Rollup merge of #152164 - mu001999-contrib:lint/unused_features, r=JonathanBrouwer

Lint unused features

*[View all comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/rust/pull/152164)*

Fixes rust-lang/rust#44232
Fixes rust-lang/rust#151752

---

This PR records used features through query side effect, then reports unsued features finally.

compiler/rustc_driver_impl/src/lib.rs

@@ -338,7 +338,11 @@ pub fn run_compiler(at_args: &[String], callbacks: &mut (dyn Callbacks + Send))
                 }
             }
 
-            Some(Linker::codegen_and_build_linker(tcx, &*compiler.codegen_backend))
+            let linker = Linker::codegen_and_build_linker(tcx, &*compiler.codegen_backend);
+
+            tcx.report_unused_features();
+
+            Some(linker)
         });
 
         // Linking is done outside the `compiler.enter()` so that the

compiler/rustc_errors/src/lib.rs

@@ -7,9 +7,7 @@
 #![allow(rustc::direct_use_of_rustc_type_ir)]
 #![cfg_attr(bootstrap, feature(assert_matches))]
 #![feature(associated_type_defaults)]
-#![feature(box_patterns)]
 #![feature(default_field_values)]
-#![feature(error_reporter)]
 #![feature(macro_metavar_expr_concat)]
 #![feature(negative_impls)]
 #![feature(never_type)]

compiler/rustc_feature/src/builtin_attrs.rs

@@ -1330,7 +1330,7 @@ pub struct BuiltinAttribute {
         safety: AttributeSafety::Normal,
         template: template!(NameValueStr: "name"),
         duplicates: ErrorFollowing,
-        gate: Gated{
+        gate: Gated {
             feature: sym::rustc_attrs,
             message: "use of an internal attribute",
             check: Features::rustc_attrs,

compiler/rustc_feature/src/lib.rs

@@ -137,5 +137,5 @@ pub fn find_feature_issue(feature: Symbol, issue: GateIssue) -> Option<NonZero<u
 pub use removed::REMOVED_LANG_FEATURES;
 pub use unstable::{
     DEPENDENT_FEATURES, EnabledLangFeature, EnabledLibFeature, Features, INCOMPATIBLE_FEATURES,
-    UNSTABLE_LANG_FEATURES,
+    TRACK_FEATURE, UNSTABLE_LANG_FEATURES,
 };

compiler/rustc_feature/src/unstable.rs

@@ -3,11 +3,18 @@
 use std::path::PathBuf;
 use std::time::{SystemTime, UNIX_EPOCH};
 
+use rustc_data_structures::AtomicRef;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_span::{Span, Symbol, sym};
 
 use super::{Feature, to_nonzero};
 
+fn default_track_feature(_: Symbol) {}
+
+/// Recording used features in the dependency graph so incremental can
+/// replay used features when needed.
+pub static TRACK_FEATURE: AtomicRef<fn(Symbol)> = AtomicRef::new(&(default_track_feature as _));
+
 #[derive(PartialEq)]
 enum FeatureStatus {
     Default,
@@ -103,7 +110,12 @@ pub fn enabled_features_iter_stable_order(
 
     /// Is the given feature enabled (via `#[feature(...)]`)?
     pub fn enabled(&self, feature: Symbol) -> bool {
-        self.enabled_features.contains(&feature)
+        if self.enabled_features.contains(&feature) {
+            TRACK_FEATURE(feature);
+            true
+        } else {
+            false
+        }
     }
 }
 
@@ -124,7 +136,7 @@ macro_rules! declare_features {
         impl Features {
             $(
                 pub fn $feature(&self) -> bool {
-                    self.enabled_features.contains(&sym::$feature)
+                    self.enabled(sym::$feature)
                 }
             )*
 

compiler/rustc_interface/src/callbacks.rs

@@ -12,8 +12,9 @@
 use std::fmt;
 
 use rustc_errors::DiagInner;
-use rustc_middle::dep_graph::TaskDepsRef;
+use rustc_middle::dep_graph::{DepNodeIndex, QuerySideEffect, TaskDepsRef};
 use rustc_middle::ty::tls;
+use rustc_span::Symbol;
 
 fn track_span_parent(def_id: rustc_span::def_id::LocalDefId) {
     tls::with_context_opt(|icx| {
@@ -51,6 +52,25 @@ fn track_diagnostic<R>(diagnostic: DiagInner, f: &mut dyn FnMut(DiagInner) -> R)
     })
 }
 
+fn track_feature(feature: Symbol) {
+    tls::with_context_opt(|icx| {
+        let Some(icx) = icx else {
+            return;
+        };
+        let tcx = icx.tcx;
+
+        if let Some(dep_node_index) = tcx.sess.used_features.lock().get(&feature).copied() {
+            tcx.dep_graph.read_index(DepNodeIndex::from_u32(dep_node_index));
+        } else {
+            let dep_node_index = tcx
+                .dep_graph
+                .encode_side_effect(tcx, QuerySideEffect::CheckFeature { symbol: feature });
+            tcx.sess.used_features.lock().insert(feature, dep_node_index.as_u32());
+            tcx.dep_graph.read_index(dep_node_index);
+        }
+    })
+}
+
 /// This is a callback from `rustc_hir` as it cannot access the implicit state
 /// in `rustc_middle` otherwise.
 fn def_id_debug(def_id: rustc_hir::def_id::DefId, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -70,4 +90,5 @@ pub fn setup_callbacks() {
     rustc_span::SPAN_TRACK.swap(&(track_span_parent as fn(_)));
     rustc_hir::def_id::DEF_ID_DEBUG.swap(&(def_id_debug as fn(_, &mut fmt::Formatter<'_>) -> _));
     rustc_errors::TRACK_DIAGNOSTIC.swap(&(track_diagnostic as _));
+    rustc_feature::TRACK_FEATURE.swap(&(track_feature as _));
 }

compiler/rustc_lint_defs/src/builtin.rs

@@ -1088,11 +1088,6 @@
     /// crate-level [`feature` attributes].
     ///
     /// [`feature` attributes]: https://doc.rust-lang.org/nightly/unstable-book/
-    ///
-    /// Note: This lint is currently not functional, see [issue #44232] for
-    /// more details.
-    ///
-    /// [issue #44232]: https://github.com/rust-lang/rust/issues/44232
     pub UNUSED_FEATURES,
     Warn,
     "unused features found in crate-level `#[feature]` directives"

compiler/rustc_middle/src/dep_graph/graph.rs

@@ -17,6 +17,7 @@
 use rustc_macros::{Decodable, Encodable};
 use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
 use rustc_session::Session;
+use rustc_span::Symbol;
 use tracing::{debug, instrument};
 #[cfg(debug_assertions)]
 use {super::debug::EdgeFilter, std::env};
@@ -45,6 +46,11 @@ pub enum QuerySideEffect {
     /// the query as green, as that query will have the side
     /// effect dep node as a dependency.
     Diagnostic(DiagInner),
+    /// Records the feature used during query execution.
+    /// This feature will be inserted into `sess.used_features`
+    /// if we mark the query as green, as that query will have
+    /// the side effect dep node as a dependency.
+    CheckFeature { symbol: Symbol },
 }
 #[derive(Clone)]
 pub struct DepGraph {
@@ -514,29 +520,40 @@ pub fn read_index(&self, dep_node_index: DepNodeIndex) {
         }
     }
 
