Unify optional param info with object lifetime default boolean into an enum that exhaustively supports all call sites

8 files changed, 75 insertions, 53 deletions

diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index f5bcbf852bd..d84dcb78ad2 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -44,7 +44,7 @@ use std::ops::Bound;
 
 use crate::check::intrinsic::intrinsic_operation_unsafety;
 use crate::errors;
-use crate::hir_ty_lowering::HirTyLowerer;
+use crate::hir_ty_lowering::{HirTyLowerer, RegionInferReason};
 pub use type_of::test_opaque_hidden_types;
 
 mod generics_of;
@@ -374,13 +374,8 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
         self.item_def_id
     }
 
-    fn re_infer(
-        &self,
-        _: Option<&ty::GenericParamDef>,
-        span: Span,
-        object_lifetime_default: bool,
-    ) -> ty::Region<'tcx> {
-        if object_lifetime_default {
+    fn re_infer(&self, span: Span, reason: RegionInferReason<'_>) -> ty::Region<'tcx> {
+        if let RegionInferReason::BorrowedObjectLifetimeDefault = reason {
             let e = struct_span_code_err!(
                 self.tcx().dcx(),
                 span,
diff --git a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
index 0abe4f07e19..913fae6b5b6 100644
--- a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
@@ -1,7 +1,7 @@
 use crate::bounds::Bounds;
 use crate::collect::ItemCtxt;
 use crate::constrained_generic_params as cgp;
-use crate::hir_ty_lowering::{HirTyLowerer, OnlySelfBounds, PredicateFilter};
+use crate::hir_ty_lowering::{HirTyLowerer, OnlySelfBounds, PredicateFilter, RegionInferReason};
 use hir::{HirId, Node};
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
@@ -243,12 +243,15 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
             }
 
             hir::WherePredicate::RegionPredicate(region_pred) => {
-                let r1 = icx.lowerer().lower_lifetime(region_pred.lifetime, None);
+                let r1 = icx
+                    .lowerer()
+                    .lower_lifetime(region_pred.lifetime, RegionInferReason::RegionPredicate);
                 predicates.extend(region_pred.bounds.iter().map(|bound| {
                     let (r2, span) = match bound {
-                        hir::GenericBound::Outlives(lt) => {
-                            (icx.lowerer().lower_lifetime(lt, None), lt.ident.span)
-                        }
+                        hir::GenericBound::Outlives(lt) => (
+                            icx.lowerer().lower_lifetime(lt, RegionInferReason::RegionPredicate),
+                            lt.ident.span,
+                        ),
                         bound => {
                             span_bug!(
                                 bound.span(),
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
index b6a1799c03f..73ce577907e 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
@@ -18,6 +18,8 @@ use crate::bounds::Bounds;
 use crate::errors;
 use crate::hir_ty_lowering::{HirTyLowerer, OnlySelfBounds, PredicateFilter};
 
+use super::RegionInferReason;
+
 impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     /// Add a `Sized` bound to the `bounds` if appropriate.
     ///
@@ -166,7 +168,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     );
                 }
                 hir::GenericBound::Outlives(lifetime) => {
-                    let region = self.lower_lifetime(lifetime, None);
+                    let region = self.lower_lifetime(lifetime, RegionInferReason::OutlivesBound);
                     bounds.push_region_bound(
                         self.tcx(),
                         ty::Binder::bind_with_vars(
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index 87c34ac535f..9b8edbc10ad 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -80,6 +80,20 @@ pub enum PredicateFilter {
     SelfAndAssociatedTypeBounds,
 }
 
+#[derive(Debug)]
+pub enum RegionInferReason<'a> {
+    /// Lifetime on a trait object behind a reference.
+    /// This allows inferring information from the reference.
+    BorrowedObjectLifetimeDefault,
+    /// A trait object's lifetime.
+    ObjectLifetimeDefault,
+    /// Generic lifetime parameter
+    Param(&'a ty::GenericParamDef),
+    RegionPredicate,
+    Reference,
+    OutlivesBound,
+}
+
 /// A context which can lower type-system entities from the [HIR][hir] to
 /// the [`rustc_middle::ty`] representation.
 ///
@@ -91,14 +105,7 @@ pub trait HirTyLowerer<'tcx> {
     fn item_def_id(&self) -> LocalDefId;
 
