1 use crate::attr::HasAttrs;
2 use crate::feature_gate::{
4 EXPLAIN_STMT_ATTR_SYNTAX,
11 use crate::edition::Edition;
12 use crate::mut_visit::*;
15 use crate::sess::ParseSess;
16 use crate::symbol::sym;
17 use crate::util::map_in_place::MapInPlace;
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 = 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(ast::Attribute {
139 kind: ast::AttrKind::Normal(item),
140 id: attr::mk_attr_id(),
150 /// Determines if a node with the given attributes should be included in this configuration.
151 pub fn in_cfg(&mut self, attrs: &[ast::Attribute]) -> bool {
152 attrs.iter().all(|attr| {
157 let error = |span, msg, suggestion: &str| {
158 let mut err = self.sess.span_diagnostic.struct_span_err(span, msg);
159 if !suggestion.is_empty() {
162 "expected syntax is",
164 Applicability::MaybeIncorrect,
171 let meta_item = match attr.parse_meta(self.sess) {
172 Ok(meta_item) => meta_item,
173 Err(mut err) => { err.emit(); return true; }
175 let nested_meta_items = if let Some(nested_meta_items) = meta_item.meta_item_list() {
178 return error(meta_item.span, "`cfg` is not followed by parentheses",
179 "cfg(/* predicate */)");
182 if nested_meta_items.is_empty() {
183 return error(meta_item.span, "`cfg` predicate is not specified", "");
184 } else if nested_meta_items.len() > 1 {
185 return error(nested_meta_items.last().unwrap().span(),
186 "multiple `cfg` predicates are specified", "");
189 match nested_meta_items[0].meta_item() {
190 Some(meta_item) => attr::cfg_matches(meta_item, self.sess, self.features),
191 None => error(nested_meta_items[0].span(),
192 "`cfg` predicate key cannot be a literal", ""),
197 /// Visit attributes on expression and statements (but not attributes on items in blocks).
198 fn visit_expr_attrs(&mut self, attrs: &[ast::Attribute]) {
199 // flag the offending attributes
200 for attr in attrs.iter() {
201 self.maybe_emit_expr_attr_err(attr);
205 /// If attributes are not allowed on expressions, emit an error for `attr`
206 pub fn maybe_emit_expr_attr_err(&self, attr: &ast::Attribute) {
207 if !self.features.map(|features| features.stmt_expr_attributes).unwrap_or(true) {
208 let mut err = feature_err(self.sess,
209 sym::stmt_expr_attributes,
212 EXPLAIN_STMT_ATTR_SYNTAX);
214 if attr.is_doc_comment() {
215 err.help("`///` is for documentation comments. For a plain comment, use `//`.");
222 pub fn configure_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
223 let ast::ForeignMod { abi: _, items } = foreign_mod;
224 items.flat_map_in_place(|item| self.configure(item));
227 pub fn configure_generic_params(&mut self, params: &mut Vec<ast::GenericParam>) {
228 params.flat_map_in_place(|param| self.configure(param));
231 fn configure_variant_data(&mut self, vdata: &mut ast::VariantData) {
233 ast::VariantData::Struct(fields, ..) | ast::VariantData::Tuple(fields, _) =>
234 fields.flat_map_in_place(|field| self.configure(field)),
235 ast::VariantData::Unit(_) => {}
239 pub fn configure_item_kind(&mut self, item: &mut ast::ItemKind) {
241 ast::ItemKind::Struct(def, _generics) |
242 ast::ItemKind::Union(def, _generics) => self.configure_variant_data(def),
243 ast::ItemKind::Enum(ast::EnumDef { variants }, _generics) => {
244 variants.flat_map_in_place(|variant| self.configure(variant));
245 for variant in variants {
246 self.configure_variant_data(&mut variant.data);
253 pub fn configure_expr_kind(&mut self, expr_kind: &mut ast::ExprKind) {
255 ast::ExprKind::Match(_m, arms) => {
256 arms.flat_map_in_place(|arm| self.configure(arm));
258 ast::ExprKind::Struct(_path, fields, _base) => {
259 fields.flat_map_in_place(|field| self.configure(field));
265 pub fn configure_expr(&mut self, expr: &mut P<ast::Expr>) {
266 self.visit_expr_attrs(expr.attrs());
268 // If an expr is valid to cfg away it will have been removed by the
269 // outer stmt or expression folder before descending in here.
270 // Anything else is always required, and thus has to error out
271 // in case of a cfg attr.
273 // N.B., this is intentionally not part of the visit_expr() function
274 // in order for filter_map_expr() to be able to avoid this check
275 if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(a)) {
276 let msg = "removing an expression is not supported in this position";
277 self.sess.span_diagnostic.span_err(attr.span, msg);
280 self.process_cfg_attrs(expr)
283 pub fn configure_pat(&mut self, pat: &mut P<ast::Pat>) {
284 if let ast::PatKind::Struct(_path, fields, _etc) = &mut pat.kind {
285 fields.flat_map_in_place(|field| self.configure(field));
289 pub fn configure_fn_decl(&mut self, fn_decl: &mut ast::FnDecl) {
290 fn_decl.inputs.flat_map_in_place(|arg| self.configure(arg));
294 impl<'a> MutVisitor for StripUnconfigured<'a> {
295 fn visit_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
296 self.configure_foreign_mod(foreign_mod);
297 noop_visit_foreign_mod(foreign_mod, self);
300 fn visit_item_kind(&mut self, item: &mut ast::ItemKind) {
301 self.configure_item_kind(item);
302 noop_visit_item_kind(item, self);
305 fn visit_expr(&mut self, expr: &mut P<ast::Expr>) {
306 self.configure_expr(expr);
307 self.configure_expr_kind(&mut expr.kind);
308 noop_visit_expr(expr, self);
311 fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
312 let mut expr = configure!(self, expr);
313 self.configure_expr_kind(&mut expr.kind);
314 noop_visit_expr(&mut expr, self);
318 fn flat_map_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
319 noop_flat_map_stmt(configure!(self, stmt), self)
322 fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
323 noop_flat_map_item(configure!(self, item), self)
326 fn flat_map_impl_item(&mut self, item: ast::ImplItem) -> SmallVec<[ast::ImplItem; 1]> {
327 noop_flat_map_impl_item(configure!(self, item), self)
330 fn flat_map_trait_item(&mut self, item: ast::TraitItem) -> SmallVec<[ast::TraitItem; 1]> {
331 noop_flat_map_trait_item(configure!(self, item), self)
334 fn visit_mac(&mut self, _mac: &mut ast::Mac) {
335 // Don't configure interpolated AST (cf. issue #34171).
336 // Interpolated AST will get configured once the surrounding tokens are parsed.
339 fn visit_pat(&mut self, pat: &mut P<ast::Pat>) {
340 self.configure_pat(pat);
341 noop_visit_pat(pat, self)
344 fn visit_fn_decl(&mut self, mut fn_decl: &mut P<ast::FnDecl>) {
345 self.configure_fn_decl(&mut fn_decl);
346 noop_visit_fn_decl(fn_decl, self);
350 fn is_cfg(attr: &ast::Attribute) -> bool {
351 attr.check_name(sym::cfg)