diff --git a/compiler/rustc_ast_lowering/src/asm.rs b/compiler/rustc_ast_lowering/src/asm.rs
index 46d7beae8fe58..e8df8ce6e6dc3 100644
--- a/compiler/rustc_ast_lowering/src/asm.rs
+++ b/compiler/rustc_ast_lowering/src/asm.rs
@@ -5,7 +5,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
 use rustc_errors::msg;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::{Span, sym};
 use rustc_target::asm;
 
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 4e1b46d568099..86eb721ad284c 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -1693,7 +1693,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             && !self.tcx.features().coroutines()
             && !self.tcx.features().gen_blocks()
         {
-            rustc_session::parse::feature_err(
+            rustc_session::errors::feature_err(
                 &self.tcx.sess,
                 sym::yield_expr,
                 span,
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 6ca6bf3e1f6dc..49790c2da6de4 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -62,7 +62,7 @@ use rustc_macros::extension;
 use rustc_middle::hir::{self as mid_hir};
 use rustc_middle::span_bug;
 use rustc_middle::ty::{DelegationInfo, ResolverAstLowering, TyCtxt};
-use rustc_session::parse::add_feature_diagnostics;
+use rustc_session::errors::add_feature_diagnostics;
 use rustc_span::symbol::{Ident, Symbol, kw, sym};
 use rustc_span::{DUMMY_SP, DesugaringKind, Span};
 use smallvec::SmallVec;
diff --git a/compiler/rustc_ast_lowering/src/path.rs b/compiler/rustc_ast_lowering/src/path.rs
index 49c5f060e2a1e..ef60dc6fc4f1c 100644
--- a/compiler/rustc_ast_lowering/src/path.rs
+++ b/compiler/rustc_ast_lowering/src/path.rs
@@ -6,7 +6,7 @@ use rustc_hir::def::{DefKind, PartialRes, PerNS, Res};
 use rustc_hir::def_id::DefId;
 use rustc_hir::{self as hir, GenericArg};
 use rustc_middle::{span_bug, ty};
-use rustc_session::parse::add_feature_diagnostics;
+use rustc_session::errors::add_feature_diagnostics;
 use rustc_span::{BytePos, DUMMY_SP, DesugaringKind, Ident, Span, Symbol, sym};
 use smallvec::smallvec;
 use tracing::{debug, instrument};
diff --git a/compiler/rustc_ast_lowering/src/stability.rs b/compiler/rustc_ast_lowering/src/stability.rs
index d185cc9163eb6..326576bb14881 100644
--- a/compiler/rustc_ast_lowering/src/stability.rs
+++ b/compiler/rustc_ast_lowering/src/stability.rs
@@ -3,7 +3,7 @@ use std::fmt;
 use rustc_abi::ExternAbi;
 use rustc_feature::Features;
 use rustc_session::Session;
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::symbol::sym;
 use rustc_span::{Span, Symbol};
 
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index 770189d8c7999..8ba2d955a80ad 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -30,11 +30,11 @@ use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::{DiagCtxtHandle, Diagnostic, LintBuffer};
 use rustc_feature::Features;
 use rustc_session::Session;
+use rustc_session::errors::feature_err;
 use rustc_session::lint::builtin::{
     DEPRECATED_WHERE_CLAUSE_LOCATION, MISSING_ABI, MISSING_UNSAFE_ON_EXTERN,
     PATTERNS_IN_FNS_WITHOUT_BODY, UNUSED_VISIBILITIES,
 };
-use rustc_session::parse::feature_err;
 use rustc_span::{Ident, Span, kw, sym};
 use rustc_target::spec::{AbiMap, AbiMapping};
 use thin_vec::thin_vec;
diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index 5831636a81b2c..54de8965e6a03 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -6,7 +6,7 @@ use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP, BuiltinAttribute, Feat
 use rustc_hir::Attribute;
 use rustc_hir::attrs::AttributeKind;
 use rustc_session::Session;
-use rustc_session::parse::{feature_err, feature_warn};
+use rustc_session::errors::{feature_err, feature_warn};
 use rustc_span::{Span, Spanned, Symbol, sym};
 use thin_vec::ThinVec;
 
diff --git a/compiler/rustc_attr_parsing/src/attributes/cfg.rs b/compiler/rustc_attr_parsing/src/attributes/cfg.rs
index 80a1d9aa5defd..4cc07ceaf231f 100644
--- a/compiler/rustc_attr_parsing/src/attributes/cfg.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/cfg.rs
@@ -13,8 +13,9 @@ use rustc_parse::parser::{ForceCollect, Parser, Recovery};
 use rustc_parse::{exp, parse_in};
 use rustc_session::Session;
 use rustc_session::config::ExpectedValues;
+use rustc_session::errors::feature_err;
 use rustc_session::lint::builtin::UNEXPECTED_CFGS;
-use rustc_session::parse::{ParseSess, feature_err};
+use rustc_session::parse::ParseSess;
 use rustc_span::{ErrorGuaranteed, Span, Symbol, sym};
 use thin_vec::ThinVec;
 
diff --git a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
index a20813406b024..a6cf25330b557 100644
--- a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
@@ -1,5 +1,5 @@
 use rustc_hir::attrs::{CoverageAttrKind, OptimizeAttr, RtsanSetting, SanitizerSet, UsedBy};
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::edition::Edition::Edition2024;
 