-    /// This encodes a diagnostic by creating a node with an unique index and associating
-    /// `diagnostic` with it, for use in the next session.
+    /// This encodes a side effect by creating a node with an unique index and associating
+    /// it with the node, for use in the next session.
     #[inline]
     pub fn record_diagnostic<'tcx>(&self, tcx: TyCtxt<'tcx>, diagnostic: &DiagInner) {
         if let Some(ref data) = self.data {
             read_deps(|task_deps| match task_deps {
                 TaskDepsRef::EvalAlways | TaskDepsRef::Ignore => return,
                 TaskDepsRef::Forbid | TaskDepsRef::Allow(..) => {
-                    self.read_index(data.encode_diagnostic(tcx, diagnostic));
+                    let dep_node_index = data
+                        .encode_side_effect(tcx, QuerySideEffect::Diagnostic(diagnostic.clone()));
+                    self.read_index(dep_node_index);
                 }
             })
         }
     }
-    /// This forces a diagnostic node green by running its side effect. `prev_index` would
-    /// refer to a node created used `encode_diagnostic` in the previous session.
+    /// This forces a side effect node green by running its side effect. `prev_index` would
+    /// refer to a node created used `encode_side_effect` in the previous session.
     #[inline]
-    pub fn force_diagnostic_node<'tcx>(
+    pub fn force_side_effect<'tcx>(&self, tcx: TyCtxt<'tcx>, prev_index: SerializedDepNodeIndex) {
+        if let Some(ref data) = self.data {
+            data.force_side_effect(tcx, prev_index);
+        }
+    }
+
+    #[inline]
+    pub fn encode_side_effect<'tcx>(
         &self,
         tcx: TyCtxt<'tcx>,
-        prev_index: SerializedDepNodeIndex,
-    ) {
+        side_effect: QuerySideEffect,
+    ) -> DepNodeIndex {
         if let Some(ref data) = self.data {
-            data.force_diagnostic_node(tcx, prev_index);
+            data.encode_side_effect(tcx, side_effect)
+        } else {
+            self.next_virtual_depnode_index()
         }
     }
 
@@ -673,10 +690,14 @@ pub fn mark_debug_loaded_from_disk(&self, dep_node: DepNode) {
         self.debug_loaded_from_disk.lock().insert(dep_node);
     }
 
-    /// This encodes a diagnostic by creating a node with an unique index and associating
-    /// `diagnostic` with it, for use in the next session.
+    /// This encodes a side effect by creating a node with an unique index and associating
+    /// it with the node, for use in the next session.
     #[inline]
-    fn encode_diagnostic<'tcx>(&self, tcx: TyCtxt<'tcx>, diagnostic: &DiagInner) -> DepNodeIndex {
+    fn encode_side_effect<'tcx>(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        side_effect: QuerySideEffect,
+    ) -> DepNodeIndex {
         // Use `send_new` so we get an unique index, even though the dep node is not.
         let dep_node_index = self.current.encoder.send_new(
             DepNode {
@@ -684,28 +705,21 @@ fn encode_diagnostic<'tcx>(&self, tcx: TyCtxt<'tcx>, diagnostic: &DiagInner) ->
                 key_fingerprint: PackedFingerprint::from(Fingerprint::ZERO),
             },
             Fingerprint::ZERO,
-            // We want the side effect node to always be red so it will be forced and emit the
-            // diagnostic.
+            // We want the side effect node to always be red so it will be forced and run the
+            // side effect.
             std::iter::once(DepNodeIndex::FOREVER_RED_NODE).collect(),
         );
-        let side_effect = QuerySideEffect::Diagnostic(diagnostic.clone());
         tcx.store_side_effect(dep_node_index, side_effect);
         dep_node_index
     }
 
-    /// This forces a diagnostic node green by running its side effect. `prev_index` would
-    /// refer to a node created used `encode_diagnostic` in the previous session.
+    /// This forces a side effect node green by running its side effect. `prev_index` would
+    /// refer to a node created used `encode_side_effect` in the previous session.
     #[inline]
-    fn force_diagnostic_node<'tcx>(&self, tcx: TyCtxt<'tcx>, prev_index: SerializedDepNodeIndex) {
+    fn force_side_effect<'tcx>(&self, tcx: TyCtxt<'tcx>, prev_index: SerializedDepNodeIndex) {
         with_deps(TaskDepsRef::Ignore, || {
             let side_effect = tcx.load_side_effect(prev_index).unwrap();
 
-            match &side_effect {
-                QuerySideEffect::Diagnostic(diagnostic) => {
-                    tcx.dcx().emit_diagnostic(diagnostic.clone());
-                }
-            }
-
             // Use `send_and_color` as `promote_node_and_deps_to_current` expects all
             // green dependencies. `send_and_color` will also prevent multiple nodes
             // being encoded for concurrent calls.
@@ -720,6 +734,16 @@ fn force_diagnostic_node<'tcx>(&self, tcx: TyCtxt<'tcx>, prev_index: SerializedD
                 std::iter::once(DepNodeIndex::FOREVER_RED_NODE).collect(),
                 true,
             );
+
+            match &side_effect {
+                QuerySideEffect::Diagnostic(diagnostic) => {
+                    tcx.dcx().emit_diagnostic(diagnostic.clone());
+                }
+                QuerySideEffect::CheckFeature { symbol } => {
+                    tcx.sess.used_features.lock().insert(*symbol, dep_node_index.as_u32());
+                }
+            }
+
             // This will just overwrite the same value for concurrent calls.
             tcx.store_side_effect(dep_node_index, side_effect);
         })

