1 //! Parsing and validation of builtin attributes
3 use rustc_ast::{self as ast, Attribute, Lit, LitKind, MetaItem, MetaItemKind, NestedMetaItem};
4 use rustc_ast_pretty::pprust;
5 use rustc_errors::{struct_span_err, Applicability};
6 use rustc_feature::{find_gated_cfg, is_builtin_attr_name, Features, GatedCfg};
7 use rustc_macros::HashStable_Generic;
8 use rustc_session::parse::{feature_err, ParseSess};
9 use rustc_session::Session;
10 use rustc_span::hygiene::Transparency;
11 use rustc_span::{symbol::sym, symbol::Symbol, Span};
12 use std::num::NonZeroU32;
14 pub fn is_builtin_attr(attr: &Attribute) -> bool {
15 attr.is_doc_comment() || attr.ident().filter(|ident| is_builtin_attr_name(ident.name)).is_some()
20 UnknownMetaItem(String, &'static [&'static str]),
24 MultipleStabilityLevels,
25 UnsupportedLiteral(&'static str, /* is_bytestr */ bool),
28 fn handle_errors(sess: &ParseSess, span: Span, error: AttrError) {
29 let diag = &sess.span_diagnostic;
31 AttrError::MultipleItem(item) => {
32 struct_span_err!(diag, span, E0538, "multiple '{}' items", item).emit();
34 AttrError::UnknownMetaItem(item, expected) => {
35 let expected = expected.iter().map(|name| format!("`{}`", name)).collect::<Vec<_>>();
36 struct_span_err!(diag, span, E0541, "unknown meta item '{}'", item)
37 .span_label(span, format!("expected one of {}", expected.join(", ")))
40 AttrError::MissingSince => {
41 struct_span_err!(diag, span, E0542, "missing 'since'").emit();
43 AttrError::NonIdentFeature => {
44 struct_span_err!(diag, span, E0546, "'feature' is not an identifier").emit();
46 AttrError::MissingFeature => {
47 struct_span_err!(diag, span, E0546, "missing 'feature'").emit();
49 AttrError::MultipleStabilityLevels => {
50 struct_span_err!(diag, span, E0544, "multiple stability levels").emit();
52 AttrError::UnsupportedLiteral(msg, is_bytestr) => {
53 let mut err = struct_span_err!(diag, span, E0565, "{}", msg);
55 if let Ok(lint_str) = sess.source_map().span_to_snippet(span) {
58 "consider removing the prefix",
59 lint_str[1..].to_string(),
60 Applicability::MaybeIncorrect,
69 #[derive(Copy, Clone, PartialEq, Encodable, Decodable, Debug)]
77 #[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
78 pub enum InstructionSetAttr {
83 #[derive(Clone, Encodable, Decodable, Debug)]
84 pub enum OptimizeAttr {
90 #[derive(Copy, Clone, PartialEq)]
96 /// Determine what `#[unwind]` attribute is present in `attrs`, if any.
97 pub fn find_unwind_attr(sess: &Session, attrs: &[Attribute]) -> Option<UnwindAttr> {
98 attrs.iter().fold(None, |ia, attr| {
99 if sess.check_name(attr, sym::unwind) {
100 if let Some(meta) = attr.meta() {
101 if let MetaItemKind::List(items) = meta.kind {
102 if items.len() == 1 {
103 if items[0].has_name(sym::allowed) {
104 return Some(UnwindAttr::Allowed);
105 } else if items[0].has_name(sym::aborts) {
106 return Some(UnwindAttr::Aborts);
114 "malformed `unwind` attribute input"
116 .span_label(attr.span, "invalid argument")
119 "the allowed arguments are `allowed` and `aborts`",
120 (vec!["allowed", "aborts"])
122 .map(|s| format!("#[unwind({})]", s)),
123 Applicability::MachineApplicable,
134 /// Represents the following attributes:
138 #[derive(Encodable, Decodable, Copy, Clone, Debug, PartialEq, Eq, Hash)]
139 #[derive(HashStable_Generic)]
140 pub struct Stability {
141 pub level: StabilityLevel,
145 /// Represents the `#[rustc_const_unstable]` and `#[rustc_const_stable]` attributes.
