Auto merge of #114451 - matthiaskrgr:rollup-37qmv19, r=matthiaskrgr

Rollup of 5 pull requests

Successful merges:

 - #114022 (Perform OpaqueCast field projection on HIR, too.)
 - #114253 (Compute variances for lazy type aliases)
 - #114355 (resolve before canonicalization in new solver, ICE if unresolved)
 - #114427 (Handle non-utf8 rpaths (fix FIXME))
 - #114440 (bootstrap: config: fix version comparison bug)

r? `@ghost`
`@rustbot` modify labels: rollup

21 files changed, 331 insertions, 213 deletions

diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index abb11ce7396..50d875dfae9 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -498,14 +498,13 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
 
     /// Checks that the types internal to the `place` match up with
     /// what would be expected.
+    #[instrument(level = "debug", skip(self, location), ret)]
     fn sanitize_place(
         &mut self,
         place: &Place<'tcx>,
         location: Location,
         context: PlaceContext,
     ) -> PlaceTy<'tcx> {
-        debug!("sanitize_place: {:?}", place);
-
         let mut place_ty = PlaceTy::from_ty(self.body().local_decls[place.local].ty);
 
         for elem in place.projection.iter() {
@@ -608,7 +607,7 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
         }
     }
 
-    #[instrument(skip(self), level = "debug")]
+    #[instrument(skip(self, location), ret, level = "debug")]
     fn sanitize_projection(
         &mut self,
         base: PlaceTy<'tcx>,
@@ -617,7 +616,6 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
         location: Location,
         context: PlaceContext,
     ) -> PlaceTy<'tcx> {
-        debug!("sanitize_projection: {:?} {:?} {:?}", base, pi, place);
         let tcx = self.tcx();
         let base_ty = base.ty;
         match pi {
diff --git a/compiler/rustc_codegen_ssa/src/back/rpath.rs b/compiler/rustc_codegen_ssa/src/back/rpath.rs
index 18268622341..ebf04e7a399 100644
--- a/compiler/rustc_codegen_ssa/src/back/rpath.rs
+++ b/compiler/rustc_codegen_ssa/src/back/rpath.rs
@@ -1,6 +1,7 @@
 use pathdiff::diff_paths;
 use rustc_data_structures::fx::FxHashSet;
 use std::env;
+use std::ffi::OsString;
 use std::fs;
 use std::path::{Path, PathBuf};
 
@@ -12,7 +13,7 @@ pub struct RPathConfig<'a> {
     pub linker_is_gnu: bool,
 }
 
-pub fn get_rpath_flags(config: &mut RPathConfig<'_>) -> Vec<String> {
+pub fn get_rpath_flags(config: &mut RPathConfig<'_>) -> Vec<OsString> {
     // No rpath on windows
     if !config.has_rpath {
         return Vec::new();
@@ -21,36 +22,38 @@ pub fn get_rpath_flags(config: &mut RPathConfig<'_>) -> Vec<String> {
     debug!("preparing the RPATH!");
 
     let rpaths = get_rpaths(config);
-    let mut flags = rpaths_to_flags(&rpaths);
+    let mut flags = rpaths_to_flags(rpaths);
 
     if config.linker_is_gnu {
         // Use DT_RUNPATH instead of DT_RPATH if available
-        flags.push("-Wl,--enable-new-dtags".to_owned());
+        flags.push("-Wl,--enable-new-dtags".into());
 
         // Set DF_ORIGIN for substitute $ORIGIN
-        flags.push("-Wl,-z,origin".to_owned());
+        flags.push("-Wl,-z,origin".into());
     }
 
     flags
 }
 
-fn rpaths_to_flags(rpaths: &[String]) -> Vec<String> {
+fn rpaths_to_flags(rpaths: Vec<OsString>) -> Vec<OsString> {
     let mut ret = Vec::with_capacity(rpaths.len()); // the minimum needed capacity
 
     for rpath in rpaths {
-        if rpath.contains(',') {
+        if rpath.to_string_lossy().contains(',') {
             ret.push("-Wl,-rpath".into());
             ret.push("-Xlinker".into());
-            ret.push(rpath.clone());
+            ret.push(rpath);
         } else {
-            ret.push(format!("-Wl,-rpath,{}", &(*rpath)));
+            let mut single_arg = OsString::from("-Wl,-rpath,");
+            single_arg.push(rpath);
+            ret.push(single_arg);
         }
     }
 
     ret
 }
 
-fn get_rpaths(config: &mut RPathConfig<'_>) -> Vec<String> {
+fn get_rpaths(config: &mut RPathConfig<'_>) -> Vec<OsString> {
     debug!("output: {:?}", config.out_filename.display());
     debug!("libs:");
     for libpath in config.libs {
@@ -64,18 +67,18 @@ fn get_rpaths(config: &mut RPathConfig<'_>) -> Vec<String> {
 
     debug!("rpaths:");
     for rpath in &rpaths {
-        debug!("    {}", rpath);
+        debug!("    {:?}", rpath);
     }
 
     // Remove duplicates
     minimize_rpaths(&rpaths)
 }
 
-fn get_rpaths_relative_to_output(config: &mut RPathConfig<'_>) -> Vec<String> {
+fn get_rpaths_relative_to_output(config: &mut RPathConfig<'_>) -> Vec<OsString> {
     config.libs.iter().map(|a| get_rpath_relative_to_output(config, a)).collect()
 }
 
-fn get_rpath_relative_to_output(config: &mut RPathConfig<'_>, lib: &Path) -> String {
+fn get_rpath_relative_to_output(config: &mut RPathConfig<'_>, lib: &Path) -> OsString {
     // Mac doesn't appear to support $ORIGIN
     let prefix = if config.is_like_osx { "@loader_path" } else { "$ORIGIN" };
 
@@ -87,8 +90,11 @@ fn get_rpath_relative_to_output(config: &mut RPathConfig<'_>, lib: &Path) -> Str
     let output = fs::canonicalize(&output).unwrap_or(output);
     let relative = path_relative_from(&lib, &output)
         .unwrap_or_else(|| panic!("couldn't create relative path from {output:?} to {lib:?}"));
-    // FIXME (#9639): This needs to handle non-utf8 paths
-    format!("{}/{}", prefix, relative.to_str().expect("non-utf8 component in path"))
+
+    let mut rpath = OsString::from(prefix);
+    rpath.push("/");
+    rpath.push(relative);
+    rpath
 }
 
