4 EXPLAIN_STMT_ATTR_SYNTAX,
11 use source_map::Spanned;
13 use parse::{token, ParseSess};
14 use smallvec::SmallVec;
15 use errors::Applicability;
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, node: T) -> Option<T> {
68 let node = self.process_cfg_attrs(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: T) -> T {
79 node.map_attrs(|attrs| {
80 attrs.into_iter().flat_map(|attr| self.process_cfg_attr(attr)).collect()
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() {
158 err.span_suggestion_with_applicability(
160 "expected syntax is",
162 Applicability::MaybeIncorrect,
169 let meta_item = if let Some(meta_item) = attr.meta() {
172 // Not a well-formed meta-item. Why? We don't know.
173 return error(attr.span, "`cfg` is not a well-formed meta-item",
174 "#[cfg(/* predicate */)]");
176 let nested_meta_items = if let Some(nested_meta_items) = meta_item.meta_item_list() {
179 return error(meta_item.span, "`cfg` is not followed by parentheses",
180 "cfg(/* predicate */)");
183 if nested_meta_items.is_empty() {
184 return error(meta_item.span, "`cfg` predicate is not specified", "");
185 } else if nested_meta_items.len() > 1 {
186 return error(nested_meta_items.last().unwrap().span,
187 "multiple `cfg` predicates are specified", "");
190 match nested_meta_items[0].meta_item() {
191 Some(meta_item) => attr::cfg_matches(meta_item, self.sess, self.features),
192 None => error(nested_meta_items[0].span,
193 "`cfg` predicate key cannot be a literal", ""),
198 /// Visit attributes on expression and statements (but not attributes on items in blocks).
199 fn visit_expr_attrs(&mut self, attrs: &[ast::Attribute]) {
200 // flag the offending attributes
201 for attr in attrs.iter() {
202 self.maybe_emit_expr_attr_err(attr);
206 /// If attributes are not allowed on expressions, emit an error for `attr`
207 pub fn maybe_emit_expr_attr_err(&self, attr: &ast::Attribute) {
208 if !self.features.map(|features| features.stmt_expr_attributes).unwrap_or(true) {
209 let mut err = feature_err(self.sess,
210 "stmt_expr_attributes",
213 EXPLAIN_STMT_ATTR_SYNTAX);
215 if attr.is_sugared_doc {
216 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
223 pub fn configure_foreign_mod(&mut self, foreign_mod: ast::ForeignMod) -> ast::ForeignMod {
225 abi: foreign_mod.abi,
226 items: foreign_mod.items.into_iter().filter_map(|item| self.configure(item)).collect(),
230 fn configure_variant_data(&mut self, vdata: ast::VariantData) -> ast::VariantData {
232 ast::VariantData::Struct(fields, id) => {
233 let fields = fields.into_iter().filter_map(|field| self.configure(field));
234 ast::VariantData::Struct(fields.collect(), id)
236 ast::VariantData::Tuple(fields, id) => {
237 let fields = fields.into_iter().filter_map(|field| self.configure(field));
238 ast::VariantData::Tuple(fields.collect(), id)
240 ast::VariantData::Unit(id) => ast::VariantData::Unit(id)
244 pub fn configure_item_kind(&mut self, item: ast::ItemKind) -> ast::ItemKind {
246 ast::ItemKind::Struct(def, generics) => {
247 ast::ItemKind::Struct(self.configure_variant_data(def), generics)
249 ast::ItemKind::Union(def, generics) => {
250 ast::ItemKind::Union(self.configure_variant_data(def), generics)
252 ast::ItemKind::Enum(def, generics) => {
253 let variants = def.variants.into_iter().filter_map(|v| {
254 self.configure(v).map(|v| {
256 node: ast::Variant_ {
259 data: self.configure_variant_data(v.node.data),
260 disr_expr: v.node.disr_expr,
266 ast::ItemKind::Enum(ast::EnumDef {
267 variants: variants.collect(),
274 pub fn configure_expr_kind(&mut self, expr_kind: ast::ExprKind) -> ast::ExprKind {
276 ast::ExprKind::Match(m, arms) => {
277 let arms = arms.into_iter().filter_map(|a| self.configure(a)).collect();
278 ast::ExprKind::Match(m, arms)
280 ast::ExprKind::Struct(path, fields, base) => {
281 let fields = fields.into_iter()
282 .filter_map(|field| {
283 self.configure(field)
286 ast::ExprKind::Struct(path, fields, base)
292 pub fn configure_expr(&mut self, expr: P<ast::Expr>) -> P<ast::Expr> {
293 self.visit_expr_attrs(expr.attrs());
295 // If an expr is valid to cfg away it will have been removed by the
296 // outer stmt or expression folder before descending in here.