146 #[derive(Encodable, Decodable, Copy, Clone, Debug, PartialEq, Eq, Hash)]
147 #[derive(HashStable_Generic)]
148 pub struct ConstStability {
149 pub level: StabilityLevel,
151 /// whether the function has a `#[rustc_promotable]` attribute
152 pub promotable: bool,
155 /// The available stability levels.
156 #[derive(Encodable, Decodable, PartialEq, Copy, Clone, Debug, Eq, Hash)]
157 #[derive(HashStable_Generic)]
158 pub enum StabilityLevel {
159 // Reason for the current stability level and the relevant rust-lang issue
160 Unstable { reason: Option<Symbol>, issue: Option<NonZeroU32>, is_soft: bool },
161 Stable { since: Symbol },
164 impl StabilityLevel {
165 pub fn is_unstable(&self) -> bool {
166 matches!(self, StabilityLevel::Unstable { .. })
168 pub fn is_stable(&self) -> bool {
169 matches!(self, StabilityLevel::Stable { .. })
173 /// Collects stability info from all stability attributes in `attrs`.
174 /// Returns `None` if no stability attributes are found.
175 pub fn find_stability(
179 ) -> (Option<(Stability, Span)>, Option<(ConstStability, Span)>) {
180 find_stability_generic(sess, attrs.iter(), item_sp)
183 fn find_stability_generic<'a, I>(
187 ) -> (Option<(Stability, Span)>, Option<(ConstStability, Span)>)
189 I: Iterator<Item = &'a Attribute>,
191 use StabilityLevel::*;
193 let mut stab: Option<(Stability, Span)> = None;
194 let mut const_stab: Option<(ConstStability, Span)> = None;
195 let mut promotable = false;
197 let diagnostic = &sess.parse_sess.span_diagnostic;
199 'outer: for attr in attrs_iter {
201 sym::rustc_const_unstable,
202 sym::rustc_const_stable,
205 sym::rustc_promotable,
208 .any(|&s| attr.has_name(s))
210 continue; // not a stability level
213 sess.mark_attr_used(attr);
215 let meta = attr.meta();
217 if attr.has_name(sym::rustc_promotable) {
220 // attributes with data
221 else if let Some(MetaItem { kind: MetaItemKind::List(ref metas), .. }) = meta {
222 let meta = meta.as_ref().unwrap();
223 let get = |meta: &MetaItem, item: &mut Option<Symbol>| {
228 AttrError::MultipleItem(pprust::path_to_string(&meta.path)),
232 if let Some(v) = meta.value_str() {
236 struct_span_err!(diagnostic, meta.span, E0539, "incorrect meta item").emit();
241 let meta_name = meta.name_or_empty();
243 sym::rustc_const_unstable | sym::unstable => {
244 if meta_name == sym::unstable && stab.is_some() {
248 AttrError::MultipleStabilityLevels,
251 } else if meta_name == sym::rustc_const_unstable && const_stab.is_some() {
255 AttrError::MultipleStabilityLevels,
260 let mut feature = None;
261 let mut reason = None;
262 let mut issue = None;
263 let mut issue_num = None;
264 let mut is_soft = false;
266 if let Some(mi) = meta.meta_item() {
267 match mi.name_or_empty() {
269 if !get(mi, &mut feature) {
274 if !get(mi, &mut reason) {
279 if !get(mi, &mut issue) {
283 // These unwraps are safe because `get` ensures the meta item
284 // is a name/value pair string literal.
