Move some utils out of rustc_const_eval

This allows us to get rid of the `rustc_const_eval->rustc_borrowck`
dependency edge which was delaying the compilation of borrowck.

The added utils in `rustc_middle` are small and should not affect
compile times there.

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1,5 +1,4 @@
 use either::Either;
-use rustc_const_eval::util::CallKind;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::{
@@ -18,6 +17,7 @@ use rustc_middle::mir::{
     ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind, VarBindingForm,
 };
 use rustc_middle::ty::{self, suggest_constraining_type_params, PredicateKind, Ty};
+use rustc_middle::util::CallKind;
 use rustc_mir_dataflow::move_paths::{InitKind, MoveOutIndex, MovePathIndex};
 use rustc_span::def_id::LocalDefId;
 use rustc_span::hygiene::DesugaringKind;
@@ -2424,7 +2424,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             Some((method_did, method_substs)),
         ) = (
             &self.body[loan.reserve_location.block].terminator,
-            rustc_const_eval::util::find_self_call(
+            rustc_middle::util::find_self_call(
                 tcx,
                 self.body,
                 loan.assigned_place.local,

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -1,7 +1,6 @@
 //! Borrow checker diagnostics.
 
 use itertools::Itertools;
-use rustc_const_eval::util::{call_kind, CallDesugaringKind};
 use rustc_errors::{Applicability, Diagnostic};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, Namespace};
@@ -15,6 +14,7 @@ use rustc_middle::mir::{
 };
 use rustc_middle::ty::print::Print;
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
+use rustc_middle::util::{call_kind, CallDesugaringKind};
 use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult};
 use rustc_span::def_id::LocalDefId;
 use rustc_span::{symbol::sym, Span, Symbol, DUMMY_SP};
@@ -45,7 +45,7 @@ pub(crate) use mutability_errors::AccessKind;
 pub(crate) use outlives_suggestion::OutlivesSuggestionBuilder;
 pub(crate) use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};
 pub(crate) use region_name::{RegionName, RegionNameSource};
-pub(crate) use rustc_const_eval::util::CallKind;
+pub(crate) use rustc_middle::util::CallKind;
 
 pub(super) struct DescribePlaceOpt {
     pub including_downcast: bool,
@@ -874,7 +874,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         }) = &self.body[location.block].terminator
         {
             let Some((method_did, method_substs)) =
-                rustc_const_eval::util::find_self_call(
+            rustc_middle::util::find_self_call(
                     self.infcx.tcx,
                     &self.body,
                     target_temp,

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -15,8 +15,8 @@ use rustc_span::{sym, BytePos, Span};
 use rustc_target::abi::FieldIdx;
 
 use crate::diagnostics::BorrowedContentSource;
+use crate::util::FindAssignments;
 use crate::MirBorrowckCtxt;
-use rustc_const_eval::util::collect_writes::FindAssignments;
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub(crate) enum AccessKind {

compiler/rustc_borrowck/src/lib.rs

@@ -88,6 +88,7 @@ mod session_diagnostics;
 mod type_check;
 mod universal_regions;
 mod used_muts;
+mod util;
 
 /// A public API provided for the Rust compiler consumers.
 pub mod consumers;

compiler/rustc_borrowck/src/util/collect_writes.rs

@@ -0,0 +1,36 @@
+use rustc_middle::mir::visit::PlaceContext;
+use rustc_middle::mir::visit::Visitor;
+use rustc_middle::mir::{Body, Local, Location};
+
+pub trait FindAssignments {
+    // Finds all statements that assign directly to local (i.e., X = ...)
+    // and returns their locations.
+    fn find_assignments(&self, local: Local) -> Vec<Location>;
+}
+
+impl<'tcx> FindAssignments for Body<'tcx> {
+    fn find_assignments(&self, local: Local) -> Vec<Location> {
+        let mut visitor = FindLocalAssignmentVisitor { needle: local, locations: vec![] };
+        visitor.visit_body(self);
+        visitor.locations
+    }
+}
+
+// The Visitor walks the MIR to return the assignment statements corresponding
+// to a Local.
+struct FindLocalAssignmentVisitor {
+    needle: Local,
+    locations: Vec<Location>,
+}
+
+impl<'tcx> Visitor<'tcx> for FindLocalAssignmentVisitor {
+    fn visit_local(&mut self, local: Local, place_context: PlaceContext, location: Location) {
+        if self.needle != local {
+            return;
+        }
+
+        if place_context.is_place_assignment() {
+            self.locations.push(location);
+        }
+    }
+}

compiler/rustc_borrowck/src/util/mod.rs

@@ -0,0 +1,3 @@
+mod collect_writes;
+
+pub use collect_writes::FindAssignments;