+//! Process the potential `cfg` attributes on a module.
+//! Also determine if the module should be included in this configuration.
+//!
+//! This module properly belongs in syntax_expand, but for now it's tied into
+//! parsing, so we leave it here to avoid complicated out-of-line dependencies.
+//!
+//! A principled solution to this wrong location would be to implement [#64197].
+//!
+//! [#64197]: https://github.com/rust-lang/rust/issues/64197
+
+use crate::validate_attr;
+use syntax::attr::HasAttrs;
+use syntax::feature_gate::{
+ feature_err,
+ EXPLAIN_STMT_ATTR_SYNTAX,
+ Features,
+ get_features,
+ GateIssue,
+};
+use syntax::attr;
+use syntax::ast;
+use syntax::edition::Edition;
+use syntax::mut_visit::*;
+use syntax::ptr::P;
+use syntax::sess::ParseSess;
+use syntax::util::map_in_place::MapInPlace;
+use syntax_pos::symbol::sym;
+
+use errors::Applicability;
+use smallvec::SmallVec;
+
+/// A folder that strips out items that do not belong in the current configuration.
+pub struct StripUnconfigured<'a> {
+ pub sess: &'a ParseSess,
+ pub features: Option<&'a Features>,
+}
+
+// `cfg_attr`-process the crate's attributes and compute the crate's features.
+pub fn features(mut krate: ast::Crate, sess: &ParseSess, edition: Edition,
+ allow_features: &Option<Vec<String>>) -> (ast::Crate, Features) {
+ let features;
+ {
+ let mut strip_unconfigured = StripUnconfigured {
+ sess,
+ features: None,
+ };
+
+ let unconfigured_attrs = krate.attrs.clone();
+ let err_count = sess.span_diagnostic.err_count();
+ if let Some(attrs) = strip_unconfigured.configure(krate.attrs) {
+ krate.attrs = attrs;
+ } else { // the entire crate is unconfigured
+ krate.attrs = Vec::new();
+ krate.module.items = Vec::new();
+ return (krate, Features::new());
+ }
+
+ features = get_features(&sess.span_diagnostic, &krate.attrs, edition, allow_features);
+
+ // Avoid reconfiguring malformed `cfg_attr`s
+ if err_count == sess.span_diagnostic.err_count() {
+ strip_unconfigured.features = Some(&features);
+ strip_unconfigured.configure(unconfigured_attrs);
+ }
+ }
+
+ (krate, features)
+}
+
+#[macro_export]
+macro_rules! configure {
+ ($this:ident, $node:ident) => {
+ match $this.configure($node) {
+ Some(node) => node,
+ None => return Default::default(),
+ }
+ }
+}
+
+impl<'a> StripUnconfigured<'a> {
+ pub fn configure<T: HasAttrs>(&mut self, mut node: T) -> Option<T> {
+ self.process_cfg_attrs(&mut node);
+ if self.in_cfg(node.attrs()) { Some(node) } else { None }
+ }
+
+ /// Parse and expand all `cfg_attr` attributes into a list of attributes
+ /// that are within each `cfg_attr` that has a true configuration predicate.
+ ///
+ /// Gives compiler warnigns if any `cfg_attr` does not contain any
+ /// attributes and is in the original source code. Gives compiler errors if
+ /// the syntax of any `cfg_attr` is incorrect.
+ pub fn process_cfg_attrs<T: HasAttrs>(&mut self, node: &mut T) {
+ node.visit_attrs(|attrs| {
+ attrs.flat_map_in_place(|attr| self.process_cfg_attr(attr));
+ });
+ }
+
+ /// Parse and expand a single `cfg_attr` attribute into a list of attributes
+ /// when the configuration predicate is true, or otherwise expand into an
+ /// empty list of attributes.
+ ///
+ /// Gives a compiler warning when the `cfg_attr` contains no attributes and
+ /// is in the original source file. Gives a compiler error if the syntax of
+ /// the attribute is incorrect.
+ fn process_cfg_attr(&mut self, attr: ast::Attribute) -> Vec<ast::Attribute> {
+ if !attr.has_name(sym::cfg_attr) {
+ return vec![attr];
+ }
+ if attr.get_normal_item().tokens.is_empty() {
+ self.sess.span_diagnostic
+ .struct_span_err(
+ attr.span,
+ "malformed `cfg_attr` attribute input",
+ ).span_suggestion(
+ attr.span,
+ "missing condition and attribute",
+ "#[cfg_attr(condition, attribute, other_attribute, ...)]".to_owned(),
+ Applicability::HasPlaceholders,
+ ).note("for more information, visit \
+ <https://doc.rust-lang.org/reference/conditional-compilation.html\
+ #the-cfg_attr-attribute>")
+ .emit();
+ return vec![];
+ }
+
+ let res = crate::parse_in_attr(self.sess, &attr, |p| p.parse_cfg_attr());
+ let (cfg_predicate, expanded_attrs) = match res {
+ Ok(result) => result,
+ Err(mut e) => {
+ e.emit();
+ return vec![];
+ }
+ };
+
+ // Lint on zero attributes in source.
