cfg(&mut self, attrs: &[ast::Attribute]) -> bool {
181 attrs.iter().all(|attr| {
186 let error = |span, msg, suggestion: &str| {
187 let mut err = self.sess.span_diagnostic.struct_span_err(span, msg);
188 if !suggestion.is_empty() {
189 err.span_suggestion_with_applicability(
191 "expected syntax is",
193 Applicability::MaybeIncorrect,
200 let meta_item = if let Some(meta_item) = attr.meta() {
203 // Not a well-formed meta-item. Why? We don't know.
204 return error(attr.span, "`cfg` is not a well-formed meta-item",
205 "#[cfg(/* predicate */)]");
207 let nested_meta_items = if let Some(nested_meta_items) = meta_item.meta_item_list() {
210 return error(meta_item.span, "`cfg` is not followed by parentheses",
211 "cfg(/* predicate */)");
214 if nested_meta_items.is_empty() {
215 return error(meta_item.span, "`cfg` predicate is not specified", "");
216 } else if nested_meta_items.len() > 1 {
217 return error(nested_meta_items.last().unwrap().span,
218 "multiple `cfg` predicates are specified", "");
221 match nested_meta_items[0].meta_item() {
222 Some(meta_item) => attr::cfg_matches(meta_item, self.sess, self.features),
223 None => error(nested_meta_items[0].span,
224 "`cfg` predicate key cannot be a literal", ""),
229 /// Visit attributes on expression and statements (but not attributes on items in blocks).
230 fn visit_expr_attrs(&mut self, attrs: &[ast::Attribute]) {
231 // flag the offending attributes
232 for attr in attrs.iter() {
233 self.maybe_emit_expr_attr_err(attr);
237 /// If attributes are not allowed on expressions, emit an error for `attr`
238 pub fn maybe_emit_expr_attr_err(&self, attr: &ast::Attribute) {
239 if !self.features.map(|features| features.stmt_expr_attributes).unwrap_or(true) {
240 let mut err = feature_err(self.sess,
241 "stmt_expr_attributes",
244 EXPLAIN_STMT_ATTR_SYNTAX);
246 if attr.is_sugared_doc {
247 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
254 pub fn configure_foreign_mod(&mut self, foreign_mod: ast::ForeignMod) -> ast::ForeignMod {
256 abi: foreign_mod.abi,
257 items: foreign_mod.items.into_iter().filter_map(|item| self.configure(item)).collect(),
261 fn configure_variant_data(&mut self, vdata: ast::VariantData) -> ast::VariantData {
263 ast::VariantData::Struct(fields, id) => {
264 let fields = fields.into_iter().filter_map(|field| self.configure(field));
265 ast::VariantData::Struct(fields.collect(), id)
267 ast::VariantData::Tuple(fields, id) => {
268 let fields = fields.into_iter().filter_map(|field| self.configure(field));
269 ast::VariantData::Tuple(fields.collect(), id)
271 ast::VariantData::Unit(id) => ast::VariantData::Unit(id)
275 pub fn configure_item_kind(&mut self, item: ast::ItemKind) -> ast::ItemKind {
277 ast::ItemKind::Struct(def, generics) => {
278 ast::ItemKind::Struct(self.configure_variant_data(def), generics)
280 ast::ItemKind::Union(def, generics) => {
281 ast::ItemKind::Union(self.configure_variant_data(def), generics)
283 ast::ItemKind::Enum(def, generics) => {
284 let variants = def.variants.into_iter().filter_map(|v| {
285 self.configure(v).map(|v| {
287 node: ast::Variant_ {
290 data: self.configure_variant_data(v.node.data),
291 disr_expr: v.node.disr_expr,
297 ast::ItemKind::Enum(ast::EnumDef {
298 variants: variants.collect(),
305 pub fn configure_expr_kind(&mut self, expr_kind: ast::ExprKind) -> ast::ExprKind {
307 ast::ExprKind::Match(m, arms) => {
308 let arms = arms.into_iter().filter_map(|a| self.configure(a)).collect();
309 ast::ExprKind::Match(m, arms)
311 ast::ExprKind::Struct(path, fields, base) => {
312 let fields = fields.into_iter()
313 .filter_map(|field| {
314 self.configure(field)
317 ast::ExprKind::Struct(path, fields, base)
323 pub fn configure_expr(&mut self, expr: P<ast::Expr>) -> P<ast::Expr> {
324 self.visit_expr_attrs(expr.attrs());
326 // If an expr is valid to cfg away it will have been removed by the
327 // outer stmt or expression folder before descending in here.
