Arrange methods on HirTyLowerer more logically

This makes it easier to read the trait definition for newcomers:
Sorted from least “complex” to most “complex” followed by trivial “plumbing”
and grouped by area.

* Move `allow_infer` above all `*_infer` methods
  * It's the least complex method of those
  * Allows the `*_infer` to be placed right next to each other
* Move `probe_ty_param_bounds` further down right next to `lower_assoc_ty` and `probe_adt`
  * It's more complex than the `infer` methods, it should come “later”
  * Now all required lowering functions are grouped together
* Move the “plumbing” function `set_tainted_by_errors` further down
  below any actual lowering methods.
* Provided method should come last

compiler/rustc_hir_analysis/src/collect.rs

@@ -372,23 +372,14 @@ fn item_def_id(&self) -> DefId {
         self.item_def_id.to_def_id()
     }
 
-    fn probe_ty_param_bounds(
-        &self,
-        span: Span,
-        def_id: LocalDefId,
-        assoc_name: Ident,
-    ) -> ty::GenericPredicates<'tcx> {
-        self.tcx.at(span).type_param_predicates((self.item_def_id, def_id, assoc_name))
+    fn allow_infer(&self) -> bool {
+        false
     }
 
     fn re_infer(&self, _: Option<&ty::GenericParamDef>, _: Span) -> Option<ty::Region<'tcx>> {
         None
     }
 
-    fn allow_infer(&self) -> bool {
-        false
-    }
-
     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
         Ty::new_error_with_message(self.tcx(), span, "bad placeholder type")
     }
@@ -403,6 +394,15 @@ fn ct_infer(&self, ty: Ty<'tcx>, _: Option<&ty::GenericParamDef>, span: Span) ->
         ty::Const::new_error_with_message(self.tcx(), ty, span, "bad placeholder constant")
     }
 
+    fn probe_ty_param_bounds(
+        &self,
+        span: Span,
+        def_id: LocalDefId,
+        assoc_name: Ident,
+    ) -> ty::GenericPredicates<'tcx> {
+        self.tcx.at(span).type_param_predicates((self.item_def_id, def_id, assoc_name))
+    }
+
     fn lower_assoc_ty(
         &self,
         span: Span,
@@ -496,10 +496,6 @@ fn probe_adt(&self, _span: Span, ty: Ty<'tcx>) -> Option<ty::AdtDef<'tcx>> {
         ty.ty_adt_def()
     }
 
-    fn set_tainted_by_errors(&self, err: ErrorGuaranteed) {
-        self.tainted_by_errors.set(Some(err));
-    }
-
     fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
         // There's no place to record types from signatures?
     }
@@ -507,6 +503,10 @@ fn record_ty(&self, _hir_id: hir::HirId, _ty: Ty<'tcx>, _span: Span) {
     fn infcx(&self) -> Option<&InferCtxt<'tcx>> {
         None
     }
+
+    fn set_tainted_by_errors(&self, err: ErrorGuaranteed) {
+        self.tainted_by_errors.set(Some(err));
+    }
 }
 
 /// Synthesize a new lifetime name that doesn't clash with any of the lifetimes already present.

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -89,6 +89,24 @@ pub trait HirTyLowerer<'tcx> {
     /// Returns the [`DefId`] of the overarching item whose constituents get lowered.
     fn item_def_id(&self) -> DefId;
 
+    /// Returns `true` if the current context allows the use of inference variables.
+    fn allow_infer(&self) -> bool;
+
+    /// Returns the region to use when a lifetime is omitted (and not elided).
+    fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
+    -> Option<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>;
+
+    /// Returns the const to use when a const is omitted.
+    fn ct_infer(
+        &self,
+        ty: Ty<'tcx>,
+        param: Option<&ty::GenericParamDef>,
+        span: Span,
+    ) -> Const<'tcx>;
+
     /// Probe bounds in scope where the bounded type coincides with the given type parameter.
     ///
     /// Rephrased, this returns bounds of the form `T: Trait`, where `T` is a type parameter
@@ -110,24 +128,6 @@ fn probe_ty_param_bounds(
         assoc_name: Ident,
     ) -> ty::GenericPredicates<'tcx>;
 
-    /// Returns the region to use when a lifetime is omitted (and not elided).
-    fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
-    -> Option<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>;
-
-    /// Returns `true` if the current context allows the use of inference variables.
-    fn allow_infer(&self) -> bool;
-
-    /// Returns the const to use when a const is omitted.
-    fn ct_infer(
-        &self,
-        ty: Ty<'tcx>,
-        param: Option<&ty::GenericParamDef>,
-        span: Span,
-    ) -> Const<'tcx>;
-
     /// Lower an associated type to a projection.
     ///
     /// This method has to be defined by the concrete lowering context because
@@ -156,15 +156,18 @@ fn lower_assoc_ty(
     /// or to an enum variant depending on the result of this function.
     fn probe_adt(&self, span: Span, ty: Ty<'tcx>) -> Option<ty::AdtDef<'tcx>>;
 