285 issue_num = match &*issue.unwrap().as_str() {
288 let emit_diag = |msg: &str| {
293 "`issue` must be a non-zero numeric string \
297 mi.name_value_literal_span().unwrap(),
302 match issue.parse() {
305 "`issue` must not be \"0\", \
306 use \"none\" instead",
310 Ok(num) => NonZeroU32::new(num),
312 emit_diag(&err.to_string());
321 let msg = "`soft` should not have any arguments";
322 sess.parse_sess.span_diagnostic.span_err(mi.span, msg);
330 AttrError::UnknownMetaItem(
331 pprust::path_to_string(&mi.path),
332 &["feature", "reason", "issue", "soft"],
342 AttrError::UnsupportedLiteral("unsupported literal", false),
348 match (feature, reason, issue) {
349 (Some(feature), reason, Some(_)) => {
350 if !rustc_lexer::is_ident(&feature.as_str()) {
354 AttrError::NonIdentFeature,
358 let level = Unstable { reason, issue: issue_num, is_soft };
359 if sym::unstable == meta_name {
360 stab = Some((Stability { level, feature }, attr.span));
363 ConstStability { level, feature, promotable: false },
369 handle_errors(&sess.parse_sess, attr.span, AttrError::MissingFeature);
373 struct_span_err!(diagnostic, attr.span, E0547, "missing 'issue'")
379 sym::rustc_const_stable | sym::stable => {
380 if meta_name == sym::stable && stab.is_some() {
384 AttrError::MultipleStabilityLevels,
387 } else if meta_name == sym::rustc_const_stable && const_stab.is_some() {
391 AttrError::MultipleStabilityLevels,
396 let mut feature = None;
397 let mut since = None;
400 NestedMetaItem::MetaItem(mi) => match mi.name_or_empty() {
402 if !get(mi, &mut feature) {
407 if !get(mi, &mut since) {
415 AttrError::UnknownMetaItem(
416 pprust::path_to_string(&mi.path),
423 NestedMetaItem::Literal(lit) => {
427 AttrError::UnsupportedLiteral("unsupported literal", false),
434 match (feature, since) {
435 (Some(feature), Some(since)) => {
436 let level = Stable { since };
437 if sym::stable == meta_name {
438 stab = Some((Stability { level, feature }, attr.span));
441 ConstStability { level, feature, promotable: false },
447 handle_errors(&sess.parse_sess, attr.span, AttrError::MissingFeature);
451 handle_errors(&sess.parse_sess, attr.span, AttrError::MissingSince);
461 // Merge the const-unstable info into the stability info
463 if let Some((ref mut stab, _)) = const_stab {
464 stab.promotable = promotable;
470 "`rustc_promotable` attribute must be paired with either a `rustc_const_unstable` \
471 or a `rustc_const_stable` attribute"
480 pub fn find_crate_name(sess: &Session, attrs: &[Attribute]) -> Option<Symbol> {
481 sess.first_attr_value_str_by_name(attrs, sym::crate_name)
484 /// Tests if a cfg-pattern matches the cfg set
485 pub fn cfg_matches(cfg: &ast::MetaItem, sess: &ParseSess, features: Option<&Features>) -> bool {
486 eval_condition(cfg, sess, features, &mut |cfg| {
487 try_gate_cfg(cfg, sess, features);
488 let error = |span, msg| {
489 sess.span_diagnostic.span_err(span, msg);
492 if cfg.path.segments.len() != 1 {
493 return error(cfg.path.span, "`cfg` predicate key must be an identifier");
496 MetaItemKind::List(..) => {
497 error(cfg.span, "unexpected parentheses after `cfg` predicate key")
499 MetaItemKind::NameValue(lit) if !lit.kind.is_str() => {
503 AttrError::UnsupportedLiteral(
504 "literal in `cfg` predicate value must be a string",
505 lit.kind.is_bytestr(),
510 MetaItemKind::NameValue(..) | MetaItemKind::Word => {
511 let ident = cfg.ident().expect("multi-segment cfg predicate");
512 sess.config.contains(&(ident.name, cfg.value_str()))
518 fn try_gate_cfg(cfg: &ast::MetaItem, sess: &ParseSess, features: Option<&Features>) {
519 let gate = find_gated_cfg(|sym| cfg.has_name(sym));
520 if let (Some(feats), Some(gated_cfg)) = (features, gate) {
521 gate_cfg(&gated_cfg, cfg.span, sess, feats);
525 fn gate_cfg(gated_cfg: &GatedCfg, cfg_span: Span, sess: &ParseSess, features: &Features) {
526 let (cfg, feature, has_feature) = gated_cfg;
527 if !has_feature(features) && !cfg_span.allows_unstable(*feature) {
528 let explain = format!("`cfg({})` is experimental and subject to change", cfg);
529 feature_err(sess, *feature, cfg_span, &explain).emit();
533 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
540 fn parse_version(s: &str, allow_appendix: bool) -> Option<Version> {
541 let mut components = s.split('-');
542 let d = components.next()?;
543 if !allow_appendix && components.next().is_some() {
546 let mut digits = d.splitn(3, '.');
547 let major = digits.next()?.parse().ok()?;
548 let minor = digits.next()?.parse().ok()?;
549 let patch = digits.next().unwrap_or("0").parse().ok()?;
550 Some(Version { major, minor, patch })
553 /// Evaluate a cfg-like condition (with `any` and `all`), using `eval` to
554 /// evaluate individual items.
