Port feature to the new attribute system

Cargo.lock

@@ -3417,6 +3417,7 @@ dependencies = [
  "rustc_errors",
  "rustc_feature",
  "rustc_fluent_macro",
+ "rustc_hir",
  "rustc_macros",
  "rustc_session",
  "rustc_span",

compiler/rustc_ast_passes/Cargo.toml

@@ -14,6 +14,7 @@ rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_feature = { path = "../rustc_feature" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
+rustc_hir = { path = "../rustc_hir" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -1,11 +1,14 @@
 use rustc_ast as ast;
 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
 use rustc_ast::{NodeId, PatKind, attr, token};
+use rustc_attr_parsing::AttributeParser;
 use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP, BuiltinAttribute, Features};
+use rustc_hir::Attribute;
+use rustc_hir::attrs::AttributeKind;
 use rustc_session::Session;
 use rustc_session::parse::{feature_err, feature_warn};
 use rustc_span::source_map::Spanned;
-use rustc_span::{Span, Symbol, sym};
+use rustc_span::{DUMMY_SP, Span, Symbol, sym};
 use thin_vec::ThinVec;
 
 use crate::errors;
@@ -587,17 +590,27 @@ fn maybe_stage_features(sess: &Session, features: &Features, krate: &ast::Crate)
         return;
     }
     let mut errored = false;
-    for attr in krate.attrs.iter().filter(|attr| attr.has_name(sym::feature)) {
+
+    if let Some(Attribute::Parsed(AttributeKind::Feature(feature_idents, first_span))) =
+        AttributeParser::parse_limited(
+            sess,
+            &krate.attrs,
+            sym::feature,
+            DUMMY_SP,
+            krate.id,
+            Some(&features),
+        )
+    {
         // `feature(...)` used on non-nightly. This is definitely an error.
         let mut err = errors::FeatureOnNonNightly {
-            span: attr.span,
+            span: first_span,
             channel: option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)"),
             stable_features: vec![],
             sugg: None,
         };
 
         let mut all_stable = true;
-        for ident in attr.meta_item_list().into_iter().flatten().flat_map(|nested| nested.ident()) {
+        for ident in feature_idents {
             let name = ident.name;
             let stable_since = features
                 .enabled_lang_features()
@@ -612,7 +625,7 @@ fn maybe_stage_features(sess: &Session, features: &Features, krate: &ast::Crate)
             }
         }
         if all_stable {
-            err.sugg = Some(attr.span);
+            err.sugg = Some(first_span);
         }
         sess.dcx().emit_err(err);
         errored = true;

compiler/rustc_attr_parsing/messages.ftl

@@ -259,3 +259,7 @@ attr_parsing_whole_archive_needs_static =
 attr_parsing_limit_invalid =
     `limit` must be a non-negative integer
     .label = {$error_str}
+
+attr_parsing_feature_single_word =
+    rust features are always a single identifier, not paths with multiple segments
+    .help = did you maybe mean `{$first_segment}`?

compiler/rustc_attr_parsing/src/attributes/crate_level.rs

@@ -1,4 +1,5 @@
 use super::prelude::*;
+use crate::session_diagnostics::{FeatureExpectedSingleWord, LimitInvalid};
 
 pub(crate) struct CrateNameParser;
 