 use super::prelude::*;
diff --git a/compiler/rustc_attr_parsing/src/attributes/doc.rs b/compiler/rustc_attr_parsing/src/attributes/doc.rs
index c0b90c2c6d97f..ecb136edad5fc 100644
--- a/compiler/rustc_attr_parsing/src/attributes/doc.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/doc.rs
@@ -5,7 +5,7 @@ use rustc_hir::Target;
 use rustc_hir::attrs::{
     AttributeKind, CfgEntry, CfgHideShow, CfgInfo, DocAttribute, DocInline, HideOrShow,
 };
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::{Span, Symbol, edition, sym};
 use thin_vec::ThinVec;
 
diff --git a/compiler/rustc_attr_parsing/src/attributes/link_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/link_attrs.rs
index 0ca059bf4030b..039977c74c1bb 100644
--- a/compiler/rustc_attr_parsing/src/attributes/link_attrs.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/link_attrs.rs
@@ -3,8 +3,8 @@ use rustc_feature::Features;
 use rustc_hir::attrs::AttributeKind::{LinkName, LinkOrdinal, LinkSection};
 use rustc_hir::attrs::*;
 use rustc_session::Session;
+use rustc_session::errors::feature_err;
 use rustc_session::lint::builtin::ILL_FORMED_ATTRIBUTE_INPUT;
-use rustc_session::parse::feature_err;
 use rustc_span::edition::Edition::Edition2024;
 use rustc_span::kw;
 use rustc_target::spec::{Arch, BinaryFormat};
diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
index 820436bb6a265..3e19f7f95470f 100644
--- a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
+++ b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
@@ -12,8 +12,8 @@ use rustc_middle::middle::codegen_fn_attrs::{
 use rustc_middle::mono::Visibility;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{self as ty, TyCtxt};
+use rustc_session::errors::feature_err;
 use rustc_session::lint;
-use rustc_session::parse::feature_err;
 use rustc_span::{Span, sym};
 use rustc_target::spec::Os;
 
diff --git a/compiler/rustc_codegen_ssa/src/target_features.rs b/compiler/rustc_codegen_ssa/src/target_features.rs
index 4b1b0866f2eb9..b7d09d69aaecd 100644
--- a/compiler/rustc_codegen_ssa/src/target_features.rs
+++ b/compiler/rustc_codegen_ssa/src/target_features.rs
@@ -7,8 +7,8 @@ use rustc_middle::middle::codegen_fn_attrs::{TargetFeature, TargetFeatureKind};
 use rustc_middle::query::Providers;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
+use rustc_session::errors::feature_err;
 use rustc_session::lint::builtin::AARCH64_SOFTFLOAT_NEON;
-use rustc_session::parse::feature_err;
 use rustc_span::{Span, Symbol, edit_distance, sym};
 use rustc_target::spec::{Arch, SanitizerSet};
 use rustc_target::target_features::{RUSTC_SPECIFIC_FEATURES, Stability};
diff --git a/compiler/rustc_const_eval/src/check_consts/ops.rs b/compiler/rustc_const_eval/src/check_consts/ops.rs
index d64cf8e032935..c776fa69ba5c1 100644
--- a/compiler/rustc_const_eval/src/check_consts/ops.rs
+++ b/compiler/rustc_const_eval/src/check_consts/ops.rs
@@ -14,7 +14,7 @@ use rustc_middle::ty::{
     self, AssocContainer, Closure, FnDef, FnPtr, GenericArgKind, GenericArgsRef, Param, TraitRef,
     Ty, suggest_constraining_type_param,
 };
-use rustc_session::parse::add_feature_diagnostics;
+use rustc_session::errors::add_feature_diagnostics;
 use rustc_span::{BytePos, Pos, Span, Symbol, sym};
 use rustc_trait_selection::error_reporting::traits::call_kind::{
     CallDesugaringKind, CallKind, call_kind,
diff --git a/compiler/rustc_expand/src/config.rs b/compiler/rustc_expand/src/config.rs
index b5f85536d9cac..2b914a2664fe5 100644
--- a/compiler/rustc_expand/src/config.rs
+++ b/compiler/rustc_expand/src/config.rs
@@ -27,7 +27,7 @@ use rustc_hir::{
 };
 use rustc_parse::parser::Recovery;
 use rustc_session::Session;
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::{STDLIB_STABLE_CRATES, Span, Symbol, sym};
 use tracing::instrument;
 
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index fe363e7d4a511..3629b72a93ec2 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -30,8 +30,8 @@ use rustc_parse::parser::{
     RecoverColon, RecoverComma, Recovery, token_descr,
 };
 use rustc_session::Session;
+use rustc_session::errors::feature_err;
 use rustc_session::lint::builtin::{UNUSED_ATTRIBUTES, UNUSED_DOC_COMMENTS};
-use rustc_session::parse::feature_err;
 use rustc_span::hygiene::SyntaxContext;
 use rustc_span::{ErrorGuaranteed, FileName, Ident, LocalExpnId, Span, Symbol, sym};
 use smallvec::SmallVec;
diff --git a/compiler/rustc_expand/src/mbe/macro_rules.rs b/compiler/rustc_expand/src/mbe/macro_rules.rs
index eed13a13fa911..cb22ad136645b 100644
--- a/compiler/rustc_expand/src/mbe/macro_rules.rs
+++ b/compiler/rustc_expand/src/mbe/macro_rules.rs
@@ -23,7 +23,8 @@ use rustc_lint_defs::builtin::{
 use rustc_parse::exp;
 use rustc_parse::parser::{Parser, Recovery};
 use rustc_session::Session;
-use rustc_session::parse::{ParseSess, feature_err};
+use rustc_session::errors::feature_err;
+use rustc_session::parse::ParseSess;
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::Transparency;
 use rustc_span::{Ident, Span, Symbol, kw, sym};
diff --git a/compiler/rustc_expand/src/mbe/quoted.rs b/compiler/rustc_expand/src/mbe/quoted.rs
index 92d19820848b4..443a17287d734 100644
--- a/compiler/rustc_expand/src/mbe/quoted.rs
+++ b/compiler/rustc_expand/src/mbe/quoted.rs
@@ -5,7 +5,7 @@ use rustc_ast_pretty::pprust;
 use rustc_errors::Applicability;
 use rustc_feature::Features;
 use rustc_session::Session;
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::edition::Edition;
 use rustc_span::{Ident, Span, kw, sym};
 
diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index fcdbb11b297c1..3225e00b24b26 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -92,7 +92,7 @@ use rustc_middle::ty::{
     Unnormalized,
 };
 use rustc_middle::{bug, span_bug};
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::def_id::CRATE_DEF_ID;
 use rustc_span::{BytePos, DUMMY_SP, Ident, Span, Symbol, kw, sym};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
@@ -312,7 +312,7 @@ fn default_body_is_unstable(
     });
 
     let inject_span = item_did.is_local().then(|| tcx.crate_level_attribute_injection_span());
-    rustc_session::parse::add_feature_diagnostics_for_issue(
+    rustc_session::errors::add_feature_diagnostics_for_issue(
         &mut err,
         &tcx.sess,
         feature,
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index 05d16d2ddb49c..d0277d2e24264 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -27,7 +27,7 @@ use rustc_middle::ty::{
     Unnormalized, Upcast,
 };
 use rustc_middle::{bug, span_bug};
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::{DUMMY_SP, Span, sym};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::regions::{InferCtxtRegionExt, OutlivesEnvironmentBuildExt};
diff --git a/compiler/rustc_hir_analysis/src/coherence/mod.rs b/compiler/rustc_hir_analysis/src/coherence/mod.rs
index 07ad5db47b6d8..05a9f68131819 100644
--- a/compiler/rustc_hir_analysis/src/coherence/mod.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/mod.rs
@@ -11,7 +11,7 @@ use rustc_hir::LangItem;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt, elaborate};
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::{ErrorGuaranteed, sym};
 use tracing::debug;
 
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
index 3a2f3948f0abc..d8cf13db265fd 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -1272,7 +1272,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                         && !self.tcx.asyncness(lifetime_ref.hir_id.owner.def_id).is_async()
                         && !self.tcx.features().anonymous_lifetime_in_impl_trait()
                     {
-                        let mut diag: rustc_errors::Diag<'_> = rustc_session::parse::feature_err(
+                        let mut diag: rustc_errors::Diag<'_> = rustc_session::errors::feature_err(
                             &self.tcx.sess,
                             sym::anonymous_lifetime_in_impl_trait,
                             lifetime_ref.ident.span,
diff --git a/compiler/rustc_hir_analysis/src/collect/type_of.rs b/compiler/rustc_hir_analysis/src/collect/type_of.rs
index 41b1ec91e0e75..3ac603fc715f3 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of.rs
@@ -505,7 +505,7 @@ fn infer_placeholder_type<'tcx>(
 
 fn check_feature_inherent_assoc_ty(tcx: TyCtxt<'_>, span: Span) {
     if !tcx.features().inherent_associated_types() {
-        use rustc_session::parse::feature_err;
+        use rustc_session::errors::feature_err;
         use rustc_span::sym;
         feature_err(
             &tcx.sess,
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
index 0aa478f99200b..5e11819805e15 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
@@ -16,7 +16,7 @@ use rustc_middle::ty::{
     self, AdtDef, GenericParamDefKind, Ty, TyCtxt, TypeVisitableExt,
     suggest_constraining_type_param,
 };
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::{BytePos, DUMMY_SP, Ident, Span, Symbol, kw, sym};
 use rustc_trait_selection::error_reporting::traits::report_dyn_incompatibility;
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index 5096e5ef76f0d..75ea42a38ff4c 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -43,8 +43,8 @@ use rustc_middle::ty::{
     const_lit_matches_ty, fold_regions,
 };
 use rustc_middle::{bug, span_bug};
+use rustc_session::errors::feature_err;
 use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
-use rustc_session::parse::feature_err;
 use rustc_span::{DUMMY_SP, Ident, Span, kw, sym};
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::wf::object_region_bounds;
diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index 0721bfcab519a..9cadaef8f886b 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -89,7 +89,7 @@ use rustc_middle::mir::interpret::GlobalId;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{Const, Ty, TyCtxt};
 use rustc_middle::{middle, ty};
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::traits;
 
