auto merge of #5966 : alexcrichton/rust/issue-3083, r=graydon

Closes #3083.

This takes a similar approach to #5797 where a set is present on the `tcx` of used mutable definitions. Everything is by default warned about, and analyses must explicitly add mutable definitions to this set so they're not warned about.

Most of this was pretty straightforward, although there was one caveat that I ran into when implementing it. Apparently when the old modes are used (or maybe `legacy_modes`, I'm not sure) some different code paths are taken to cause spurious warnings to be issued which shouldn't be issued. I'm not really sure how modes even worked, so I was having a lot of trouble tracking this down. I figured that because they're a legacy thing that I'd just de-mode the compiler so that the warnings wouldn't be a problem anymore (or at least for the compiler).

Other than that, the entire compiler compiles without warnings of unused mutable variables. To prevent bad warnings, #5965 should be landed (which in turn is waiting on #5963) before landing this. I figured I'd stick it out for review anyway though.

9 files changed, 20 insertions, 22 deletions

diff --git a/src/libstd/bitv.rs b/src/libstd/bitv.rs
index d89ce4232b1..d1f6bf982a7 100644
--- a/src/libstd/bitv.rs
+++ b/src/libstd/bitv.rs
@@ -891,7 +891,7 @@ mod tests {
     #[test]
     fn test_0_elements() {
         let mut act;
-        let mut exp;
+        let exp;
         act = Bitv::new(0u, false);
         exp = vec::from_elem::<uint>(0u, 0u);
         assert!(act.eq_vec(exp));
diff --git a/src/libstd/deque.rs b/src/libstd/deque.rs
index a88d13fda66..b120e40ec25 100644
--- a/src/libstd/deque.rs
+++ b/src/libstd/deque.rs
@@ -113,7 +113,7 @@ pub impl<T> Deque<T> {
     ///
     /// Fails if the deque is empty
     fn pop_front(&mut self) -> T {
-        let mut result = self.elts[self.lo].swap_unwrap();
+        let result = self.elts[self.lo].swap_unwrap();
         self.lo = (self.lo + 1u) % self.elts.len();
         self.nelts -= 1u;
         result
@@ -126,7 +126,7 @@ pub impl<T> Deque<T> {
         if self.hi == 0u {
             self.hi = self.elts.len() - 1u;
         } else { self.hi -= 1u; }
-        let mut result = self.elts[self.hi].swap_unwrap();
+        let result = self.elts[self.hi].swap_unwrap();
         self.elts[self.hi] = None;
         self.nelts -= 1u;
         result
@@ -204,7 +204,7 @@ pub impl<T> Deque<T> {
     ///
     /// Fails if the deque is empty
     fn pop_front(&mut self) -> T {
-        let mut result = self.elts[self.lo].swap_unwrap();
+        let result = self.elts[self.lo].swap_unwrap();
         self.lo = (self.lo + 1u) % self.elts.len();
         self.nelts -= 1u;
         result
@@ -217,7 +217,7 @@ pub impl<T> Deque<T> {
         if self.hi == 0u {
             self.hi = self.elts.len() - 1u;
         } else { self.hi -= 1u; }
-        let mut result = self.elts[self.hi].swap_unwrap();
+        let result = self.elts[self.hi].swap_unwrap();
         self.elts[self.hi] = None;
         self.nelts -= 1u;
         result
diff --git a/src/libstd/dlist.rs b/src/libstd/dlist.rs
index f9de2e0f58a..e736273a5ee 100644
--- a/src/libstd/dlist.rs
+++ b/src/libstd/dlist.rs
@@ -220,7 +220,7 @@ pub impl<T> DList<T> {
      * node. O(1).
      */
     fn push_head_n(@mut self, data: T) -> @mut DListNode<T> {
-        let mut nobe = DList::new_link(data);
+        let nobe = DList::new_link(data);
         self.add_head(nobe);
         nobe.get()
     }
@@ -233,7 +233,7 @@ pub impl<T> DList<T> {
      * node. O(1).
      */
     fn push_n(@mut self, data: T) -> @mut DListNode<T> {
-        let mut nobe = DList::new_link(data);
+        let nobe = DList::new_link(data);
         self.add_tail(nobe);
         nobe.get()
     }
@@ -263,7 +263,7 @@ pub impl<T> DList<T> {
         data: T,
         neighbour: @mut DListNode<T>
     ) -> @mut DListNode<T> {
-        let mut nobe = DList::new_link(data);
+        let nobe = DList::new_link(data);
         self.insert_left(nobe, neighbour);
         nobe.get()
     }
@@ -293,7 +293,7 @@ pub impl<T> DList<T> {
         data: T,
         neighbour: @mut DListNode<T>
     ) -> @mut DListNode<T> {
-        let mut nobe = DList::new_link(data);
+        let nobe = DList::new_link(data);
         self.insert_right(neighbour, nobe);
         nobe.get()
     }
diff --git a/src/libstd/num/rational.rs b/src/libstd/num/rational.rs
index ee6879e31d9..36652380bff 100644
--- a/src/libstd/num/rational.rs
+++ b/src/libstd/num/rational.rs
@@ -60,7 +60,7 @@ impl<T: Copy + Num + Ord>
 