@@ -147,3 +148,55 @@ impl<S: Stage> NoArgsAttributeParser<S> for RustcCoherenceIsCoreParser {
     const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::CrateLevel;
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::RustcCoherenceIsCore;
 }
+
+pub(crate) struct FeatureParser;
+
+impl<S: Stage> CombineAttributeParser<S> for FeatureParser {
+    const PATH: &[Symbol] = &[sym::feature];
+    type Item = Ident;
+    const CONVERT: ConvertFn<Self::Item> = AttributeKind::Feature;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::CrateLevel;
+    const TEMPLATE: AttributeTemplate = template!(List: &["feature1, feature2, ..."]);
+
+    fn extend<'c>(
+        cx: &'c mut AcceptContext<'_, '_, S>,
+        args: &'c ArgParser<'_>,
+    ) -> impl IntoIterator<Item = Self::Item> + 'c {
+        let ArgParser::List(list) = args else {
+            cx.expected_list(cx.attr_span);
+            return Vec::new();
+        };
+
+        if list.is_empty() {
+            cx.warn_empty_attribute(cx.attr_span);
+        }
+
+        let mut res = Vec::new();
+
+        for elem in list.mixed() {
+            let Some(elem) = elem.meta_item() else {
+                cx.expected_identifier(elem.span());
+                continue;
+            };
+            if let Err(arg_span) = elem.args().no_args() {
+                cx.expected_no_args(arg_span);
+                continue;
+            }
+
+            let path = elem.path();
+            let Some(ident) = path.word() else {
+                let first_segment = elem.path().segments().next().expect("at least one segment");
+                cx.emit_err(FeatureExpectedSingleWord {
+                    span: path.span(),
+                    first_segment_span: first_segment.span,
+                    first_segment: first_segment.name,
+                });
+                continue;
+            };
+
+            res.push(ident);
+        }
+
+        res
+    }
+}

compiler/rustc_attr_parsing/src/context.rs

@@ -25,8 +25,9 @@ use crate::attributes::codegen_attrs::{
 };
 use crate::attributes::confusables::ConfusablesParser;
 use crate::attributes::crate_level::{
-    CrateNameParser, MoveSizeLimitParser, NoCoreParser, NoStdParser, PatternComplexityLimitParser,
-    RecursionLimitParser, RustcCoherenceIsCoreParser, TypeLengthLimitParser,
+    CrateNameParser, FeatureParser, MoveSizeLimitParser, NoCoreParser, NoStdParser,
+    PatternComplexityLimitParser, RecursionLimitParser, RustcCoherenceIsCoreParser,
+    TypeLengthLimitParser,
 };
 use crate::attributes::debugger::DebuggerViualizerParser;
 use crate::attributes::deprecation::DeprecationParser;
@@ -165,6 +166,7 @@ attribute_parsers!(
         Combine<AllowConstFnUnstableParser>,
         Combine<AllowInternalUnstableParser>,
         Combine<DebuggerViualizerParser>,
+        Combine<FeatureParser>,
         Combine<ForceTargetFeatureParser>,
         Combine<LinkParser>,
         Combine<ReprParser>,

compiler/rustc_attr_parsing/src/session_diagnostics.rs

@@ -968,3 +968,14 @@ pub(crate) struct LimitInvalid<'a> {
     pub value_span: Span,
     pub error_str: &'a str,
 }
+
+#[derive(Diagnostic)]
+#[diag(attr_parsing_feature_single_word)]
+pub(crate) struct FeatureExpectedSingleWord {
+    #[primary_span]
+    pub span: Span,
+
+    #[help]
+    pub first_segment_span: Span,
+    pub first_segment: Symbol,
+}

compiler/rustc_error_codes/src/error_codes/E0556.md

@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 The `feature` attribute was badly formed.
 
 Erroneous code example:
 
-```compile_fail,E0556
+```compile_fail
 #![feature(foo_bar_baz, foo(bar), foo = "baz", foo)] // error!
 #![feature] // error!
 #![feature = "foo"] // error!

compiler/rustc_error_codes/src/lib.rs

@@ -338,7 +338,7 @@ E0550: 0550,
 E0551: 0551,
 E0552: 0552,
 E0554: 0554,
-E0556: 0556,
+E0556: 0556, // REMOVED: merged with other attribute error codes
 E0557: 0557,
 E0559: 0559,
 E0560: 0560,

