implied_bounds: clarify our assumptions

Author: lcnr

compiler/rustc_middle/src/query/mod.rs

@@ -765,6 +765,14 @@ rustc_queries! {
         desc { |tcx| "processing `{}`", tcx.def_path_str(key.to_def_id()) }
     }
 
+    /// Returns the types assumed to be well formed while "inside" of the given item.
+    ///
+    /// Note that we've liberated the late bound regions of function signatures, so
+    /// this can not be used to check whether these types are well formed.
+    query assumed_wf_types(key: DefId) -> &'tcx ty::List<Ty<'tcx>> {
+        desc { |tcx| "computing the implied bounds of {}", tcx.def_path_str(key) }
+    }
+
     /// Computes the signature of the function.
     query fn_sig(key: DefId) -> ty::PolyFnSig<'tcx> {
         desc { |tcx| "computing function signature of `{}`", tcx.def_path_str(key) }

compiler/rustc_ty_utils/src/implied_bounds.rs

@@ -0,0 +1,60 @@
+use crate::rustc_middle::ty::DefIdTree;
+use rustc_hir::{def::DefKind, def_id::DefId};
+use rustc_middle::ty::{self, Ty, TyCtxt};
+
+pub fn provide(providers: &mut ty::query::Providers) {
+    *providers = ty::query::Providers { assumed_wf_types, ..*providers };
+}
+
+fn assumed_wf_types<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> &'tcx ty::List<Ty<'tcx>> {
+    match tcx.def_kind(def_id) {
+        DefKind::Fn => {
+            let sig = tcx.fn_sig(def_id);
+            let liberated_sig = tcx.liberate_late_bound_regions(def_id, sig);
+            liberated_sig.inputs_and_output
+        }
+        DefKind::AssocFn => {
+            let sig = tcx.fn_sig(def_id);
+            let liberated_sig = tcx.liberate_late_bound_regions(def_id, sig);
+            let mut assumed_wf_types: Vec<_> =
+                tcx.assumed_wf_types(tcx.parent(def_id)).as_slice().into();
+            assumed_wf_types.extend(liberated_sig.inputs_and_output);
+            tcx.intern_type_list(&assumed_wf_types)
+        }
+        DefKind::Impl => match tcx.impl_trait_ref(def_id) {
+            Some(trait_ref) => {
+                let types: Vec<_> = trait_ref.substs.types().collect();
+                tcx.intern_type_list(&types)
+            }
+            // Only the impl self type
+            None => tcx.intern_type_list(&[tcx.type_of(def_id)]),
+        },
+        DefKind::AssocConst | DefKind::AssocTy => tcx.assumed_wf_types(tcx.parent(def_id)),
+        DefKind::Mod
+        | DefKind::Struct
+        | DefKind::Union
+        | DefKind::Enum
+        | DefKind::Variant
+        | DefKind::Trait
+        | DefKind::TyAlias
+        | DefKind::ForeignTy
+        | DefKind::TraitAlias
+        | DefKind::TyParam
+        | DefKind::Const
+        | DefKind::ConstParam
+        | DefKind::Static(_)
+        | DefKind::Ctor(_, _)
+        | DefKind::Macro(_)
+        | DefKind::ExternCrate
+        | DefKind::Use
+        | DefKind::ForeignMod
+        | DefKind::AnonConst
+        | DefKind::InlineConst
+        | DefKind::OpaqueTy
+        | DefKind::Field
+        | DefKind::LifetimeParam
+        | DefKind::GlobalAsm
+        | DefKind::Closure
+        | DefKind::Generator => ty::List::empty(),
+    }
+}

compiler/rustc_ty_utils/src/lib.rs

@@ -21,6 +21,7 @@ use rustc_middle::ty::query::Providers;
 mod assoc;
 mod common_traits;
 mod consts;
+mod implied_bounds;
 pub mod instance;
 mod needs_drop;
 pub mod representability;
@@ -30,6 +31,7 @@ pub fn provide(providers: &mut Providers) {
     assoc::provide(providers);
     common_traits::provide(providers);
     consts::provide(providers);
+    implied_bounds::provide(providers);
     needs_drop::provide(providers);
     ty::provide(providers);
     instance::provide(providers);

compiler/rustc_typeck/src/check/compare_method.rs

@@ -1,6 +1,5 @@
 use super::potentially_plural_count;
 use crate::check::regionck::OutlivesEnvironmentExt;
-use crate::check::wfcheck;
 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed};
@@ -1445,14 +1444,24 @@ pub fn check_type_bounds<'tcx>(
     };
     debug!(?normalize_param_env);
 
+    let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
     let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
     let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs);
 
     tcx.infer_ctxt().enter(move |infcx| {
         let ocx = ObligationCtxt::new(&infcx);
 