compiler/rustc_middle/src/ty/context.rs

@@ -36,7 +36,7 @@
 use rustc_hir::intravisit::VisitorExt;
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::limit::Limit;
-use rustc_hir::{self as hir, HirId, Node, TraitCandidate, find_attr};
+use rustc_hir::{self as hir, CRATE_HIR_ID, HirId, Node, TraitCandidate, find_attr};
 use rustc_index::IndexVec;
 use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
 use rustc_session::Session;
@@ -1688,6 +1688,36 @@ pub fn finish(self) {
             self.sess.dcx().emit_fatal(crate::error::FailedWritingFile { path: &path, error });
         }
     }
+
+    pub fn report_unused_features(self) {
+        // Collect first to avoid holding the lock while linting.
+        let used_features = self.sess.used_features.lock();
+        let unused_features = self
+            .features()
+            .enabled_features_iter_stable_order()
+            .filter(|(f, _)| {
+                !used_features.contains_key(f)
+                // FIXME: `restricted_std` is used to tell a standard library built
+                // for a platform that it doesn't know how to support. But it
+                // could only gate a private mod (see `__restricted_std_workaround`)
+                // with `cfg(not(restricted_std))`, so it cannot be recorded as used
+                // in downstream crates. It should never be linted, but should we
+                // hack this in the linter to ignore it?
+                && f.as_str() != "restricted_std"
+            })
+            .collect::<Vec<_>>();
+
+        for (feature, span) in unused_features {
+            self.node_span_lint(
+                rustc_session::lint::builtin::UNUSED_FEATURES,
+                CRATE_HIR_ID,
+                span,
+                |lint| {
+                    lint.primary_message(format!("feature `{}` is declared but not used", feature));
+                },
+            );
+        }
+    }
 }
 
 macro_rules! nop_lift {

compiler/rustc_query_impl/src/dep_kind_vtables.rs

@@ -40,7 +40,7 @@ pub(crate) fn SideEffect<'tcx>() -> DepKindVTable<'tcx> {
             is_eval_always: false,
             key_fingerprint_style: KeyFingerprintStyle::Unit,
             force_from_dep_node_fn: Some(|tcx, _, prev_index| {
-                tcx.dep_graph.force_diagnostic_node(tcx, prev_index);
+                tcx.dep_graph.force_side_effect(tcx, prev_index);
                 true
             }),
             promote_from_disk_fn: None,

compiler/rustc_session/src/session.rs

@@ -166,6 +166,11 @@ pub struct Session {
     /// Used by `-Zmir-opt-bisect-limit` to assign an index to each
     /// optimization-pass execution candidate during this compilation.
     pub mir_opt_bisect_eval_count: AtomicUsize,
+
+    /// Enabled features that are used in the current compilation.
+    ///
+    /// The value is the `DepNodeIndex` of the node encodes the used feature.
+    pub used_features: Lock<FxHashMap<Symbol, u32>>,
 }
 
 #[derive(Clone, Copy)]
@@ -1096,6 +1101,7 @@ pub fn build_session(
         replaced_intrinsics: FxHashSet::default(), // filled by `run_compiler`
         thin_lto_supported: true,                  // filled by `run_compiler`
         mir_opt_bisect_eval_count: AtomicUsize::new(0),
+        used_features: Lock::default(),
     };
 
     validate_commandline_args_with_session_available(&sess);

library/alloctests/tests/lib.rs

@@ -1,6 +1,5 @@
 #![feature(allocator_api)]
 #![feature(binary_heap_pop_if)]
-#![feature(btree_merge)]
 #![feature(const_heap)]
 #![feature(deque_extend_front)]
 #![feature(iter_array_chunks)]

library/core/src/num/f16.rs

@@ -1521,7 +1521,11 @@ pub const fn algebraic_rem(self, rhs: f16) -> f16 {
 // Functions in this module fall into `core_float_math`
 // #[unstable(feature = "core_float_math", issue = "137578")]
 #[cfg(not(test))]
-#[doc(test(attr(feature(cfg_target_has_reliable_f16_f128), expect(internal_features))))]
+#[doc(test(attr(
+    feature(cfg_target_has_reliable_f16_f128),
+    expect(internal_features),
+    allow(unused_features)
+)))]
 impl f16 {
     /// Returns the largest integer less than or equal to `self`.
     ///

library/core/src/num/f32.rs

@@ -393,6 +393,7 @@ pub mod consts {
     pub const LN_10: f32 = 2.30258509299404568401799145468436421_f32;
 }
 
+#[doc(test(attr(allow(unused_features))))]
 impl f32 {
     /// The radix or base of the internal representation of `f32`.
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]

library/core/src/num/f64.rs

@@ -393,6 +393,7 @@ pub mod consts {
     pub const LN_10: f64 = 2.30258509299404568401799145468436421_f64;
 }
 
+#[doc(test(attr(allow(unused_features))))]
 impl f64 {
     /// The radix or base of the internal representation of `f64`.
     #[stable(feature = "assoc_int_consts", since = "1.43.0")]

library/coretests/tests/lib.rs

@@ -50,7 +50,6 @@
 #![feature(f16)]
 #![feature(f128)]
 #![feature(float_algebraic)]
-#![feature(float_bits_const)]
 #![feature(float_exact_integer_constants)]
 #![feature(float_gamma)]
 #![feature(float_minimum_maximum)]

library/std/src/num/f16.rs

@@ -16,6 +16,7 @@
 use crate::sys::cmath;
 
 #[cfg(not(test))]
+#[doc(test(attr(allow(unused_features))))]
 impl f16 {
     /// Raises a number to a floating point power.
     ///

library/std/src/process.rs

@@ -1381,6 +1381,7 @@ impl Output {
     /// # Examples
     ///
     /// ```
+    /// # #![allow(unused_features)]
     /// #![feature(exit_status_error)]
     /// # #[cfg(all(unix, not(target_os = "android"), not(all(target_vendor = "apple", not(target_os = "macos")))))] {
     /// use std::process::Command;
@@ -1960,6 +1961,7 @@ impl crate::sealed::Sealed for ExitStatusError {}
 pub struct ExitStatusError(imp::ExitStatusError);
 
 #[unstable(feature = "exit_status_error", issue = "84908")]
+#[doc(test(attr(allow(unused_features))))]
 impl ExitStatusError {
     /// Reports the exit code, if applicable, from an `ExitStatusError`.
     ///

src/tools/miri/src/lib.rs

@@ -43,6 +43,8 @@
     clippy::collapsible_match,
     // We are not implementing queries here so it's fine
     rustc::potential_query_instability,
+    // FIXME: Unused features should be removed in the future
+    unused_features,
 )]
 #![warn(
     rust_2018_idioms,

src/tools/rust-analyzer/crates/proc-macro-api/src/lib.rs

@@ -10,7 +10,7 @@
     feature = "sysroot-abi",
     feature(proc_macro_internals, proc_macro_diagnostic, proc_macro_span)
 )]
-#![allow(internal_features)]
+#![allow(internal_features, unused_features)]
 #![cfg_attr(feature = "in-rust-tree", feature(rustc_private))]
 
