rustc_ast_passes/
feature_gate.rs

1use rustc_ast as ast;
2use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
3use rustc_ast::{NodeId, PatKind, attr, token};
4use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP, BuiltinAttribute, Features};
5use rustc_session::Session;
6use rustc_session::parse::{feature_err, feature_warn};
7use rustc_span::source_map::Spanned;
8use rustc_span::{Span, Symbol, sym};
9use thin_vec::ThinVec;
10
11use crate::errors;
12
13/// The common case.
14macro_rules! gate {
15    ($visitor:expr, $feature:ident, $span:expr, $explain:expr) => {{
16        if !$visitor.features.$feature() && !$span.allows_unstable(sym::$feature) {
17            #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
18            feature_err(&$visitor.sess, sym::$feature, $span, $explain).emit();
19        }
20    }};
21    ($visitor:expr, $feature:ident, $span:expr, $explain:expr, $help:expr) => {{
22        if !$visitor.features.$feature() && !$span.allows_unstable(sym::$feature) {
23            // FIXME: make this translatable
24            #[allow(rustc::diagnostic_outside_of_impl)]
25            #[allow(rustc::untranslatable_diagnostic)]
26            feature_err(&$visitor.sess, sym::$feature, $span, $explain).with_help($help).emit();
27        }
28    }};
29}
30
31/// The unusual case, where the `has_feature` condition is non-standard.
32macro_rules! gate_alt {
33    ($visitor:expr, $has_feature:expr, $name:expr, $span:expr, $explain:expr) => {{
34        if !$has_feature && !$span.allows_unstable($name) {
35            #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
36            feature_err(&$visitor.sess, $name, $span, $explain).emit();
37        }
38    }};
39}
40
41/// The case involving a multispan.
42macro_rules! gate_multi {
43    ($visitor:expr, $feature:ident, $spans:expr, $explain:expr) => {{
44        if !$visitor.features.$feature() {
45            let spans: Vec<_> =
46                $spans.filter(|span| !span.allows_unstable(sym::$feature)).collect();
47            if !spans.is_empty() {
48                feature_err(&$visitor.sess, sym::$feature, spans, $explain).emit();
49            }
50        }
51    }};
52}
53
54/// The legacy case.
55macro_rules! gate_legacy {
56    ($visitor:expr, $feature:ident, $span:expr, $explain:expr) => {{
57        if !$visitor.features.$feature() && !$span.allows_unstable(sym::$feature) {
58            feature_warn(&$visitor.sess, sym::$feature, $span, $explain);
59        }
60    }};
61}
62
63pub fn check_attribute(attr: &ast::Attribute, sess: &Session, features: &Features) {
64    PostExpansionVisitor { sess, features }.visit_attribute(attr)
65}
66
67struct PostExpansionVisitor<'a> {
68    sess: &'a Session,
69
70    // `sess` contains a `Features`, but this might not be that one.
71    features: &'a Features,
72}
73
74impl<'a> PostExpansionVisitor<'a> {
75    /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
76    fn check_impl_trait(&self, ty: &ast::Ty, in_associated_ty: bool) {
77        struct ImplTraitVisitor<'a> {
78            vis: &'a PostExpansionVisitor<'a>,
79            in_associated_ty: bool,
80        }
81        impl Visitor<'_> for ImplTraitVisitor<'_> {
82            fn visit_ty(&mut self, ty: &ast::Ty) {
83                if let ast::TyKind::ImplTrait(..) = ty.kind {
84                    if self.in_associated_ty {
85                        gate!(
86                            &self.vis,
87                            impl_trait_in_assoc_type,
88                            ty.span,
89                            "`impl Trait` in associated types is unstable"
90                        );
91                    } else {
92                        gate!(
93                            &self.vis,
94                            type_alias_impl_trait,
95                            ty.span,
96                            "`impl Trait` in type aliases is unstable"
97                        );
98                    }
99                }
100                visit::walk_ty(self, ty);
101            }
102        }
103        ImplTraitVisitor { vis: self, in_associated_ty }.visit_ty(ty);
104    }
105
106    fn check_late_bound_lifetime_defs(&self, params: &[ast::GenericParam]) {
107        // Check only lifetime parameters are present and that the
108        // generic parameters that are present have no bounds.