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
index 71c02dc32f6b5..664c3c457876c 100644
--- a/compiler/rustc_hir_typeck/src/expr.rs
+++ b/compiler/rustc_hir_typeck/src/expr.rs
@@ -30,8 +30,7 @@ use rustc_middle::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase};
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::{self, AdtKind, GenericArgsRef, Ty, TypeVisitableExt, Unnormalized};
 use rustc_middle::{bug, span_bug};
-use rustc_session::errors::ExprParenthesesNeeded;
-use rustc_session::parse::feature_err;
+use rustc_session::errors::{ExprParenthesesNeeded, feature_err};
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::hygiene::DesugaringKind;
 use rustc_span::{Ident, Span, Spanned, Symbol, kw, sym};
@@ -3767,7 +3766,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         self.tcx.adjust_ident_and_get_scope(field, container_def.did(), block);
 
                     if !self.tcx.features().offset_of_enum() {
-                        rustc_session::parse::feature_err(
+                        rustc_session::errors::feature_err(
                             &self.tcx.sess,
                             sym::offset_of_enum,
                             ident.span,
diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs
index 5a4cd6d24a8b6..d7f15222376c8 100644
--- a/compiler/rustc_hir_typeck/src/pat.rs
+++ b/compiler/rustc_hir_typeck/src/pat.rs
@@ -21,8 +21,8 @@ use rustc_infer::infer::RegionVariableOrigin;
 use rustc_middle::traits::PatternOriginExpr;
 use rustc_middle::ty::{self, Pinnedness, Ty, TypeVisitableExt, Unnormalized};
 use rustc_middle::{bug, span_bug};
+use rustc_session::errors::feature_err;
 use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
-use rustc_session::parse::feature_err;
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::edition::Edition;
 use rustc_span::{BytePos, DUMMY_SP, Ident, Span, kw, sym};
diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index 38d899853cd5b..cc05fffa1daa2 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -39,8 +39,8 @@ use rustc_resolve::{Resolver, ResolverOutputs};
 use rustc_session::Session;
 use rustc_session::config::{CrateType, Input, OutFileName, OutputFilenames, OutputType};
 use rustc_session::cstore::Untracked;
+use rustc_session::errors::feature_err;
 use rustc_session::output::{filename_for_input, invalid_output_for_target};
-use rustc_session::parse::feature_err;
 use rustc_session::search_paths::PathKind;
 use rustc_span::{
     DUMMY_SP, ErrorGuaranteed, ExpnKind, SourceFileHash, SourceFileHashAlgorithm, Span, Symbol, sym,
diff --git a/compiler/rustc_lint/src/levels.rs b/compiler/rustc_lint/src/levels.rs
index 2b859b65c9f8f..0c308e18b1533 100644
--- a/compiler/rustc_lint/src/levels.rs
+++ b/compiler/rustc_lint/src/levels.rs
@@ -966,7 +966,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                 let mut lint = Diag::new(dcx, level, msg!("unknown lint: `{$name}`"))
                     .with_arg("name", lint_id.lint.name_lower())
                     .with_note(msg!("the `{$name}` lint is unstable"));
-                rustc_session::parse::add_feature_diagnostics_for_issue(
+                rustc_session::errors::add_feature_diagnostics_for_issue(
                     &mut lint,
                     sess,
                     feature,
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index 1e3ce972a3667..6d9f486f627f6 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -306,7 +306,7 @@ impl<'a> Diagnostic<'a, ()> for BuiltinUngatedAsyncFnTrackCaller<'_> {
     fn into_diag(self, dcx: DiagCtxtHandle<'a>, level: Level) -> Diag<'a, ()> {
         let mut diag = Diag::new(dcx, level, "`#[track_caller]` on async functions is a no-op")
             .with_span_label(self.label, "this function will not propagate the caller location");
-        rustc_session::parse::add_feature_diagnostics(
+        rustc_session::errors::add_feature_diagnostics(
             &mut diag,
             self.session,
             sym::async_fn_track_caller,
diff --git a/compiler/rustc_middle/src/middle/stability.rs b/compiler/rustc_middle/src/middle/stability.rs
index f9821c92df369..2c59517847370 100644
--- a/compiler/rustc_middle/src/middle/stability.rs
+++ b/compiler/rustc_middle/src/middle/stability.rs
@@ -11,9 +11,9 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::{self as hir, ConstStability, DefaultBodyStability, HirId, Stability};
 use rustc_macros::{Decodable, Encodable, HashStable, Subdiagnostic};
 use rustc_session::Session;
+use rustc_session::errors::feature_err_issue;
 use rustc_session::lint::builtin::{DEPRECATED, DEPRECATED_IN_FUTURE};
 use rustc_session::lint::{DeprecatedSinceKind, Level, Lint};
-use rustc_session::parse::feature_err_issue;
 use rustc_span::{Span, Symbol, sym};
 use tracing::debug;
 
