Use expand_weak_alias_tys when collecting constrained generics params in impls

Author: fmease

compiler/rustc_hir_analysis/src/constrained_generic_params.rs

@@ -1,8 +1,8 @@
 use rustc_data_structures::fx::FxHashSet;
-use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::Span;
+use rustc_type_ir::fold::TypeFoldable;
 use std::ops::ControlFlow;
 
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
@@ -33,62 +33,47 @@ pub fn parameters_for_impl<'tcx>(
     impl_trait_ref: Option<ty::TraitRef<'tcx>>,
 ) -> FxHashSet<Parameter> {
     let vec = match impl_trait_ref {
-        Some(tr) => parameters_for(tcx, &tr, false),
-        None => parameters_for(tcx, &impl_self_ty, false),
+        Some(tr) => parameters_for(tcx, tr, false),
+        None => parameters_for(tcx, impl_self_ty, false),
     };
     vec.into_iter().collect()
 }
 
 /// If `include_nonconstraining` is false, returns the list of parameters that are
-/// constrained by `t` - i.e., the value of each parameter in the list is
-/// uniquely determined by `t` (see RFC 447). If it is true, return the list
-/// of parameters whose values are needed in order to constrain `ty` - these
+/// constrained by `value` - i.e., the value of each parameter in the list is
+/// uniquely determined by `value` (see RFC 447). If it is true, return the list
+/// of parameters whose values are needed in order to constrain `value` - these
 /// differ, with the latter being a superset, in the presence of projections.
 pub fn parameters_for<'tcx>(
     tcx: TyCtxt<'tcx>,
-    t: &impl TypeVisitable<TyCtxt<'tcx>>,
+    value: impl TypeFoldable<TyCtxt<'tcx>>,
     include_nonconstraining: bool,
 ) -> Vec<Parameter> {
-    let mut collector =
-        ParameterCollector { tcx, parameters: vec![], include_nonconstraining, depth: 0 };
-    t.visit_with(&mut collector);
+    let mut collector = ParameterCollector { parameters: vec![], include_nonconstraining };
+    let value = if !include_nonconstraining { tcx.expand_weak_alias_tys(value) } else { value };
+    value.visit_with(&mut collector);
     collector.parameters
 }
 
-struct ParameterCollector<'tcx> {
-    tcx: TyCtxt<'tcx>,
+struct ParameterCollector {
     parameters: Vec<Parameter>,
     include_nonconstraining: bool,
-    depth: usize,
 }
 
-impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ParameterCollector<'tcx> {
+impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ParameterCollector {
     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         match *t.kind() {
+            // Projections are not injective in general.
             ty::Alias(ty::Projection | ty::Inherent | ty::Opaque, _)
                 if !self.include_nonconstraining =>
             {
-                // Projections are not injective in general.
                 return ControlFlow::Continue(());
             }
-            ty::Alias(ty::Weak, alias) if !self.include_nonconstraining => {
-                if !self.tcx.recursion_limit().value_within_limit(self.depth) {
-                    // Other constituent types may still constrain some generic params, consider
-                    // `<T> (Overflow, T)` for example. Therefore we want to continue instead of
-                    // breaking. Only affects diagnostics.
-                    return ControlFlow::Continue(());
-                }
-                self.depth += 1;
-                return ensure_sufficient_stack(|| {
-                    self.tcx
-                        .type_of(alias.def_id)
-                        .instantiate(self.tcx, alias.args)
-                        .visit_with(self)
-                });
-            }
-            ty::Param(data) => {
-                self.parameters.push(Parameter::from(data));
+            // All weak alias types should've been expanded beforehand.
+            ty::Alias(ty::Weak, _) if !self.include_nonconstraining => {
+                bug!("unexpected weak alias type")
             }
+            ty::Param(param) => self.parameters.push(Parameter::from(param)),
             _ => {}
         }
 
@@ -224,12 +209,12 @@ pub fn setup_constraining_predicates<'tcx>(
                 //     `<<T as Bar>::Baz as Iterator>::Output = <U as Iterator>::Output`
                 // Then the projection only applies if `T` is known, but it still
                 // does not determine `U`.
-                let inputs = parameters_for(tcx, &projection.projection_ty, true);
+                let inputs = parameters_for(tcx, projection.projection_ty, true);
                 let relies_only_on_inputs = inputs.iter().all(|p| input_parameters.contains(p));
                 if !relies_only_on_inputs {
                     continue;
                 }
-                input_parameters.extend(parameters_for(tcx, &projection.term, false));
+                input_parameters.extend(parameters_for(tcx, projection.term, false));
             } else {
                 continue;
             }

compiler/rustc_hir_analysis/src/impl_wf_check.rs

@@ -111,7 +111,7 @@ fn enforce_impl_params_are_constrained(
             match item.kind {
                 ty::AssocKind::Type => {
                     if item.defaultness(tcx).has_value() {
-                        cgp::parameters_for(tcx, &tcx.type_of(def_id).instantiate_identity(), true)
+                        cgp::parameters_for(tcx, tcx.type_of(def_id).instantiate_identity(), true)
                     } else {
                         vec![]
                     }

compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs

@@ -133,7 +133,7 @@ fn check_always_applicable(
 
     res = res.and(check_constness(tcx, impl1_def_id, impl2_node, span));
     res = res.and(check_static_lifetimes(tcx, &parent_args, span));
-    res = res.and(check_duplicate_params(tcx, impl1_args, &parent_args, span));
+    res = res.and(check_duplicate_params(tcx, impl1_args, parent_args, span));
     res = res.and(check_predicates(tcx, impl1_def_id, impl1_args, impl2_node, impl2_args, span));
 
     res
@@ -266,15 +266,15 @@ fn unconstrained_parent_impl_args<'tcx>(
                 continue;
             }
 
-            unconstrained_parameters.extend(cgp::parameters_for(tcx, &projection_ty, true));
+            unconstrained_parameters.extend(cgp::parameters_for(tcx, projection_ty, true));
 
-            for param in cgp::parameters_for(tcx, &projected_ty, false) {
+            for param in cgp::parameters_for(tcx, projected_ty, false) {
                 if !unconstrained_parameters.contains(&param) {
                     constrained_params.insert(param.0);
                 }
             }
 
-            unconstrained_parameters.extend(cgp::parameters_for(tcx, &projected_ty, true));
+            unconstrained_parameters.extend(cgp::parameters_for(tcx, projected_ty, true));
         }
     }
 
@@ -309,7 +309,7 @@ fn unconstrained_parent_impl_args<'tcx>(
 fn check_duplicate_params<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl1_args: GenericArgsRef<'tcx>,
-    parent_args: &Vec<GenericArg<'tcx>>,
+    parent_args: Vec<GenericArg<'tcx>>,
     span: Span,
 ) -> Result<(), ErrorGuaranteed> {
     let mut base_params = cgp::parameters_for(tcx, parent_args, true);