 #[cfg(feature = "in-rust-tree")]

src/tools/rust-analyzer/crates/proc-macro-srv/src/lib.rs

@@ -18,7 +18,8 @@
     internal_features,
     clippy::disallowed_types,
     clippy::print_stderr,
-    unused_crate_dependencies
+    unused_crate_dependencies,
+    unused_features
 )]
 #![deny(deprecated_safe, clippy::undocumented_unsafe_blocks)]
 

src/tools/test-float-parse/src/lib.rs

@@ -1,5 +1,5 @@
-#![feature(f16)]
 #![feature(cfg_target_has_reliable_f16_f128)]
+#![cfg_attr(target_has_reliable_f16, feature(f16))]
 #![expect(internal_features)] // reliable_f16_f128
 
 mod traits;

tests/incremental/add_private_fn_at_krate_root_cc/struct_point.rs

@@ -9,7 +9,6 @@
 //@ ignore-backends: gcc
 
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 #![allow(dead_code)]
 #![crate_type = "rlib"]
 

tests/incremental/change_add_field/struct_point.rs

@@ -9,7 +9,6 @@
 //@ ignore-backends: gcc
 
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 #![allow(dead_code)]
 #![crate_type = "rlib"]
 

tests/incremental/change_crate_dep_kind.rs

@@ -8,7 +8,7 @@
 //@ build-pass (FIXME(62277): could be check-pass?)
 //@ ignore-backends: gcc
 
-#![feature(panic_unwind)]
+#![cfg_attr(cfail1, feature(panic_unwind))]
 
 // Turn the panic_unwind crate from an explicit into an implicit query:
 #[cfg(cfail1)]

tests/incremental/change_private_fn/struct_point.rs

@@ -7,7 +7,6 @@
 //@ ignore-backends: gcc
 
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 #![allow(dead_code)]
 #![crate_type = "rlib"]
 

tests/incremental/change_private_fn_cc/struct_point.rs

@@ -9,7 +9,6 @@
 
 #![crate_type = "rlib"]
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 #![allow(dead_code)]
 
 #![rustc_partition_reused(module="struct_point-fn_calls_methods_in_same_impl", cfg="cfail2")]

tests/incremental/change_private_impl_method/struct_point.rs

@@ -7,7 +7,6 @@
 //@ ignore-backends: gcc
 
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 #![allow(dead_code)]
 #![crate_type = "rlib"]
 

tests/incremental/change_private_impl_method_cc/struct_point.rs

@@ -9,7 +9,6 @@
 
 #![crate_type = "rlib"]
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 #![allow(dead_code)]
 
 #![rustc_partition_reused(module="struct_point-fn_read_field", cfg="cfail2")]

tests/incremental/change_pub_inherent_method_body/struct_point.rs

@@ -7,7 +7,6 @@
 
 #![crate_type = "rlib"]
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 #![allow(dead_code)]
 
 #![rustc_partition_codegened(module="struct_point-point", cfg="cfail2")]

tests/incremental/change_pub_inherent_method_sig/struct_point.rs

@@ -7,7 +7,6 @@
 
 #![crate_type = "rlib"]
 #![feature(rustc_attrs)]
-#![feature(stmt_expr_attributes)]
 #![allow(dead_code)]
 
 // These are expected to require codegen.

tests/incremental/lint-unused-features.rs

@@ -0,0 +1,41 @@
+//@ revisions: rpass cfail
+//@ ignore-backends: gcc
+
+#![deny(unused_features)]
+
+// Used language features
+#![feature(box_patterns)]
+#![feature(decl_macro)]
+#![cfg_attr(all(), feature(rustc_attrs))]
+
+// Used library features
+#![feature(error_iter)]
+//[cfail]~^ ERROR feature `error_iter` is declared but not used
+#![cfg_attr(all(), feature(allocator_api))]
+//[cfail]~^ ERROR feature `allocator_api` is declared but not used
+
+pub fn use_box_patterns(b: Box<i32>) -> i32 {
+    let box x = b;
+    x
+}
+
+macro m() {}
+pub fn use_decl_macro() {
+    m!();
+}
+
+#[rustc_dummy]
+pub fn use_rustc_attrs() {}
+
+#[cfg(rpass)]
+pub fn use_error_iter(e: &(dyn std::error::Error + 'static)) {
+    for _ in e.sources() {}
+}
+
+#[cfg(rpass)]
+pub fn use_allocator_api() {
+    use std::alloc::Global;
+    let _ = Vec::<i32>::new_in(Global);
+}
+
+fn main() {}

tests/ui-fulldeps/rustc_public/check_abi.rs

@@ -6,7 +6,6 @@
 //@ ignore-remote
 
 #![feature(rustc_private)]
-#![feature(ascii_char, ascii_char_variants)]
 
 extern crate rustc_driver;
 extern crate rustc_hir;

tests/ui-fulldeps/rustc_public/check_transform.rs

@@ -6,7 +6,6 @@
 //@ ignore-remote
 
 #![feature(rustc_private)]
-#![feature(ascii_char, ascii_char_variants)]
 
 extern crate rustc_hir;
 extern crate rustc_middle;

tests/ui/allocator/xcrate-use2.rs

@@ -5,7 +5,6 @@
 //@ aux-build:helper.rs
 //@ no-prefer-dynamic
 
-#![feature(allocator_api)]
 
 extern crate custom;
 extern crate custom_as_global;

tests/ui/associated-types/associated-types-impl-redirect.rs

@@ -9,7 +9,6 @@
 // for `ByRef`. The right answer was to consider the result ambiguous
 // until more type information was available.
 
-#![feature(lang_items)]
 #![no_implicit_prelude]
 
 use std::marker::Sized;

tests/ui/associated-types/associated-types-where-clause-impl-ambiguity.rs

@@ -8,7 +8,6 @@
 // for `ByRef`. The right answer was to consider the result ambiguous
 // until more type information was available.
 
-#![feature(lang_items)]
 #![no_implicit_prelude]
 
 use std::marker::Sized;

tests/ui/async-await/async-drop/async-drop-initial.rs

@@ -5,7 +5,7 @@
 // please consider modifying miri's async drop test at
 // `src/tools/miri/tests/pass/async-drop.rs`.
 