 // This routine is adapted from the *old* Path's `path_relative_from`
@@ -99,7 +105,7 @@ fn path_relative_from(path: &Path, base: &Path) -> Option<PathBuf> {
     diff_paths(path, base)
 }
 
-fn minimize_rpaths(rpaths: &[String]) -> Vec<String> {
+fn minimize_rpaths(rpaths: &[OsString]) -> Vec<OsString> {
     let mut set = FxHashSet::default();
     let mut minimized = Vec::new();
     for rpath in rpaths {
diff --git a/compiler/rustc_codegen_ssa/src/back/rpath/tests.rs b/compiler/rustc_codegen_ssa/src/back/rpath/tests.rs
index 604f19144a6..ac2e54072c4 100644
--- a/compiler/rustc_codegen_ssa/src/back/rpath/tests.rs
+++ b/compiler/rustc_codegen_ssa/src/back/rpath/tests.rs
@@ -1,32 +1,33 @@
 use super::RPathConfig;
 use super::{get_rpath_relative_to_output, minimize_rpaths, rpaths_to_flags};
+use std::ffi::OsString;
 use std::path::{Path, PathBuf};
 
 #[test]
 fn test_rpaths_to_flags() {
-    let flags = rpaths_to_flags(&["path1".to_string(), "path2".to_string()]);
+    let flags = rpaths_to_flags(vec!["path1".into(), "path2".into()]);
     assert_eq!(flags, ["-Wl,-rpath,path1", "-Wl,-rpath,path2"]);
 }
 
 #[test]
 fn test_minimize1() {
-    let res = minimize_rpaths(&["rpath1".to_string(), "rpath2".to_string(), "rpath1".to_string()]);
+    let res = minimize_rpaths(&["rpath1".into(), "rpath2".into(), "rpath1".into()]);
     assert!(res == ["rpath1", "rpath2",]);
 }
 
 #[test]
 fn test_minimize2() {
     let res = minimize_rpaths(&[
-        "1a".to_string(),
-        "2".to_string(),
-        "2".to_string(),
-        "1a".to_string(),
-        "4a".to_string(),
-        "1a".to_string(),
-        "2".to_string(),
-        "3".to_string(),
-        "4a".to_string(),
-        "3".to_string(),
+        "1a".into(),
+        "2".into(),
+        "2".into(),
+        "1a".into(),
+        "4a".into(),
+        "1a".into(),
+        "2".into(),
+        "3".into(),
+        "4a".into(),
+        "3".into(),
     ]);
     assert!(res == ["1a", "2", "4a", "3",]);
 }
@@ -58,15 +59,15 @@ fn test_rpath_relative() {
 
 #[test]
 fn test_xlinker() {
-    let args = rpaths_to_flags(&["a/normal/path".to_string(), "a,comma,path".to_string()]);
+    let args = rpaths_to_flags(vec!["a/normal/path".into(), "a,comma,path".into()]);
 
     assert_eq!(
         args,
         vec![
-            "-Wl,-rpath,a/normal/path".to_string(),
-            "-Wl,-rpath".to_string(),
-            "-Xlinker".to_string(),
-            "a,comma,path".to_string()
+            OsString::from("-Wl,-rpath,a/normal/path"),
+            OsString::from("-Wl,-rpath"),
+            OsString::from("-Xlinker"),
+            OsString::from("a,comma,path")
         ]
     );
 }
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index e64848da86b..16d4d099c7e 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -245,13 +245,14 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
         }
         // `ForeignItem`s are handled separately.
         hir::ItemKind::ForeignMod { .. } => {}
-        hir::ItemKind::TyAlias(hir_ty, ..) => {
+        hir::ItemKind::TyAlias(hir_ty, ast_generics) => {
             if tcx.features().lazy_type_alias
                 || tcx.type_of(item.owner_id).skip_binder().has_opaque_types()
             {
                 // Bounds of lazy type aliases and of eager ones that contain opaque types are respected.
                 // E.g: `type X = impl Trait;`, `type X = (impl Trait, Y);`.
                 check_item_type(tcx, def_id, hir_ty.span, UnsizedHandling::Allow);
+                check_variances_for_type_defn(tcx, item, ast_generics);
             }
         }
         _ => {}
@@ -1700,10 +1701,27 @@ fn check_variances_for_type_defn<'tcx>(
     hir_generics: &hir::Generics<'_>,
 ) {
     let identity_args = ty::GenericArgs::identity_for_item(tcx, item.owner_id);
-    for field in tcx.adt_def(item.owner_id).all_fields() {
-        if field.ty(tcx, identity_args).references_error() {
-            return;
+
+    match item.kind {
+        ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
+            for field in tcx.adt_def(item.owner_id).all_fields() {
+                if field.ty(tcx, identity_args).references_error() {
+                    return;
+                }
+            }
+        }
+        ItemKind::TyAlias(..) => {
+            let ty = tcx.type_of(item.owner_id).instantiate_identity();
+
+            if tcx.features().lazy_type_alias || ty.has_opaque_types() {
+                if ty.references_error() {
+                    return;
+                }
+            } else {
+                bug!();
+            }
         }
+        _ => bug!(),
     }
 
     let ty_predicates = tcx.predicates_of(item.owner_id);
diff --git a/compiler/rustc_hir_analysis/src/variance/constraints.rs b/compiler/rustc_hir_analysis/src/variance/constraints.rs
index ec8889781f4..4a3d522e488 100644
--- a/compiler/rustc_hir_analysis/src/variance/constraints.rs
+++ b/compiler/rustc_hir_analysis/src/variance/constraints.rs
@@ -6,7 +6,7 @@
 use hir::def_id::{DefId, LocalDefId};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
 use rustc_middle::ty::{GenericArgKind, GenericArgsRef};
 
 use super::terms::VarianceTerm::*;
@@ -78,6 +78,12 @@ pub fn add_constraints_from_crate<'a, 'tcx>(
                 }
             }
             DefKind::Fn | DefKind::AssocFn => constraint_cx.build_constraints_for_item(def_id),
+            DefKind::TyAlias
+                if tcx.features().lazy_type_alias
+                    || tcx.type_of(def_id).instantiate_identity().has_opaque_types() =>
+            {
+                constraint_cx.build_constraints_for_item(def_id)
+            }
             _ => {}
         }
     }
@@ -101,7 +107,18 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
 
         let inferred_start = self.terms_cx.inferred_starts[&def_id];
         let current_item = &CurrentItem { inferred_start };
-        match tcx.type_of(def_id).instantiate_identity().kind() {
+        let ty = tcx.type_of(def_id).instantiate_identity();
+
+        // The type as returned by `type_of` is the underlying type and generally not a weak projection.
+        // Therefore we need to check the `DefKind` first.
+        if let DefKind::TyAlias = tcx.def_kind(def_id)
+            && (tcx.features().lazy_type_alias || ty.has_opaque_types())
+        {
+            self.add_constraints_from_ty(current_item, ty, self.covariant);
+            return;
+        }
+
+        match ty.kind() {
             ty::Adt(def, _) => {
                 // Not entirely obvious: constraints on structs/enums do not
                 // affect the variance of their type parameters. See discussion
@@ -127,6 +144,7 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
             }
 
             ty::Error(_) => {}
+
             _ => {
                 span_bug!(
                     tcx.def_span(def_id),
@@ -252,10 +270,14 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
                 self.add_constraints_from_args(current, def.did(), args, variance);
             }
 