+ if expanded_attrs.is_empty() {
+ return vec![attr];
+ }
+
+ // At this point we know the attribute is considered used.
+ attr::mark_used(&attr);
+
+ if attr::cfg_matches(&cfg_predicate, self.sess, self.features) {
+ // We call `process_cfg_attr` recursively in case there's a
+ // `cfg_attr` inside of another `cfg_attr`. E.g.
+ // `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
+ expanded_attrs.into_iter()
+ .flat_map(|(item, span)| self.process_cfg_attr(attr::mk_attr_from_item(
+ attr.style,
+ item,
+ span,
+ )))
+ .collect()
+ } else {
+ vec![]
+ }
+ }
+
+ /// Determines if a node with the given attributes should be included in this configuration.
+ pub fn in_cfg(&self, attrs: &[ast::Attribute]) -> bool {
+ attrs.iter().all(|attr| {
+ if !is_cfg(attr) {
+ return true;
+ }
+
+ let error = |span, msg, suggestion: &str| {
+ let mut err = self.sess.span_diagnostic.struct_span_err(span, msg);
+ if !suggestion.is_empty() {
+ err.span_suggestion(
+ span,
+ "expected syntax is",
+ suggestion.into(),
+ Applicability::MaybeIncorrect,
+ );
+ }
+ err.emit();
+ true
+ };
+
+ let meta_item = match validate_attr::parse_meta(self.sess, attr) {
+ Ok(meta_item) => meta_item,
+ Err(mut err) => { err.emit(); return true; }
+ };
+ let nested_meta_items = if let Some(nested_meta_items) = meta_item.meta_item_list() {
+ nested_meta_items
+ } else {
+ return error(meta_item.span, "`cfg` is not followed by parentheses",
+ "cfg(/* predicate */)");
+ };
+
+ if nested_meta_items.is_empty() {
+ return error(meta_item.span, "`cfg` predicate is not specified", "");
+ } else if nested_meta_items.len() > 1 {
+ return error(nested_meta_items.last().unwrap().span(),
+ "multiple `cfg` predicates are specified", "");
+ }
+
+ match nested_meta_items[0].meta_item() {
+ Some(meta_item) => attr::cfg_matches(meta_item, self.sess, self.features),
+ None => error(nested_meta_items[0].span(),
+ "`cfg` predicate key cannot be a literal", ""),
+ }
+ })
+ }
+
+ /// Visit attributes on expression and statements (but not attributes on items in blocks).
+ fn visit_expr_attrs(&mut self, attrs: &[ast::Attribute]) {
+ // flag the offending attributes
+ for attr in attrs.iter() {
+ self.maybe_emit_expr_attr_err(attr);
+ }
+ }
+
+ /// If attributes are not allowed on expressions, emit an error for `attr`
+ pub fn maybe_emit_expr_attr_err(&self, attr: &ast::Attribute) {
+ if !self.features.map(|features| features.stmt_expr_attributes).unwrap_or(true) {
+ let mut err = feature_err(self.sess,
+ sym::stmt_expr_attributes,
+ attr.span,
+ GateIssue::Language,
+ EXPLAIN_STMT_ATTR_SYNTAX);
+
+ if attr.is_doc_comment() {
+ err.help("`///` is for documentation comments. For a plain comment, use `//`.");
+ }
+
+ err.emit();
+ }
+ }
+
+ pub fn configure_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
+ let ast::ForeignMod { abi: _, items } = foreign_mod;
+ items.flat_map_in_place(|item| self.configure(item));
+ }
+
+ pub fn configure_generic_params(&mut self, params: &mut Vec<ast::GenericParam>) {
+ params.flat_map_in_place(|param| self.configure(param));
+ }
+
+ fn configure_variant_data(&mut self, vdata: &mut ast::VariantData) {
+ match vdata {
+ ast::VariantData::Struct(fields, ..) | ast::VariantData::Tuple(fields, _) =>
+ fields.flat_map_in_place(|field| self.configure(field)),
+ ast::VariantData::Unit(_) => {}
+ }
+ }
+
+ pub fn configure_item_kind(&mut self, item: &mut ast::ItemKind) {
+ match item {
+ ast::ItemKind::Struct(def, _generics) |
+ ast::ItemKind::Union(def, _generics) => self.configure_variant_data(def),
+ ast::ItemKind::Enum(ast::EnumDef { variants }, _generics) => {
+ variants.flat_map_in_place(|variant| self.configure(variant));
+ for variant in variants {
+ self.configure_variant_data(&mut variant.data);
+ }
+ }
+ _ => {}
+ }
+ }
+
+ pub fn configure_expr_kind(&mut self, expr_kind: &mut ast::ExprKind) {
+ match expr_kind {
+ ast::ExprKind::Match(_m, arms) => {
+ arms.flat_map_in_place(|arm| self.configure(arm));
+ }
+ ast::ExprKind::Struct(_path, fields, _base) => {
+ fields.flat_map_in_place(|field| self.configure(field));
+ }
+ _ => {}
+ }
+ }
+
+ pub fn configure_expr(&mut self, expr: &mut P<ast::Expr>) {
+ self.visit_expr_attrs(expr.attrs());
+
+ // If an expr is valid to cfg away it will have been removed by the
+ // outer stmt or expression folder before descending in here.
