1 use rustc_parse::validate_attr;
2 use syntax::attr::HasAttrs;
3 use syntax::feature_gate::{
5 EXPLAIN_STMT_ATTR_SYNTAX,
12 use syntax::edition::Edition;
13 use syntax::mut_visit::*;
15 use syntax::sess::ParseSess;
16 use syntax::util::map_in_place::MapInPlace;
17 use syntax_pos::symbol::sym;
19 use errors::Applicability;
20 use smallvec::SmallVec;
22 /// A folder that strips out items that do not belong in the current configuration.
23 pub struct StripUnconfigured<'a> {
24 pub sess: &'a ParseSess,
25 pub features: Option<&'a Features>,
28 // `cfg_attr`-process the crate's attributes and compute the crate's features.
29 pub fn features(mut krate: ast::Crate, sess: &ParseSess, edition: Edition,
30 allow_features: &Option<Vec<String>>) -> (ast::Crate, Features) {
33 let mut strip_unconfigured = StripUnconfigured {
38 let unconfigured_attrs = krate.attrs.clone();
39 let err_count = sess.span_diagnostic.err_count();
40 if let Some(attrs) = strip_unconfigured.configure(krate.attrs) {
42 } else { // the entire crate is unconfigured
43 krate.attrs = Vec::new();
44 krate.module.items = Vec::new();
45 return (krate, Features::new());
48 features = get_features(&sess.span_diagnostic, &krate.attrs, edition, allow_features);
50 // Avoid reconfiguring malformed `cfg_attr`s
51 if err_count == sess.span_diagnostic.err_count() {
52 strip_unconfigured.features = Some(&features);
53 strip_unconfigured.configure(unconfigured_attrs);
61 macro_rules! configure {
62 ($this:ident, $node:ident) => {
63 match $this.configure($node) {
65 None => return Default::default(),
70 impl<'a> StripUnconfigured<'a> {
71 pub fn configure<T: HasAttrs>(&mut self, mut node: T) -> Option<T> {
72 self.process_cfg_attrs(&mut node);
73 if self.in_cfg(node.attrs()) { Some(node) } else { None }
76 /// Parse and expand all `cfg_attr` attributes into a list of attributes
77 /// that are within each `cfg_attr` that has a true configuration predicate.
79 /// Gives compiler warnigns if any `cfg_attr` does not contain any
80 /// attributes and is in the original source code. Gives compiler errors if
81 /// the syntax of any `cfg_attr` is incorrect.
82 pub fn process_cfg_attrs<T: HasAttrs>(&mut self, node: &mut T) {
83 node.visit_attrs(|attrs| {
84 attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
88 /// Parse and expand a single `cfg_attr` attribute into a list of attributes
89 /// when the configuration predicate is true, or otherwise expand into an
90 /// empty list of attributes.
92 /// Gives a compiler warning when the `cfg_attr` contains no attributes and
93 /// is in the original source file. Gives a compiler error if the syntax of
94 /// the attribute is incorrect.
95 fn process_cfg_attr(&mut self, attr: ast::Attribute) -> Vec<ast::Attribute> {
96 if !attr.has_name(sym::cfg_attr) {
99 if attr.get_normal_item().tokens.is_empty() {
100 self.sess.span_diagnostic
103 "malformed `cfg_attr` attribute input",
106 "missing condition and attribute",
107 "#[cfg_attr(condition, attribute, other_attribute, ...)]".to_owned(),
108 Applicability::HasPlaceholders,
109 ).note("for more information, visit \
110 <https://doc.rust-lang.org/reference/conditional-compilation.html\
111 #the-cfg_attr-attribute>")
116 let res = rustc_parse::parse_in_attr(self.sess, &attr, |p| p.parse_cfg_attr());
117 let (cfg_predicate, expanded_attrs) = match res {
118 Ok(result) => result,
125 // Lint on zero attributes in source.