109        let non_lt_param_spans = params.iter().filter_map(|param| match param.kind {
110            ast::GenericParamKind::Lifetime { .. } => None,
111            _ => Some(param.ident.span),
112        });
113        gate_multi!(
114            &self,
115            non_lifetime_binders,
116            non_lt_param_spans,
117            crate::fluent_generated::ast_passes_forbidden_non_lifetime_param
118        );
119
120        // FIXME(non_lifetime_binders): Const bound params are pretty broken.
121        // Let's keep users from using this feature accidentally.
122        if self.features.non_lifetime_binders() {
123            let const_param_spans: Vec<_> = params
124                .iter()
125                .filter_map(|param| match param.kind {
126                    ast::GenericParamKind::Const { .. } => Some(param.ident.span),
127                    _ => None,
128                })
129                .collect();
130
131            if !const_param_spans.is_empty() {
132                self.sess.dcx().emit_err(errors::ForbiddenConstParam { const_param_spans });
133            }
134        }
135
136        for param in params {
137            if !param.bounds.is_empty() {
138                let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
139                self.sess.dcx().emit_err(errors::ForbiddenBound { spans });
140            }
141        }
142    }
143}
144
145impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
146    fn visit_attribute(&mut self, attr: &ast::Attribute) {
147        let attr_info = attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name));
148        // Check feature gates for built-in attributes.
149        if let Some(BuiltinAttribute {
150            gate: AttributeGate::Gated(_, name, descr, has_feature),
151            ..
152        }) = attr_info
153        {
154            gate_alt!(self, has_feature(self.features), *name, attr.span, *descr);
155        }
156        // Check unstable flavors of the `#[doc]` attribute.
157        if attr.has_name(sym::doc) {
158            for meta_item_inner in attr.meta_item_list().unwrap_or_default() {
159                macro_rules! gate_doc { ($($s:literal { $($name:ident => $feature:ident)* })*) => {
160                    $($(if meta_item_inner.has_name(sym::$name) {
161                        let msg = concat!("`#[doc(", stringify!($name), ")]` is ", $s);
162                        gate!(self, $feature, attr.span, msg);
163                    })*)*
164                }}
165
166                gate_doc!(
167                    "experimental" {
168                        cfg => doc_cfg
169                        cfg_hide => doc_cfg_hide
170                        masked => doc_masked
171                        notable_trait => doc_notable_trait
172                    }
173                    "meant for internal use only" {
174                        keyword => rustdoc_internals
175                        fake_variadic => rustdoc_internals
176                        search_unbox => rustdoc_internals
177                    }
178                );
179            }
180        }
181    }
182
183    fn visit_item(&mut self, i: &'a ast::Item) {
184        match &i.kind {
185            ast::ItemKind::ForeignMod(_foreign_module) => {
186                // handled during lowering
187            }
188            ast::ItemKind::Struct(..) | ast::ItemKind::Enum(..) | ast::ItemKind::Union(..) => {
189                for attr in attr::filter_by_name(&i.attrs, sym::repr) {
190                    for item in attr.meta_item_list().unwrap_or_else(ThinVec::new) {
191                        if item.has_name(sym::simd) {
192                            gate!(
193                                &self,
194                                repr_simd,
195                                attr.span,
196                                "SIMD types are experimental and possibly buggy"
197                            );
198                        }
199                    }
200                }
201            }
202
203            ast::ItemKind::Impl(box ast::Impl { polarity, defaultness, of_trait, .. }) => {
204                if let &ast::ImplPolarity::Negative(span) = polarity {
205                    gate!(
206                        &self,