     /// Returns the region to use when a lifetime is omitted (and not elided).
-    ///
-    /// The `object_lifetime_default` argument states whether this lifetime is from a reference.
-    fn re_infer(
-        &self,
-        param: Option<&ty::GenericParamDef>,
-        span: Span,
-        object_lifetime_default: bool,
-    ) -> ty::Region<'tcx>;
+    fn re_infer(&self, span: Span, reason: RegionInferReason<'_>) -> ty::Region<'tcx>;
 
     /// Returns the type to use when a type is omitted.
     fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
@@ -267,7 +274,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     pub fn lower_lifetime(
         &self,
         lifetime: &hir::Lifetime,
-        def: Option<&ty::GenericParamDef>,
+        reason: RegionInferReason<'_>,
     ) -> ty::Region<'tcx> {
         let tcx = self.tcx();
         let lifetime_name = |def_id| tcx.hir().name(tcx.local_def_id_to_hir_id(def_id));
@@ -301,7 +308,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
             Some(rbv::ResolvedArg::Error(guar)) => ty::Region::new_error(tcx, guar),
 
-            None => self.re_infer(def, lifetime.ident.span, false),
+            None => self.re_infer(lifetime.ident.span, reason),
         }
     }
 
@@ -466,7 +473,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
                 match (&param.kind, arg) {
                     (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
-                        self.lowerer.lower_lifetime(lt, Some(param)).into()
+                        self.lowerer.lower_lifetime(lt, RegionInferReason::Param(param)).into()
                     }
                     (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
                         handle_ty_args(has_default, ty)
@@ -509,7 +516,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 }
                 match param.kind {
                     GenericParamDefKind::Lifetime => {
-                        self.lowerer.re_infer(Some(param), self.span, false).into()
+                        self.lowerer.re_infer(self.span, RegionInferReason::Param(param)).into()
                     }
                     GenericParamDefKind::Type { has_default, .. } => {
                         if !infer_args && has_default {
@@ -2041,7 +2048,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             hir::TyKind::Slice(ty) => Ty::new_slice(tcx, self.lower_ty(ty)),
             hir::TyKind::Ptr(mt) => Ty::new_ptr(tcx, self.lower_ty(mt.ty), mt.mutbl),
             hir::TyKind::Ref(region, mt) => {
-                let r = self.lower_lifetime(region, None);
+                let r = self.lower_lifetime(region, RegionInferReason::Reference);
                 debug!(?r);
                 let t = self.lower_ty_common(mt.ty, true, false);
                 Ty::new_ref(tcx, r, t, mt.mutbl)
@@ -2270,7 +2277,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         &lifetimes[i]
                     )
                 };
-                self.lower_lifetime(lifetime, None).into()
+                self.lower_lifetime(lifetime, RegionInferReason::Param(&param)).into()
             } else {
                 tcx.mk_param_from_def(param)
             }
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/object_safety.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/object_safety.rs
index fef80102b62..b9c5ae0c65b 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/object_safety.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/object_safety.rs
@@ -1,5 +1,7 @@
 use crate::bounds::Bounds;
-use crate::hir_ty_lowering::{GenericArgCountMismatch, GenericArgCountResult, OnlySelfBounds};
+use crate::hir_ty_lowering::{
+    GenericArgCountMismatch, GenericArgCountResult, OnlySelfBounds, RegionInferReason,
+};
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_errors::{codes::*, struct_span_code_err};
 use rustc_hir as hir;
@@ -321,13 +323,20 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
 