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 831199a59a432..2817cf3020ff9 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -36,12 +36,12 @@ use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::{self, TyCtxt, TypingMode, Unnormalized};
 use rustc_middle::{bug, span_bug};
 use rustc_session::config::CrateType;
+use rustc_session::errors::feature_err;
 use rustc_session::lint;
 use rustc_session::lint::builtin::{
     CONFLICTING_REPR_HINTS, INVALID_DOC_ATTRIBUTES, MALFORMED_DIAGNOSTIC_FORMAT_LITERALS,
     MISPLACED_DIAGNOSTIC_ATTRIBUTES, UNUSED_ATTRIBUTES,
 };
-use rustc_session::parse::feature_err;
 use rustc_span::edition::Edition;
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, sym};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
index 5fae50041a02d..febdb085f7ee1 100644
--- a/compiler/rustc_resolve/src/ident.rs
+++ b/compiler/rustc_resolve/src/ident.rs
@@ -6,8 +6,8 @@ use rustc_ast::{self as ast, NodeId};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::{DefKind, MacroKinds, Namespace, NonMacroAttrKind, PartialRes, PerNS};
 use rustc_middle::{bug, span_bug};
+use rustc_session::errors::feature_err;
 use rustc_session::lint::builtin::PROC_MACRO_DERIVE_RESOLUTION_FALLBACK;
-use rustc_session::parse::feature_err;
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::{ExpnId, ExpnKind, LocalExpnId, MacroKind, SyntaxContext};
 use rustc_span::{Ident, Span, kw, sym};
diff --git a/compiler/rustc_resolve/src/imports.rs b/compiler/rustc_resolve/src/imports.rs
index 2695655278fb4..5a98a17add701 100644
--- a/compiler/rustc_resolve/src/imports.rs
+++ b/compiler/rustc_resolve/src/imports.rs
@@ -18,11 +18,11 @@ use rustc_hir::def_id::{DefId, LocalDefIdMap};
 use rustc_middle::metadata::{AmbigModChild, ModChild, Reexport};
 use rustc_middle::span_bug;
 use rustc_middle::ty::{TyCtxt, Visibility};
+use rustc_session::errors::feature_err;
 use rustc_session::lint::builtin::{
     AMBIGUOUS_GLOB_REEXPORTS, EXPORTED_PRIVATE_DEPENDENCIES, HIDDEN_GLOB_REEXPORTS,
     PUB_USE_OF_PRIVATE_EXTERN_CRATE, REDUNDANT_IMPORTS, UNUSED_IMPORTS,
 };
-use rustc_session::parse::feature_err;
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::hygiene::LocalExpnId;
 use rustc_span::{Ident, Span, Symbol, kw, sym};
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 6eb5fe17bc169..014a472c2c1bb 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -32,8 +32,8 @@ use rustc_middle::middle::resolve_bound_vars::Set1;
 use rustc_middle::ty::{AssocTag, DelegationInfo, Visibility};
 use rustc_middle::{bug, span_bug};
 use rustc_session::config::{CrateType, ResolveDocLinks};
+use rustc_session::errors::feature_err;
 use rustc_session::lint;
-use rustc_session::parse::feature_err;
 use rustc_span::{BytePos, DUMMY_SP, Ident, Span, Spanned, Symbol, kw, respan, sym};
 use smallvec::{SmallVec, smallvec};
 use thin_vec::ThinVec;
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index dc20d4fcf36b7..998cf27a85de1 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -23,11 +23,11 @@ use rustc_hir::{Attribute, StabilityLevel};
 use rustc_middle::middle::stability;
 use rustc_middle::ty::{RegisteredTools, TyCtxt};
 use rustc_session::Session;
+use rustc_session::errors::feature_err;
 use rustc_session::lint::builtin::{
     LEGACY_DERIVE_HELPERS, OUT_OF_SCOPE_MACRO_CALLS, UNKNOWN_DIAGNOSTIC_ATTRIBUTES,
     UNUSED_MACRO_RULES, UNUSED_MACROS,
 };
-use rustc_session::parse::feature_err;
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::{self, AstPass, ExpnData, ExpnKind, LocalExpnId, MacroKind};
diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index 54f88aa22bdc4..bc4c5e98282a5 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -5,14 +5,179 @@ use rustc_ast::util::literal::LitError;
 use rustc_errors::codes::*;
 use rustc_errors::{
     Diag, DiagCtxtHandle, DiagMessage, Diagnostic, EmissionGuarantee, ErrorGuaranteed, Level,
-    MultiSpan,
+    MultiSpan, StashKey,
 };
+use rustc_feature::{GateIssue, find_feature_issue};
 use rustc_macros::{Diagnostic, Subdiagnostic};
-use rustc_span::{Span, Symbol};
+use rustc_span::{Span, Symbol, sym};
 use rustc_target::spec::{SplitDebuginfo, StackProtector, TargetTuple};
 
+use crate::Session;
+use crate::lint::builtin::UNSTABLE_SYNTAX_PRE_EXPANSION;
 use crate::parse::ParseSess;
 