-            ty::Alias(_, ref data) => {
+            ty::Alias(ty::Projection | ty::Inherent | ty::Opaque, ref data) => {
                 self.add_constraints_from_invariant_args(current, data.args, variance);
             }
 
+            ty::Alias(ty::Weak, ref data) => {
+                self.add_constraints_from_args(current, data.def_id, data.args, variance);
+            }
+
             ty::Dynamic(data, r, _) => {
                 // The type `dyn Trait<T> +'a` is covariant w/r/t `'a`:
                 self.add_constraints_from_region(current, r, variance);
diff --git a/compiler/rustc_hir_analysis/src/variance/mod.rs b/compiler/rustc_hir_analysis/src/variance/mod.rs
index 6952a3fa66f..2ef294c6793 100644
--- a/compiler/rustc_hir_analysis/src/variance/mod.rs
+++ b/compiler/rustc_hir_analysis/src/variance/mod.rs
@@ -8,7 +8,7 @@ use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{self, CrateVariancesMap, GenericArgsRef, Ty, TyCtxt};
-use rustc_middle::ty::{TypeSuperVisitable, TypeVisitable};
+use rustc_middle::ty::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt};
 use std::ops::ControlFlow;
 
 /// Defines the `TermsContext` basically houses an arena where we can
@@ -56,6 +56,14 @@ fn variances_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Variance] {
             let crate_map = tcx.crate_variances(());
             return crate_map.variances.get(&item_def_id.to_def_id()).copied().unwrap_or(&[]);
         }
+        DefKind::TyAlias
+            if tcx.features().lazy_type_alias
+                || tcx.type_of(item_def_id).instantiate_identity().has_opaque_types() =>
+        {
+            // These are inferred.
+            let crate_map = tcx.crate_variances(());
+            return crate_map.variances.get(&item_def_id.to_def_id()).copied().unwrap_or(&[]);
+        }
         DefKind::OpaqueTy => {
             return variance_of_opaque(tcx, item_def_id);
         }
diff --git a/compiler/rustc_hir_analysis/src/variance/terms.rs b/compiler/rustc_hir_analysis/src/variance/terms.rs
index ed03c5da26f..1ef3d383bd8 100644
--- a/compiler/rustc_hir_analysis/src/variance/terms.rs
+++ b/compiler/rustc_hir_analysis/src/variance/terms.rs
@@ -12,7 +12,7 @@
 use rustc_arena::DroplessArena;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{LocalDefId, LocalDefIdMap};
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
 use std::fmt;
 
 use self::VarianceTerm::*;
@@ -97,6 +97,12 @@ pub fn determine_parameters_to_be_inferred<'a, 'tcx>(
                 }
             }
             DefKind::Fn | DefKind::AssocFn => terms_cx.add_inferreds_for_item(def_id),
+            DefKind::TyAlias
+                if tcx.features().lazy_type_alias
+                    || tcx.type_of(def_id).instantiate_identity().has_opaque_types() =>
+            {
+                terms_cx.add_inferreds_for_item(def_id)
+            }
             _ => {}
         }
     }
diff --git a/compiler/rustc_hir_typeck/src/mem_categorization.rs b/compiler/rustc_hir_typeck/src/mem_categorization.rs
index 0700e2e0554..e91103f2130 100644
--- a/compiler/rustc_hir_typeck/src/mem_categorization.rs
+++ b/compiler/rustc_hir_typeck/src/mem_categorization.rs
@@ -198,13 +198,14 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
     }
 
     /// Like `pat_ty`, but ignores implicit `&` patterns.
+    #[instrument(level = "debug", skip(self), ret)]
     fn pat_ty_unadjusted(&self, pat: &hir::Pat<'_>) -> McResult<Ty<'tcx>> {
         let base_ty = self.node_ty(pat.hir_id)?;
-        debug!("pat_ty(pat={:?}) base_ty={:?}", pat, base_ty);
+        trace!(?base_ty);
 
         // This code detects whether we are looking at a `ref x`,
         // and if so, figures out what the type *being borrowed* is.
-        let ret_ty = match pat.kind {
+        match pat.kind {
             PatKind::Binding(..) => {
                 let bm = *self
                     .typeck_results
@@ -217,21 +218,18 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
                     // but what we want here is the type of the underlying value being borrowed.
                     // So peel off one-level, turning the &T into T.
                     match base_ty.builtin_deref(false) {
-                        Some(t) => t.ty,
+                        Some(t) => Ok(t.ty),
                         None => {
-                            debug!("By-ref binding of non-derefable type {:?}", base_ty);
-                            return Err(());
+                            debug!("By-ref binding of non-derefable type");
+                            Err(())
                         }
                     }
                 } else {
-                    base_ty
+                    Ok(base_ty)
                 }
             }
-            _ => base_ty,
-        };
-        debug!("pat_ty(pat={:?}) ret_ty={:?}", pat, ret_ty);
-
-        Ok(ret_ty)
+            _ => Ok(base_ty),
+        }
     }
 
     pub(crate) fn cat_expr(&self, expr: &hir::Expr<'_>) -> McResult<PlaceWithHirId<'tcx>> {
@@ -299,13 +297,11 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
         }
     }
 
-    #[instrument(level = "debug", skip(self))]
+    #[instrument(level = "debug", skip(self), ret)]
     pub(crate) fn cat_expr_unadjusted(
         &self,
         expr: &hir::Expr<'_>,
     ) -> McResult<PlaceWithHirId<'tcx>> {
-        debug!("cat_expr: id={} expr={:?}", expr.hir_id, expr);
-
         let expr_ty = self.expr_ty(expr)?;
         match expr.kind {
             hir::ExprKind::Unary(hir::UnOp::Deref, ref e_base) => {
@@ -319,7 +315,7 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
 
             hir::ExprKind::Field(ref base, _) => {
                 let base = self.cat_expr(base)?;
-                debug!("cat_expr(cat_field): id={} expr={:?} base={:?}", expr.hir_id, expr, base);
+                debug!(?base);
 
                 let field_idx = self
                     .typeck_results
@@ -389,7 +385,7 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
         }
     }
 