         // Use explicitly-specified region bound.
         let region_bound = if !lifetime.is_elided() {
-            self.lower_lifetime(lifetime, None)
+            self.lower_lifetime(lifetime, RegionInferReason::ObjectLifetimeDefault)
         } else {
             self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
                 if tcx.named_bound_var(lifetime.hir_id).is_some() {
-                    self.lower_lifetime(lifetime, None)
+                    self.lower_lifetime(lifetime, RegionInferReason::ObjectLifetimeDefault)
                 } else {
-                    self.re_infer(None, span, !borrowed)
+                    self.re_infer(
+                        span,
+                        if borrowed {
+                            RegionInferReason::ObjectLifetimeDefault
+                        } else {
+                            RegionInferReason::BorrowedObjectLifetimeDefault
+                        },
+                    )
                 }
             })
         };
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
index fb44e542f7a..250e9c3c313 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
@@ -16,7 +16,7 @@ use rustc_hir_analysis::hir_ty_lowering::generics::{
 };
 use rustc_hir_analysis::hir_ty_lowering::{
     ExplicitLateBound, GenericArgCountMismatch, GenericArgCountResult, GenericArgsLowerer,
-    GenericPathSegment, HirTyLowerer, IsMethodCall,
+    GenericPathSegment, HirTyLowerer, IsMethodCall, RegionInferReason,
 };
 use rustc_infer::infer::canonical::{Canonical, OriginalQueryValues, QueryResponse};
 use rustc_infer::infer::error_reporting::TypeAnnotationNeeded::E0282;
@@ -1280,9 +1280,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 arg: &GenericArg<'tcx>,
             ) -> ty::GenericArg<'tcx> {
                 match (&param.kind, arg) {
-                    (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
-                        self.fcx.lowerer().lower_lifetime(lt, Some(param)).into()
-                    }
+                    (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => self
+                        .fcx
+                        .lowerer()
+                        .lower_lifetime(lt, RegionInferReason::Param(param))
+                        .into(),
                     (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
                         self.fcx.lower_ty(ty).raw.into()
                     }
@@ -1324,9 +1326,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ) -> ty::GenericArg<'tcx> {
                 let tcx = self.fcx.tcx();
                 match param.kind {
-                    GenericParamDefKind::Lifetime => {
-                        self.fcx.re_infer(Some(param), self.span, false).into()
-                    }
+                    GenericParamDefKind::Lifetime => self
+                        .fcx
+                        .re_infer(
+                            self.span,
+                            rustc_hir_analysis::hir_ty_lowering::RegionInferReason::Param(param),
+                        )
+                        .into(),
                     GenericParamDefKind::Type { has_default, .. } => {
                         if !infer_args && has_default {
                             // If we have a default, then it doesn't matter that we're not
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs
index 954a0956b70..b9ff348c42f 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs
@@ -15,7 +15,7 @@ use hir::def_id::CRATE_DEF_ID;
 use rustc_errors::DiagCtxt;
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer;
+use rustc_hir_analysis::hir_ty_lowering::{HirTyLowerer, RegionInferReason};
 use rustc_infer::infer;
 use rustc_infer::infer::error_reporting::sub_relations::SubRelations;
 use rustc_infer::infer::error_reporting::TypeErrCtxt;
@@ -222,15 +222,10 @@ impl<'tcx> HirTyLowerer<'tcx> for FnCtxt<'_, 'tcx> {
         self.body_id
     }
 
-    fn re_infer(
-        &self,
-        def: Option<&ty::GenericParamDef>,
-        span: Span,
-        _object_lifetime_default: bool,
-    ) -> ty::Region<'tcx> {
-        let v = match def {
-            Some(def) => infer::RegionParameterDefinition(span, def.name),
-            None => infer::MiscVariable(span),
+    fn re_infer(&self, span: Span, reason: RegionInferReason<'_>) -> ty::Region<'tcx> {
+        let v = match reason {
+            RegionInferReason::Param(def) => infer::RegionParameterDefinition(span, def.name),
+            _ => infer::MiscVariable(span),
         };
         self.next_region_var(v)
     }
diff --git a/compiler/rustc_hir_typeck/src/method/confirm.rs b/compiler/rustc_hir_typeck/src/method/confirm.rs
index 0825e661373..949b9241005 100644
--- a/compiler/rustc_hir_typeck/src/method/confirm.rs
+++ b/compiler/rustc_hir_typeck/src/method/confirm.rs
@@ -7,7 +7,9 @@ use rustc_hir::GenericArg;
 use rustc_hir_analysis::hir_ty_lowering::generics::{
     check_generic_arg_count_for_call, lower_generic_args,
 };
-use rustc_hir_analysis::hir_ty_lowering::{GenericArgsLowerer, HirTyLowerer, IsMethodCall};
+use rustc_hir_analysis::hir_ty_lowering::{
+    GenericArgsLowerer, HirTyLowerer, IsMethodCall, RegionInferReason,
+};
 use rustc_infer::infer::{self, DefineOpaqueTypes, InferOk};
 use rustc_middle::traits::{ObligationCauseCode, UnifyReceiverContext};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCoercion};
@@ -388,9 +390,12 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                 arg: &GenericArg<'tcx>,
             ) -> ty::GenericArg<'tcx> {
                 match (&param.kind, arg) {
-                    (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
-                        self.cfcx.fcx.lowerer().lower_lifetime(lt, Some(param)).into()
-                    }
+                    (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => self
+                        .cfcx
+                        .fcx
+                        .lowerer()
+                        .lower_lifetime(lt, RegionInferReason::Param(param))
+                        .into(),
                     (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
                         self.cfcx.lower_ty(ty).raw.into()
                     }