207                        negative_impls,
208                        span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
209                        "negative trait bounds are not fully implemented; \
210                         use marker types for now"
211                    );
212                }
213
214                if let ast::Defaultness::Default(_) = defaultness {
215                    gate!(&self, specialization, i.span, "specialization is unstable");
216                }
217            }
218
219            ast::ItemKind::Trait(box ast::Trait { is_auto: ast::IsAuto::Yes, .. }) => {
220                gate!(
221                    &self,
222                    auto_traits,
223                    i.span,
224                    "auto traits are experimental and possibly buggy"
225                );
226            }
227
228            ast::ItemKind::TraitAlias(..) => {
229                gate!(&self, trait_alias, i.span, "trait aliases are experimental");
230            }
231
232            ast::ItemKind::MacroDef(ast::MacroDef { macro_rules: false, .. }) => {
233                let msg = "`macro` is experimental";
234                gate!(&self, decl_macro, i.span, msg);
235            }
236
237            ast::ItemKind::TyAlias(box ast::TyAlias { ty: Some(ty), .. }) => {
238                self.check_impl_trait(ty, false)
239            }
240
241            _ => {}
242        }
243
244        visit::walk_item(self, i);
245    }
246
247    fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
248        match i.kind {
249            ast::ForeignItemKind::Fn(..) | ast::ForeignItemKind::Static(..) => {
250                let link_name = attr::first_attr_value_str_by_name(&i.attrs, sym::link_name);
251                let links_to_llvm = link_name.is_some_and(|val| val.as_str().starts_with("llvm."));
252                if links_to_llvm {
253                    gate!(
254                        &self,
255                        link_llvm_intrinsics,
256                        i.span,
257                        "linking to LLVM intrinsics is experimental"
258                    );
259                }
260            }
261            ast::ForeignItemKind::TyAlias(..) => {
262                gate!(&self, extern_types, i.span, "extern types are experimental");
263            }
264            ast::ForeignItemKind::MacCall(..) => {}
265        }
266
267        visit::walk_item(self, i)
268    }
269
270    fn visit_ty(&mut self, ty: &'a ast::Ty) {
271        match &ty.kind {
272            ast::TyKind::BareFn(bare_fn_ty) => {
273                // Function pointers cannot be `const`
274                self.check_late_bound_lifetime_defs(&bare_fn_ty.generic_params);
275            }
276            ast::TyKind::Never => {
277                gate!(&self, never_type, ty.span, "the `!` type is experimental");
278            }
279            ast::TyKind::Pat(..) => {
280                gate!(&self, pattern_types, ty.span, "pattern types are unstable");
281            }
282            _ => {}
283        }
284        visit::walk_ty(self, ty)
285    }
286
287    fn visit_generics(&mut self, g: &'a ast::Generics) {
288        for predicate in &g.where_clause.predicates {
289            match &predicate.kind {
290                ast::WherePredicateKind::BoundPredicate(bound_pred) => {
291                    // A type bound (e.g., `for<'c> Foo: Send + Clone + 'c`).
292                    self.check_late_bound_lifetime_defs(&bound_pred.bound_generic_params);
293                }
294                _ => {}
295            }
296        }
297        visit::walk_generics(self, g);
298    }
299
300    fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FnRetTy) {
301        if let ast::FnRetTy::Ty(output_ty) = ret_ty {
302            if let ast::TyKind::Never = output_ty.kind {
303                // Do nothing.
304            } else {
305                self.visit_ty(output_ty)
306            }
307        }
308    }
309
310    fn visit_generic_args(&mut self, args: &'a ast::GenericArgs) {
311        // This check needs to happen here because the never type can be returned from a function,
312        // but cannot be used in any other context. If this check was in `visit_fn_ret_ty`, it
313        // include both functions and generics like `impl Fn() -> !`.