-    #[instrument(level = "debug", skip(self, span))]
+    #[instrument(level = "debug", skip(self, span), ret)]
     pub(crate) fn cat_res(
         &self,
         hir_id: hir::HirId,
@@ -430,6 +426,7 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
     /// Note: the actual upvar access contains invisible derefs of closure
     /// environment and upvar reference as appropriate. Only regionck cares
     /// about these dereferences, so we let it compute them as needed.
+    #[instrument(level = "debug", skip(self), ret)]
     fn cat_upvar(&self, hir_id: hir::HirId, var_id: hir::HirId) -> McResult<PlaceWithHirId<'tcx>> {
         let closure_expr_def_id = self.body_owner;
 
@@ -439,24 +436,20 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
         };
         let var_ty = self.node_ty(var_id)?;
 
-        let ret = PlaceWithHirId::new(hir_id, var_ty, PlaceBase::Upvar(upvar_id), Vec::new());
-
-        debug!("cat_upvar ret={:?}", ret);
-        Ok(ret)
+        Ok(PlaceWithHirId::new(hir_id, var_ty, PlaceBase::Upvar(upvar_id), Vec::new()))
     }
 
+    #[instrument(level = "debug", skip(self), ret)]
     pub(crate) fn cat_rvalue(
         &self,
         hir_id: hir::HirId,
         span: Span,
         expr_ty: Ty<'tcx>,
     ) -> PlaceWithHirId<'tcx> {
-        debug!("cat_rvalue hir_id={:?}, expr_ty={:?}, span={:?}", hir_id, expr_ty, span);
-        let ret = PlaceWithHirId::new(hir_id, expr_ty, PlaceBase::Rvalue, Vec::new());
-        debug!("cat_rvalue ret={:?}", ret);
-        ret
+        PlaceWithHirId::new(hir_id, expr_ty, PlaceBase::Rvalue, Vec::new())
     }
 
+    #[instrument(level = "debug", skip(self, node), ret)]
     pub(crate) fn cat_projection<N: HirNode>(
         &self,
         node: &N,
@@ -464,16 +457,23 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
         ty: Ty<'tcx>,
         kind: ProjectionKind,
     ) -> PlaceWithHirId<'tcx> {
+        let place_ty = base_place.place.ty();
         let mut projections = base_place.place.projections;
+
+        let node_ty = self.typeck_results.node_type(node.hir_id());
+        // Opaque types can't have field projections, but we can instead convert
+        // the current place in-place (heh) to the hidden type, and then apply all
+        // follow up projections on that.
+        if node_ty != place_ty && place_ty.has_opaque_types() {
+            projections.push(Projection { kind: ProjectionKind::OpaqueCast, ty: node_ty });
+        }
         projections.push(Projection { kind, ty });
-        let ret = PlaceWithHirId::new(
+        PlaceWithHirId::new(
             node.hir_id(),
             base_place.place.base_ty,
             base_place.place.base,
             projections,
-        );
-        debug!("cat_field ret {:?}", ret);
-        ret
+        )
     }
 
     #[instrument(level = "debug", skip(self))]
@@ -497,7 +497,7 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
         self.cat_deref(expr, base)
     }
 
-    #[instrument(level = "debug", skip(self, node))]
+    #[instrument(level = "debug", skip(self, node), ret)]
     fn cat_deref(
         &self,
         node: &impl HirNode,
@@ -514,14 +514,12 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
         let mut projections = base_place.place.projections;
         projections.push(Projection { kind: ProjectionKind::Deref, ty: deref_ty });
 
-        let ret = PlaceWithHirId::new(
+        Ok(PlaceWithHirId::new(
             node.hir_id(),
             base_place.place.base_ty,
             base_place.place.base,
             projections,
-        );
-        debug!("cat_deref ret {:?}", ret);
-        Ok(ret)
+        ))
     }
 
     pub(crate) fn cat_pattern<F>(
@@ -603,6 +601,13 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
         }
     }
 
+    /// Here, `place` is the `PlaceWithHirId` being matched and pat is the pattern it
+    /// is being matched against.
+    ///
+    /// In general, the way that this works is that we walk down the pattern,
+    /// constructing a `PlaceWithHirId` that represents the path that will be taken
+    /// to reach the value being matched.
+    #[instrument(skip(self, op), ret, level = "debug")]
     fn cat_pattern_<F>(
         &self,
         mut place_with_id: PlaceWithHirId<'tcx>,
@@ -612,15 +617,6 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
     where
         F: FnMut(&PlaceWithHirId<'tcx>, &hir::Pat<'_>),
     {
-        // Here, `place` is the `PlaceWithHirId` being matched and pat is the pattern it
-        // is being matched against.
-        //
-        // In general, the way that this works is that we walk down the pattern,
-        // constructing a `PlaceWithHirId` that represents the path that will be taken
-        // to reach the value being matched.
-
-        debug!("cat_pattern(pat={:?}, place_with_id={:?})", pat, place_with_id);
-
         // If (pattern) adjustments are active for this pattern, adjust the `PlaceWithHirId` correspondingly.
         // `PlaceWithHirId`s are constructed differently from patterns. For example, in
         //
@@ -654,11 +650,11 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
         // `deref { deref { place_foo }}` instead of `place_foo` since the pattern is now `Some(x,)`
         // and not `&&Some(x,)`, even though its assigned type is that of `&&Some(x,)`.
         for _ in 0..self.typeck_results.pat_adjustments().get(pat.hir_id).map_or(0, |v| v.len()) {
-            debug!("cat_pattern: applying adjustment to place_with_id={:?}", place_with_id);
+            debug!("applying adjustment to place_with_id={:?}", place_with_id);
             place_with_id = self.cat_deref(pat, place_with_id)?;
         }
         let place_with_id = place_with_id; // lose mutability
-        debug!("cat_pattern: applied adjustment derefs to get place_with_id={:?}", place_with_id);
+        debug!("applied adjustment derefs to get place_with_id={:?}", place_with_id);
 
