Setup unstable feature attr parser

Author: tiif

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -162,6 +162,7 @@ pub enum AttributeKind {
     // tidy-alphabetical-start
     AllowConstFnUnstable(ThinVec<Symbol>),
     AllowInternalUnstable(ThinVec<(Symbol, Span)>),
+    AllowUnstableFeature(ThinVec<(Symbol, Span)>),
     BodyStability {
         stability: DefaultBodyStability,
         /// Span of the `#[rustc_default_body_unstable(...)]` attribute

compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs

@@ -22,6 +22,20 @@ impl CombineAttributeParser for AllowInternalUnstableParser {
     }
 }
 
+pub(crate) struct AllowUnstableFeatureParser;
+impl CombineAttributeParser for AllowUnstableFeatureParser {
+    const PATH: &'static [rustc_span::Symbol] = &[sym::allow_unstable_feature];
+    type Item = (Symbol, Span);
+    const CONVERT: ConvertFn<Self::Item> = AttributeKind::AllowUnstableFeature;
+
+    fn extend<'a>(
+        cx: &'a AcceptContext<'a>,
+        args: &'a ArgParser<'a>,
+    ) -> impl IntoIterator<Item = Self::Item> + 'a {
+        parse_unstable(cx, args, Self::PATH[0]).into_iter().zip(iter::repeat(cx.attr_span))
+    }
+}
+
 pub(crate) struct AllowConstFnUnstableParser;
 impl CombineAttributeParser for AllowConstFnUnstableParser {
     const PATH: &'static [rustc_span::Symbol] = &[sym::rustc_allow_const_fn_unstable];

compiler/rustc_attr_parsing/src/context.rs

@@ -11,7 +11,7 @@ use rustc_hir::{AttrArgs, AttrItem, AttrPath, Attribute, HashIgnoredAttrId};
 use rustc_session::Session;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, Symbol, sym};
 
-use crate::attributes::allow_unstable::{AllowConstFnUnstableParser, AllowInternalUnstableParser};
+use crate::attributes::allow_unstable::{AllowConstFnUnstableParser, AllowInternalUnstableParser, AllowUnstableFeatureParser};
 use crate::attributes::confusables::ConfusablesParser;
 use crate::attributes::deprecation::DeprecationParser;
 use crate::attributes::repr::ReprParser;
@@ -70,6 +70,7 @@ attribute_groups!(
         // tidy-alphabetical-start
         Combine<AllowConstFnUnstableParser>,
         Combine<AllowInternalUnstableParser>,
+        Combine<AllowUnstableFeatureParser>,
         Combine<ReprParser>,
         // tidy-alphabetical-end
 

compiler/rustc_span/src/symbol.rs

@@ -448,6 +448,7 @@ symbols! {
         allow_fail,
         allow_internal_unsafe,
         allow_internal_unstable,
+        allow_unstable_feature,
         altivec,
         alu32,
         always,