Auto merge of #113086 - lcnr:rust8, r=compiler-errors

implement deep normalization via the new solver

together with #112869 this should remove all uses of the old solver with `-Ztrait-solver=next`.

see https://hackmd.io/V0qsUB_fTxexfQO_pcOcrg for a description of this PR. Will move that doc to the `rustc-dev-guide` after merging this.

r? `@compiler-errors`

Author: bors

Cargo.lock

@@ -4136,6 +4136,7 @@ dependencies = [
 name = "rustc_ty_utils"
 version = "0.0.0"
 dependencies = [
+ "itertools",
  "rustc_data_structures",
  "rustc_errors",
  "rustc_fluent_macro",

compiler/rustc_hir_analysis/src/check/check.rs

@@ -224,7 +224,8 @@ fn check_opaque(tcx: TyCtxt<'_>, id: hir::ItemId) {
     if check_opaque_for_cycles(tcx, item.owner_id.def_id, substs, span, &origin).is_err() {
         return;
     }
-    check_opaque_meets_bounds(tcx, item.owner_id.def_id, span, &origin);
+
+    let _ = check_opaque_meets_bounds(tcx, item.owner_id.def_id, span, &origin);
 }
 
 /// Checks that an opaque type does not use `Self` or `T::Foo` projections that would result
@@ -395,7 +396,7 @@ fn check_opaque_meets_bounds<'tcx>(
     def_id: LocalDefId,
     span: Span,
     origin: &hir::OpaqueTyOrigin,
-) {
+) -> Result<(), ErrorGuaranteed> {
     let defining_use_anchor = match *origin {
         hir::OpaqueTyOrigin::FnReturn(did) | hir::OpaqueTyOrigin::AsyncFn(did) => did,
         hir::OpaqueTyOrigin::TyAlias { .. } => tcx.impl_trait_parent(def_id),
@@ -429,10 +430,10 @@ fn check_opaque_meets_bounds<'tcx>(
         Ok(()) => {}
         Err(ty_err) => {
             let ty_err = ty_err.to_string(tcx);
-            tcx.sess.delay_span_bug(
+            return Err(tcx.sess.delay_span_bug(
                 span,
                 format!("could not unify `{hidden_ty}` with revealed type:\n{ty_err}"),
-            );
+            ));
         }
     }
 
@@ -447,7 +448,8 @@ fn check_opaque_meets_bounds<'tcx>(
     // version.
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        infcx.err_ctxt().report_fulfillment_errors(&errors);
+        let guar = infcx.err_ctxt().report_fulfillment_errors(&errors);
+        return Err(guar);
     }
     match origin {
         // Checked when type checking the function containing them.
@@ -461,14 +463,15 @@ fn check_opaque_meets_bounds<'tcx>(
             if tcx.def_kind(tcx.parent(def_id.to_def_id())) == DefKind::OpaqueTy => {}
         // Can have different predicates to their defining use
         hir::OpaqueTyOrigin::TyAlias { .. } => {
-            let wf_tys = ocx.assumed_wf_types(param_env, span, def_id);
+            let wf_tys = ocx.assumed_wf_types_and_report_errors(param_env, def_id)?;
             let implied_bounds = infcx.implied_bounds_tys(param_env, def_id, wf_tys);
             let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
-            let _ = ocx.resolve_regions_and_report_errors(defining_use_anchor, &outlives_env);
+            ocx.resolve_regions_and_report_errors(defining_use_anchor, &outlives_env)?;
         }
     }
     // Clean up after ourselves
     let _ = infcx.take_opaque_types();
+    Ok(())
 }
 
 fn is_enum_of_nonnullable_ptr<'tcx>(

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -2121,7 +2121,7 @@ pub(super) fn check_type_bounds<'tcx>(
             _ => bug!(),
         }
     };
-    let assumed_wf_types = ocx.assumed_wf_types(param_env, impl_ty_span, impl_ty_def_id);
+    let assumed_wf_types = ocx.assumed_wf_types_and_report_errors(param_env, impl_ty_def_id)?;
 
     let normalize_cause = ObligationCause::new(
         impl_ty_span,

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -105,7 +105,12 @@ pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
     }
     f(&mut wfcx);
 