314        if let ast::GenericArgs::Parenthesized(generic_args) = args
315            && let ast::FnRetTy::Ty(ref ty) = generic_args.output
316            && matches!(ty.kind, ast::TyKind::Never)
317        {
318            gate!(&self, never_type, ty.span, "the `!` type is experimental");
319        }
320        visit::walk_generic_args(self, args);
321    }
322
323    fn visit_expr(&mut self, e: &'a ast::Expr) {
324        match e.kind {
325            ast::ExprKind::TryBlock(_) => {
326                gate!(&self, try_blocks, e.span, "`try` expression is experimental");
327            }
328            ast::ExprKind::Lit(token::Lit { kind: token::LitKind::Float, suffix, .. }) => {
329                match suffix {
330                    Some(sym::f16) => {
331                        gate!(&self, f16, e.span, "the type `f16` is unstable")
332                    }
333                    Some(sym::f128) => {
334                        gate!(&self, f128, e.span, "the type `f128` is unstable")
335                    }
336                    _ => (),
337                }
338            }
339            _ => {}
340        }
341        visit::walk_expr(self, e)
342    }
343
344    fn visit_pat(&mut self, pattern: &'a ast::Pat) {
345        match &pattern.kind {
346            PatKind::Slice(pats) => {
347                for pat in pats {
348                    let inner_pat = match &pat.kind {
349                        PatKind::Ident(.., Some(pat)) => pat,
350                        _ => pat,
351                    };
352                    if let PatKind::Range(Some(_), None, Spanned { .. }) = inner_pat.kind {
353                        gate!(
354                            &self,
355                            half_open_range_patterns_in_slices,
356                            pat.span,
357                            "`X..` patterns in slices are experimental"
358                        );
359                    }
360                }
361            }
362            PatKind::Box(..) => {
363                gate!(&self, box_patterns, pattern.span, "box pattern syntax is experimental");
364            }
365            _ => {}
366        }
367        visit::walk_pat(self, pattern)
368    }
369
370    fn visit_poly_trait_ref(&mut self, t: &'a ast::PolyTraitRef) {
371        self.check_late_bound_lifetime_defs(&t.bound_generic_params);
372        visit::walk_poly_trait_ref(self, t);
373    }
374
375    fn visit_fn(&mut self, fn_kind: FnKind<'a>, span: Span, _: NodeId) {
376        if let Some(_header) = fn_kind.header() {
377            // Stability of const fn methods are covered in `visit_assoc_item` below.
378        }
379
380        if let FnKind::Closure(ast::ClosureBinder::For { generic_params, .. }, ..) = fn_kind {
381            self.check_late_bound_lifetime_defs(generic_params);
382        }
383
384        if fn_kind.ctxt() != Some(FnCtxt::Foreign) && fn_kind.decl().c_variadic() {
385            gate!(&self, c_variadic, span, "C-variadic functions are unstable");
386        }
387
388        visit::walk_fn(self, fn_kind)
389    }
390
391    fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
392        let is_fn = match &i.kind {
393            ast::AssocItemKind::Fn(_) => true,
394            ast::AssocItemKind::Type(box ast::TyAlias { ty, .. }) => {
395                if let (Some(_), AssocCtxt::Trait) = (ty, ctxt) {
396                    gate!(
397                        &self,
398                        associated_type_defaults,
399                        i.span,
400                        "associated type defaults are unstable"
401                    );
402                }
403                if let Some(ty) = ty {
404                    self.check_impl_trait(ty, true);
405                }
406                false
407            }
408            _ => false,
409        };
410        if let ast::Defaultness::Default(_) = i.kind.defaultness() {
411            // Limit `min_specialization` to only specializing functions.
412            gate_alt!(
413                &self,
414                self.features.specialization() || (is_fn && self.features.min_specialization()),
415                sym::specialization,
416                i.span,
417                "specialization is unstable"
418            );
419        }
420        visit::walk_assoc_item(self, i, ctxt)
421    }
422}
423
424pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
425    maybe_stage_features(sess, features, krate);
426    check_incompatible_features(sess, features);
427    check_new_solver_banned_features(sess, features);
428
429    let mut visitor = PostExpansionVisitor { sess, features };
430
431    let spans = sess.psess.gated_spans.spans.borrow();
432    macro_rules! gate_all {
433        ($gate:ident, $msg:literal) => {
434            if let Some(spans) = spans.get(&sym::$gate) {
435                for span in spans {
436                    gate!(&visitor, $gate, *span, $msg);
437                }
438            }
439        };
440        ($gate:ident, $msg:literal, $help:literal) => {
441            if let Some(spans) = spans.get(&sym::$gate) {
442                for span in spans {
443                    gate!(&visitor, $gate, *span, $msg, $help);
444                }
445            }
446        };
447    }
448    gate_all!(
449        if_let_guard,
450        "`if let` guards are experimental",
451        "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
452    );
453    gate_all!(let_chains, "`let` expressions in this position are unstable");
454    gate_all!(
455        async_trait_bounds,
456        "`async` trait bounds are unstable",
457        "use the desugared name of the async trait, such as `AsyncFn`"
458    );
459    gate_all!(async_for_loop, "`for await` loops are experimental");
460    gate_all!(
461        closure_lifetime_binder,
462        "`for<...>` binders for closures are experimental",
463        "consider removing `for<...>`"
464    );
465    gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
466    // yield can be enabled either by `coroutines` or `gen_blocks`
467    if let Some(spans) = spans.get(&sym::yield_expr) {
468        for span in spans {
469            if (!visitor.features.coroutines() && !span.allows_unstable(sym::coroutines))
470                && (!visitor.features.gen_blocks() && !span.allows_unstable(sym::gen_blocks))
471            {
472                #[allow(rustc::untranslatable_diagnostic)]
473                // Don't know which of the two features to include in the
474                // error message, so I am arbitrarily picking one.
