Auto merge of #111473 - compiler-errors:opaques, r=lcnr

Handle opaques in the new solver (take 2?)

Implement a new strategy for handling opaques in the new solver.

First, queries now carry both their defining anchor and the opaques that were defined in the inference context at the time of canonicalization. These are both used to pre-populate the inference context used by the canonical query.

Second, use the normalizes-to goal to handle opaque types in the new solver. This means that opaques are handled like projection aliases, but with their own rules:
* Can only define opaques if they're "defining uses" (i.e. have unique params in all their substs).
* Can only define opaques that are from the anchor.
* Opaque type definitions are modulo regions. So that means `Opaque<'?0r> = HiddenTy1` and `Opaque<?'1r> = HiddenTy2` equate `HiddenTy1` and `HiddenTy2` instead of defining them as different opaque type keys.

3 files changed, 47 insertions, 11 deletions

diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 6c931a24462..2bde55bc4fd 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -21,7 +21,9 @@ use crate::query::{IntoQueryParam, TyCtxtAt};
 use crate::thir::Thir;
 use crate::traits;
 use crate::traits::solve;
-use crate::traits::solve::{ExternalConstraints, ExternalConstraintsData};
+use crate::traits::solve::{
+    ExternalConstraints, ExternalConstraintsData, PredefinedOpaques, PredefinedOpaquesData,
+};
 use crate::ty::{
     self, AdtDef, AdtDefData, AdtKind, Binder, Const, ConstData, FloatTy, FloatVar, FloatVid,
     GenericParamDefKind, ImplPolarity, InferTy, IntTy, IntVar, IntVid, List, ParamConst, ParamTy,
@@ -140,6 +142,7 @@ pub struct CtxtInterners<'tcx> {
     layout: InternedSet<'tcx, LayoutS>,
     adt_def: InternedSet<'tcx, AdtDefData>,
     external_constraints: InternedSet<'tcx, ExternalConstraintsData<'tcx>>,
+    predefined_opaques_in_body: InternedSet<'tcx, PredefinedOpaquesData<'tcx>>,
     fields: InternedSet<'tcx, List<FieldIdx>>,
 }
 
@@ -164,6 +167,7 @@ impl<'tcx> CtxtInterners<'tcx> {
             layout: Default::default(),
             adt_def: Default::default(),
             external_constraints: Default::default(),
+            predefined_opaques_in_body: Default::default(),
             fields: Default::default(),
         }
     }
@@ -1520,6 +1524,8 @@ direct_interners! {
     adt_def: pub mk_adt_def_from_data(AdtDefData): AdtDef -> AdtDef<'tcx>,
     external_constraints: pub mk_external_constraints(ExternalConstraintsData<'tcx>):
         ExternalConstraints -> ExternalConstraints<'tcx>,
+    predefined_opaques_in_body: pub mk_predefined_opaques_in_body(PredefinedOpaquesData<'tcx>):
+        PredefinedOpaques -> PredefinedOpaques<'tcx>,
 }
 
 macro_rules! slice_interners {
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index c51548501ef..73f435d4840 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -996,17 +996,11 @@ impl<'tcx> Term<'tcx> {
         }
     }
 
-    /// This function returns the inner `AliasTy` if this term is a projection.
-    ///
-    /// FIXME: rename `AliasTy` to `AliasTerm` and make sure we correctly
-    /// deal with constants.
-    pub fn to_projection_term(&self, tcx: TyCtxt<'tcx>) -> Option<AliasTy<'tcx>> {
+    /// This function returns the inner `AliasTy` for a `ty::Alias` or `ConstKind::Unevaluated`.
+    pub fn to_alias_ty(&self, tcx: TyCtxt<'tcx>) -> Option<AliasTy<'tcx>> {
         match self.unpack() {
-            TermKind::Ty(ty) => match ty.kind() {
-                ty::Alias(kind, alias_ty) => match kind {
-                    AliasKind::Projection | AliasKind::Inherent => Some(*alias_ty),
-                    AliasKind::Opaque => None,
-                },
+            TermKind::Ty(ty) => match *ty.kind() {
+                ty::Alias(_kind, alias_ty) => Some(alias_ty),
                 _ => None,
             },
             TermKind::Const(ct) => match ct.kind() {
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index eb903ebfd99..ba05135638e 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -518,6 +518,42 @@ impl<'tcx> TyCtxt<'tcx> {
         Ok(())
     }
 
+    /// Checks whether each generic argument is simply a unique generic placeholder.
+    ///
+    /// This is used in the new solver, which canonicalizes params to placeholders
+    /// for better caching.
+    pub fn uses_unique_placeholders_ignoring_regions(
+        self,
+        substs: SubstsRef<'tcx>,
+    ) -> Result<(), NotUniqueParam<'tcx>> {
+        let mut seen = GrowableBitSet::default();
+        for arg in substs {
+            match arg.unpack() {
+                // Ignore regions, since we can't resolve those in a canonicalized
+                // query in the trait solver.
+                GenericArgKind::Lifetime(_) => {}
+                GenericArgKind::Type(t) => match t.kind() {
+                    ty::Placeholder(p) => {
+                        if !seen.insert(p.bound.var) {
+                            return Err(NotUniqueParam::DuplicateParam(t.into()));
+                        }
+                    }
+                    _ => return Err(NotUniqueParam::NotParam(t.into())),
+                },
+                GenericArgKind::Const(c) => match c.kind() {
+                    ty::ConstKind::Placeholder(p) => {
+                        if !seen.insert(p.bound) {
+                            return Err(NotUniqueParam::DuplicateParam(c.into()));
+                        }
+                    }
+                    _ => return Err(NotUniqueParam::NotParam(c.into())),
+                },
+            }
+        }
+
+        Ok(())
+    }
+
     /// Returns `true` if `def_id` refers to a closure (e.g., `|x| x * 2`). Note
     /// that closures have a `DefId`, but the closure *expression* also
     /// has a `HirId` that is located within the context where the