From 70ef08f213b10e514915e2ab838bc0ff03197758 Mon Sep 17 00:00:00 2001
From: Basile Desloges <basile.desloges@gmail.com>
Date: Thu, 21 Sep 2017 16:13:03 +0200
Subject: [PATCH 1/4] mir-borrowck: Add method to MIR borrowck context to
 retrieve the span of a given borrow

---
 src/librustc_mir/borrow_check.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/librustc_mir/borrow_check.rs b/src/librustc_mir/borrow_check.rs
index 063cbc7755915..127ef1f0e0e5f 100644
--- a/src/librustc_mir/borrow_check.rs
+++ b/src/librustc_mir/borrow_check.rs
@@ -1024,6 +1024,13 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
             }
         }
     }
+
+    // Retrieve span of given borrow from the current MIR representation
+    fn retrieve_borrow_span(&self, borrow: &BorrowData) -> Span {
+        self.mir.basic_blocks()[borrow.location.block]
+            .statements[borrow.location.statement_index]
+            .source_info.span
+    }
 }
 
 impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx> {

From 86a7347fa1096688ff886d6bb92969ed7e20be9b Mon Sep 17 00:00:00 2001
From: Basile Desloges <basile.desloges@gmail.com>
Date: Thu, 21 Sep 2017 16:29:54 +0200
Subject: [PATCH 2/4] mir-borrowck: Add borrow data parameter to
 `report_use_while_mutably_borrowed()`

---
 src/librustc_mir/borrow_check.rs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/librustc_mir/borrow_check.rs b/src/librustc_mir/borrow_check.rs
index 127ef1f0e0e5f..6ec01faf00025 100644
--- a/src/librustc_mir/borrow_check.rs
+++ b/src/librustc_mir/borrow_check.rs
@@ -419,7 +419,7 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
             self.each_borrow_involving_path(
                 context, lvalue_span.0, flow_state, |this, _idx, borrow| {
                     if !borrow.compatible_with(BorrowKind::Shared) {
-                        this.report_use_while_mutably_borrowed(context, lvalue_span);
+                        this.report_use_while_mutably_borrowed(context, lvalue_span, borrow);
                         Control::Break
                     } else {
                         Control::Continue
@@ -914,7 +914,8 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
 
     fn report_use_while_mutably_borrowed(&mut self,
                                          _context: Context,
-                                         (lvalue, span): (&Lvalue, Span)) {
+                                         (lvalue, span): (&Lvalue, Span),
+                                         borrow : &BorrowData) {
         let mut err = self.tcx.cannot_use_when_mutably_borrowed(
             span, &self.describe_lvalue(lvalue), Origin::Mir);
         // FIXME 1: add span_label for "borrow of `()` occurs here"

From e84581192d2629be07d622736ecbe6ce95f3ece0 Mon Sep 17 00:00:00 2001
From: Basile Desloges <basile.desloges@gmail.com>
Date: Thu, 21 Sep 2017 16:31:34 +0200
Subject: [PATCH 3/4] mir-borrowck: Add span labels to
 `report_use_while_mutably_borrowed()`

---
 src/librustc_mir/borrow_check.rs | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/librustc_mir/borrow_check.rs b/src/librustc_mir/borrow_check.rs
index 6ec01faf00025..f718038bb0714 100644
--- a/src/librustc_mir/borrow_check.rs
+++ b/src/librustc_mir/borrow_check.rs
@@ -916,10 +916,15 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
                                          _context: Context,
                                          (lvalue, span): (&Lvalue, Span),
                                          borrow : &BorrowData) {
+        let described_lvalue = self.describe_lvalue(lvalue);
+        let borrow_span = self.retrieve_borrow_span(borrow);
+
         let mut err = self.tcx.cannot_use_when_mutably_borrowed(
-            span, &self.describe_lvalue(lvalue), Origin::Mir);
-        // FIXME 1: add span_label for "borrow of `()` occurs here"
-        // FIXME 2: add span_label for "use of `{}` occurs here"
+            span, &described_lvalue, Origin::Mir);
+
+        err.span_label(borrow_span, format!("borrow of `{}` occurs here", described_lvalue));
+        err.span_label(span, format!("use of borrowed `{}`", described_lvalue));
+
         err.emit();
     }
 

From 8c1b958cf7ee4143deaf963249f6bbfd2446121e Mon Sep 17 00:00:00 2001
From: Basile Desloges <basile.desloges@gmail.com>
Date: Thu, 21 Sep 2017 16:33:41 +0200
Subject: [PATCH 4/4] mir-borrowck: Add FIXME comment to report name of field
 instead of index at a later date

---
 src/librustc_mir/borrow_check.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/librustc_mir/borrow_check.rs b/src/librustc_mir/borrow_check.rs
index f718038bb0714..5133e528b099a 100644
--- a/src/librustc_mir/borrow_check.rs
+++ b/src/librustc_mir/borrow_check.rs
@@ -1004,7 +1004,7 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
                     ProjectionElem::Downcast(..) =>
                         ("",   format!(""), None), // (dont emit downcast info)
                     ProjectionElem::Field(field, _ty) =>
-                        ("",   format!(".{}", field.index()), None),
+                        ("",   format!(".{}", field.index()), None), // FIXME: report name of field
                     ProjectionElem::Index(index) =>
                         ("",   format!(""), Some(index)),
                     ProjectionElem::ConstantIndex { offset, min_length, from_end: true } =>