475                feature_err(&visitor.sess, sym::coroutines, *span, "yield syntax is experimental")
476                    .emit();
477            }
478        }
479    }
480    gate_all!(gen_blocks, "gen blocks are experimental");
481    gate_all!(const_trait_impl, "const trait impls are experimental");
482    gate_all!(
483        half_open_range_patterns_in_slices,
484        "half-open range patterns in slices are unstable"
485    );
486    gate_all!(inline_const_pat, "inline-const in pattern position is experimental");
487    gate_all!(associated_const_equality, "associated const equality is incomplete");
488    gate_all!(yeet_expr, "`do yeet` expression is experimental");
489    gate_all!(dyn_star, "`dyn*` trait objects are experimental");
490    gate_all!(const_closures, "const closures are experimental");
491    gate_all!(builtin_syntax, "`builtin #` syntax is unstable");
492    gate_all!(ergonomic_clones, "ergonomic clones are experimental");
493    gate_all!(explicit_tail_calls, "`become` expression is experimental");
494    gate_all!(generic_const_items, "generic const items are experimental");
495    gate_all!(guard_patterns, "guard patterns are experimental", "consider using match arm guards");
496    gate_all!(default_field_values, "default values on fields are experimental");
497    gate_all!(fn_delegation, "functions delegation is not yet fully implemented");
498    gate_all!(postfix_match, "postfix match is experimental");
499    gate_all!(mut_ref, "mutable by-reference bindings are experimental");
500    gate_all!(global_registration, "global registration is experimental");
501    gate_all!(return_type_notation, "return type notation is experimental");
502    gate_all!(pin_ergonomics, "pinned reference syntax is experimental");
503    gate_all!(unsafe_fields, "`unsafe` fields are experimental");
504    gate_all!(unsafe_binders, "unsafe binder types are experimental");
505    gate_all!(contracts, "contracts are incomplete");
506    gate_all!(contracts_internals, "contract internal machinery is for internal use only");
507    gate_all!(where_clause_attrs, "attributes in `where` clause are unstable");
508
509    if !visitor.features.never_patterns() {
510        if let Some(spans) = spans.get(&sym::never_patterns) {
511            for &span in spans {
512                if span.allows_unstable(sym::never_patterns) {
513                    continue;
514                }
515                let sm = sess.source_map();
516                // We gate two types of spans: the span of a `!` pattern, and the span of a
517                // match arm without a body. For the latter we want to give the user a normal
518                // error.
519                if let Ok(snippet) = sm.span_to_snippet(span)
520                    && snippet == "!"
521                {
522                    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
523                    feature_err(sess, sym::never_patterns, span, "`!` patterns are experimental")
524                        .emit();
525                } else {
526                    let suggestion = span.shrink_to_hi();
527                    sess.dcx().emit_err(errors::MatchArmWithNoBody { span, suggestion });
528                }
529            }
530        }
531    }
532
533    if !visitor.features.negative_bounds() {
534        for &span in spans.get(&sym::negative_bounds).iter().copied().flatten() {
535            sess.dcx().emit_err(errors::NegativeBoundUnsupported { span });
536        }
537    }
538
539    // All uses of `gate_all_legacy_dont_use!` below this point were added in #65742,
540    // and subsequently disabled (with the non-early gating readded).
541    // We emit an early future-incompatible warning for these.
542    // New syntax gates should go above here to get a hard error gate.