297 // Anything else is always required, and thus has to error out
298 // in case of a cfg attr.
300 // N.B., this is intentionally not part of the fold_expr() function
301 // in order for fold_opt_expr() to be able to avoid this check
302 if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(a)) {
303 let msg = "removing an expression is not supported in this position";
304 self.sess.span_diagnostic.span_err(attr.span, msg);
307 self.process_cfg_attrs(expr)
310 pub fn configure_stmt(&mut self, stmt: ast::Stmt) -> Option<ast::Stmt> {
314 pub fn configure_struct_expr_field(&mut self, field: ast::Field) -> Option<ast::Field> {
315 self.configure(field)
318 pub fn configure_pat(&mut self, pattern: P<ast::Pat>) -> P<ast::Pat> {
319 pattern.map(|mut pattern| {
320 if let ast::PatKind::Struct(path, fields, etc) = pattern.node {
321 let fields = fields.into_iter()
322 .filter_map(|field| {
323 self.configure(field)
326 pattern.node = ast::PatKind::Struct(path, fields, etc);
332 // deny #[cfg] on generic parameters until we decide what to do with it.
334 pub fn disallow_cfg_on_generic_param(&mut self, param: &ast::GenericParam) {
335 for attr in param.attrs() {
336 let offending_attr = if attr.check_name("cfg") {
338 } else if attr.check_name("cfg_attr") {
343 let msg = format!("#[{}] cannot be applied on a generic parameter", offending_attr);
344 self.sess.span_diagnostic.span_err(attr.span, &msg);
349 impl<'a> fold::Folder for StripUnconfigured<'a> {
350 fn fold_foreign_mod(&mut self, foreign_mod: ast::ForeignMod) -> ast::ForeignMod {
351 let foreign_mod = self.configure_foreign_mod(foreign_mod);
352 fold::noop_fold_foreign_mod(foreign_mod, self)
355 fn fold_item_kind(&mut self, item: ast::ItemKind) -> ast::ItemKind {
356 let item = self.configure_item_kind(item);
357 fold::noop_fold_item_kind(item, self)
360 fn fold_expr(&mut self, expr: P<ast::Expr>) -> P<ast::Expr> {
361 let mut expr = self.configure_expr(expr).into_inner();
362 expr.node = self.configure_expr_kind(expr.node);
363 P(fold::noop_fold_expr(expr, self))
366 fn fold_opt_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
367 let mut expr = configure!(self, expr).into_inner();
368 expr.node = self.configure_expr_kind(expr.node);
369 Some(P(fold::noop_fold_expr(expr, self)))
372 fn fold_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
373 match self.configure_stmt(stmt) {
374 Some(stmt) => fold::noop_fold_stmt(stmt, self),
375 None => return SmallVec::new(),
379 fn fold_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
380 fold::noop_fold_item(configure!(self, item), self)
383 fn fold_impl_item(&mut self, item: ast::ImplItem) -> SmallVec<[ast::ImplItem; 1]>
385 fold::noop_fold_impl_item(configure!(self, item), self)
388 fn fold_trait_item(&mut self, item: ast::TraitItem) -> SmallVec<[ast::TraitItem; 1]> {
389 fold::noop_fold_trait_item(configure!(self, item), self)
392 fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
393 // Don't configure interpolated AST (cf. issue #34171).
394 // Interpolated AST will get configured once the surrounding tokens are parsed.
398 fn fold_pat(&mut self, pattern: P<ast::Pat>) -> P<ast::Pat> {
399 fold::noop_fold_pat(self.configure_pat(pattern), self)
403 fn is_cfg(attr: &ast::Attribute) -> bool {
404 attr.check_name("cfg")