compiler/rustc_expand/src/config.rs

@@ -7,8 +7,8 @@ use rustc_ast::tokenstream::{
     AttrTokenStream, AttrTokenTree, LazyAttrTokenStream, Spacing, TokenTree,
 };
 use rustc_ast::{
-    self as ast, AttrKind, AttrStyle, Attribute, HasAttrs, HasTokens, MetaItem, MetaItemInner,
-    NodeId, NormalAttr,
+    self as ast, AttrKind, AttrStyle, Attribute, DUMMY_NODE_ID, HasAttrs, HasTokens, MetaItem,
+    MetaItemInner, NodeId, NormalAttr,
 };
 use rustc_attr_parsing as attr;
 use rustc_attr_parsing::validate_attr::deny_builtin_meta_unsafety;
@@ -21,16 +21,16 @@ use rustc_feature::{
     ACCEPTED_LANG_FEATURES, AttributeSafety, EnabledLangFeature, EnabledLibFeature, Features,
     REMOVED_LANG_FEATURES, UNSTABLE_LANG_FEATURES,
 };
+use rustc_hir::attrs::AttributeKind;
+use rustc_hir::{self as hir};
 use rustc_session::Session;
 use rustc_session::parse::feature_err;
-use rustc_span::{STDLIB_STABLE_CRATES, Span, Symbol, sym};
-use thin_vec::ThinVec;
+use rustc_span::{DUMMY_SP, STDLIB_STABLE_CRATES, Span, Symbol, sym};
 use tracing::instrument;
 
 use crate::errors::{
     CrateNameInCfgAttr, CrateTypeInCfgAttr, FeatureNotAllowed, FeatureRemoved,
-    FeatureRemovedReason, InvalidCfg, MalformedFeatureAttribute, MalformedFeatureAttributeHelp,
-    RemoveExprNotSupported,
+    FeatureRemovedReason, InvalidCfg, RemoveExprNotSupported,
 };
 
 /// A folder that strips out items that do not belong in the current configuration.
@@ -45,44 +45,23 @@ pub struct StripUnconfigured<'a> {
 }
 
 pub fn features(sess: &Session, krate_attrs: &[Attribute], crate_name: Symbol) -> Features {
-    fn feature_list(attr: &Attribute) -> ThinVec<ast::MetaItemInner> {
-        if attr.has_name(sym::feature)
-            && let Some(list) = attr.meta_item_list()
-        {
-            list
-        } else {
-            ThinVec::new()
-        }
-    }
-
     let mut features = Features::default();
 
-    // Process all features enabled in the code.
-    for attr in krate_attrs {
-        for mi in feature_list(attr) {
-            let name = match mi.ident() {
-                Some(ident) if mi.is_word() => ident.name,
-                Some(ident) => {
-                    sess.dcx().emit_err(MalformedFeatureAttribute {
-                        span: mi.span(),
-                        help: MalformedFeatureAttributeHelp::Suggestion {
-                            span: mi.span(),
-                            suggestion: ident.name,
-                        },
-                    });
-                    continue;
-                }
-                None => {
-                    sess.dcx().emit_err(MalformedFeatureAttribute {
-                        span: mi.span(),
-                        help: MalformedFeatureAttributeHelp::Label { span: mi.span() },
-                    });
-                    continue;
-                }
-            };
-
+    if let Some(hir::Attribute::Parsed(AttributeKind::Feature(feature_idents, _))) =
+        AttributeParser::parse_limited(
+            sess,
+            krate_attrs,
+            sym::feature,
+            DUMMY_SP,
+            DUMMY_NODE_ID,
+            Some(&features),
+        )
+    {
+        for feature_ident in feature_idents {
             // If the enabled feature has been removed, issue an error.
-            if let Some(f) = REMOVED_LANG_FEATURES.iter().find(|f| name == f.feature.name) {
+            if let Some(f) =
+                REMOVED_LANG_FEATURES.iter().find(|f| feature_ident.name == f.feature.name)
+            {
                 let pull_note = if let Some(pull) = f.pull {
                     format!(
                         "; see <https://github.com/rust-lang/rust/pull/{}> for more information",
@@ -92,7 +71,7 @@ pub fn features(sess: &Session, krate_attrs: &[Attribute], crate_name: Symbol) -
                     "".to_owned()
                 };
                 sess.dcx().emit_err(FeatureRemoved {
-                    span: mi.span(),
+                    span: feature_ident.span,
                     reason: f.reason.map(|reason| FeatureRemovedReason { reason }),
                     removed_rustc_version: f.feature.since,
                     pull_note,
@@ -101,10 +80,10 @@ pub fn features(sess: &Session, krate_attrs: &[Attribute], crate_name: Symbol) -
             }
 