-    let assumed_wf_types = wfcx.ocx.assumed_wf_types(param_env, span, body_def_id);
+    let assumed_wf_types = match wfcx.ocx.assumed_wf_types_and_report_errors(param_env, body_def_id)
+    {
+        Ok(wf_types) => wf_types,
+        Err(_guar) => return,
+    };
+
     let implied_bounds = infcx.implied_bounds_tys(param_env, body_def_id, assumed_wf_types);
 
     let errors = wfcx.select_all_or_error();

compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs

@@ -77,7 +77,7 @@ use rustc_infer::traits::specialization_graph::Node;
 use rustc_middle::ty::subst::{GenericArg, InternalSubsts, SubstsRef};
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
-use rustc_span::Span;
+use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
 use rustc_trait_selection::traits::{self, translate_substs_with_cause, wf, ObligationCtxt};
@@ -113,7 +113,7 @@ fn check_always_applicable(tcx: TyCtxt<'_>, impl1_def_id: LocalDefId, impl2_node
     let span = tcx.def_span(impl1_def_id);
     check_has_items(tcx, impl1_def_id, impl2_node, span);
 
-    if let Some((impl1_substs, impl2_substs)) = get_impl_substs(tcx, impl1_def_id, impl2_node) {
+    if let Ok((impl1_substs, impl2_substs)) = get_impl_substs(tcx, impl1_def_id, impl2_node) {
         let impl2_def_id = impl2_node.def_id();
         debug!(?impl2_def_id, ?impl2_substs);
 
@@ -171,16 +171,14 @@ fn get_impl_substs(
     tcx: TyCtxt<'_>,
     impl1_def_id: LocalDefId,
     impl2_node: Node,
-) -> Option<(SubstsRef<'_>, SubstsRef<'_>)> {
+) -> Result<(SubstsRef<'_>, SubstsRef<'_>), ErrorGuaranteed> {
     let infcx = &tcx.infer_ctxt().build();
     let ocx = ObligationCtxt::new(infcx);
     let param_env = tcx.param_env(impl1_def_id);
-
-    let assumed_wf_types =
-        ocx.assumed_wf_types(param_env, tcx.def_span(impl1_def_id), impl1_def_id);
+    let impl1_span = tcx.def_span(impl1_def_id);
+    let assumed_wf_types = ocx.assumed_wf_types_and_report_errors(param_env, impl1_def_id)?;
 
     let impl1_substs = InternalSubsts::identity_for_item(tcx, impl1_def_id);
-    let impl1_span = tcx.def_span(impl1_def_id);
     let impl2_substs = translate_substs_with_cause(
         infcx,
         param_env,
@@ -198,19 +196,19 @@ fn get_impl_substs(
 
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        ocx.infcx.err_ctxt().report_fulfillment_errors(&errors);
-        return None;
+        let guar = ocx.infcx.err_ctxt().report_fulfillment_errors(&errors);
+        return Err(guar);
     }
 
     let implied_bounds = infcx.implied_bounds_tys(param_env, impl1_def_id, assumed_wf_types);
     let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
     let _ = ocx.resolve_regions_and_report_errors(impl1_def_id, &outlives_env);
     let Ok(impl2_substs) = infcx.fully_resolve(impl2_substs) else {
         let span = tcx.def_span(impl1_def_id);
-        tcx.sess.emit_err(SubstsOnOverriddenImpl { span });
-        return None;
+        let guar = tcx.sess.emit_err(SubstsOnOverriddenImpl { span });
+        return Err(guar);
     };
-    Some((impl1_substs, impl2_substs))
+    Ok((impl1_substs, impl2_substs))
 }
 
 /// Returns a list of all of the unconstrained subst of the given impl.

compiler/rustc_hir_typeck/src/callee.rs

@@ -89,7 +89,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             _ => self.check_expr(callee_expr),
         };
 