         // Invoke the callback, but only now, after the `place_with_id` has adjusted.
         //
diff --git a/compiler/rustc_hir_typeck/src/upvar.rs b/compiler/rustc_hir_typeck/src/upvar.rs
index be939560c45..1a41786d251 100644
--- a/compiler/rustc_hir_typeck/src/upvar.rs
+++ b/compiler/rustc_hir_typeck/src/upvar.rs
@@ -264,12 +264,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self.demand_eqtype(span, closure_kind.to_ty(self.tcx), closure_kind_ty);
 
             // If we have an origin, store it.
-            if let Some(origin) = origin {
-                let origin = if enable_precise_capture(span) {
-                    (origin.0, origin.1)
-                } else {
-                    (origin.0, Place { projections: vec![], ..origin.1 })
-                };
+            if let Some(mut origin) = origin {
+                if !enable_precise_capture(span) {
+                    // Without precise captures, we just capture the base and ignore
+                    // the projections.
+                    origin.1.projections.clear()
+                }
 
                 self.typeck_results
                     .borrow_mut()
@@ -294,10 +294,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // Equate the type variables for the upvars with the actual types.
         let final_upvar_tys = self.final_upvar_tys(closure_def_id);
-        debug!(
-            "analyze_closure: id={:?} args={:?} final_upvar_tys={:?}",
-            closure_hir_id, args, final_upvar_tys
-        );
+        debug!(?closure_hir_id, ?args, ?final_upvar_tys);
 
         // Build a tuple (U0..Un) of the final upvar types U0..Un
         // and unify the upvar tuple type in the closure with it:
@@ -338,10 +335,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 let upvar_ty = captured_place.place.ty();
                 let capture = captured_place.info.capture_kind;
 
-                debug!(
-                    "final_upvar_tys: place={:?} upvar_ty={:?} capture={:?}, mutability={:?}",
-                    captured_place.place, upvar_ty, capture, captured_place.mutability,
-                );
+                debug!(?captured_place.place, ?upvar_ty, ?capture, ?captured_place.mutability);
 
                 apply_capture_kind_on_capture_ty(self.tcx, upvar_ty, capture, captured_place.region)
             })
@@ -679,6 +673,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     match (p1.kind, p2.kind) {
                         // Paths are the same, continue to next loop.
                         (ProjectionKind::Deref, ProjectionKind::Deref) => {}
+                        (ProjectionKind::OpaqueCast, ProjectionKind::OpaqueCast) => {}
                         (ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _))
                             if i1 == i2 => {}
 
@@ -701,10 +696,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             l @ (ProjectionKind::Index
                             | ProjectionKind::Subslice
                             | ProjectionKind::Deref
+                            | ProjectionKind::OpaqueCast
                             | ProjectionKind::Field(..)),
                             r @ (ProjectionKind::Index
                             | ProjectionKind::Subslice
                             | ProjectionKind::Deref
+                            | ProjectionKind::OpaqueCast
                             | ProjectionKind::Field(..)),
                         ) => bug!(
                             "ProjectionKinds Index or Subslice were unexpected: ({:?}, {:?})",
@@ -1890,6 +1887,7 @@ fn restrict_capture_precision(
                 return (place, curr_mode);
             }
             ProjectionKind::Deref => {}
+            ProjectionKind::OpaqueCast => {}
             ProjectionKind::Field(..) => {} // ignore
         }
     }
@@ -1946,6 +1944,7 @@ fn construct_place_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String
             ProjectionKind::Deref => String::from("Deref"),
             ProjectionKind::Index => String::from("Index"),
             ProjectionKind::Subslice => String::from("Subslice"),
+            ProjectionKind::OpaqueCast => String::from("OpaqueCast"),
         };
         if i != 0 {
             projections_str.push(',');
diff --git a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
index 54d901f20da..9d7a9fefd08 100644
--- a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
+++ b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
@@ -562,15 +562,9 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
         V: TypeFoldable<TyCtxt<'tcx>>,
     {
         let needs_canonical_flags = if canonicalize_region_mode.any() {
-            TypeFlags::HAS_INFER |
-            TypeFlags::HAS_FREE_REGIONS | // `HAS_RE_PLACEHOLDER` implies `HAS_FREE_REGIONS`
-            TypeFlags::HAS_TY_PLACEHOLDER |
-            TypeFlags::HAS_CT_PLACEHOLDER
+            TypeFlags::HAS_INFER | TypeFlags::HAS_PLACEHOLDER | TypeFlags::HAS_FREE_REGIONS
         } else {
-            TypeFlags::HAS_INFER
-                | TypeFlags::HAS_RE_PLACEHOLDER
-                | TypeFlags::HAS_TY_PLACEHOLDER
-                | TypeFlags::HAS_CT_PLACEHOLDER
+            TypeFlags::HAS_INFER | TypeFlags::HAS_PLACEHOLDER
         };
 
         // Fast path: nothing that needs to be canonicalized.
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index d72053ca985..f12094a271f 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -30,6 +30,7 @@ use rustc_middle::query::Providers;
 use rustc_middle::traits::specialization_graph;
 use rustc_middle::ty::codec::TyEncoder;
 use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
+use rustc_middle::ty::TypeVisitableExt;
 use rustc_middle::ty::{self, AssocItemContainer, SymbolName, Ty, TyCtxt};
 use rustc_middle::util::common::to_readable_str;
 use rustc_serialize::{opaque, Decodable, Decoder, Encodable, Encoder};
@@ -1034,7 +1035,7 @@ fn should_encode_mir(tcx: TyCtxt<'_>, def_id: LocalDefId) -> (bool, bool) {
     }
 }
 
-fn should_encode_variances(def_kind: DefKind) -> bool {
+fn should_encode_variances<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, def_kind: DefKind) -> bool {
     match def_kind {
         DefKind::Struct
         | DefKind::Union
@@ -1053,7 +1054,6 @@ fn should_encode_variances(def_kind: DefKind) -> bool {
         | DefKind::Static(..)
         | DefKind::Const
         | DefKind::ForeignMod
-        | DefKind::TyAlias
         | DefKind::Impl { .. }
         | DefKind::Trait
         | DefKind::TraitAlias
@@ -1067,6 +1067,10 @@ fn should_encode_variances(def_kind: DefKind) -> bool {
         | DefKind::Closure
         | DefKind::Generator
         | DefKind::ExternCrate => false,
+        DefKind::TyAlias => {
+            tcx.features().lazy_type_alias
+                || tcx.type_of(def_id).instantiate_identity().has_opaque_types()
+        }
     }
 }
 