             // If the enabled feature is stable, record it.
-            if let Some(f) = ACCEPTED_LANG_FEATURES.iter().find(|f| name == f.name) {
+            if let Some(f) = ACCEPTED_LANG_FEATURES.iter().find(|f| feature_ident.name == f.name) {
                 features.set_enabled_lang_feature(EnabledLangFeature {
-                    gate_name: name,
-                    attr_sp: mi.span(),
+                    gate_name: feature_ident.name,
+                    attr_sp: feature_ident.span,
                     stable_since: Some(Symbol::intern(f.since)),
                 });
                 continue;
@@ -114,38 +93,46 @@ pub fn features(sess: &Session, krate_attrs: &[Attribute], crate_name: Symbol) -
             // unstable and not also listed as one of the allowed features,
             // issue an error.
             if let Some(allowed) = sess.opts.unstable_opts.allow_features.as_ref() {
-                if allowed.iter().all(|f| name.as_str() != f) {
-                    sess.dcx().emit_err(FeatureNotAllowed { span: mi.span(), name });
+                if allowed.iter().all(|f| feature_ident.name.as_str() != f) {
+                    sess.dcx().emit_err(FeatureNotAllowed {
+                        span: feature_ident.span,
+                        name: feature_ident.name,
+                    });
                     continue;
                 }
             }
 
             // If the enabled feature is unstable, record it.
-            if UNSTABLE_LANG_FEATURES.iter().find(|f| name == f.name).is_some() {
+            if UNSTABLE_LANG_FEATURES.iter().find(|f| feature_ident.name == f.name).is_some() {
                 // When the ICE comes a standard library crate, there's a chance that the person
                 // hitting the ICE may be using -Zbuild-std or similar with an untested target.
                 // The bug is probably in the standard library and not the compiler in that case,
                 // but that doesn't really matter - we want a bug report.
-                if features.internal(name) && !STDLIB_STABLE_CRATES.contains(&crate_name) {
+                if features.internal(feature_ident.name)
+                    && !STDLIB_STABLE_CRATES.contains(&crate_name)
+                {
                     sess.using_internal_features.store(true, std::sync::atomic::Ordering::Relaxed);
                 }
 
                 features.set_enabled_lang_feature(EnabledLangFeature {
-                    gate_name: name,
-                    attr_sp: mi.span(),
+                    gate_name: feature_ident.name,
+                    attr_sp: feature_ident.span,
                     stable_since: None,
                 });
                 continue;
             }
 
             // Otherwise, the feature is unknown. Enable it as a lib feature.
             // It will be checked later whether the feature really exists.
-            features
-                .set_enabled_lib_feature(EnabledLibFeature { gate_name: name, attr_sp: mi.span() });
+            features.set_enabled_lib_feature(EnabledLibFeature {
+                gate_name: feature_ident.name,
+                attr_sp: feature_ident.span,
+            });
 
             // Similar to above, detect internal lib features to suppress
             // the ICE message that asks for a report.
-            if features.internal(name) && !STDLIB_STABLE_CRATES.contains(&crate_name) {
+            if features.internal(feature_ident.name) && !STDLIB_STABLE_CRATES.contains(&crate_name)
+            {
                 sess.using_internal_features.store(true, std::sync::atomic::Ordering::Relaxed);
             }
         }

compiler/rustc_expand/src/errors.rs

@@ -143,30 +143,6 @@ pub(crate) struct RecursionLimitReached {
     pub crate_name: Symbol,
 }
 
-#[derive(Diagnostic)]
-#[diag(expand_malformed_feature_attribute, code = E0556)]
-pub(crate) struct MalformedFeatureAttribute {
-    #[primary_span]
-    pub span: Span,
-    #[subdiagnostic]
-    pub help: MalformedFeatureAttributeHelp,
-}
-
-#[derive(Subdiagnostic)]
-pub(crate) enum MalformedFeatureAttributeHelp {
-    #[label(expand_expected)]
-    Label {
-        #[primary_span]
-        span: Span,
-    },
-    #[suggestion(expand_expected, code = "{suggestion}", applicability = "maybe-incorrect")]
-    Suggestion {
-        #[primary_span]
-        span: Span,
-        suggestion: Symbol,
-    },
-}
-
 #[derive(Diagnostic)]
 #[diag(expand_remove_expr_not_supported)]
 pub(crate) struct RemoveExprNotSupported {