-#![feature(async_drop, impl_trait_in_assoc_type)]
+#![feature(async_drop)]
 #![allow(incomplete_features, dead_code)]
 
 //@ edition: 2021

tests/ui/backtrace/line-tables-only.rs

@@ -18,7 +18,6 @@
 //@ needs-unwind
 //@ aux-build: line-tables-only-helper.rs
 
-#![feature(backtrace_frames)]
 
 extern crate line_tables_only_helper;
 

tests/ui/borrowck/super-let-lifetime-and-drop.rs

@@ -7,7 +7,7 @@
 //@ [borrowck] check-fail
 
 #![allow(dropping_references)]
-#![feature(super_let, stmt_expr_attributes)]
+#![feature(super_let)]
 
 use std::convert::identity;
 

tests/ui/cfg/cfg_stmt_expr.rs

@@ -3,7 +3,6 @@
 #![allow(unused_mut)]
 #![allow(unused_variables)]
 #![deny(non_snake_case)]
-#![feature(stmt_expr_attributes)]
 
 fn main() {
     let a = 413;

tests/ui/const-generics/transmute.rs

@@ -1,6 +1,5 @@
 //@ run-pass
 #![feature(generic_const_exprs)]
-#![feature(transmute_generic_consts)]
 #![allow(incomplete_features)]
 
 fn ident<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [[u32; H]; W] {

tests/ui/consts/const-fn-type-name.rs

@@ -1,7 +1,6 @@
 //@ run-pass
 
 #![feature(core_intrinsics)]
-#![feature(const_type_name)]
 #![allow(dead_code)]
 
 const fn type_name_wrapper<T>(_: &T) -> &'static str {

tests/ui/consts/const-ptr-nonnull-rpass.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 
-#![feature(ptr_internals, test)]
+#![feature(test)]
 
 extern crate test;
 use test::black_box as b; // prevent promotion of the argument and const-propagation of the result

tests/ui/consts/try-operator.rs

@@ -1,7 +1,6 @@
 //@ ignore-backends: gcc
 //@ run-pass
 
-#![feature(try_trait_v2)]
 #![feature(const_trait_impl)]
 #![feature(const_try)]
 

tests/ui/contracts/internal_machinery/lowering/basics.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 #![expect(incomplete_features)]
-#![feature(contracts, cfg_contract_checks, contracts_internals, core_intrinsics)]
+#![feature(contracts, contracts_internals, core_intrinsics)]
 
 extern crate core;
 

tests/ui/coroutine/control-flow.rs

@@ -3,7 +3,7 @@
 //@ revisions: default nomiropt
 //@[nomiropt]compile-flags: -Z mir-opt-level=0
 
-#![feature(coroutines, coroutine_trait, stmt_expr_attributes)]
+#![feature(coroutines, coroutine_trait)]
 
 use std::ops::{CoroutineState, Coroutine};
 use std::pin::Pin;

tests/ui/coroutine/missing_coroutine_attr_suggestion.fixed

@@ -1,6 +1,6 @@
 //@ run-rustfix
 
-#![feature(coroutines, gen_blocks, stmt_expr_attributes)]
+#![feature(coroutines, stmt_expr_attributes)]
 
 fn main() {
     let _ = #[coroutine] || yield;

tests/ui/coroutine/missing_coroutine_attr_suggestion.rs

@@ -1,6 +1,6 @@
 //@ run-rustfix
 
-#![feature(coroutines, gen_blocks, stmt_expr_attributes)]
+#![feature(coroutines, stmt_expr_attributes)]
 
 fn main() {
     let _ = || yield;

tests/ui/coroutine/non-static-is-unpin.rs

@@ -3,7 +3,7 @@
 //@[next] compile-flags: -Znext-solver
 //@ run-pass
 
-#![feature(coroutines, coroutine_trait, stmt_expr_attributes)]
+#![feature(coroutines)]
 #![allow(dropping_copy_types)]
 
 use std::marker::PhantomPinned;

tests/ui/coroutine/other-attribute-on-gen.rs

@@ -2,7 +2,6 @@
 //@ run-pass
 #![feature(gen_blocks)]
 #![feature(optimize_attribute)]
-#![feature(stmt_expr_attributes)]
 #![feature(async_iterator)]
 #![allow(dead_code)]
 

tests/ui/coroutine/pin-box-coroutine.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 
-#![feature(coroutines, coroutine_trait, stmt_expr_attributes)]
+#![feature(coroutines, coroutine_trait)]
 
 use std::ops::Coroutine;
 

tests/ui/coroutine/xcrate.rs

@@ -2,7 +2,7 @@
 
 //@ aux-build:xcrate.rs
 
-#![feature(coroutines, coroutine_trait)]
+#![feature(coroutine_trait)]
 
 extern crate xcrate;
 

tests/ui/eii/default/call_default.rs

@@ -7,7 +7,6 @@
 //@ ignore-windows
 // Tests EIIs with default implementations.
 // When there's no explicit declaration, the default should be called from the declaring crate.
-#![feature(extern_item_impls)]
 
 extern crate decl_with_default;
 

tests/ui/eii/default/call_default_panics.rs

@@ -23,7 +23,6 @@
 // ```
 // This is a simple test to make sure that we can unwind through these,
 // and that this wrapper function effectively doesn't show up in the trace.
-#![feature(extern_item_impls)]
 
 extern crate decl_with_default_panics;
 

tests/ui/eii/default/call_impl.rs

@@ -9,7 +9,6 @@
 // Tests EIIs with default implementations.
 // When an explicit implementation is given in one dependency, and the declaration is in another,
 // the explicit implementation is preferred.
-#![feature(extern_item_impls)]
 
 extern crate decl_with_default;
 extern crate impl1;

tests/ui/eii/linking/codegen_cross_crate.rs

@@ -6,7 +6,6 @@
 // FIXME: linking on windows (speciifcally mingw) not yet supported, see tracking issue #125418
 //@ ignore-windows
 // Tests whether calling EIIs works with the declaration in another crate.
-#![feature(extern_item_impls)]
 
 extern crate codegen_cross_crate_other_crate as codegen;
 

tests/ui/eii/privacy1.rs

@@ -5,7 +5,6 @@
 // FIXME: linking on windows (specifically mingw) not yet supported, see tracking issue #125418
 //@ ignore-windows
 // Tests whether re-exports work.
-#![feature(extern_item_impls)]
 
 extern crate other_crate_privacy1 as codegen;
 

tests/ui/extern/extern-prelude-core.rs

@@ -1,5 +1,4 @@
 //@ run-pass
-#![feature(lang_items)]
 #![no_std]
 
 extern crate std as other;

tests/ui/feature-gates/feature-gate-explicit-extern-abis.current.fixed

@@ -22,7 +22,6 @@
 //@ [future_feature] compile-flags: -Z unstable-options
 
 #![cfg_attr(future_feature, feature(explicit_extern_abis))]
-#![cfg_attr(current_feature, feature(explicit_extern_abis))]
 
 extern "C" fn _foo() {}
 //[current]~^ WARN `extern` declarations without an explicit ABI are deprecated

tests/ui/feature-gates/feature-gate-explicit-extern-abis.current.stderr

@@ -1,5 +1,5 @@
 warning: `extern` declarations without an explicit ABI are deprecated
-  --> $DIR/feature-gate-explicit-extern-abis.rs:27:1
+  --> $DIR/feature-gate-explicit-extern-abis.rs:26:1
    |
 LL | extern fn _foo() {}
    | ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`
@@ -7,13 +7,13 @@ LL | extern fn _foo() {}
    = note: `#[warn(missing_abi)]` on by default
 
 warning: `extern` declarations without an explicit ABI are deprecated
-  --> $DIR/feature-gate-explicit-extern-abis.rs:33:8
+  --> $DIR/feature-gate-explicit-extern-abis.rs:32:8
    |
 LL | unsafe extern fn _bar() {}
    |        ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`
 