+        let assumed_wf_types = tcx.assumed_wf_types(impl_ty.def_id);
+        let mut implied_bounds = FxHashSet::default();
+        let cause = ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
+        for ty in assumed_wf_types {
+            implied_bounds.insert(ty);
+            let normalized = ocx.normalize(cause.clone(), param_env, ty);
+            implied_bounds.insert(normalized);
+        }
+        let implied_bounds = implied_bounds;
+
         let mut selcx = traits::SelectionContext::new(&infcx);
-        let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
         let normalize_cause = ObligationCause::new(
             impl_ty_span,
             impl_ty_hir_id,
@@ -1508,15 +1517,6 @@ pub fn check_type_bounds<'tcx>(
 
         // Finally, resolve all regions. This catches wily misuses of
         // lifetime parameters.
-        let implied_bounds = match impl_ty.container {
-            ty::TraitContainer => FxHashSet::default(),
-            ty::ImplContainer => wfcheck::impl_implied_bounds(
-                tcx,
-                param_env,
-                container_id.expect_local(),
-                impl_ty_span,
-            ),
-        };
         let mut outlives_environment = OutlivesEnvironment::new(param_env);
         outlives_environment.add_implied_bounds(&infcx, implied_bounds, impl_ty_hir_id);
         infcx.check_region_obligations_and_report_errors(

compiler/rustc_typeck/src/check/wfcheck.rs

@@ -10,7 +10,6 @@ use rustc_hir::ItemKind;
 use rustc_infer::infer::outlives::env::{OutlivesEnvironment, RegionBoundPairs};
 use rustc_infer::infer::outlives::obligations::TypeOutlives;
 use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
-use rustc_infer::traits::Normalized;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts, Subst};
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
@@ -24,8 +23,6 @@ use rustc_span::{Span, DUMMY_SP};
 use rustc_trait_selection::autoderef::Autoderef;
 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
-use rustc_trait_selection::traits::query::normalize::AtExt;
-use rustc_trait_selection::traits::query::NoSolution;
 use rustc_trait_selection::traits::{
     self, ObligationCause, ObligationCauseCode, ObligationCtxt, WellFormedLoc,
 };
@@ -86,26 +83,37 @@ pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
     body_def_id: LocalDefId,
     f: F,
 ) where
-    F: for<'a> FnOnce(&WfCheckingCtxt<'a, 'tcx>) -> FxHashSet<Ty<'tcx>>,
+    F: for<'a> FnOnce(&WfCheckingCtxt<'a, 'tcx>),
 {
     let param_env = tcx.param_env(body_def_id);
     let body_id = tcx.hir().local_def_id_to_hir_id(body_def_id);
     tcx.infer_ctxt().enter(|ref infcx| {
         let ocx = ObligationCtxt::new(infcx);
+
+        let assumed_wf_types = tcx.assumed_wf_types(body_def_id);
+        let mut implied_bounds = FxHashSet::default();
+        let cause = ObligationCause::misc(span, body_id);
+        for ty in assumed_wf_types {
+            implied_bounds.insert(ty);
+            let normalized = ocx.normalize(cause.clone(), param_env, ty);
+            implied_bounds.insert(normalized);
+        }
+        let implied_bounds = implied_bounds;
+
         let mut wfcx = WfCheckingCtxt { ocx, span, body_id, param_env };
 
         if !tcx.features().trivial_bounds {
             wfcx.check_false_global_bounds()
         }
-        let wf_tys = f(&mut wfcx);
+        f(&mut wfcx);
         let errors = wfcx.select_all_or_error();
         if !errors.is_empty() {
             infcx.report_fulfillment_errors(&errors, None, false);
             return;
         }
 
         let mut outlives_environment = OutlivesEnvironment::new(param_env);
-        outlives_environment.add_implied_bounds(infcx, wf_tys, body_id);
+        outlives_environment.add_implied_bounds(infcx, implied_bounds, body_id);
         infcx.check_region_obligations_and_report_errors(body_def_id, &outlives_environment);
     })
 }
@@ -976,15 +984,9 @@ fn check_associated_item(
     enter_wf_checking_ctxt(tcx, span, item_id, |wfcx| {
         let item = tcx.associated_item(item_id);
 
