Fix all violations of stronger guarantees for mutable borrows

Fix all violations in the Rust source tree of the stronger guarantee
of a unique access path for mutable borrows as described in #12624.

Author: Cameron Zwarich

src/libarena/lib.rs

@@ -406,7 +406,8 @@ impl<T> TypedArenaChunk<T> {
             None => {}
             Some(mut next) => {
                 // We assume that the next chunk is completely filled.
-                next.destroy(next.capacity)
+                let capacity = next.capacity;
+                next.destroy(capacity)
             }
         }
     }

src/libcollections/ringbuf.rs

@@ -66,7 +66,8 @@ impl<T> Deque<T> for RingBuf<T> {
 
     /// Return a mutable reference to the last element in the RingBuf
     fn back_mut<'a>(&'a mut self) -> Option<&'a mut T> {
-        if self.nelts > 0 { Some(self.get_mut(self.nelts - 1)) } else { None }
+        let nelts = self.nelts;
+        if nelts > 0 { Some(self.get_mut(nelts - 1)) } else { None }
     }
 
     /// Remove and return the first element in the RingBuf, or None if it is empty

src/libcollections/vec.rs

@@ -114,7 +114,8 @@ impl<T> Vec<T> {
         unsafe {
             let mut xs = Vec::with_capacity(length);
             while xs.len < length {
-                ptr::write(xs.as_mut_slice().unsafe_mut_ref(xs.len), op(xs.len));
+                let len = xs.len;
+                ptr::write(xs.as_mut_slice().unsafe_mut_ref(len), op(len));
                 xs.len += 1;
             }
             xs
@@ -210,7 +211,8 @@ impl<T: Clone> Vec<T> {
         unsafe {
             let mut xs = Vec::with_capacity(length);
             while xs.len < length {
-                ptr::write(xs.as_mut_slice().unsafe_mut_ref(xs.len),
+                let len = xs.len;
+                ptr::write(xs.as_mut_slice().unsafe_mut_ref(len),
                            value.clone());
                 xs.len += 1;
             }
@@ -321,9 +323,10 @@ impl<T:Clone> Clone for Vec<T> {
             let this_slice = self.as_slice();
             while vector.len < len {
                 unsafe {
+                    let len = vector.len;
                     ptr::write(
-                        vector.as_mut_slice().unsafe_mut_ref(vector.len),
-                        this_slice.unsafe_ref(vector.len).clone());
+                        vector.as_mut_slice().unsafe_mut_ref(len),
+                        this_slice.unsafe_ref(len).clone());
                 }
                 vector.len += 1;
             }

src/libdebug/repr.rs

@@ -127,13 +127,15 @@ impl<'a> ReprVisitor<'a> {
     #[inline]
     pub fn get<T>(&mut self, f: |&mut ReprVisitor, &T| -> bool) -> bool {
         unsafe {
-            f(self, mem::transmute::<*u8,&T>(self.ptr))
+            let ptr = self.ptr;
+            f(self, mem::transmute::<*u8,&T>(ptr))
         }
     }
 
     #[inline]
     pub fn visit_inner(&mut self, inner: *TyDesc) -> bool {
-        self.visit_ptr_inner(self.ptr, inner)
+        let ptr = self.ptr;
+        self.visit_ptr_inner(ptr, inner)
     }
 
     #[inline]

src/libnative/io/net.rs

@@ -637,16 +637,15 @@ impl rtio::RtioUdpSocket for UdpSocket {
                 mem::size_of::<libc::sockaddr_storage>() as libc::socklen_t;
 
         let dolock = || self.lock_nonblocking();
-        let doread = |nb| unsafe {
+        let n = try!(read(fd, self.read_deadline, dolock, |nb| unsafe {
             let flags = if nb {c::MSG_DONTWAIT} else {0};
             libc::recvfrom(fd,
                            buf.as_mut_ptr() as *mut libc::c_void,
                            buf.len() as msglen_t,
                            flags,
                            storagep,
                            &mut addrlen) as libc::c_int
-        };
-        let n = try!(read(fd, self.read_deadline, dolock, doread));
+        }));
         sockaddr_to_addr(&storage, addrlen as uint).and_then(|addr| {
             Ok((n as uint, addr))
         })

src/libregex/parse/mod.rs

@@ -345,18 +345,19 @@ impl<'a> Parser<'a> {
     }
 
     fn push_literal(&mut self, c: char) -> Result<(), Error> {
+        let flags = self.flags;
         match c {
             '.' => {
-                self.push(Dot(self.flags))
+                self.push(Dot(flags))
             }
             '^' => {
-                self.push(Begin(self.flags))
+                self.push(Begin(flags))
             }
             '$' => {
-                self.push(End(self.flags))
+                self.push(End(flags))
             }
             _ => {
-                self.push(Literal(c, self.flags))
+                self.push(Literal(c, flags))
             }
         }
         Ok(())

src/librustc/middle/dataflow.rs

@@ -300,12 +300,13 @@ impl<'a, O:DataFlowOperator+Clone+'static> DataFlowContext<'a, O> {
         }
 