126 if expanded_attrs.is_empty() {
130 // At this point we know the attribute is considered used.
131 attr::mark_used(&attr);
133 if attr::cfg_matches(&cfg_predicate, self.sess, self.features) {
134 // We call `process_cfg_attr` recursively in case there's a
135 // `cfg_attr` inside of another `cfg_attr`. E.g.
136 // `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
137 expanded_attrs.into_iter()
138 .flat_map(|(item, span)| self.process_cfg_attr(attr::mk_attr_from_item(
149 /// Determines if a node with the given attributes should be included in this configuration.
150 pub fn in_cfg(&self, attrs: &[ast::Attribute]) -> bool {
151 attrs.iter().all(|attr| {
156 let error = |span, msg, suggestion: &str| {
157 let mut err = self.sess.span_diagnostic.struct_span_err(span, msg);
158 if !suggestion.is_empty() {
161 "expected syntax is",
163 Applicability::MaybeIncorrect,
170 let meta_item = match validate_attr::parse_meta(self.sess, attr) {
171 Ok(meta_item) => meta_item,
172 Err(mut err) => { err.emit(); return true; }
174 let nested_meta_items = if let Some(nested_meta_items) = meta_item.meta_item_list() {
177 return error(meta_item.span, "`cfg` is not followed by parentheses",
178 "cfg(/* predicate */)");
181 if nested_meta_items.is_empty() {
182 return error(meta_item.span, "`cfg` predicate is not specified", "");
183 } else if nested_meta_items.len() > 1 {
184 return error(nested_meta_items.last().unwrap().span(),
185 "multiple `cfg` predicates are specified", "");
188 match nested_meta_items[0].meta_item() {
189 Some(meta_item) => attr::cfg_matches(meta_item, self.sess, self.features),
190 None => error(nested_meta_items[0].span(),
191 "`cfg` predicate key cannot be a literal", ""),
196 /// Visit attributes on expression and statements (but not attributes on items in blocks).
197 fn visit_expr_attrs(&mut self, attrs: &[ast::Attribute]) {
198 // flag the offending attributes
199 for attr in attrs.iter() {
200 self.maybe_emit_expr_attr_err(attr);
204 /// If attributes are not allowed on expressions, emit an error for `attr`
205 pub fn maybe_emit_expr_attr_err(&self, attr: &ast::Attribute) {
206 if !self.features.map(|features| features.stmt_expr_attributes).unwrap_or(true) {
207 let mut err = feature_err(self.sess,
208 sym::stmt_expr_attributes,
211 EXPLAIN_STMT_ATTR_SYNTAX);
213 if attr.is_doc_comment() {
214 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
221 pub fn configure_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
222 let ast::ForeignMod { abi: _, items } = foreign_mod;
223 items.flat_map_in_place(|item| self.configure(item));
226 pub fn configure_generic_params(&mut self, params: &mut Vec<ast::GenericParam>) {
227 params.flat_map_in_place(|param| self.configure(param));
230 fn configure_variant_data(&mut self, vdata: &mut ast::VariantData) {
232 ast::VariantData::Struct(fields, ..) | ast::VariantData::Tuple(fields, _) =>
233 fields.flat_map_in_place(|field| self.configure(field)),
234 ast::VariantData::Unit(_) => {}
238 pub fn configure_item_kind(&mut self, item: &mut ast::ItemKind) {
240 ast::ItemKind::Struct(def, _generics) |
241 ast::ItemKind::Union(def, _generics) => self.configure_variant_data(def),
242 ast::ItemKind::Enum(ast::EnumDef { variants }, _generics) => {
243 variants.flat_map_in_place(|variant| self.configure(variant));
244 for variant in variants {
245 self.configure_variant_data(&mut variant.data);
252 pub fn configure_expr_kind(&mut self, expr_kind: &mut ast::ExprKind) {
254 ast::ExprKind::Match(_m, arms) => {
255 arms.flat_map_in_place(|arm| self.configure(arm));
257 ast::ExprKind::Struct(_path, fields, _base) => {
258 fields.flat_map_in_place(|field| self.configure(field));
264 pub fn configure_expr(&mut self, expr: &mut P<ast::Expr>) {
265 self.visit_expr_attrs(expr.attrs());
267 // If an expr is valid to cfg away it will have been removed by the
268 // outer stmt or expression folder before descending in here.