-        let (mut implied_bounds, self_ty) = match item.container {
-            ty::TraitContainer => (FxHashSet::default(), tcx.types.self_param),
-            ty::ImplContainer => {
-                let def_id = item.container_id(tcx);
-                (
-                    impl_implied_bounds(tcx, wfcx.param_env, def_id.expect_local(), span),
-                    tcx.type_of(def_id),
-                )
-            }
+        let self_ty = match item.container {
+            ty::TraitContainer => tcx.types.self_param,
+            ty::ImplContainer => tcx.type_of(item.container_id(tcx)),
         };
 
         match item.kind {
@@ -1002,7 +1004,6 @@ fn check_associated_item(
                     sig,
                     hir_sig.decl,
                     item.def_id.expect_local(),
-                    &mut implied_bounds,
                 );
                 check_method_receiver(wfcx, hir_sig, item, self_ty);
             }
@@ -1017,8 +1018,6 @@ fn check_associated_item(
                 }
             }
         }
-
-        implied_bounds
     })
 }
 
@@ -1118,9 +1117,6 @@ fn check_type_defn<'tcx, F>(
         }
 
         check_where_clauses(wfcx, item.span, item.def_id);
-
-        // No implied bounds in a struct definition.
-        FxHashSet::default()
     });
 }
 
@@ -1144,9 +1140,7 @@ fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
     }
 
     enter_wf_checking_ctxt(tcx, item.span, item.def_id, |wfcx| {
-        check_where_clauses(wfcx, item.span, item.def_id);
-
-        FxHashSet::default()
+        check_where_clauses(wfcx, item.span, item.def_id)
     });
 
     // Only check traits, don't check trait aliases
@@ -1186,9 +1180,7 @@ fn check_item_fn(
 ) {
     enter_wf_checking_ctxt(tcx, span, def_id, |wfcx| {
         let sig = tcx.fn_sig(def_id);
-        let mut implied_bounds = FxHashSet::default();
-        check_fn_or_method(wfcx, ident.span, sig, decl, def_id, &mut implied_bounds);
-        implied_bounds
+        check_fn_or_method(wfcx, ident.span, sig, decl, def_id);
     })
 }
 
@@ -1231,9 +1223,6 @@ fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_fo
                 tcx.require_lang_item(LangItem::Sync, Some(ty_span)),
             );
         }
-
-        // No implied bounds in a const, etc.
-        FxHashSet::default()
     });
 }
 
@@ -1284,8 +1273,6 @@ fn check_impl<'tcx>(
         }
 
         check_where_clauses(wfcx, item.span, item.def_id);
-
-        impl_implied_bounds(tcx, wfcx.param_env, item.def_id, item.span)
     });
 }
 
@@ -1479,7 +1466,6 @@ fn check_fn_or_method<'tcx>(
     sig: ty::PolyFnSig<'tcx>,
     hir_decl: &hir::FnDecl<'_>,
     def_id: LocalDefId,
-    implied_bounds: &mut FxHashSet<Ty<'tcx>>,
 ) {
     let tcx = wfcx.tcx();
     let sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), sig);
@@ -1521,15 +1507,8 @@ fn check_fn_or_method<'tcx>(
         );
     }
 
-    implied_bounds.extend(sig.inputs());
-
     wfcx.register_wf_obligation(hir_decl.output.span(), None, sig.output().into());
 
-    // FIXME(#27579) return types should not be implied bounds
-    implied_bounds.insert(sig.output());
-
-    debug!(?implied_bounds);
-
     check_where_clauses(wfcx, span, def_id);
 }
 
@@ -1924,40 +1903,6 @@ impl<'a, 'tcx> WfCheckingCtxt<'a, 'tcx> {
     }
 }
 
-pub fn impl_implied_bounds<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    impl_def_id: LocalDefId,
-    span: Span,
-) -> FxHashSet<Ty<'tcx>> {
-    // We completely ignore any obligations caused by normalizing the types
-    // we assume to be well formed. Considering that the user of the implied
-    // bounds will also normalize them, we leave it to them to emit errors
-    // which should result in better causes and spans.
-    tcx.infer_ctxt().enter(|infcx| {
-        let cause = ObligationCause::misc(span, tcx.hir().local_def_id_to_hir_id(impl_def_id));
-        match tcx.impl_trait_ref(impl_def_id) {
-            Some(trait_ref) => {
-                // Trait impl: take implied bounds from all types that
-                // appear in the trait reference.
-                match infcx.at(&cause, param_env).normalize(trait_ref) {
-                    Ok(Normalized { value, obligations: _ }) => value.substs.types().collect(),
-                    Err(NoSolution) => FxHashSet::default(),
-                }
-            }
-
-            None => {
-                // Inherent impl: take implied bounds from the `self` type.
-                let self_ty = tcx.type_of(impl_def_id);
-                match infcx.at(&cause, param_env).normalize(self_ty) {
-                    Ok(Normalized { value, obligations: _ }) => FxHashSet::from_iter([value]),
-                    Err(NoSolution) => FxHashSet::default(),
-                }
-            }
-        }
-    })
-}
-
 fn error_392(
     tcx: TyCtxt<'_>,
     span: Span,