+/// Construct a diagnostic for a language feature error due to the given `span`.
+/// The `feature`'s `Symbol` is the one you used in `unstable.rs` and `rustc_span::symbol`.
+#[track_caller]
+pub fn feature_err(
+    sess: &Session,
+    feature: Symbol,
+    span: impl Into<MultiSpan>,
+    explain: impl Into<DiagMessage>,
+) -> Diag<'_> {
+    feature_err_issue(sess, feature, span, GateIssue::Language, explain)
+}
+
+/// Construct a diagnostic for a feature gate error.
+///
+/// This variant allows you to control whether it is a library or language feature.
+/// Almost always, you want to use this for a language feature. If so, prefer `feature_err`.
+#[track_caller]
+pub fn feature_err_issue(
+    sess: &Session,
+    feature: Symbol,
+    span: impl Into<MultiSpan>,
+    issue: GateIssue,
+    explain: impl Into<DiagMessage>,
+) -> Diag<'_> {
+    let span = span.into();
+
+    // Cancel an earlier warning for this same error, if it exists.
+    if let Some(span) = span.primary_span()
+        && let Some(err) = sess.dcx().steal_non_err(span, StashKey::EarlySyntaxWarning)
+    {
+        err.cancel()
+    }
+
+    let mut err = sess.dcx().create_err(FeatureGateError { span, explain: explain.into() });
+    add_feature_diagnostics_for_issue(&mut err, sess, feature, issue, false, None);
+    err
+}
+
+/// Construct a future incompatibility diagnostic for a feature gate.
+///
+/// This diagnostic is only a warning and *does not cause compilation to fail*.
+#[track_caller]
+pub fn feature_warn(sess: &Session, feature: Symbol, span: Span, explain: &'static str) {
+    feature_warn_issue(sess, feature, span, GateIssue::Language, explain);
+}
+
+/// Construct a future incompatibility diagnostic for a feature gate.
+///
+/// This diagnostic is only a warning and *does not cause compilation to fail*.
+///
+/// This variant allows you to control whether it is a library or language feature.
+/// Almost always, you want to use this for a language feature. If so, prefer `feature_warn`.
+#[track_caller]
+pub fn feature_warn_issue(
+    sess: &Session,
+    feature: Symbol,
+    span: Span,
+    issue: GateIssue,
+    explain: &'static str,
+) {
+    let mut err = sess.dcx().struct_span_warn(span, explain);
+    add_feature_diagnostics_for_issue(&mut err, sess, feature, issue, false, None);
+
+    // Decorate this as a future-incompatibility lint as in rustc_middle::lint::lint_level
+    let lint = UNSTABLE_SYNTAX_PRE_EXPANSION;
+    let future_incompatible = lint.future_incompatible.as_ref().unwrap();
+    err.is_lint(lint.name_lower(), /* has_future_breakage */ false);
+    err.warn(lint.desc);
+    err.note(format!("for more information, see {}", future_incompatible.reason.reference()));
+
+    // A later feature_err call can steal and cancel this warning.
+    err.stash(span, StashKey::EarlySyntaxWarning);
+}
+
+/// Adds the diagnostics for a feature to an existing error.
+/// Must be a language feature!
+pub fn add_feature_diagnostics<G: EmissionGuarantee>(
+    err: &mut Diag<'_, G>,
+    sess: &Session,
+    feature: Symbol,
+) {
+    add_feature_diagnostics_for_issue(err, sess, feature, GateIssue::Language, false, None);
+}
+
+/// Adds the diagnostics for a feature to an existing error.
+///
+/// This variant allows you to control whether it is a library or language feature.
+/// Almost always, you want to use this for a language feature. If so, prefer
+/// `add_feature_diagnostics`.
+pub fn add_feature_diagnostics_for_issue<G: EmissionGuarantee>(
+    err: &mut Diag<'_, G>,
+    sess: &Session,
+    feature: Symbol,
+    issue: GateIssue,
+    feature_from_cli: bool,
+    inject_span: Option<Span>,
+) {
+    if let Some(n) = find_feature_issue(feature, issue) {
+        err.subdiagnostic(FeatureDiagnosticForIssue { n });
+    }
+
+    // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
+    if sess.unstable_features.is_nightly_build() {
+        if feature_from_cli {
+            err.subdiagnostic(CliFeatureDiagnosticHelp { feature });
+        } else if let Some(span) = inject_span {
+            err.subdiagnostic(FeatureDiagnosticSuggestion { feature, span });
+        } else {
+            err.subdiagnostic(FeatureDiagnosticHelp { feature });
+        }
+        if feature == sym::rustc_attrs {
+            // We're unlikely to stabilize something out of `rustc_attrs`
+            // without at least renaming it, so pointing out how old
+            // the compiler is will do little good.
+        } else if sess.opts.unstable_opts.ui_testing {
+            err.subdiagnostic(SuggestUpgradeCompiler::ui_testing());
+        } else if let Some(suggestion) = SuggestUpgradeCompiler::new() {
+            err.subdiagnostic(suggestion);
+        }
+    }
+}
+
+/// This is only used by unstable_feature_bound as it does not have issue number information for now.
+/// This is basically the same as `feature_err_issue`
+/// but without the feature issue note. If we can do a lookup for issue number from feature name,
+/// then we should directly use `feature_err_issue` for ambiguity error of
+/// `#[unstable_feature_bound]`.
+#[track_caller]
+pub fn feature_err_unstable_feature_bound(
+    sess: &Session,
+    feature: Symbol,
+    span: impl Into<MultiSpan>,
+    explain: impl Into<DiagMessage>,
+) -> Diag<'_> {
+    let span = span.into();
+
+    // Cancel an earlier warning for this same error, if it exists.
+    if let Some(span) = span.primary_span() {
+        if let Some(err) = sess.dcx().steal_non_err(span, StashKey::EarlySyntaxWarning) {
+            err.cancel()
+        }
+    }
+
+    let mut err = sess.dcx().create_err(FeatureGateError { span, explain: explain.into() });
+
+    // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
+    if sess.unstable_features.is_nightly_build() {
+        err.subdiagnostic(FeatureDiagnosticHelp { feature });
+
+        if feature == sym::rustc_attrs {
+            // We're unlikely to stabilize something out of `rustc_attrs`
+            // without at least renaming it, so pointing out how old
+            // the compiler is will do little good.
+        } else if sess.opts.unstable_opts.ui_testing {
+            err.subdiagnostic(SuggestUpgradeCompiler::ui_testing());
+        } else if let Some(suggestion) = SuggestUpgradeCompiler::new() {
+            err.subdiagnostic(suggestion);
+        }
+    }
+    err
+}
+
 #[derive(Diagnostic)]
 pub(crate) enum AppleDeploymentTarget {
     #[diag("failed to parse deployment target specified in {$env_var}: {$error}")]
diff --git a/compiler/rustc_session/src/parse.rs b/compiler/rustc_session/src/parse.rs
index c09e3eed37125..54058e9f5f046 100644
--- a/compiler/rustc_session/src/parse.rs
+++ b/compiler/rustc_session/src/parse.rs
@@ -1,7 +1,6 @@
 //! Contains `ParseSess` which holds state living beyond what one `Parser` might.
 //! It also serves as an input to the parser itself.
 
