Auto merge of #105733 - compiler-errors:ty-ct-late-flags, r=cjgillot

Add type flags support for `Ty` and `Const` late-bound variables

I've been working on `for<T>` binders, and these will eventually be useful.

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1912,7 +1912,7 @@ impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
             }
             let pred = obligation.predicate;
             // Match the existing behavior.
-            if pred.is_global() && !pred.has_late_bound_regions() {
+            if pred.is_global() && !pred.has_late_bound_vars() {
                 let pred = self.normalize(span, None, pred);
                 let hir_node = tcx.hir().find(self.body_id);
 

compiler/rustc_middle/src/ty/erase_regions.rs

@@ -21,7 +21,7 @@ impl<'tcx> TyCtxt<'tcx> {
         T: TypeFoldable<'tcx>,
     {
         // If there's nothing to erase avoid performing the query at all
-        if !value.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND | TypeFlags::HAS_FREE_REGIONS) {
+        if !value.has_type_flags(TypeFlags::HAS_LATE_BOUND | TypeFlags::HAS_FREE_REGIONS) {
             return value;
         }
         debug!("erase_regions({:?})", value);

compiler/rustc_middle/src/ty/flags.rs

@@ -59,8 +59,18 @@ impl FlagComputation {
     {
         let mut computation = FlagComputation::new();
 
-        if !value.bound_vars().is_empty() {
-            computation.flags = computation.flags | TypeFlags::HAS_RE_LATE_BOUND;
+        for bv in value.bound_vars() {
+            match bv {
+                ty::BoundVariableKind::Ty(_) => {
+                    computation.flags |= TypeFlags::HAS_TY_LATE_BOUND;
+                }
+                ty::BoundVariableKind::Region(_) => {
+                    computation.flags |= TypeFlags::HAS_RE_LATE_BOUND;
+                }
+                ty::BoundVariableKind::Const => {
+                    computation.flags |= TypeFlags::HAS_CT_LATE_BOUND;
+                }
+            }
         }
 
         f(&mut computation, value.skip_binder());
@@ -131,6 +141,7 @@ impl FlagComputation {
 
             &ty::Bound(debruijn, _) => {
                 self.add_bound_var(debruijn);
+                self.add_flags(TypeFlags::HAS_TY_LATE_BOUND);
             }
 
             &ty::Placeholder(..) => {
@@ -303,6 +314,7 @@ impl FlagComputation {
             }
             ty::ConstKind::Bound(debruijn, _) => {
                 self.add_bound_var(debruijn);
+                self.add_flags(TypeFlags::HAS_CT_LATE_BOUND);
             }
             ty::ConstKind::Param(_) => {
                 self.add_flags(TypeFlags::HAS_CT_PARAM);

compiler/rustc_middle/src/ty/visit.rs

@@ -165,6 +165,14 @@ pub trait TypeVisitable<'tcx>: fmt::Debug + Clone {
     fn has_late_bound_regions(&self) -> bool {
         self.has_type_flags(TypeFlags::HAS_RE_LATE_BOUND)
     }
+    /// True if there are any late-bound non-region variables
+    fn has_non_region_late_bound(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_LATE_BOUND - TypeFlags::HAS_RE_LATE_BOUND)
+    }
+    /// True if there are any late-bound variables
+    fn has_late_bound_vars(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_LATE_BOUND)
+    }
 
     /// Indicates whether this value still has parameters/placeholders/inference variables
     /// which could be replaced later, in a way that would change the results of `impl`

compiler/rustc_symbol_mangling/src/v0.rs

@@ -206,6 +206,7 @@ impl<'tcx> SymbolMangler<'tcx> {
     where
         T: TypeVisitable<'tcx>,
     {
+        // FIXME(non-lifetime-binders): What to do here?
         let regions = if value.has_late_bound_regions() {
             self.tcx.collect_referenced_late_bound_regions(value)
         } else {

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -755,7 +755,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     // contain the "'static" lifetime (any other lifetime
                     // would either be late-bound or local), so it is guaranteed
                     // to outlive any other lifetime
-                    if pred.0.is_global() && !pred.0.has_late_bound_regions() {
+                    if pred.0.is_global() && !pred.0.has_late_bound_vars() {
                         Ok(EvaluatedToOk)
                     } else {
                         Ok(EvaluatedToOkModuloRegions)
@@ -1785,9 +1785,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // Check if a bound would previously have been removed when normalizing
         // the param_env so that it can be given the lowest priority. See
         // #50825 for the motivation for this.
-        let is_global = |cand: &ty::PolyTraitPredicate<'tcx>| {
-            cand.is_global() && !cand.has_late_bound_regions()
-        };
+        let is_global =
+            |cand: &ty::PolyTraitPredicate<'tcx>| cand.is_global() && !cand.has_late_bound_vars();
 
         // (*) Prefer `BuiltinCandidate { has_nested: false }`, `PointeeCandidate`,
         // `DiscriminantKindCandidate`, `ConstDestructCandidate`

compiler/rustc_type_ir/src/lib.rs

@@ -241,22 +241,30 @@ bitflags! {
         /// Basically anything but `ReLateBound` and `ReErased`.
         const HAS_FREE_REGIONS            = 1 << 14;
 
-        /// Does this have any `ReLateBound` regions? Used to check
-        /// if a global bound is safe to evaluate.
+        /// Does this have any `ReLateBound` regions?
         const HAS_RE_LATE_BOUND           = 1 << 15;
+        /// Does this have any `Bound` types?
+        const HAS_TY_LATE_BOUND           = 1 << 16;
+        /// Does this have any `ConstKind::Bound` consts?
+        const HAS_CT_LATE_BOUND           = 1 << 17;
+        /// Does this have any bound variables?
+        /// Used to check if a global bound is safe to evaluate.
+        const HAS_LATE_BOUND              = TypeFlags::HAS_RE_LATE_BOUND.bits
+                                          | TypeFlags::HAS_TY_LATE_BOUND.bits
+                                          | TypeFlags::HAS_CT_LATE_BOUND.bits;
 
         /// Does this have any `ReErased` regions?
-        const HAS_RE_ERASED               = 1 << 16;
+        const HAS_RE_ERASED               = 1 << 18;
 
         /// Does this value have parameters/placeholders/inference variables which could be
         /// replaced later, in a way that would change the results of `impl` specialization?
-        const STILL_FURTHER_SPECIALIZABLE = 1 << 17;
+        const STILL_FURTHER_SPECIALIZABLE = 1 << 19;
 
         /// Does this value have `InferTy::FreshTy/FreshIntTy/FreshFloatTy`?
-        const HAS_TY_FRESH                = 1 << 18;
+        const HAS_TY_FRESH                = 1 << 20;
 
         /// Does this value have `InferConst::Fresh`?
-        const HAS_CT_FRESH                = 1 << 19;
+        const HAS_CT_FRESH                = 1 << 21;
     }
 }