555 pub fn eval_condition(
558 features: Option<&Features>,
559 eval: &mut impl FnMut(&ast::MetaItem) -> bool,
562 ast::MetaItemKind::List(ref mis) if cfg.name_or_empty() == sym::version => {
563 try_gate_cfg(cfg, sess, features);
564 let (min_version, span) = match &mis[..] {
565 [NestedMetaItem::Literal(Lit { kind: LitKind::Str(sym, ..), span, .. })] => {
568 [NestedMetaItem::Literal(Lit { span, .. })
569 | NestedMetaItem::MetaItem(MetaItem { span, .. })] => {
571 .struct_span_err(*span, "expected a version literal")
577 .struct_span_err(cfg.span, "expected single version literal")
582 let min_version = match parse_version(&min_version.as_str(), false) {
588 "unknown version literal format, assuming it refers to a future version",
594 let rustc_version = parse_version(env!("CFG_RELEASE"), true).unwrap();
596 // See https://github.com/rust-lang/rust/issues/64796#issuecomment-640851454 for details
597 if sess.assume_incomplete_release {
598 rustc_version > min_version
600 rustc_version >= min_version
603 ast::MetaItemKind::List(ref mis) => {
604 for mi in mis.iter() {
605 if !mi.is_meta_item() {
609 AttrError::UnsupportedLiteral("unsupported literal", false),
615 // The unwraps below may look dangerous, but we've already asserted
616 // that they won't fail with the loop above.
617 match cfg.name_or_empty() {
620 .any(|mi| eval_condition(mi.meta_item().unwrap(), sess, features, eval)),
623 .all(|mi| eval_condition(mi.meta_item().unwrap(), sess, features, eval)),
627 sess.span_diagnostic,
630 "expected 1 cfg-pattern"
636 !eval_condition(mis[0].meta_item().unwrap(), sess, features, eval)
640 sess.span_diagnostic,
643 "invalid predicate `{}`",
644 pprust::path_to_string(&cfg.path)
651 ast::MetaItemKind::Word | ast::MetaItemKind::NameValue(..) => eval(cfg),
655 #[derive(Debug, Encodable, Decodable, Clone, HashStable_Generic)]
656 pub struct Deprecation {
657 pub since: Option<Symbol>,
658 /// The note to issue a reason.
659 pub note: Option<Symbol>,
660 /// A text snippet used to completely replace any use of the deprecated item in an expression.
662 /// This is currently unstable.
663 pub suggestion: Option<Symbol>,
665 /// Whether to treat the since attribute as being a Rust version identifier
666 /// (rather than an opaque string).
667 pub is_since_rustc_version: bool,
670 /// Finds the deprecation attribute. `None` if none exists.
671 pub fn find_deprecation(sess: &Session, attrs: &[Attribute]) -> Option<(Deprecation, Span)> {
672 find_deprecation_generic(sess, attrs.iter())
675 fn find_deprecation_generic<'a, I>(sess: &Session, attrs_iter: I) -> Option<(Deprecation, Span)>
677 I: Iterator<Item = &'a Attribute>,
679 let mut depr: Option<(Deprecation, Span)> = None;
680 let diagnostic = &sess.parse_sess.span_diagnostic;
682 'outer: for attr in attrs_iter {
683 if !(sess.check_name(attr, sym::deprecated) || sess.check_name(attr, sym::rustc_deprecated))
688 if let Some((_, span)) = &depr {
689 struct_span_err!(diagnostic, attr.span, E0550, "multiple deprecated attributes")
690 .span_label(attr.span, "repeated deprecation attribute")
691 .span_label(*span, "first deprecation attribute")
696 let meta = match attr.meta() {
700 let mut since = None;
702 let mut suggestion = None;
704 MetaItemKind::Word => {}
705 MetaItemKind::NameValue(..) => note = meta.value_str(),
706 MetaItemKind::List(list) => {
707 let get = |meta: &MetaItem, item: &mut Option<Symbol>| {
712 AttrError::MultipleItem(pprust::path_to_string(&meta.path)),
716 if let Some(v) = meta.value_str() {