543    macro_rules! gate_all_legacy_dont_use {
544        ($gate:ident, $msg:literal) => {
545            for span in spans.get(&sym::$gate).unwrap_or(&vec![]) {
546                gate_legacy!(&visitor, $gate, *span, $msg);
547            }
548        };
549    }
550
551    gate_all_legacy_dont_use!(box_patterns, "box pattern syntax is experimental");
552    gate_all_legacy_dont_use!(trait_alias, "trait aliases are experimental");
553    gate_all_legacy_dont_use!(decl_macro, "`macro` is experimental");
554    gate_all_legacy_dont_use!(try_blocks, "`try` blocks are unstable");
555    gate_all_legacy_dont_use!(auto_traits, "`auto` traits are unstable");
556
557    visit::walk_crate(&mut visitor, krate);
558}
559
560fn maybe_stage_features(sess: &Session, features: &Features, krate: &ast::Crate) {
561    // checks if `#![feature]` has been used to enable any feature.
562    if sess.opts.unstable_features.is_nightly_build() {
563        return;
564    }
565    if features.enabled_features().is_empty() {
566        return;
567    }
568    let mut errored = false;
569    for attr in krate.attrs.iter().filter(|attr| attr.has_name(sym::feature)) {
570        // `feature(...)` used on non-nightly. This is definitely an error.
571        let mut err = errors::FeatureOnNonNightly {
572            span: attr.span,
573            channel: option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)"),
574            stable_features: vec![],
575            sugg: None,
576        };
577
578        let mut all_stable = true;
579        for ident in attr.meta_item_list().into_iter().flatten().flat_map(|nested| nested.ident()) {
580            let name = ident.name;
581            let stable_since = features
582                .enabled_lang_features()
583                .iter()
584                .find(|feat| feat.gate_name == name)
585                .map(|feat| feat.stable_since)
586                .flatten();
587            if let Some(since) = stable_since {
588                err.stable_features.push(errors::StableFeature { name, since });
589            } else {
590                all_stable = false;
591            }
592        }
593        if all_stable {
594            err.sugg = Some(attr.span);
595        }
596        sess.dcx().emit_err(err);
597        errored = true;
598    }
599    // Just make sure we actually error if anything is listed in `enabled_features`.
600    assert!(errored);
601}
602
603fn check_incompatible_features(sess: &Session, features: &Features) {
604    let enabled_lang_features =
605        features.enabled_lang_features().iter().map(|feat| (feat.gate_name, feat.attr_sp));
606    let enabled_lib_features =
607        features.enabled_lib_features().iter().map(|feat| (feat.gate_name, feat.attr_sp));
608    let enabled_features = enabled_lang_features.chain(enabled_lib_features);
609
610    for (f1, f2) in rustc_feature::INCOMPATIBLE_FEATURES
611        .iter()
612        .filter(|(f1, f2)| features.enabled(*f1) && features.enabled(*f2))
613    {
614        if let Some((f1_name, f1_span)) = enabled_features.clone().find(|(name, _)| name == f1) {
615            if let Some((f2_name, f2_span)) = enabled_features.clone().find(|(name, _)| name == f2)
616            {
617                let spans = vec![f1_span, f2_span];
618                sess.dcx().emit_err(errors::IncompatibleFeatures {
619                    spans,
620                    f1: f1_name,
621                    f2: f2_name,
622                });
623            }
624        }
625    }
626}
627
628fn check_new_solver_banned_features(sess: &Session, features: &Features) {
629    if !sess.opts.unstable_opts.next_solver.globally {
630        return;
631    }
632
633    // Ban GCE with the new solver, because it does not implement GCE correctly.
634    if let Some(gce_span) = features
635        .enabled_lang_features()
636        .iter()
637        .find(|feat| feat.gate_name == sym::generic_const_exprs)
638        .map(|feat| feat.attr_sp)
639    {
640        #[allow(rustc::symbol_intern_string_literal)]
641        sess.dcx().emit_err(errors::IncompatibleFeatures {
642            spans: vec![gce_span],
643            f1: Symbol::intern("-Znext-solver=globally"),
644            f2: sym::generic_const_exprs,
645        });
646    }
647}