+    /// Record the lowered type of a HIR node in this context.
+    fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
+
+    /// The inference context of the lowering context if applicable.
+    fn infcx(&self) -> Option<&InferCtxt<'tcx>>;
+
     /// Taint the context with errors.
     ///
     /// Invoke this when you encounter an error from some prior pass like name resolution.
     /// This is used to help suppress derived errors typeck might otherwise report.
     fn set_tainted_by_errors(&self, e: ErrorGuaranteed);
 
-    /// Record the lowered type of a HIR node in this context.
-    fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
-
     /// Convenience method for coercing the lowering context into a trait object type.
     ///
     /// Most lowering routines are defined on the trait object type directly
@@ -175,9 +178,6 @@ fn lowerer(&self) -> &dyn HirTyLowerer<'tcx>
     {
         self
     }
-
-    /// The inference context of the lowering context if applicable.
-    fn infcx(&self) -> Option<&InferCtxt<'tcx>>;
 }
 
 /// New-typed boolean indicating whether explicit late-bound lifetimes

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -221,31 +221,8 @@ fn item_def_id(&self) -> DefId {
         self.body_id.to_def_id()
     }
 
-    fn probe_ty_param_bounds(
-        &self,
-        _: Span,
-        def_id: LocalDefId,
-        _: Ident,
-    ) -> ty::GenericPredicates<'tcx> {
-        let tcx = self.tcx;
-        let item_def_id = tcx.hir().ty_param_owner(def_id);
-        let generics = tcx.generics_of(item_def_id);
-        let index = generics.param_def_id_to_index[&def_id.to_def_id()];
-        // HACK(eddyb) should get the original `Span`.
-        let span = tcx.def_span(def_id);
-        ty::GenericPredicates {
-            parent: None,
-            predicates: tcx.arena.alloc_from_iter(
-                self.param_env.caller_bounds().iter().filter_map(|predicate| {
-                    match predicate.kind().skip_binder() {
-                        ty::ClauseKind::Trait(data) if data.self_ty().is_param(index) => {
-                            Some((predicate, span))
-                        }
-                        _ => None,
-                    }
-                }),
-            ),
-        }
+    fn allow_infer(&self) -> bool {
+        true
     }
 
     fn re_infer(&self, def: Option<&ty::GenericParamDef>, span: Span) -> Option<ty::Region<'tcx>> {
@@ -256,10 +233,6 @@ fn re_infer(&self, def: Option<&ty::GenericParamDef>, span: Span) -> Option<ty::
         Some(self.next_region_var(v))
     }
 
-    fn allow_infer(&self) -> bool {
-        true
-    }
-
     fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
         match param {
             Some(param) => self.var_for_def(span, param).as_type().unwrap(),
@@ -292,6 +265,33 @@ fn ct_infer(
         }
     }
 
+    fn probe_ty_param_bounds(
+        &self,
+        _: Span,
+        def_id: LocalDefId,
+        _: Ident,
+    ) -> ty::GenericPredicates<'tcx> {
+        let tcx = self.tcx;
+        let item_def_id = tcx.hir().ty_param_owner(def_id);
+        let generics = tcx.generics_of(item_def_id);
+        let index = generics.param_def_id_to_index[&def_id.to_def_id()];
+        // HACK(eddyb) should get the original `Span`.
+        let span = tcx.def_span(def_id);
+        ty::GenericPredicates {
+            parent: None,
+            predicates: tcx.arena.alloc_from_iter(
+                self.param_env.caller_bounds().iter().filter_map(|predicate| {
+                    match predicate.kind().skip_binder() {
+                        ty::ClauseKind::Trait(data) if data.self_ty().is_param(index) => {
+                            Some((predicate, span))
+                        }
+                        _ => None,
+                    }
+                }),
+            ),
+        }
+    }
+
     fn lower_assoc_ty(
         &self,
         span: Span,
@@ -328,10 +328,6 @@ fn probe_adt(&self, span: Span, ty: Ty<'tcx>) -> Option<ty::AdtDef<'tcx>> {
         }
     }
 
-    fn set_tainted_by_errors(&self, e: ErrorGuaranteed) {
-        self.infcx.set_tainted_by_errors(e)
-    }
-
     fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span) {
         // FIXME: normalization and escaping regions
         let ty = if !ty.has_escaping_bound_vars() {
@@ -355,6 +351,10 @@ fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span) {
     fn infcx(&self) -> Option<&infer::InferCtxt<'tcx>> {
         Some(&self.infcx)
     }
+
+    fn set_tainted_by_errors(&self, e: ErrorGuaranteed) {
+        self.infcx.set_tainted_by_errors(e)
+    }
 }
 
 /// The `ty` representation of a user-provided type. Depending on the use-site