@@ -1349,7 +1353,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 self.encode_default_body_stability(def_id);
                 self.encode_deprecation(def_id);
             }
-            if should_encode_variances(def_kind) {
+            if should_encode_variances(tcx, def_id, def_kind) {
                 let v = self.tcx.variances_of(def_id);
                 record_array!(self.tables.variances_of[def_id] <- v);
             }
diff --git a/compiler/rustc_middle/src/hir/place.rs b/compiler/rustc_middle/src/hir/place.rs
index 8a22de931c3..32f3a177508 100644
--- a/compiler/rustc_middle/src/hir/place.rs
+++ b/compiler/rustc_middle/src/hir/place.rs
@@ -36,6 +36,10 @@ pub enum ProjectionKind {
 
     /// A subslice covering a range of values like `B[x..y]`.
     Subslice,
+
+    /// A conversion from an opaque type to its hidden type so we can
+    /// do further projections on it.
+    OpaqueCast,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable, HashStable)]
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 1189dcdfcbb..a02f9a9f796 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -749,7 +749,7 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    /// Gets a map with the variance of every item; use `item_variance` instead.
+    /// Gets a map with the variance of every item; use `variances_of` instead.
     query crate_variances(_: ()) -> &'tcx ty::CrateVariancesMap<'tcx> {
         arena_cache
         desc { "computing the variances for items in this crate" }
diff --git a/compiler/rustc_middle/src/traits/solve.rs b/compiler/rustc_middle/src/traits/solve.rs
index b21a00e4122..90139f925ed 100644
--- a/compiler/rustc_middle/src/traits/solve.rs
+++ b/compiler/rustc_middle/src/traits/solve.rs
@@ -147,7 +147,7 @@ impl<'tcx> std::ops::Deref for ExternalConstraints<'tcx> {
 }
 
 /// Additional constraints returned on success.
-#[derive(Debug, PartialEq, Eq, Clone, Hash, HashStable, Default)]
+#[derive(Debug, PartialEq, Eq, Clone, Hash, HashStable, Default, TypeVisitable, TypeFoldable)]
 pub struct ExternalConstraintsData<'tcx> {
     // FIXME: implement this.
     pub region_constraints: QueryRegionConstraints<'tcx>,
diff --git a/compiler/rustc_middle/src/ty/closure.rs b/compiler/rustc_middle/src/ty/closure.rs
index 42f22604975..2e5c6a44579 100644
--- a/compiler/rustc_middle/src/ty/closure.rs
+++ b/compiler/rustc_middle/src/ty/closure.rs
@@ -174,6 +174,8 @@ impl<'tcx> CapturedPlace<'tcx> {
                 // Ignore derefs for now, as they are likely caused by
                 // autoderefs that don't appear in the original code.
                 HirProjectionKind::Deref => {}
+                // Just change the type to the hidden type, so we can actually project.
+                HirProjectionKind::OpaqueCast => {}
                 proj => bug!("Unexpected projection {:?} in captured place", proj),
             }
             ty = proj.ty;
diff --git a/compiler/rustc_middle/src/ty/visit.rs b/compiler/rustc_middle/src/ty/visit.rs
index 520bb55e031..156eda477ad 100644
--- a/compiler/rustc_middle/src/ty/visit.rs
+++ b/compiler/rustc_middle/src/ty/visit.rs
@@ -88,14 +88,10 @@ pub trait TypeVisitableExt<'tcx>: TypeVisitable<TyCtxt<'tcx>> {
         self.has_type_flags(TypeFlags::HAS_INFER)
     }
     fn has_placeholders(&self) -> bool {
-        self.has_type_flags(
-            TypeFlags::HAS_RE_PLACEHOLDER
-                | TypeFlags::HAS_TY_PLACEHOLDER
-                | TypeFlags::HAS_CT_PLACEHOLDER,
-        )
+        self.has_type_flags(TypeFlags::HAS_PLACEHOLDER)
     }
     fn has_non_region_placeholders(&self) -> bool {
-        self.has_type_flags(TypeFlags::HAS_TY_PLACEHOLDER | TypeFlags::HAS_CT_PLACEHOLDER)
+        self.has_type_flags(TypeFlags::HAS_PLACEHOLDER - TypeFlags::HAS_RE_PLACEHOLDER)
     }
     fn has_param(&self) -> bool {
         self.has_type_flags(TypeFlags::HAS_PARAM)
diff --git a/compiler/rustc_mir_build/src/build/expr/as_place.rs b/compiler/rustc_mir_build/src/build/expr/as_place.rs
index 7756d5d4879..2e7ef265a93 100644
--- a/compiler/rustc_mir_build/src/build/expr/as_place.rs
+++ b/compiler/rustc_mir_build/src/build/expr/as_place.rs
@@ -236,6 +236,9 @@ fn strip_prefix<'a, 'tcx>(
                 }
                 assert_matches!(iter.next(), Some(ProjectionElem::Field(..)));
             }
+            HirProjectionKind::OpaqueCast => {
+                assert_matches!(iter.next(), Some(ProjectionElem::OpaqueCast(..)));
+            }
             HirProjectionKind::Index | HirProjectionKind::Subslice => {
                 bug!("unexpected projection kind: {:?}", projection);
             }
diff --git a/compiler/rustc_mir_build/src/thir/cx/expr.rs b/compiler/rustc_mir_build/src/thir/cx/expr.rs
index ff4620948fa..b907b69224c 100644
--- a/compiler/rustc_mir_build/src/thir/cx/expr.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/expr.rs
@@ -1072,6 +1072,9 @@ impl<'tcx> Cx<'tcx> {
                     variant_index,
                     name: field,
                 },
+                HirProjectionKind::OpaqueCast => {
+                    ExprKind::Use { source: self.thir.exprs.push(captured_place_expr) }
+                }
                 HirProjectionKind::Index | HirProjectionKind::Subslice => {
                     // We don't capture these projections, so we can ignore them here
                     continue;
diff --git a/compiler/rustc_trait_selection/src/solve/canonicalize.rs b/compiler/rustc_trait_selection/src/solve/canonicalize.rs
index 88771f90756..a9d182abfb7 100644
--- a/compiler/rustc_trait_selection/src/solve/canonicalize.rs
+++ b/compiler/rustc_trait_selection/src/solve/canonicalize.rs
@@ -207,23 +207,18 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
         t
     }
 