 warning: `extern` declarations without an explicit ABI are deprecated
-  --> $DIR/feature-gate-explicit-extern-abis.rs:39:8
+  --> $DIR/feature-gate-explicit-extern-abis.rs:38:8
    |
 LL | unsafe extern {}
    |        ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`

tests/ui/feature-gates/feature-gate-explicit-extern-abis.current_feature.fixed

@@ -22,7 +22,6 @@
 //@ [future_feature] compile-flags: -Z unstable-options
 
 #![cfg_attr(future_feature, feature(explicit_extern_abis))]
-#![cfg_attr(current_feature, feature(explicit_extern_abis))]
 
 extern "C" fn _foo() {}
 //[current]~^ WARN `extern` declarations without an explicit ABI are deprecated

tests/ui/feature-gates/feature-gate-explicit-extern-abis.current_feature.stderr

@@ -1,5 +1,5 @@
 warning: `extern` declarations without an explicit ABI are deprecated
-  --> $DIR/feature-gate-explicit-extern-abis.rs:27:1
+  --> $DIR/feature-gate-explicit-extern-abis.rs:26:1
    |
 LL | extern fn _foo() {}
    | ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`
@@ -7,13 +7,13 @@ LL | extern fn _foo() {}
    = note: `#[warn(missing_abi)]` on by default
 
 warning: `extern` declarations without an explicit ABI are deprecated
-  --> $DIR/feature-gate-explicit-extern-abis.rs:33:8
+  --> $DIR/feature-gate-explicit-extern-abis.rs:32:8
    |
 LL | unsafe extern fn _bar() {}
    |        ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`
 
 warning: `extern` declarations without an explicit ABI are deprecated
-  --> $DIR/feature-gate-explicit-extern-abis.rs:39:8
+  --> $DIR/feature-gate-explicit-extern-abis.rs:38:8
    |
 LL | unsafe extern {}
    |        ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`

tests/ui/feature-gates/feature-gate-explicit-extern-abis.future.fixed

@@ -22,7 +22,6 @@
 //@ [future_feature] compile-flags: -Z unstable-options
 
 #![cfg_attr(future_feature, feature(explicit_extern_abis))]
-#![cfg_attr(current_feature, feature(explicit_extern_abis))]
 
 extern "C" fn _foo() {}
 //[current]~^ WARN `extern` declarations without an explicit ABI are deprecated

tests/ui/feature-gates/feature-gate-explicit-extern-abis.future.stderr

@@ -1,5 +1,5 @@
 warning: `extern` declarations without an explicit ABI are deprecated
-  --> $DIR/feature-gate-explicit-extern-abis.rs:27:1
+  --> $DIR/feature-gate-explicit-extern-abis.rs:26:1
    |
 LL | extern fn _foo() {}
    | ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`
@@ -7,13 +7,13 @@ LL | extern fn _foo() {}
    = note: `#[warn(missing_abi)]` on by default
 
 warning: `extern` declarations without an explicit ABI are deprecated
-  --> $DIR/feature-gate-explicit-extern-abis.rs:33:8
+  --> $DIR/feature-gate-explicit-extern-abis.rs:32:8
    |
 LL | unsafe extern fn _bar() {}
    |        ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`
 
 warning: `extern` declarations without an explicit ABI are deprecated
-  --> $DIR/feature-gate-explicit-extern-abis.rs:39:8
+  --> $DIR/feature-gate-explicit-extern-abis.rs:38:8
    |
 LL | unsafe extern {}
    |        ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`

tests/ui/feature-gates/feature-gate-explicit-extern-abis.future_feature.stderr

@@ -1,5 +1,5 @@
 error: `extern` declarations without an explicit ABI are disallowed
-  --> $DIR/feature-gate-explicit-extern-abis.rs:27:1
+  --> $DIR/feature-gate-explicit-extern-abis.rs:26:1
    |
 LL | extern fn _foo() {}
    | ^^^^^^ help: specify an ABI: `extern "<abi>"`
@@ -7,7 +7,7 @@ LL | extern fn _foo() {}
    = help: prior to Rust 2024, a default ABI was inferred
 
 error: `extern` declarations without an explicit ABI are disallowed
-  --> $DIR/feature-gate-explicit-extern-abis.rs:33:8
+  --> $DIR/feature-gate-explicit-extern-abis.rs:32:8
    |
 LL | unsafe extern fn _bar() {}
    |        ^^^^^^ help: specify an ABI: `extern "<abi>"`
@@ -15,7 +15,7 @@ LL | unsafe extern fn _bar() {}
    = help: prior to Rust 2024, a default ABI was inferred
 
 error: `extern` declarations without an explicit ABI are disallowed
-  --> $DIR/feature-gate-explicit-extern-abis.rs:39:8
+  --> $DIR/feature-gate-explicit-extern-abis.rs:38:8
    |
 LL | unsafe extern {}
    |        ^^^^^^ help: specify an ABI: `extern "<abi>"`

tests/ui/feature-gates/feature-gate-explicit-extern-abis.rs

@@ -22,7 +22,6 @@
 //@ [future_feature] compile-flags: -Z unstable-options
 
 #![cfg_attr(future_feature, feature(explicit_extern_abis))]
-#![cfg_attr(current_feature, feature(explicit_extern_abis))]
 
 extern fn _foo() {}
 //[current]~^ WARN `extern` declarations without an explicit ABI are deprecated

tests/ui/float/classify-runtime-const.rs

@@ -6,8 +6,6 @@
 
 // This tests the float classification functions, for regular runtime code and for const evaluation.
 
-#![feature(f16)]
-#![feature(f128)]
 
 use std::num::FpCategory::*;
 

tests/ui/float/conv-bits-runtime-const.rs

@@ -3,9 +3,10 @@
 
 // This tests the float classification functions, for regular runtime code and for const evaluation.
 