         {
+            let words_per_id = self.words_per_id;
             let mut propcx = PropagationContext {
                 dfcx: &mut *self,
                 changed: true
             };
 
-            let mut temp = Vec::from_elem(self.words_per_id, 0u);
+            let mut temp = Vec::from_elem(words_per_id, 0u);
             let mut loop_scopes = Vec::new();
 
             while propcx.changed {

src/librustc/middle/liveness.rs

@@ -547,11 +547,13 @@ struct Liveness<'a> {
 
 impl<'a> Liveness<'a> {
     fn new(ir: &'a mut IrMaps<'a>, specials: Specials) -> Liveness<'a> {
+        let num_live_nodes = ir.num_live_nodes;
+        let num_vars = ir.num_vars;
         Liveness {
             ir: ir,
             s: specials,
-            successors: Vec::from_elem(ir.num_live_nodes, invalid_node()),
-            users: Vec::from_elem(ir.num_live_nodes * ir.num_vars, invalid_users()),
+            successors: Vec::from_elem(num_live_nodes, invalid_node()),
+            users: Vec::from_elem(num_live_nodes * num_vars, invalid_users()),
             loop_scope: Vec::new(),
             break_ln: NodeMap::new(),
             cont_ln: NodeMap::new(),
@@ -826,8 +828,9 @@ impl<'a> Liveness<'a> {
 
         debug!("compute: using id for block, {}", block_to_str(body));
 
+        let exit_ln = self.s.exit_ln;
         let entry_ln: LiveNode =
-            self.with_loop_nodes(body.id, self.s.exit_ln, self.s.exit_ln,
+            self.with_loop_nodes(body.id, exit_ln, exit_ln,
               |this| this.propagate_through_fn_block(decl, body));
 
         // hack to skip the loop unless debug! is enabled:
@@ -847,12 +850,13 @@ impl<'a> Liveness<'a> {
                                   -> LiveNode {
         // the fallthrough exit is only for those cases where we do not
         // explicitly return:
-        self.init_from_succ(self.s.fallthrough_ln, self.s.exit_ln);
+        let s = self.s;
+        self.init_from_succ(s.fallthrough_ln, s.exit_ln);
         if blk.expr.is_none() {
-            self.acc(self.s.fallthrough_ln, self.s.no_ret_var, ACC_READ)
+            self.acc(s.fallthrough_ln, s.no_ret_var, ACC_READ)
         }
 
-        self.propagate_through_block(blk, self.s.fallthrough_ln)
+        self.propagate_through_block(blk, s.fallthrough_ln)
     }
 
     fn propagate_through_block(&mut self, blk: &Block, succ: LiveNode)
@@ -1036,7 +1040,8 @@ impl<'a> Liveness<'a> {
 
           ExprRet(o_e) => {
             // ignore succ and subst exit_ln:
-            self.propagate_through_opt_expr(o_e, self.s.exit_ln)
+            let exit_ln = self.s.exit_ln;
+            self.propagate_through_opt_expr(o_e, exit_ln)
           }
 
           ExprBreak(opt_label) => {

src/librustc/middle/privacy.rs

@@ -1019,9 +1019,10 @@ impl<'a> Visitor<()> for SanePrivacyVisitor<'a> {
             self.check_sane_privacy(item);
         }
 
+        let in_fn = self.in_fn;
         let orig_in_fn = replace(&mut self.in_fn, match item.node {
             ast::ItemMod(..) => false, // modules turn privacy back on
-            _ => self.in_fn,           // otherwise we inherit
+            _ => in_fn,           // otherwise we inherit
         });
         visit::walk_item(self, item, ());
         self.in_fn = orig_in_fn;

src/libsyntax/ext/format.rs

@@ -202,7 +202,8 @@ impl<'a, 'b> Context<'a, 'b> {
             }
             parse::CountIsNextParam => {
                 if self.check_positional_ok() {
-                    self.verify_arg_type(Exact(self.next_arg), Unsigned);
+                    let next_arg = self.next_arg;
+                    self.verify_arg_type(Exact(next_arg), Unsigned);
                     self.next_arg += 1;
                 }
             }

src/libsyntax/parse/attr.rs

@@ -73,7 +73,8 @@ impl<'a> ParserAttr for Parser<'a> {
 
                 let style = if self.eat(&token::NOT) {
                     if !permit_inner {
-                        self.span_err(self.span,
+                        let span = self.span;
+                        self.span_err(span,
                                       "an inner attribute is not permitted in \
                                        this context");
                     }