-        let expr_ty = self.structurally_resolved_type(call_expr.span, original_callee_ty);
+        let expr_ty = self.structurally_resolve_type(call_expr.span, original_callee_ty);
 
         let mut autoderef = self.autoderef(callee_expr.span, expr_ty);
         let mut result = None;
@@ -138,7 +138,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         autoderef: &Autoderef<'a, 'tcx>,
     ) -> Option<CallStep<'tcx>> {
         let adjusted_ty =
-            self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
+            self.structurally_resolve_type(autoderef.span(), autoderef.final_ty(false));
 
         // If the callee is a bare function or a closure, then we're all set.
         match *adjusted_ty.kind() {

compiler/rustc_hir_typeck/src/cast.rs

@@ -717,8 +717,8 @@ impl<'a, 'tcx> CastCheck<'tcx> {
 
     #[instrument(skip(fcx), level = "debug")]
     pub fn check(mut self, fcx: &FnCtxt<'a, 'tcx>) {
-        self.expr_ty = fcx.structurally_resolved_type(self.expr_span, self.expr_ty);
-        self.cast_ty = fcx.structurally_resolved_type(self.cast_span, self.cast_ty);
+        self.expr_ty = fcx.structurally_resolve_type(self.expr_span, self.expr_ty);
+        self.cast_ty = fcx.structurally_resolve_type(self.cast_span, self.cast_ty);
 
         debug!("check_cast({}, {:?} as {:?})", self.expr.hir_id, self.expr_ty, self.cast_ty);
 

compiler/rustc_hir_typeck/src/coercion.rs

@@ -1005,7 +1005,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         allow_two_phase: AllowTwoPhase,
         cause: Option<ObligationCause<'tcx>>,
     ) -> RelateResult<'tcx, Ty<'tcx>> {
-        let source = self.resolve_vars_with_obligations(expr_ty);
+        let source = self.try_structurally_resolve_type(expr.span, expr_ty);
         debug!("coercion::try({:?}: {:?} -> {:?})", expr, source, target);
 
         let cause =

compiler/rustc_hir_typeck/src/expr.rs

@@ -380,7 +380,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let mut oprnd_t = self.check_expr_with_expectation(&oprnd, expected_inner);
 
         if !oprnd_t.references_error() {
-            oprnd_t = self.structurally_resolved_type(expr.span, oprnd_t);
+            oprnd_t = self.structurally_resolve_type(expr.span, oprnd_t);
             match unop {
                 hir::UnOp::Deref => {
                     if let Some(ty) = self.lookup_derefing(expr, oprnd, oprnd_t) {
@@ -1266,13 +1266,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> Ty<'tcx> {
         let rcvr_t = self.check_expr(&rcvr);
         // no need to check for bot/err -- callee does that
-        let rcvr_t = self.structurally_resolved_type(rcvr.span, rcvr_t);
+        let rcvr_t = self.structurally_resolve_type(rcvr.span, rcvr_t);
         let span = segment.ident.span;
 
         let method = match self.lookup_method(rcvr_t, segment, span, expr, rcvr, args) {
             Ok(method) => {
                 // We could add a "consider `foo::<params>`" suggestion here, but I wasn't able to
-                // trigger this codepath causing `structurally_resolved_type` to emit an error.
+                // trigger this codepath causing `structurally_resolve_type` to emit an error.
 
                 self.write_method_call(expr.hir_id, method);
                 Ok(method)
@@ -2252,7 +2252,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> Ty<'tcx> {
         debug!("check_field(expr: {:?}, base: {:?}, field: {:?})", expr, base, field);
         let base_ty = self.check_expr(base);
-        let base_ty = self.structurally_resolved_type(base.span, base_ty);
+        let base_ty = self.structurally_resolve_type(base.span, base_ty);
         let mut private_candidate = None;
         let mut autoderef = self.autoderef(expr.span, base_ty);
         while let Some((deref_base_ty, _)) = autoderef.next() {
@@ -2300,7 +2300,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 _ => {}
             }
         }
-        self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
+        self.structurally_resolve_type(autoderef.span(), autoderef.final_ty(false));
 