-#![feature(f16)]
-#![feature(f128)]
 #![feature(cfg_target_has_reliable_f16_f128)]
+#![cfg_attr(target_has_reliable_f16, feature(f16))]
+#![cfg_attr(target_has_reliable_f128, feature(f128))]
+
 #![allow(unused_macro_rules)]
 // expect the unexpected (`target_has_reliable_*` are not "known" configs since they are unstable)
 #![expect(unexpected_cfgs)]

tests/ui/fmt/format-macro-no-std.rs

@@ -4,7 +4,6 @@
 //@ ignore-emscripten no no_std executables
 //@ ignore-wasm different `main` convention
 
-#![feature(lang_items)]
 #![no_std]
 #![no_main]
 

tests/ui/half-open-range-patterns/half-open-range-pats-semantics.rs

@@ -6,8 +6,8 @@
 
 #![allow(unreachable_patterns)]
 #![feature(cfg_target_has_reliable_f16_f128)]
-#![feature(f128)]
-#![feature(f16)]
+#![cfg_attr(target_has_reliable_f16, feature(f16))]
+#![cfg_attr(target_has_reliable_f128, feature(f128))]
 
 macro_rules! yes {
     ($scrutinee:expr, $($t:tt)+) => {

tests/ui/hygiene/xcrate.rs

@@ -3,7 +3,6 @@
 
 //@ aux-build:xcrate.rs
 
-#![feature(decl_macro)]
 
 extern crate xcrate;
 

tests/ui/impl-trait/example-calendar.rs

@@ -1,7 +1,6 @@
 //@ run-pass
 
-#![feature(fn_traits,
-           step_trait,
+#![feature(step_trait,
            unboxed_closures,
 )]
 

tests/ui/intrinsics/intrinsic-alignment.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 
-#![feature(core_intrinsics, rustc_attrs)]
+#![feature(rustc_attrs)]
 
 #[cfg(any(
     target_os = "aix",

tests/ui/io-checks/write-macro-error.rs

@@ -4,7 +4,6 @@
 //@ run-pass
 //@ needs-unwind
 
-#![feature(io_error_uncategorized)]
 
 use std::fmt;
 use std::io::{self, Error, Write};

tests/ui/linkage-attr/raw-dylib/elf/as_needed.rs

@@ -15,7 +15,7 @@
 
 #![allow(incomplete_features)]
 #![feature(raw_dylib_elf)]
-#![feature(native_link_modifiers_as_needed)]
+#![cfg_attr(not(no_modifier), feature(native_link_modifiers_as_needed))]
 
 #[cfg_attr(
     as_needed,

tests/ui/lint/lint-expr-stmt-attrs-for-early-lints.rs

@@ -1,6 +1,5 @@
 //@ run-pass
 
-#![feature(stmt_expr_attributes)]
 #![deny(unused_parens)]
 
 // Tests that lint attributes on statements/expressions are

tests/ui/lint/lint-unknown-feature.rs

@@ -4,6 +4,5 @@
 
 #![allow(stable_features)]
 // FIXME(#44232) we should warn that this isn't used.
-#![feature(rust1)]
 
 fn main() {}

tests/ui/lint/unnecessary-qualification/lint-unnecessary-qualification-issue-121331.fixed

@@ -2,7 +2,7 @@
 //@ edition:2021
 #![deny(unused_qualifications)]
 #![deny(unused_imports)]
-#![feature(coroutines, coroutine_trait)]
+#![feature(coroutine_trait)]
 
 use std::ops::{
     Coroutine,

tests/ui/lint/unnecessary-qualification/lint-unnecessary-qualification-issue-121331.rs

@@ -2,7 +2,7 @@
 //@ edition:2021
 #![deny(unused_qualifications)]
 #![deny(unused_imports)]
-#![feature(coroutines, coroutine_trait)]
+#![feature(coroutine_trait)]
 
 use std::ops::{
     Coroutine,

tests/ui/lint/unused-features/unused-language-features.rs

@@ -0,0 +1,25 @@
+#![crate_type = "lib"]
+#![deny(unused_features)]
+
+// Unused language features
+#![feature(coroutines)]
+//~^ ERROR feature `coroutines` is declared but not used
+#![feature(coroutine_clone)]
+//~^ ERROR feature `coroutine_clone` is declared but not used
+#![feature(stmt_expr_attributes)]
+//~^ ERROR feature `stmt_expr_attributes` is declared but not used
+#![feature(asm_unwind)]
+//~^ ERROR feature `asm_unwind` is declared but not used
+
+// Enabled via cfg_attr, unused
+#![cfg_attr(all(), feature(negative_impls))]
+//~^ ERROR feature `negative_impls` is declared but not used
+
+// Not enabled via cfg_attr, so should not warn even if unused
+#![cfg_attr(any(), feature(never_type))]
+
+macro_rules! use_asm_unwind {
+    () => {
+        unsafe { std::arch::asm!("", options(may_unwind)) };
+    }
+}

tests/ui/lint/unused-features/unused-language-features.stderr

@@ -0,0 +1,38 @@
+error: feature `coroutines` is declared but not used
+  --> $DIR/unused-language-features.rs:5:12
+   |
+LL | #![feature(coroutines)]
+   |            ^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-language-features.rs:2:9
+   |
+LL | #![deny(unused_features)]
+   |         ^^^^^^^^^^^^^^^
+
+error: feature `coroutine_clone` is declared but not used
+  --> $DIR/unused-language-features.rs:7:12
+   |
+LL | #![feature(coroutine_clone)]
+   |            ^^^^^^^^^^^^^^^
+
+error: feature `stmt_expr_attributes` is declared but not used
+  --> $DIR/unused-language-features.rs:9:12
+   |
+LL | #![feature(stmt_expr_attributes)]
+   |            ^^^^^^^^^^^^^^^^^^^^
+
+error: feature `asm_unwind` is declared but not used
+  --> $DIR/unused-language-features.rs:11:12
+   |
+LL | #![feature(asm_unwind)]
+   |            ^^^^^^^^^^
+
+error: feature `negative_impls` is declared but not used
+  --> $DIR/unused-language-features.rs:15:28
+   |
+LL | #![cfg_attr(all(), feature(negative_impls))]
+   |                            ^^^^^^^^^^^^^^
+
+error: aborting due to 5 previous errors
+

tests/ui/lint/unused-features/unused-library-features.rs

@@ -0,0 +1,13 @@
+#![crate_type = "lib"]
+#![deny(unused_features)]
+
+// Unused library features
+#![feature(step_trait)]
+//~^ ERROR feature `step_trait` is declared but not used
+#![feature(is_sorted)]
+//~^ ERROR feature `is_sorted` is declared but not used
+//~^^ WARN the feature `is_sorted` has been stable since 1.82.0 and no longer requires an attribute to enable
+
+// Enabled via cfg_attr, unused
+#![cfg_attr(all(), feature(slice_ptr_get))]
+//~^ ERROR feature `slice_ptr_get` is declared but not used

tests/ui/lint/unused-features/unused-library-features.stderr

@@ -0,0 +1,34 @@
+warning: the feature `is_sorted` has been stable since 1.82.0 and no longer requires an attribute to enable
+  --> $DIR/unused-library-features.rs:7:12
+   |
+LL | #![feature(is_sorted)]
+   |            ^^^^^^^^^
+   |
+   = note: `#[warn(stable_features)]` on by default
+
+error: feature `step_trait` is declared but not used
+  --> $DIR/unused-library-features.rs:5:12
+   |
+LL | #![feature(step_trait)]
+   |            ^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-library-features.rs:2:9
+   |
+LL | #![deny(unused_features)]
+   |         ^^^^^^^^^^^^^^^
+
+error: feature `is_sorted` is declared but not used
+  --> $DIR/unused-library-features.rs:7:12
+   |
+LL | #![feature(is_sorted)]
+   |            ^^^^^^^^^
+
+error: feature `slice_ptr_get` is declared but not used
+  --> $DIR/unused-library-features.rs:12:28
+   |
+LL | #![cfg_attr(all(), feature(slice_ptr_get))]
+   |                            ^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors; 1 warning emitted
+