720 if let Some(lit) = meta.name_value_literal() {
724 AttrError::UnsupportedLiteral(
725 "literal in `deprecated` \
726 value must be a string",
727 lit.kind.is_bytestr(),
731 struct_span_err!(diagnostic, meta.span, E0551, "incorrect meta item")
741 NestedMetaItem::MetaItem(mi) => match mi.name_or_empty() {
743 if !get(mi, &mut since) {
747 sym::note if sess.check_name(attr, sym::deprecated) => {
748 if !get(mi, &mut note) {
752 sym::reason if sess.check_name(attr, sym::rustc_deprecated) => {
753 if !get(mi, &mut note) {
757 sym::suggestion if sess.check_name(attr, sym::rustc_deprecated) => {
758 if !get(mi, &mut suggestion) {
766 AttrError::UnknownMetaItem(
767 pprust::path_to_string(&mi.path),
768 if sess.check_name(attr, sym::deprecated) {
771 &["since", "reason", "suggestion"]
778 NestedMetaItem::Literal(lit) => {
782 AttrError::UnsupportedLiteral(
783 "item in `deprecated` must be a key/value pair",
794 if suggestion.is_some() && sess.check_name(attr, sym::deprecated) {
795 unreachable!("only allowed on rustc_deprecated")
798 if sess.check_name(attr, sym::rustc_deprecated) {
800 handle_errors(&sess.parse_sess, attr.span, AttrError::MissingSince);
805 struct_span_err!(diagnostic, attr.span, E0543, "missing 'reason'").emit();
810 sess.mark_attr_used(&attr);
812 let is_since_rustc_version = sess.check_name(attr, sym::rustc_deprecated);
813 depr = Some((Deprecation { since, note, suggestion, is_since_rustc_version }, attr.span));
819 #[derive(PartialEq, Debug, Encodable, Decodable, Copy, Clone)]
830 #[derive(Eq, PartialEq, Debug, Copy, Clone)]
831 #[derive(Encodable, Decodable, HashStable_Generic)]
833 SignedInt(ast::IntTy),
834 UnsignedInt(ast::UintTy),
839 pub fn is_signed(self) -> bool {
843 SignedInt(..) => true,
844 UnsignedInt(..) => false,
849 /// Parse #[repr(...)] forms.
851 /// Valid repr contents: any of the primitive integral type names (see
852 /// `int_type_of_word`, below) to specify enum discriminant type; `C`, to use
853 /// the same discriminant size that the corresponding C enum would or C
854 /// structure layout, `packed` to remove padding, and `transparent` to elegate representation
855 /// concerns to the only non-ZST field.
856 pub fn find_repr_attrs(sess: &Session, attr: &Attribute) -> Vec<ReprAttr> {
859 let mut acc = Vec::new();
860 let diagnostic = &sess.parse_sess.span_diagnostic;
861 if attr.has_name(sym::repr) {
862 if let Some(items) = attr.meta_item_list() {
863 sess.mark_attr_used(attr);
865 if !item.is_meta_item() {
869 AttrError::UnsupportedLiteral(
870 "meta item in `repr` must be an identifier",
877 let mut recognised = false;
879 let hint = match item.name_or_empty() {
880 sym::C => Some(ReprC),
881 sym::packed => Some(ReprPacked(1)),
882 sym::simd => Some(ReprSimd),
883 sym::transparent => Some(ReprTransparent),
884 sym::no_niche => Some(ReprNoNiche),
885 name => int_type_of_word(name).map(ReprInt),
888 if let Some(h) = hint {
892 } else if let Some((name, value)) = item.name_value_literal() {
893 let parse_alignment = |node: &ast::LitKind| -> Result<u32, &'static str> {
894 if let ast::LitKind::Int(literal, ast::LitIntType::Unsuffixed) = node {
895 if literal.is_power_of_two() {
896 // rustc_middle::ty::layout::Align restricts align to <= 2^29
897 if *literal <= 1 << 29 {
900 Err("larger than 2^29")
903 Err("not a power of two")
906 Err("not an unsuffixed integer")
910 let mut literal_error = None;
911 if name == sym::align {
913 match parse_alignment(&value.kind) {
