Rollup merge of rust-lang#89012 - vishadGoyal:issue-88802-fix, r=jyn514

Suggest removing `#![feature]` for library features that have been stabilized

Issue: rust-lang#88802
Delayed the check if #![feature] has been used to enable lib features in a non-nightly build to occur after TyCtxt has been constructed.

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -702,10 +702,16 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
 }
 
 fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
+    // checks if `#![feature]` has been used to enable any lang feature
+    // does not check the same for lib features unless there's at least one
+    // declared lang feature
     use rustc_errors::Applicability;
 
     if !sess.opts.unstable_features.is_nightly_build() {
         let lang_features = &sess.features_untracked().declared_lang_features;
+        if lang_features.len() == 0 {
+            return;
+        }
         for attr in krate.attrs.iter().filter(|attr| attr.has_name(sym::feature)) {
             let mut err = struct_span_err!(
                 sess.parse_sess.span_diagnostic,

compiler/rustc_passes/src/stability.rs

@@ -929,6 +929,16 @@ pub fn check_unused_or_stable_features(tcx: TyCtxt<'_>) {
     let declared_lib_features = &tcx.features().declared_lib_features;
     let mut remaining_lib_features = FxHashMap::default();
     for (feature, span) in declared_lib_features {
+        if !tcx.sess.opts.unstable_features.is_nightly_build() {
+            struct_span_err!(
+                tcx.sess,
+                *span,
+                E0554,
+                "`#![feature]` may not be used on the {} release channel",
+                env!("CFG_RELEASE_CHANNEL")
+            )
+            .emit();
+        }
         if remaining_lib_features.contains_key(&feature) {
             // Warn if the user enables a lib feature multiple times.
             duplicate_feature_err(tcx.sess, *span, *feature);