-use std::str;
 use std::sync::Arc;
 
 use rustc_ast::attr::AttrIdGenerator;
@@ -11,21 +10,15 @@ use rustc_data_structures::sync::{AppendOnlyVec, DynSend, DynSync, Lock};
 use rustc_errors::annotate_snippet_emitter_writer::AnnotateSnippetEmitter;
 use rustc_errors::emitter::{EmitterWithNote, stderr_destination};
 use rustc_errors::{
-    BufferedEarlyLint, ColorConfig, DecorateDiagCompat, Diag, DiagCtxt, DiagCtxtHandle,
-    DiagMessage, EmissionGuarantee, Level, MultiSpan, StashKey,
+    BufferedEarlyLint, ColorConfig, DecorateDiagCompat, Diag, DiagCtxt, DiagCtxtHandle, Level,
+    MultiSpan,
 };
-use rustc_feature::{GateIssue, find_feature_issue};
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::ExpnId;
 use rustc_span::source_map::{FilePathMapping, SourceMap};
-use rustc_span::{Span, Symbol, sym};
+use rustc_span::{Span, Symbol};
 
 use crate::Session;
-use crate::errors::{
-    CliFeatureDiagnosticHelp, FeatureDiagnosticForIssue, FeatureDiagnosticHelp,
-    FeatureDiagnosticSuggestion, FeatureGateError, SuggestUpgradeCompiler,
-};
-use crate::lint::builtin::UNSTABLE_SYNTAX_PRE_EXPANSION;
 use crate::lint::{Lint, LintId};
 
 /// Collected spans during parsing for places where a certain feature was
@@ -78,169 +71,6 @@ impl SymbolGallery {
     }
 }
 
-// FIXME: this function now accepts `Session` instead of `ParseSess` and should be relocated
-/// Construct a diagnostic for a language feature error due to the given `span`.
-/// The `feature`'s `Symbol` is the one you used in `unstable.rs` and `rustc_span::symbol`.
-#[track_caller]
-pub fn feature_err(
-    sess: &Session,
-    feature: Symbol,
-    span: impl Into<MultiSpan>,
-    explain: impl Into<DiagMessage>,
-) -> Diag<'_> {
-    feature_err_issue(sess, feature, span, GateIssue::Language, explain)
-}
-
-/// Construct a diagnostic for a feature gate error.
-///
-/// This variant allows you to control whether it is a library or language feature.
-/// Almost always, you want to use this for a language feature. If so, prefer `feature_err`.
-#[track_caller]
-pub fn feature_err_issue(
-    sess: &Session,
-    feature: Symbol,
-    span: impl Into<MultiSpan>,
-    issue: GateIssue,
-    explain: impl Into<DiagMessage>,
-) -> Diag<'_> {
-    let span = span.into();
-
-    // Cancel an earlier warning for this same error, if it exists.
-    if let Some(span) = span.primary_span()
-        && let Some(err) = sess.dcx().steal_non_err(span, StashKey::EarlySyntaxWarning)
-    {
-        err.cancel()
-    }
-
-    let mut err = sess.dcx().create_err(FeatureGateError { span, explain: explain.into() });
-    add_feature_diagnostics_for_issue(&mut err, sess, feature, issue, false, None);
-    err
-}
-
-/// Construct a future incompatibility diagnostic for a feature gate.
-///
-/// This diagnostic is only a warning and *does not cause compilation to fail*.
-#[track_caller]
-pub fn feature_warn(sess: &Session, feature: Symbol, span: Span, explain: &'static str) {
-    feature_warn_issue(sess, feature, span, GateIssue::Language, explain);
-}
-
-/// Construct a future incompatibility diagnostic for a feature gate.
-///
-/// This diagnostic is only a warning and *does not cause compilation to fail*.
-///
-/// This variant allows you to control whether it is a library or language feature.
-/// Almost always, you want to use this for a language feature. If so, prefer `feature_warn`.
-#[track_caller]
-pub fn feature_warn_issue(
-    sess: &Session,
-    feature: Symbol,
-    span: Span,
-    issue: GateIssue,
-    explain: &'static str,
-) {
-    let mut err = sess.dcx().struct_span_warn(span, explain);
-    add_feature_diagnostics_for_issue(&mut err, sess, feature, issue, false, None);
-
-    // Decorate this as a future-incompatibility lint as in rustc_middle::lint::lint_level
-    let lint = UNSTABLE_SYNTAX_PRE_EXPANSION;
-    let future_incompatible = lint.future_incompatible.as_ref().unwrap();
-    err.is_lint(lint.name_lower(), /* has_future_breakage */ false);
-    err.warn(lint.desc);
-    err.note(format!("for more information, see {}", future_incompatible.reason.reference()));
-
-    // A later feature_err call can steal and cancel this warning.
-    err.stash(span, StashKey::EarlySyntaxWarning);
-}
-
-/// Adds the diagnostics for a feature to an existing error.
-/// Must be a language feature!
-pub fn add_feature_diagnostics<G: EmissionGuarantee>(
-    err: &mut Diag<'_, G>,
-    sess: &Session,
-    feature: Symbol,
-) {
-    add_feature_diagnostics_for_issue(err, sess, feature, GateIssue::Language, false, None);
-}
-
-/// Adds the diagnostics for a feature to an existing error.
-///
-/// This variant allows you to control whether it is a library or language feature.
-/// Almost always, you want to use this for a language feature. If so, prefer
-/// `add_feature_diagnostics`.
-pub fn add_feature_diagnostics_for_issue<G: EmissionGuarantee>(
-    err: &mut Diag<'_, G>,
-    sess: &Session,
-    feature: Symbol,
-    issue: GateIssue,
-    feature_from_cli: bool,
-    inject_span: Option<Span>,
-) {
-    if let Some(n) = find_feature_issue(feature, issue) {
-        err.subdiagnostic(FeatureDiagnosticForIssue { n });
-    }
-
-    // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
-    if sess.unstable_features.is_nightly_build() {
-        if feature_from_cli {
-            err.subdiagnostic(CliFeatureDiagnosticHelp { feature });
-        } else if let Some(span) = inject_span {
-            err.subdiagnostic(FeatureDiagnosticSuggestion { feature, span });
-        } else {
-            err.subdiagnostic(FeatureDiagnosticHelp { feature });
-        }
-        if feature == sym::rustc_attrs {
-            // We're unlikely to stabilize something out of `rustc_attrs`
-            // without at least renaming it, so pointing out how old
-            // the compiler is will do little good.
-        } else if sess.opts.unstable_opts.ui_testing {
-            err.subdiagnostic(SuggestUpgradeCompiler::ui_testing());
-        } else if let Some(suggestion) = SuggestUpgradeCompiler::new() {
-            err.subdiagnostic(suggestion);
-        }
-    }
-}
-
-/// This is only used by unstable_feature_bound as it does not have issue number information for now.
-/// This is basically the same as `feature_err_issue`
-/// but without the feature issue note. If we can do a lookup for issue number from feature name,
-/// then we should directly use `feature_err_issue` for ambiguity error of
-/// `#[unstable_feature_bound]`.
-#[track_caller]
-pub fn feature_err_unstable_feature_bound(
-    sess: &Session,
-    feature: Symbol,
-    span: impl Into<MultiSpan>,
-    explain: impl Into<DiagMessage>,
-) -> Diag<'_> {
-    let span = span.into();
-
-    // Cancel an earlier warning for this same error, if it exists.
-    if let Some(span) = span.primary_span() {
-        if let Some(err) = sess.dcx().steal_non_err(span, StashKey::EarlySyntaxWarning) {
-            err.cancel()
-        }
-    }
-
-    let mut err = sess.dcx().create_err(FeatureGateError { span, explain: explain.into() });
-
-    // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
-    if sess.unstable_features.is_nightly_build() {
-        err.subdiagnostic(FeatureDiagnosticHelp { feature });
-
-        if feature == sym::rustc_attrs {
-            // We're unlikely to stabilize something out of `rustc_attrs`
-            // without at least renaming it, so pointing out how old
-            // the compiler is will do little good.
-        } else if sess.opts.unstable_opts.ui_testing {
-            err.subdiagnostic(SuggestUpgradeCompiler::ui_testing());
-        } else if let Some(suggestion) = SuggestUpgradeCompiler::new() {
-            err.subdiagnostic(suggestion);
-        }
-    }
-    err
-}
-
 /// Info about a parsing session.
 pub struct ParseSess {
     dcx: DiagCtxt,
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 623a246dc1b59..21583a5416277 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -45,7 +45,7 @@ use crate::config::{
 };
 use crate::filesearch::FileSearch;
 use crate::lint::LintId;
-use crate::parse::{ParseSess, add_feature_diagnostics};
+use crate::parse::ParseSess;
 use crate::search_paths::SearchPath;
 use crate::{errors, filesearch, lint};
 
