Rollup merge of #136584 - oli-obk:pattern-types-generic, r=BoxyUwU

Prevent generic pattern types from being used in libstd

Pattern types should follow the same rules that patterns follow. So a pattern type range must not wrap and not be empty. While we reject such invalid ranges at layout computation time, that only happens during monomorphization in the case of const generics. This is the exact same issue as other const generic math has, and since there's no solution there yet, I put these pattern types behind a separate incomplete feature.

These are not necessary for the pattern types MVP (replacing the layout range attributes in libcore and rustc).

cc #136574 (new tracking issue for the `generic_pattern_types` feature gate)

r? ``@lcnr``

cc ``@scottmcm`` ``@joshtriplett``

3 files changed, 45 insertions, 2 deletions

diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 3a2e810dc6a..a4c5e4800eb 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -513,6 +513,8 @@ declare_features! (
     (incomplete, generic_const_exprs, "1.56.0", Some(76560)),
     /// Allows generic parameters and where-clauses on free & associated const items.
     (incomplete, generic_const_items, "1.73.0", Some(113521)),
+    /// Allows any generic constants being used as pattern type range ends
+    (incomplete, generic_pattern_types, "CURRENT_RUSTC_VERSION", Some(136574)),
     /// Allows registering static items globally, possibly across crates, to iterate over at runtime.
     (unstable, global_registration, "1.80.0", Some(125119)),
     /// Allows using guards in patterns.
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 16015776697..bb59b4c40bd 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1026,6 +1026,7 @@ symbols! {
         generic_const_exprs,
         generic_const_items,
         generic_param_attrs,
+        generic_pattern_types,
         get_context,
         global_alloc_ty,
         global_allocator,
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index 96051ad0aa5..c27bd269b0d 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -8,8 +8,9 @@ use rustc_middle::ty::{
     self, GenericArg, GenericArgKind, GenericArgsRef, Ty, TyCtxt, TypeSuperVisitable,
     TypeVisitable, TypeVisitableExt, TypeVisitor,
 };
-use rustc_span::Span;
+use rustc_session::parse::feature_err;
 use rustc_span::def_id::{DefId, LocalDefId};
+use rustc_span::{Span, sym};
 use tracing::{debug, instrument, trace};
 
 use crate::infer::InferCtxt;
@@ -704,8 +705,47 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
                 ));
             }
 
-            ty::Pat(subty, _) => {
+            ty::Pat(subty, pat) => {
                 self.require_sized(subty, ObligationCauseCode::Misc);
+                match *pat {
+                    ty::PatternKind::Range { start, end, include_end: _ } => {
+                        let mut check = |c| {
+                            let cause = self.cause(ObligationCauseCode::Misc);
+                            self.out.push(traits::Obligation::with_depth(
+                                tcx,
+                                cause.clone(),
+                                self.recursion_depth,
+                                self.param_env,
+                                ty::Binder::dummy(ty::PredicateKind::Clause(
+                                    ty::ClauseKind::ConstArgHasType(c, subty),
+                                )),
+                            ));
+                            if !tcx.features().generic_pattern_types() {
+                                if c.has_param() {
+                                    if self.span.is_dummy() {
+                                        self.tcx().dcx().delayed_bug(
+                                            "feature error should be reported elsewhere, too",
+                                        );
+                                    } else {
+                                        feature_err(
+                                            &self.tcx().sess,
+                                            sym::generic_pattern_types,
+                                            self.span,
+                                            "wraparound pattern type ranges cause monomorphization time errors",
+                                        )
+                                        .emit();
+                                    }
+                                }
+                            }
+                        };
+                        if let Some(start) = start {
+                            check(start)
+                        }
+                        if let Some(end) = end {
+                            check(end)
+                        }
+                    }
+                }
             }
 
             ty::Tuple(tys) => {