914 Ok(literal) => acc.push(ReprAlign(literal)),
915 Err(message) => literal_error = Some(message),
917 } else if name == sym::packed {
919 match parse_alignment(&value.kind) {
920 Ok(literal) => acc.push(ReprPacked(literal)),
921 Err(message) => literal_error = Some(message),
924 if let Some(literal_error) = literal_error {
929 "invalid `repr(align)` attribute: {}",
934 } else if let Some(meta_item) = item.meta_item() {
935 if meta_item.has_name(sym::align) {
936 if let MetaItemKind::NameValue(ref value) = meta_item.kind {
938 let mut err = struct_span_err!(
942 "incorrect `repr(align)` attribute format"
945 ast::LitKind::Int(int, ast::LitIntType::Unsuffixed) => {
948 "use parentheses instead",
949 format!("align({})", int),
950 Applicability::MachineApplicable,
953 ast::LitKind::Str(s, _) => {
956 "use parentheses instead",
957 format!("align({})", s),
958 Applicability::MachineApplicable,
968 // Not a word we recognize
973 "unrecognized representation hint"
983 fn int_type_of_word(s: Symbol) -> Option<IntType> {
987 sym::i8 => Some(SignedInt(ast::IntTy::I8)),
988 sym::u8 => Some(UnsignedInt(ast::UintTy::U8)),
989 sym::i16 => Some(SignedInt(ast::IntTy::I16)),
990 sym::u16 => Some(UnsignedInt(ast::UintTy::U16)),
991 sym::i32 => Some(SignedInt(ast::IntTy::I32)),
992 sym::u32 => Some(UnsignedInt(ast::UintTy::U32)),
993 sym::i64 => Some(SignedInt(ast::IntTy::I64)),
994 sym::u64 => Some(UnsignedInt(ast::UintTy::U64)),
995 sym::i128 => Some(SignedInt(ast::IntTy::I128)),
996 sym::u128 => Some(UnsignedInt(ast::UintTy::U128)),
997 sym::isize => Some(SignedInt(ast::IntTy::Isize)),
998 sym::usize => Some(UnsignedInt(ast::UintTy::Usize)),
1003 pub enum TransparencyError {
1004 UnknownTransparency(Symbol, Span),
1005 MultipleTransparencyAttrs(Span, Span),
1008 pub fn find_transparency(
1010 attrs: &[Attribute],
1012 ) -> (Transparency, Option<TransparencyError>) {
1013 let mut transparency = None;
1014 let mut error = None;
1016 if sess.check_name(attr, sym::rustc_macro_transparency) {
1017 if let Some((_, old_span)) = transparency {
1018 error = Some(TransparencyError::MultipleTransparencyAttrs(old_span, attr.span));
1020 } else if let Some(value) = attr.value_str() {
1021 transparency = Some((
1023 sym::transparent => Transparency::Transparent,
1024 sym::semitransparent => Transparency::SemiTransparent,
1025 sym::opaque => Transparency::Opaque,
1027 error = Some(TransparencyError::UnknownTransparency(value, attr.span));
1036 let fallback = if macro_rules { Transparency::SemiTransparent } else { Transparency::Opaque };
1037 (transparency.map_or(fallback, |t| t.0), error)
1040 pub fn allow_internal_unstable<'a>(
1042 attrs: &'a [Attribute],
1043 ) -> impl Iterator<Item = Symbol> + 'a {
1044 allow_unstable(sess, attrs, sym::allow_internal_unstable)
1047 pub fn rustc_allow_const_fn_unstable<'a>(
1049 attrs: &'a [Attribute],
1050 ) -> impl Iterator<Item = Symbol> + 'a {
1051 allow_unstable(sess, attrs, sym::rustc_allow_const_fn_unstable)
1054 fn allow_unstable<'a>(
1056 attrs: &'a [Attribute],
1058 ) -> impl Iterator<Item = Symbol> + 'a {
1059 let attrs = sess.filter_by_name(attrs, symbol);
1061 .filter_map(move |attr| {
1062 attr.meta_item_list().or_else(|| {
1063 sess.diagnostic().span_err(
1065 &format!("`{}` expects a list of feature names", symbol.to_ident_string()),
1072 list.into_iter().filter_map(move |it| {
1073 let name = it.ident().map(|ident| ident.name);
1075 sess.diagnostic().span_err(
1077 &format!("`{}` expects feature names", symbol.to_ident_string()),