From 2285e35919f5d17188401479863fdf3ac79cf5a8 Mon Sep 17 00:00:00 2001
From: Basile Desloges <basile.desloges@gmail.com>
Date: Thu, 16 Nov 2017 17:07:33 +0100
Subject: [PATCH] mir-borrowck: Use Field instead of usize for field index in
 user description functions

---
 src/librustc_mir/borrow_check.rs | 37 ++++++++++++++++----------------
 1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/src/librustc_mir/borrow_check.rs b/src/librustc_mir/borrow_check.rs
index b1fa9ba48485..08ccf2ebf22f 100644
--- a/src/librustc_mir/borrow_check.rs
+++ b/src/librustc_mir/borrow_check.rs
@@ -15,7 +15,7 @@ use rustc::hir::def_id::{DefId};
 use rustc::infer::{InferCtxt};
 use rustc::ty::{self, TyCtxt, ParamEnv};
 use rustc::ty::maps::Providers;
-use rustc::mir::{AssertMessage, BasicBlock, BorrowKind, Location, Lvalue, Local};
+use rustc::mir::{AssertMessage, BasicBlock, BorrowKind, Field, Location, Lvalue, Local};
 use rustc::mir::{Mir, Mutability, Operand, Projection, ProjectionElem, Rvalue};
 use rustc::mir::{Statement, StatementKind, Terminator, TerminatorKind};
 use transform::nll;
@@ -1611,7 +1611,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                         let is_projection_from_ty_closure = proj.base.ty(self.mir, self.tcx)
                                 .to_ty(self.tcx).is_closure();
 
-                        let field_name = self.describe_field(&proj.base, field.index());
+                        let field_name = self.describe_field(&proj.base, field);
                         if is_projection_from_ty_closure {
                             buf.push_str(&format!("{}", field_name));
                         } else {
@@ -1650,58 +1650,57 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
         }
     }
 
-    // FIXME Instead of passing usize, Field should be passed
-    // End-user visible description of the `field_index`nth field of `base`
-    fn describe_field(&self, base: &Lvalue, field_index: usize) -> String {
+    // End-user visible description of the `field`nth field of `base`
+    fn describe_field(&self, base: &Lvalue, field: Field) -> String {
         match *base {
             Lvalue::Local(local) => {
                 let local = &self.mir.local_decls[local];
-                self.describe_field_from_ty(&local.ty, field_index)
+                self.describe_field_from_ty(&local.ty, field)
             },
             Lvalue::Static(ref static_) => {
-                self.describe_field_from_ty(&static_.ty, field_index)
+                self.describe_field_from_ty(&static_.ty, field)
             },
             Lvalue::Projection(ref proj) => {
                 match proj.elem {
                     ProjectionElem::Deref =>
-                        self.describe_field(&proj.base, field_index),
+                        self.describe_field(&proj.base, field),
                     ProjectionElem::Downcast(def, variant_index) =>
-                        format!("{}", def.variants[variant_index].fields[field_index].name),
+                        format!("{}", def.variants[variant_index].fields[field.index()].name),
                     ProjectionElem::Field(_, field_type) =>
-                        self.describe_field_from_ty(&field_type, field_index),
+                        self.describe_field_from_ty(&field_type, field),
                     ProjectionElem::Index(..)
                     | ProjectionElem::ConstantIndex { .. }
                     | ProjectionElem::Subslice { .. } =>
-                        format!("{}", self.describe_field(&proj.base, field_index)),
+                        format!("{}", self.describe_field(&proj.base, field)),
                 }
             }
         }
     }
 
     // End-user visible description of the `field_index`nth field of `ty`
-    fn describe_field_from_ty(&self, ty: &ty::Ty, field_index: usize) -> String {
+    fn describe_field_from_ty(&self, ty: &ty::Ty, field: Field) -> String {
         if ty.is_box() {
             // If the type is a box, the field is described from the boxed type
-            self.describe_field_from_ty(&ty.boxed_ty(), field_index)
+            self.describe_field_from_ty(&ty.boxed_ty(), field)
         }
         else {
             match ty.sty {
                 ty::TyAdt(def, _) => {
                     if def.is_enum() {
-                        format!("{}", field_index)
+                        format!("{}", field.index())
                     }
                     else {
-                        format!("{}", def.struct_variant().fields[field_index].name)
+                        format!("{}", def.struct_variant().fields[field.index()].name)
                     }
                 },
                 ty::TyTuple(_, _) => {
-                    format!("{}", field_index)
+                    format!("{}", field.index())
                 },
                 ty::TyRef(_, tnm) | ty::TyRawPtr(tnm) => {
-                    self.describe_field_from_ty(&tnm.ty, field_index)
+                    self.describe_field_from_ty(&tnm.ty, field)
                 },
                 ty::TyArray(ty, _) | ty::TySlice(ty) => {
-                    self.describe_field_from_ty(&ty, field_index)
+                    self.describe_field_from_ty(&ty, field)
                 },
                 ty::TyClosure(closure_def_id, _) => {
                     // Convert the def-id into a node-id. node-ids are only valid for
@@ -1709,7 +1708,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                     // the closure comes from another crate. But in that case we wouldn't
                     // be borrowck'ing it, so we can just unwrap:
                     let node_id = self.tcx.hir.as_local_node_id(closure_def_id).unwrap();
-                    let freevar = self.tcx.with_freevars(node_id, |fv| fv[field_index]);
+                    let freevar = self.tcx.with_freevars(node_id, |fv| fv[field.index()]);
 
                     self.tcx.hir.name(freevar.var_id()).to_string()
                  }