-    fn fold_region(&mut self, mut r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        match self.canonicalize_mode {
-            CanonicalizeMode::Input => {
-                // Don't resolve infer vars in input, since it affects
-                // caching and may cause trait selection bugs which rely
-                // on regions to be equal.
-            }
-            CanonicalizeMode::Response { .. } => {
-                if let ty::ReVar(vid) = *r {
-                    r = self
-                        .infcx
-                        .inner
-                        .borrow_mut()
-                        .unwrap_region_constraints()
-                        .opportunistic_resolve_var(self.infcx.tcx, vid);
-                }
-            }
+    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
+        if let ty::ReVar(vid) = *r {
+            let resolved_region = self
+                .infcx
+                .inner
+                .borrow_mut()
+                .unwrap_region_constraints()
+                .opportunistic_resolve_var(self.infcx.tcx, vid);
+            assert_eq!(
+                r, resolved_region,
+                "region var should have been resolved, {r} -> {resolved_region}"
+            );
         }
 
         let kind = match *r {
@@ -278,38 +273,22 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
         ty::Region::new_late_bound(self.interner(), self.binder_index, br)
     }
 
-    fn fold_ty(&mut self, mut t: Ty<'tcx>) -> Ty<'tcx> {
+    fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
         let kind = match *t.kind() {
-            ty::Infer(ty::TyVar(mut vid)) => {
-                // We need to canonicalize the *root* of our ty var.
-                // This is so that our canonical response correctly reflects
-                // any equated inference vars correctly!
-                let root_vid = self.infcx.root_var(vid);
-                if root_vid != vid {
-                    t = Ty::new_var(self.infcx.tcx, root_vid);
-                    vid = root_vid;
-                }
-
-                match self.infcx.probe_ty_var(vid) {
-                    Ok(t) => return self.fold_ty(t),
-                    Err(ui) => CanonicalVarKind::Ty(CanonicalTyVarKind::General(ui)),
-                }
+            ty::Infer(ty::TyVar(vid)) => {
+                assert_eq!(self.infcx.root_var(vid), vid, "ty vid should have been resolved");
+                let Err(ui) = self.infcx.probe_ty_var(vid) else {
+                    bug!("ty var should have been resolved: {t}");
+                };
+                CanonicalVarKind::Ty(CanonicalTyVarKind::General(ui))
             }
             ty::Infer(ty::IntVar(vid)) => {
-                let nt = self.infcx.opportunistic_resolve_int_var(vid);
-                if nt != t {
-                    return self.fold_ty(nt);
-                } else {
-                    CanonicalVarKind::Ty(CanonicalTyVarKind::Int)
-                }
+                assert_eq!(self.infcx.opportunistic_resolve_int_var(vid), t);
+                CanonicalVarKind::Ty(CanonicalTyVarKind::Int)
             }
             ty::Infer(ty::FloatVar(vid)) => {
-                let nt = self.infcx.opportunistic_resolve_float_var(vid);
-                if nt != t {
-                    return self.fold_ty(nt);
-                } else {
-                    CanonicalVarKind::Ty(CanonicalTyVarKind::Float)
-                }
+                assert_eq!(self.infcx.opportunistic_resolve_float_var(vid), t);
+                CanonicalVarKind::Ty(CanonicalTyVarKind::Float)
             }
             ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
                 bug!("fresh var during canonicalization: {t:?}")
@@ -372,22 +351,19 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
         Ty::new_bound(self.infcx.tcx, self.binder_index, bt)
     }
 
-    fn fold_const(&mut self, mut c: ty::Const<'tcx>) -> ty::Const<'tcx> {
+    fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
         let kind = match c.kind() {
-            ty::ConstKind::Infer(ty::InferConst::Var(mut vid)) => {
-                // We need to canonicalize the *root* of our const var.
-                // This is so that our canonical response correctly reflects
-                // any equated inference vars correctly!
-                let root_vid = self.infcx.root_const_var(vid);
-                if root_vid != vid {
-                    c = ty::Const::new_var(self.infcx.tcx, root_vid, c.ty());
-                    vid = root_vid;
-                }
-
-                match self.infcx.probe_const_var(vid) {
-                    Ok(c) => return self.fold_const(c),
-                    Err(universe) => CanonicalVarKind::Const(universe, c.ty()),
-                }
+            ty::ConstKind::Infer(ty::InferConst::Var(vid)) => {
+                assert_eq!(
+                    self.infcx.root_const_var(vid),
+                    vid,
+                    "const var should have been resolved"
+                );
+                let Err(ui) = self.infcx.probe_const_var(vid) else {
+                    bug!("const var should have been resolved");
+                };
+                // FIXME: we should fold this ty eventually
+                CanonicalVarKind::Const(ui, c.ty())
             }
             ty::ConstKind::Infer(ty::InferConst::Fresh(_)) => {
                 bug!("fresh var during canonicalization: {c:?}")
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
index 7323b98b8ce..0a54b1c6433 100644
--- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
+++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
@@ -16,11 +16,15 @@ use rustc_index::IndexVec;
 use rustc_infer::infer::canonical::query_response::make_query_region_constraints;
 use rustc_infer::infer::canonical::CanonicalVarValues;
 use rustc_infer::infer::canonical::{CanonicalExt, QueryRegionConstraints};
+use rustc_infer::infer::InferCtxt;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{
-    ExternalConstraints, ExternalConstraintsData, MaybeCause, PredefinedOpaquesData, QueryInput,
+    ExternalConstraintsData, MaybeCause, PredefinedOpaquesData, QueryInput,
+};
+use rustc_middle::ty::{
+    self, BoundVar, GenericArgKind, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
+    TypeVisitableExt,
 };
-use rustc_middle::ty::{self, BoundVar, GenericArgKind, Ty, TyCtxt, TypeFoldable};
 use rustc_span::DUMMY_SP;
 use std::iter;
 use std::ops::Deref;
@@ -32,6 +36,10 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         &self,
         goal: Goal<'tcx, T>,
     ) -> (Vec<ty::GenericArg<'tcx>>, CanonicalInput<'tcx, T>) {
+        let opaque_types = self.infcx.clone_opaque_types_for_query_response();
+        let (goal, opaque_types) =
+            (goal, opaque_types).fold_with(&mut EagerResolver { infcx: self.infcx });
+
         let mut orig_values = Default::default();
         let canonical_goal = Canonicalizer::canonicalize(
             self.infcx,
@@ -40,11 +48,9 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             QueryInput {
                 goal,
                 anchor: self.infcx.defining_use_anchor,
-                predefined_opaques_in_body: self.tcx().mk_predefined_opaques_in_body(
-                    PredefinedOpaquesData {
-                        opaque_types: self.infcx.clone_opaque_types_for_query_response(),
-                    },
-                ),
+                predefined_opaques_in_body: self
+                    .tcx()
+                    .mk_predefined_opaques_in_body(PredefinedOpaquesData { opaque_types }),
             },
         );
         (orig_values, canonical_goal)
@@ -70,34 +76,43 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         );
 