269 // Anything else is always required, and thus has to error out
270 // in case of a cfg attr.
272 // N.B., this is intentionally not part of the visit_expr() function
273 // in order for filter_map_expr() to be able to avoid this check
274 if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(a)) {
275 let msg = "removing an expression is not supported in this position";
276 self.sess.span_diagnostic.span_err(attr.span, msg);
279 self.process_cfg_attrs(expr)
282 pub fn configure_pat(&mut self, pat: &mut P<ast::Pat>) {
283 if let ast::PatKind::Struct(_path, fields, _etc) = &mut pat.kind {
284 fields.flat_map_in_place(|field| self.configure(field));
288 pub fn configure_fn_decl(&mut self, fn_decl: &mut ast::FnDecl) {
289 fn_decl.inputs.flat_map_in_place(|arg| self.configure(arg));
293 impl<'a> MutVisitor for StripUnconfigured<'a> {
294 fn visit_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
295 self.configure_foreign_mod(foreign_mod);
296 noop_visit_foreign_mod(foreign_mod, self);
299 fn visit_item_kind(&mut self, item: &mut ast::ItemKind) {
300 self.configure_item_kind(item);
301 noop_visit_item_kind(item, self);
304 fn visit_expr(&mut self, expr: &mut P<ast::Expr>) {
305 self.configure_expr(expr);
306 self.configure_expr_kind(&mut expr.kind);
307 noop_visit_expr(expr, self);
310 fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
311 let mut expr = configure!(self, expr);
312 self.configure_expr_kind(&mut expr.kind);
313 noop_visit_expr(&mut expr, self);
317 fn flat_map_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
318 noop_flat_map_stmt(configure!(self, stmt), self)
321 fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
322 noop_flat_map_item(configure!(self, item), self)
325 fn flat_map_impl_item(&mut self, item: ast::ImplItem) -> SmallVec<[ast::ImplItem; 1]> {
326 noop_flat_map_impl_item(configure!(self, item), self)
329 fn flat_map_trait_item(&mut self, item: ast::TraitItem) -> SmallVec<[ast::TraitItem; 1]> {
330 noop_flat_map_trait_item(configure!(self, item), self)
333 fn visit_mac(&mut self, _mac: &mut ast::Mac) {
334 // Don't configure interpolated AST (cf. issue #34171).
335 // Interpolated AST will get configured once the surrounding tokens are parsed.
338 fn visit_pat(&mut self, pat: &mut P<ast::Pat>) {
339 self.configure_pat(pat);
340 noop_visit_pat(pat, self)
343 fn visit_fn_decl(&mut self, mut fn_decl: &mut P<ast::FnDecl>) {
344 self.configure_fn_decl(&mut fn_decl);
345 noop_visit_fn_decl(fn_decl, self);
349 fn is_cfg(attr: &ast::Attribute) -> bool {
350 attr.check_name(sym::cfg)
353 /// Process the potential `cfg` attributes on a module.
354 /// Also determine if the module should be included in this configuration.
355 pub fn process_configure_mod(
358 attrs: &[ast::Attribute],
359 ) -> (bool, Vec<ast::Attribute>) {
360 // Don't perform gated feature checking.
361 let mut strip_unconfigured = StripUnconfigured { sess, features: None };
362 let mut attrs = attrs.to_owned();
363 strip_unconfigured.process_cfg_attrs(&mut attrs);
364 (!cfg_mods || strip_unconfigured.in_cfg(&attrs), attrs)