+ // Anything else is always required, and thus has to error out
+ // in case of a cfg attr.
+ //
+ // N.B., this is intentionally not part of the visit_expr() function
+ // in order for filter_map_expr() to be able to avoid this check
+ if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(a)) {
+ let msg = "removing an expression is not supported in this position";
+ self.sess.span_diagnostic.span_err(attr.span, msg);
+ }
+
+ self.process_cfg_attrs(expr)
+ }
+
+ pub fn configure_pat(&mut self, pat: &mut P<ast::Pat>) {
+ if let ast::PatKind::Struct(_path, fields, _etc) = &mut pat.kind {
+ fields.flat_map_in_place(|field| self.configure(field));
+ }
+ }
+
+ pub fn configure_fn_decl(&mut self, fn_decl: &mut ast::FnDecl) {
+ fn_decl.inputs.flat_map_in_place(|arg| self.configure(arg));
+ }
+}
+
+impl<'a> MutVisitor for StripUnconfigured<'a> {
+ fn visit_foreign_mod(&mut self, foreign_mod: &mut ast::ForeignMod) {
+ self.configure_foreign_mod(foreign_mod);
+ noop_visit_foreign_mod(foreign_mod, self);
+ }
+
+ fn visit_item_kind(&mut self, item: &mut ast::ItemKind) {
+ self.configure_item_kind(item);
+ noop_visit_item_kind(item, self);
+ }
+
+ fn visit_expr(&mut self, expr: &mut P<ast::Expr>) {
+ self.configure_expr(expr);
+ self.configure_expr_kind(&mut expr.kind);
+ noop_visit_expr(expr, self);
+ }
+
+ fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
+ let mut expr = configure!(self, expr);
+ self.configure_expr_kind(&mut expr.kind);
+ noop_visit_expr(&mut expr, self);
+ Some(expr)
+ }
+
+ fn flat_map_stmt(&mut self, stmt: ast::Stmt) -> SmallVec<[ast::Stmt; 1]> {
+ noop_flat_map_stmt(configure!(self, stmt), self)
+ }
+
+ fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
+ noop_flat_map_item(configure!(self, item), self)
+ }
+
+ fn flat_map_impl_item(&mut self, item: ast::ImplItem) -> SmallVec<[ast::ImplItem; 1]> {
+ noop_flat_map_impl_item(configure!(self, item), self)
+ }
+
+ fn flat_map_trait_item(&mut self, item: ast::TraitItem) -> SmallVec<[ast::TraitItem; 1]> {
+ noop_flat_map_trait_item(configure!(self, item), self)
+ }
+
+ fn visit_mac(&mut self, _mac: &mut ast::Mac) {
+ // Don't configure interpolated AST (cf. issue #34171).
+ // Interpolated AST will get configured once the surrounding tokens are parsed.
+ }
+
+ fn visit_pat(&mut self, pat: &mut P<ast::Pat>) {
+ self.configure_pat(pat);
+ noop_visit_pat(pat, self)
+ }
+
+ fn visit_fn_decl(&mut self, mut fn_decl: &mut P<ast::FnDecl>) {
+ self.configure_fn_decl(&mut fn_decl);
+ noop_visit_fn_decl(fn_decl, self);
+ }
+}
+
+fn is_cfg(attr: &ast::Attribute) -> bool {
+ attr.check_name(sym::cfg)
+}
+
+/// Process the potential `cfg` attributes on a module.
+/// Also determine if the module should be included in this configuration.
+pub fn process_configure_mod(
+ sess: &ParseSess,
+ cfg_mods: bool,
+ attrs: &[ast::Attribute],
+) -> (bool, Vec<ast::Attribute>) {
+ // Don't perform gated feature checking.
+ let mut strip_unconfigured = StripUnconfigured { sess, features: None };
+ let mut attrs = attrs.to_owned();
+ strip_unconfigured.process_cfg_attrs(&mut attrs);
+ (!cfg_mods || strip_unconfigured.in_cfg(&attrs), attrs)
+}