Use fewer origins when creating type variables.

`InferCtxt::next_{ty,const}_var*` all take an origin, but the
`param_def_id` is almost always `None`. This commit changes them to just
take a `Span` and build the origin within the method, and adds new
methods for the rare cases where `param_def_id` might not be `None`.
This avoids a lot of tedious origin building.

Specifically:
- next_ty_var{,_id_in_universe,_in_universe}: now take `Span` instead of
  `TypeVariableOrigin`
- next_ty_var_with_origin: added

- next_const_var{,_in_universe}: takes Span instead of ConstVariableOrigin
- next_const_var_with_origin: added

- next_region_var, next_region_var_in_universe: these are unchanged,
  still take RegionVariableOrigin

The API inconsistency (ty/const vs region) seems worth it for the
large conciseness improvements.

compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs

@@ -19,12 +19,10 @@ 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::resolve::EagerResolver;
-use rustc_infer::infer::type_variable::TypeVariableOrigin;
 use rustc_infer::infer::RegionVariableOrigin;
 use rustc_infer::infer::{InferCtxt, InferOk};
 use rustc_infer::traits::solve::NestedNormalizationGoals;
 use rustc_middle::infer::canonical::Canonical;
-use rustc_middle::infer::unify_key::ConstVariableOrigin;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{
     ExternalConstraintsData, MaybeCause, PredefinedOpaquesData, QueryInput,
@@ -424,12 +422,8 @@ pub(in crate::solve) fn instantiate_canonical_state<'tcx, T: TypeFoldable<TyCtxt
             ty::GenericArgKind::Lifetime(_) => {
                 infcx.next_region_var(RegionVariableOrigin::MiscVariable(span)).into()
             }
-            ty::GenericArgKind::Type(_) => {
-                infcx.next_ty_var(TypeVariableOrigin { param_def_id: None, span }).into()
-            }
-            ty::GenericArgKind::Const(ct) => infcx
-                .next_const_var(ct.ty(), ConstVariableOrigin { param_def_id: None, span })
-                .into(),
+            ty::GenericArgKind::Type(_) => infcx.next_ty_var(span).into(),
+            ty::GenericArgKind::Const(ct) => infcx.next_const_var(ct.ty(), span).into(),
         };
 
         orig_values.push(unconstrained);

compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs

@@ -2,7 +2,6 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::canonical::CanonicalVarValues;
-use rustc_infer::infer::type_variable::TypeVariableOrigin;
 use rustc_infer::infer::{
     BoundRegionConversionTime, DefineOpaqueTypes, InferCtxt, InferOk, TyCtxtInferExt,
 };
@@ -11,7 +10,6 @@ use rustc_infer::traits::solve::{MaybeCause, NestedNormalizationGoals};
 use rustc_infer::traits::ObligationCause;
 use rustc_macros::{extension, HashStable};
 use rustc_middle::infer::canonical::CanonicalVarInfos;
-use rustc_middle::infer::unify_key::ConstVariableOrigin;
 use rustc_middle::traits::solve::inspect;
 use rustc_middle::traits::solve::{
     CanonicalInput, CanonicalResponse, Certainty, PredefinedOpaques, PredefinedOpaquesData,
@@ -600,15 +598,13 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     }
 
     pub(super) fn next_ty_infer(&mut self) -> Ty<'tcx> {
-        let ty = self.infcx.next_ty_var(TypeVariableOrigin { param_def_id: None, span: DUMMY_SP });
+        let ty = self.infcx.next_ty_var(DUMMY_SP);
         self.inspect.add_var_value(ty);
         ty
     }
 
     pub(super) fn next_const_infer(&mut self, ty: Ty<'tcx>) -> ty::Const<'tcx> {
-        let ct = self
-            .infcx
-            .next_const_var(ty, ConstVariableOrigin { param_def_id: None, span: DUMMY_SP });
+        let ct = self.infcx.next_const_var(ty, DUMMY_SP);
         self.inspect.add_var_value(ct);
         ct
     }

compiler/rustc_trait_selection/src/solve/inspect/analyse.rs

@@ -12,10 +12,8 @@
 use rustc_ast_ir::try_visit;
 use rustc_ast_ir::visit::VisitorResult;
 use rustc_infer::infer::resolve::EagerResolver;
-use rustc_infer::infer::type_variable::TypeVariableOrigin;
 use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk};
 use rustc_macros::extension;
-use rustc_middle::infer::unify_key::ConstVariableOrigin;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{inspect, QueryResult};
 use rustc_middle::traits::solve::{Certainty, Goal};
@@ -201,15 +199,8 @@ impl<'a, 'tcx> InspectCandidate<'a, 'tcx> {
             .map(|(source, goal)| match goal.predicate.kind().no_bound_vars() {
                 Some(ty::PredicateKind::NormalizesTo(ty::NormalizesTo { alias, term })) => {
                     let unconstrained_term = match term.unpack() {
-                        ty::TermKind::Ty(_) => infcx
-                            .next_ty_var(TypeVariableOrigin { param_def_id: None, span })
-                            .into(),
-                        ty::TermKind::Const(ct) => infcx
-                            .next_const_var(
-                                ct.ty(),
-                                ConstVariableOrigin { param_def_id: None, span },
-                            )
-                            .into(),
+                        ty::TermKind::Ty(_) => infcx.next_ty_var(span).into(),
+                        ty::TermKind::Const(ct) => infcx.next_const_var(ct.ty(), span).into(),
                     };
                     let goal =
                         goal.with(infcx.tcx, ty::NormalizesTo { alias, term: unconstrained_term });

compiler/rustc_trait_selection/src/solve/normalize.rs

@@ -3,11 +3,9 @@ use crate::traits::query::evaluate_obligation::InferCtxtExt;
 use crate::traits::{BoundVarReplacer, PlaceholderReplacer};
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_infer::infer::at::At;
-use rustc_infer::infer::type_variable::TypeVariableOrigin;
 use rustc_infer::infer::InferCtxt;
 use rustc_infer::traits::TraitEngineExt;
 use rustc_infer::traits::{FulfillmentError, Obligation, TraitEngine};
-use rustc_middle::infer::unify_key::ConstVariableOrigin;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::{self, AliasTy, Ty, TyCtxt, UniverseIndex};
 use rustc_middle::ty::{FallibleTypeFolder, TypeFolder, TypeSuperFoldable};
@@ -74,8 +72,7 @@ impl<'tcx> NormalizationFolder<'_, 'tcx> {
 
         self.depth += 1;
 
-        let new_infer_ty =
-            infcx.next_ty_var(TypeVariableOrigin { param_def_id: None, span: self.at.cause.span });
+        let new_infer_ty = infcx.next_ty_var(self.at.cause.span);
         let obligation = Obligation::new(
             tcx,
             self.at.cause.clone(),
@@ -120,10 +117,7 @@ impl<'tcx> NormalizationFolder<'_, 'tcx> {
 
         self.depth += 1;
 
-        let new_infer_ct = infcx.next_const_var(
-            ty,
-            ConstVariableOrigin { param_def_id: None, span: self.at.cause.span },
-        );
+        let new_infer_ct = infcx.next_const_var(ty, self.at.cause.span);
         let obligation = Obligation::new(
             tcx,
             self.at.cause.clone(),