         if let Some((adjustments, did)) = private_candidate {
             // (#90483) apply adjustments to avoid ExprUseVisitor from
@@ -2857,7 +2857,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         } else if idx_t.references_error() {
             idx_t
         } else {
-            let base_t = self.structurally_resolved_type(base.span, base_t);
+            let base_t = self.structurally_resolve_type(base.span, base_t);
             match self.lookup_indexing(expr, base, base_t, idx, idx_t) {
                 Some((index_ty, element_ty)) => {
                     // two-phase not needed because index_ty is never mutable
@@ -3084,7 +3084,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // allows them to be inferred based on how they are used later in the
         // function.
         if is_input {
-            let ty = self.structurally_resolved_type(expr.span, ty);
+            let ty = self.structurally_resolve_type(expr.span, ty);
             match *ty.kind() {
                 ty::FnDef(..) => {
                     let fnptr_ty = self.tcx.mk_fn_ptr(ty.fn_sig(self.tcx));
@@ -3142,7 +3142,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let mut current_container = container;
 
         for &field in fields {
-            let container = self.structurally_resolved_type(expr.span, current_container);
+            let container = self.structurally_resolve_type(expr.span, current_container);
 
             match container.kind() {
                 ty::Adt(container_def, substs) if !container_def.is_enum() => {

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -83,6 +83,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// version (resolve_vars_if_possible), this version will
     /// also select obligations if it seems useful, in an effort
     /// to get more type information.
+    // FIXME(-Ztrait-solver=next): A lot of the calls to this method should
+    // probably be `try_structurally_resolve_type` or `structurally_resolve_type` instead.
     pub(in super::super) fn resolve_vars_with_obligations(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
         self.resolve_vars_with_obligations_and_mutate_fulfillment(ty, |_| {})
     }
@@ -1465,16 +1467,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
-    /// Resolves `typ` by a single level if `typ` is a type variable.
+    /// Try to resolve `ty` to a structural type, normalizing aliases.
     ///
-    /// When the new solver is enabled, this will also attempt to normalize
-    /// the type if it's a projection (note that it will not deeply normalize
-    /// projections within the type, just the outermost layer of the type).
-    ///
-    /// If no resolution is possible, then an error is reported.
-    /// Numeric inference variables may be left unresolved.
-    pub fn structurally_resolved_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
-        let mut ty = self.resolve_vars_with_obligations(ty);
+    /// In case there is still ambiguity, the returned type may be an inference
+    /// variable. This is different from `structurally_resolve_type` which errors
+    /// in this case.
+    pub fn try_structurally_resolve_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
+        let ty = self.resolve_vars_with_obligations(ty);
 
         if self.next_trait_solver()
             && let ty::Alias(ty::Projection, _) = ty.kind()
@@ -1483,15 +1482,27 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .at(&self.misc(sp), self.param_env)
                 .structurally_normalize(ty, &mut **self.fulfillment_cx.borrow_mut())
             {
-                Ok(normalized_ty) => {
-                    ty = normalized_ty;
-                },
+                Ok(normalized_ty) => normalized_ty,
                 Err(errors) => {
                     let guar = self.err_ctxt().report_fulfillment_errors(&errors);
                     return self.tcx.ty_error(guar);
                 }
             }
-        }
+        } else {
+            ty
+       }
+    }
+
+    /// Resolves `ty` by a single level if `ty` is a type variable.
+    ///
+    /// When the new solver is enabled, this will also attempt to normalize
+    /// the type if it's a projection (note that it will not deeply normalize
+    /// projections within the type, just the outermost layer of the type).
+    ///
+    /// If no resolution is possible, then an error is reported.
+    /// Numeric inference variables may be left unresolved.
+    pub fn structurally_resolve_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
+        let ty = self.try_structurally_resolve_type(sp, ty);
 
         if !ty.is_ty_var() {
             ty