@@ -282,7 +282,7 @@ impl Session {
         if err.code.is_none() {
             err.code(E0658);
         }
-        add_feature_diagnostics(&mut err, self, feature);
+        errors::add_feature_diagnostics(&mut err, self, feature);
         err
     }
 
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
index 1a308ee334d3b..108262d507ef7 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
@@ -13,7 +13,7 @@ use rustc_infer::traits::{
 };
 use rustc_middle::ty::print::PrintPolyTraitPredicateExt;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable as _, TypeVisitableExt as _, Unnormalized};
-use rustc_session::parse::feature_err_unstable_feature_bound;
+use rustc_session::errors::feature_err_unstable_feature_bound;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span};
 use tracing::{debug, instrument};
 
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index 66a2fcaa562d1..57b14e93e277c 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -14,7 +14,7 @@ use rustc_middle::ty::{
     self, GenericArgsRef, Term, TermKind, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
     TypeVisitableExt, TypeVisitor,
 };
-use rustc_session::parse::feature_err;
+use rustc_session::errors::feature_err;
 use rustc_span::def_id::{DefId, LocalDefId};
 use rustc_span::{Span, sym};
 use tracing::{debug, instrument, trace};
diff --git a/src/librustdoc/passes/collect_intra_doc_links.rs b/src/librustdoc/passes/collect_intra_doc_links.rs
index 45061a02e7525..eb1dee2e16d7b 100644
--- a/src/librustdoc/passes/collect_intra_doc_links.rs
+++ b/src/librustdoc/passes/collect_intra_doc_links.rs
@@ -1492,7 +1492,7 @@ impl LinkCollector<'_, '_> {
             Some((sp, _)) => sp,
             None => item.attr_span(self.cx.tcx),
         };
-        rustc_session::parse::feature_err(
+        rustc_session::errors::feature_err(
             self.cx.tcx.sess,
             sym::intra_doc_pointers,
             span,