tests/ui/lint/unused-features/used-language-features.rs

@@ -0,0 +1,22 @@
+//@ check-pass
+
+#![crate_type = "lib"]
+#![deny(unused_features)]
+
+// Used language features
+#![feature(box_patterns)]
+#![feature(decl_macro)]
+#![cfg_attr(all(), feature(rustc_attrs))]
+
+pub fn use_box_patterns(b: Box<i32>) -> i32 {
+    let box x = b;
+    x
+}
+
+macro m() {}
+pub fn use_decl_macro() {
+    m!();
+}
+
+#[rustc_dummy]
+pub fn use_rustc_attrs() {}

tests/ui/lint/unused-features/used-library-features.rs

@@ -0,0 +1,17 @@
+//@ check-pass
+
+#![crate_type = "lib"]
+#![deny(unused_features)]
+
+// Used library features
+#![feature(error_iter)]
+#![cfg_attr(all(), feature(allocator_api))]
+
+pub fn use_error_iter(e: &(dyn std::error::Error + 'static)) {
+    for _ in e.sources() {}
+}
+
+pub fn use_allocator_api() {
+    use std::alloc::Global;
+    let _ = Vec::<i32>::new_in(Global);
+}

tests/ui/lint/unused/unused_attributes-must_use.fixed

@@ -1,6 +1,6 @@
 //@ run-rustfix
 
-#![allow(dead_code, path_statements)]
+#![allow(dead_code, path_statements, unused_features)]
 #![deny(unused_attributes, unused_must_use)]
 #![feature(asm_experimental_arch, stmt_expr_attributes, trait_alias)]
 

tests/ui/lint/unused/unused_attributes-must_use.rs

@@ -1,6 +1,6 @@
 //@ run-rustfix
 
-#![allow(dead_code, path_statements)]
+#![allow(dead_code, path_statements, unused_features)]
 #![deny(unused_attributes, unused_must_use)]
 #![feature(asm_experimental_arch, stmt_expr_attributes, trait_alias)]
 

tests/ui/lowering/issue-96847.rs

@@ -3,7 +3,6 @@
 // Test that this doesn't abort during AST lowering. In #96847 it did abort
 // because the attribute was being lowered twice.
 
-#![feature(stmt_expr_attributes)]
 #![feature(lang_items)]
 
 fn main() {

tests/ui/lowering/issue-96847.stderr

@@ -1,5 +1,5 @@
 error[E0522]: definition of an unknown lang item: `foo`
-  --> $DIR/issue-96847.rs:11:9
+  --> $DIR/issue-96847.rs:10:9
    |
 LL |         #![lang="foo"]
    |         ^^^^^^^^^^^^^^ definition of unknown lang item `foo`

tests/ui/macros/metavar_cross_edition_recursive_macros.rs

@@ -6,7 +6,6 @@
 // This test captures the behavior of macro-generating-macros with fragment
 // specifiers across edition boundaries.
 
-#![feature(macro_metavar_expr)]
 #![allow(incomplete_features)]
 
 extern crate metavar_2018;

tests/ui/macros/rfc-2011-nicer-assert-messages/all-expr-kinds.rs

@@ -5,7 +5,7 @@
 //@ needs-unwind Asserting on contents of error message
 
 #![allow(path_statements, unused_allocation)]
-#![feature(core_intrinsics, generic_assert)]
+#![feature(generic_assert)]
 
 macro_rules! test {
   (

tests/ui/macros/rfc-2011-nicer-assert-messages/all-not-available-cases.rs

@@ -4,7 +4,7 @@
 //@ run-pass
 //@ needs-unwind Asserting on contents of error message
 
-#![feature(core_intrinsics, generic_assert)]
+#![feature(generic_assert)]
 
 extern crate common;
 

tests/ui/macros/rfc-2011-nicer-assert-messages/assert-with-custom-errors-does-not-create-unnecessary-code.rs

@@ -3,7 +3,6 @@
 //@ compile-flags: --test -Zpanic_abort_tests
 //@ run-pass
 
-#![feature(core_intrinsics, generic_assert)]
 
 #[should_panic(expected = "Custom user message")]
 #[test]

tests/ui/macros/rfc-2011-nicer-assert-messages/assert-without-captures-does-not-create-unnecessary-code.rs

@@ -3,7 +3,7 @@
 //@ run-pass
 //@ needs-unwind Asserting on contents of error message
 
-#![feature(core_intrinsics, generic_assert)]
+#![feature(generic_assert)]
 
 extern crate common;
 

tests/ui/macros/rfc-2011-nicer-assert-messages/feature-gate-generic_assert.rs

@@ -4,7 +4,7 @@
 // ignore-tidy-linelength
 //@ run-pass
 
-#![feature(core_intrinsics, generic_assert)]
+#![feature(generic_assert)]
 
 use std::fmt::{Debug, Formatter};
 

tests/ui/macros/stringify.rs

@@ -9,12 +9,10 @@
 #![feature(const_trait_impl)]
 #![feature(coroutines)]
 #![feature(decl_macro)]
-#![feature(explicit_tail_calls)]
 #![feature(more_qualified_paths)]
 #![feature(never_patterns)]
 #![feature(trait_alias)]
 #![feature(try_blocks)]
-#![feature(type_ascription)]
 #![feature(yeet_expr)]
 #![deny(unused_macros)]
 

tests/ui/match/match-float.rs

@@ -3,8 +3,8 @@
 // Makes sure we use `==` (not bitwise) semantics for float comparison.
 
 #![feature(cfg_target_has_reliable_f16_f128)]
-#![feature(f128)]
-#![feature(f16)]
+#![cfg_attr(target_has_reliable_f16, feature(f16))]
+#![cfg_attr(target_has_reliable_f128, feature(f128))]
 
 #[cfg(target_has_reliable_f16)]
 fn check_f16() {

tests/ui/methods/supertrait-shadowing/out-of-scope.rs

@@ -1,7 +1,6 @@
 //@ run-pass
 //@ check-run-results
 
-#![feature(supertrait_item_shadowing)]
 #![allow(dead_code)]
 
 mod out_of_scope {

tests/ui/nll/issue-48623-coroutine.rs

@@ -2,7 +2,7 @@
 #![allow(path_statements)]
 #![allow(dead_code)]
 
-#![feature(coroutines, coroutine_trait)]
+#![feature(coroutines)]
 
 struct WithDrop;