         let certainty = certainty.unify_with(goals_certainty);
+        if let Certainty::OVERFLOW = certainty {
+            // If we have overflow, it's probable that we're substituting a type
+            // into itself infinitely and any partial substitutions in the query
+            // response are probably not useful anyways, so just return an empty
+            // query response.
+            //
+            // This may prevent us from potentially useful inference, e.g.
+            // 2 candidates, one ambiguous and one overflow, which both
+            // have the same inference constraints.
+            //
+            // Changing this to retain some constraints in the future
+            // won't be a breaking change, so this is good enough for now.
+            return Ok(self.make_ambiguous_response_no_constraints(MaybeCause::Overflow));
+        }
 
-        let response = match certainty {
-            Certainty::Yes | Certainty::Maybe(MaybeCause::Ambiguity) => {
-                let external_constraints = self.compute_external_query_constraints()?;
-                Response { var_values: self.var_values, external_constraints, certainty }
-            }
-            Certainty::Maybe(MaybeCause::Overflow) => {
-                // If we have overflow, it's probable that we're substituting a type
-                // into itself infinitely and any partial substitutions in the query
-                // response are probably not useful anyways, so just return an empty
-                // query response.
-                //
-                // This may prevent us from potentially useful inference, e.g.
-                // 2 candidates, one ambiguous and one overflow, which both
-                // have the same inference constraints.
-                //
-                // Changing this to retain some constraints in the future
-                // won't be a breaking change, so this is good enough for now.
-                return Ok(self.make_ambiguous_response_no_constraints(MaybeCause::Overflow));
-            }
-        };
+        let var_values = self.var_values;
+        let external_constraints = self.compute_external_query_constraints()?;
+
+        let (var_values, mut external_constraints) =
+            (var_values, external_constraints).fold_with(&mut EagerResolver { infcx: self.infcx });
+        // Remove any trivial region constraints once we've resolved regions
+        external_constraints
+            .region_constraints
+            .outlives
+            .retain(|(outlives, _)| outlives.0.as_region().map_or(true, |re| re != outlives.1));
 
         let canonical = Canonicalizer::canonicalize(
             self.infcx,
             CanonicalizeMode::Response { max_input_universe: self.max_input_universe },
             &mut Default::default(),
-            response,
+            Response {
+                var_values,
+                certainty,
+                external_constraints: self.tcx().mk_external_constraints(external_constraints),
+            },
         );
+
         Ok(canonical)
     }
 
@@ -143,7 +158,9 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     /// further constrained by inference, that will be passed back in the var
     /// values.
     #[instrument(level = "debug", skip(self), ret)]
-    fn compute_external_query_constraints(&self) -> Result<ExternalConstraints<'tcx>, NoSolution> {
+    fn compute_external_query_constraints(
+        &self,
+    ) -> Result<ExternalConstraintsData<'tcx>, NoSolution> {
         // We only check for leaks from universes which were entered inside
         // of the query.
         self.infcx.leak_check(self.max_input_universe, None).map_err(|e| {
@@ -173,9 +190,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             self.predefined_opaques_in_body.opaque_types.iter().all(|(pa, _)| pa != a)
         });
 
-        Ok(self
-            .tcx()
-            .mk_external_constraints(ExternalConstraintsData { region_constraints, opaque_types }))
+        Ok(ExternalConstraintsData { region_constraints, opaque_types })
     }
 
     /// After calling a canonical query, we apply the constraints returned
@@ -333,3 +348,65 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         Ok(())
     }
 }
+
+/// Resolves ty, region, and const vars to their inferred values or their root vars.
+struct EagerResolver<'a, 'tcx> {
+    infcx: &'a InferCtxt<'tcx>,
+}
+
+impl<'tcx> TypeFolder<TyCtxt<'tcx>> for EagerResolver<'_, 'tcx> {
+    fn interner(&self) -> TyCtxt<'tcx> {
+        self.infcx.tcx
+    }
+
+    fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
+        match *t.kind() {
+            ty::Infer(ty::TyVar(vid)) => match self.infcx.probe_ty_var(vid) {
+                Ok(t) => t.fold_with(self),
+                Err(_) => Ty::new_var(self.infcx.tcx, self.infcx.root_var(vid)),
+            },
+            ty::Infer(ty::IntVar(vid)) => self.infcx.opportunistic_resolve_int_var(vid),
+            ty::Infer(ty::FloatVar(vid)) => self.infcx.opportunistic_resolve_float_var(vid),
+            _ => {
+                if t.has_infer() {
+                    t.super_fold_with(self)
+                } else {
+                    t
+                }
+            }
+        }
+    }
+
+    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
+        match *r {
+            ty::ReVar(vid) => self
+                .infcx
+                .inner
+                .borrow_mut()
+                .unwrap_region_constraints()
+                .opportunistic_resolve_var(self.infcx.tcx, vid),
+            _ => r,
+        }
+    }
+
+    fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
+        match c.kind() {
+            ty::ConstKind::Infer(ty::InferConst::Var(vid)) => {
+                // FIXME: we need to fold the ty too, I think.
+                match self.infcx.probe_const_var(vid) {
+                    Ok(c) => c.fold_with(self),
+                    Err(_) => {
+                        ty::Const::new_var(self.infcx.tcx, self.infcx.root_const_var(vid), c.ty())
+                    }
+                }
+            }
+            _ => {
+                if c.has_infer() {
+                    c.super_fold_with(self)
+                } else {
+                    c
+                }
+            }
+        }
+    }
+}
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index 1a6a253f360..b0f8ea7a05d 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -216,6 +216,11 @@ bitflags! {
         /// Does this have `ConstKind::Placeholder`?
         const HAS_CT_PLACEHOLDER          = 1 << 8;
 
+        /// Does this have placeholders?
+        const HAS_PLACEHOLDER           = TypeFlags::HAS_TY_PLACEHOLDER.bits
+                                          | TypeFlags::HAS_RE_PLACEHOLDER.bits
+                                          | TypeFlags::HAS_CT_PLACEHOLDER.bits;
+
         /// `true` if there are "names" of regions and so forth
         /// that are local to a particular fn/inferctxt
         const HAS_FREE_LOCAL_REGIONS      = 1 << 9;