From 8fc15b5ac4475a4f29277eef3250e78b66e5f222 Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Fri, 14 Aug 2015 14:35:17 -0400
Subject: [PATCH] Update tendril to avoid double borrow. This double borrow is
 detected by the latest Nightly builds.

---
 src/fmt.rs     |  2 +-
 src/tendril.rs | 36 ++++++++++++++++++++++++++++--------
 2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/src/fmt.rs b/src/fmt.rs
index b9c5881..feb49f5 100644
--- a/src/fmt.rs
+++ b/src/fmt.rs
@@ -156,7 +156,7 @@ pub unsafe trait SubsetOf<Super>: Format
 
 /// Indicates a format which corresponds to a Rust slice type,
 /// representing exactly the same invariants.
-pub unsafe trait SliceFormat: Format {
+pub unsafe trait SliceFormat: Format + Sized {
     type Slice: ?Sized + Slice<Format = Self>;
 }
 
diff --git a/src/tendril.rs b/src/tendril.rs
index 7cb7ce1..b007f36 100644
--- a/src/tendril.rs
+++ b/src/tendril.rs
@@ -1178,15 +1178,35 @@ impl<F, A> Tendril<F, A>
     #[inline]
     pub fn pop_front_char<'a>(&'a mut self) -> Option<char> {
         unsafe {
-            let mut it = F::char_indices(self.as_byte_slice());
-            it.next().map(|(_, c)| {
-                if let Some((n, _)) = it.next() {
-                    self.unsafe_pop_front(n as u32);
-                } else {
-                    self.clear();
+            let next_char; // first char in iterator
+            let mut skip = 0;  // number of bytes to skip, or 0 to clear
+
+            { // <--+
+                //  |  Creating an iterator borrows self, so introduce a
+                //  +- scope to contain the borrow (that way we can mutate
+                //     self below, after this scope exits).
+
+                let mut iter = F::char_indices(self.as_byte_slice());
+                match iter.next() {
+                    Some((_, c)) => {
+                        next_char = Some(c);
+                        if let Some((n, _)) = iter.next() {
+                            skip = n as u32;
+                        }
+                    }
+                    None => {
+                        next_char = None;
+                    }
                 }
-                c
-            })
+            }
+
+            if skip != 0 {
+                self.unsafe_pop_front(skip);
+            } else {
+                self.clear();
+            }
+
+            next_char
         }
     }