328 // Anything else is always required, and thus has to error out
329 // in case of a cfg attr.
331 // NB: This is intentionally not part of the fold_expr() function
332 // in order for fold_opt_expr() to be able to avoid this check
333 if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(a)) {
334 let msg = "removing an expression is not supported in this position";
335 self.sess.span_diagnostic.span_err(attr.span, msg);
338 self.process_cfg_attrs(expr)
341 pub fn configure_stmt(&mut self, stmt: ast::Stmt) -> Option<ast::Stmt> {
345 pub fn configure_struct_expr_field(&mut self, field: ast::Field) -> Option<ast::Field> {
346 self.configure(field)
349 pub fn configure_pat(&mut self, pattern: P<ast::Pat>) -> P<ast::Pat> {
350 pattern.map(|mut pattern| {
351 if let ast::PatKind::Struct(path, fields, etc) = pattern.node {
352 let fields = fields.into_iter()
353 .filter_map(|field| {
354 self.configure(field)
357 pattern.node = ast::PatKind::Struct(path, fields, etc);
363 // deny #[cfg] on generic parameters until we decide what to do with it.
365 pub fn disallow_cfg_on_generic_param(&mut self, param: &ast::GenericParam) {
366 for attr in param.attrs() {
367 let offending_attr = if attr.check_name("cfg") {
369 } else if attr.check_name("cfg_attr") {
374 let msg = format!("#[{}] cannot be applied on a generic parameter", offending_attr);
375 self.sess.span_diagnostic.span_err(attr.span, &msg);
380 impl<'a> fold::Folder for StripUnconfigured<'a> {
381 fn fold_foreign_mod(&mut self, foreign_mod: ast::ForeignMod) -> ast::ForeignMod {
382 let foreign_mod = self.configure_foreign_mod(foreign_mod);
383 fold::noop_fold_foreign_mod(foreign_mod, self)
386 fn fold_item_kind(&mut self, item: ast::ItemKind) -> ast::ItemKind {
387 let item = self.configure_item_kind(item);
388 fold::noop_fold_item_kind(item, self)
391 fn fold_expr(&mut self, expr: P<ast::Expr>) -> P<ast::Expr> {
392 let mut expr = self.configure_expr(expr).into_inner();
393 expr.node = self.configure_expr_kind(expr.node);
394 P(fold::noop_fold_expr(expr, self))
397 fn fold_opt_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
398 let mut expr = configure!(self, expr).into_inner();
399 expr.node = self.configure_expr_kind(expr.node);
400 Some(P(fold::noop_fold_expr(expr, self)))
403 fn fold_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
404 match self.configure_stmt(stmt) {
405 Some(stmt) => fold::noop_fold_stmt(stmt, self),
406 None => return SmallVec::new(),
410 fn fold_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
411 fold::noop_fold_item(configure!(self, item), self)
414 fn fold_impl_item(&mut self, item: ast::ImplItem) -> SmallVec<[ast::ImplItem; 1]>
416 fold::noop_fold_impl_item(configure!(self, item), self)
419 fn fold_trait_item(&mut self, item: ast::TraitItem) -> SmallVec<[ast::TraitItem; 1]> {
420 fold::noop_fold_trait_item(configure!(self, item), self)
423 fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
424 // Don't configure interpolated AST (c.f. #34171).
425 // Interpolated AST will get configured once the surrounding tokens are parsed.
429 fn fold_pat(&mut self, pattern: P<ast::Pat>) -> P<ast::Pat> {
430 fold::noop_fold_pat(self.configure_pat(pattern), self)
434 fn is_cfg(attr: &ast::Attribute) -> bool {
435 attr.check_name("cfg")