     /// Put self into lowest terms, with denom > 0.
     fn reduce(&mut self) {
-        let mut g : T = gcd(self.numer, self.denom);
+        let g : T = gcd(self.numer, self.denom);
 
         self.numer /= g;
         self.denom /= g;
@@ -505,4 +505,4 @@ mod test {
             test(s);
         }
     }
-}
\ No newline at end of file
+}
diff --git a/src/libstd/rope.rs b/src/libstd/rope.rs
index 48ecc0fc851..33bc393e470 100644
--- a/src/libstd/rope.rs
+++ b/src/libstd/rope.rs
@@ -838,8 +838,7 @@ pub mod node {
                   option::None => break,
                   option::Some(x) => {
                     //FIXME (#2744): Replace with memcpy or something similar
-                    let mut local_buf: ~[u8] =
-                        cast::transmute(*x.content);
+                    let local_buf: ~[u8] = cast::transmute(*x.content);
                     let mut i = x.byte_offset;
                     while i < x.byte_len {
                         buf[offset] = local_buf[i];
@@ -1156,7 +1155,7 @@ pub mod node {
         }
 
         pub fn empty() -> T {
-            let mut stack : ~[@Node] = ~[];
+            let stack : ~[@Node] = ~[];
             T { stack: stack, stackpos: -1 }
         }
 
diff --git a/src/libstd/sha1.rs b/src/libstd/sha1.rs
index 6aa4d1c54bc..7371250b38a 100644
--- a/src/libstd/sha1.rs
+++ b/src/libstd/sha1.rs
@@ -93,7 +93,7 @@ pub fn sha1() -> @Sha1 {
         assert!((vec::len(st.h) == digest_buf_len));
         assert!((vec::uniq_len(st.work_buf) == work_buf_len));
         let mut t: int; // Loop counter
-        let mut w = st.work_buf;
+        let w = st.work_buf;
 
         // Initialize the first 16 words of the vector w
         t = 0;
@@ -260,7 +260,7 @@ pub fn sha1() -> @Sha1 {
             return s;
         }
     }
-    let mut st = Sha1State {
+    let st = Sha1State {
          h: vec::from_elem(digest_buf_len, 0u32),
          len_low: 0u32,
          len_high: 0u32,
diff --git a/src/libstd/sort.rs b/src/libstd/sort.rs
index 72a888fcc91..febaea637ef 100644
--- a/src/libstd/sort.rs
+++ b/src/libstd/sort.rs
@@ -239,7 +239,7 @@ fn binarysort<T:Copy + Ord>(array: &mut [T], start: uint) {
             }
         }
         assert!(left == right);
-        let mut n = start-left;
+        let n = start-left;
 
         copy_vec(array, left+1, array, left, n);
         array[left] = pivot;
@@ -416,7 +416,7 @@ impl<T:Copy + Ord> MergeState<T> {
     }
 
     fn merge_at(&mut self, n: uint, array: &mut [T]) {
-        let mut size = self.runs.len();
+        let size = self.runs.len();
         assert!(size >= 2);
         assert!(n == size-2 || n == size-3);
 
diff --git a/src/libstd/test.rs b/src/libstd/test.rs
index 4ccbf207170..addc1da6394 100644
--- a/src/libstd/test.rs
+++ b/src/libstd/test.rs
@@ -427,8 +427,7 @@ fn run_tests(opts: &TestOpts,
     let filtered_descs = filtered_tests.map(|t| t.desc);
     callback(TeFiltered(filtered_descs));
 
-    let mut (filtered_tests,
-             filtered_benchs) =
+    let (filtered_tests, filtered_benchs) =
         do vec::partition(filtered_tests) |e| {
         match e.testfn {
             StaticTestFn(_) | DynTestFn(_) => true,
diff --git a/src/libstd/time.rs b/src/libstd/time.rs
index 70dc4d8cfeb..a763aa1592e 100644
--- a/src/libstd/time.rs
+++ b/src/libstd/time.rs
@@ -147,7 +147,7 @@ pub fn empty_tm() -> Tm {
 /// Returns the specified time in UTC
 pub fn at_utc(clock: Timespec) -> Tm {
     unsafe {
-        let mut Timespec { sec, nsec } = clock;
+        let Timespec { sec, nsec } = clock;
         let mut tm = empty_tm();
         rustrt::rust_gmtime(sec, nsec, &mut tm);
         tm
@@ -162,7 +162,7 @@ pub fn now_utc() -> Tm {
 /// Returns the specified time in the local timezone
 pub fn at(clock: Timespec) -> Tm {
     unsafe {
-        let mut Timespec { sec, nsec } = clock;
+        let Timespec { sec, nsec } = clock;
         let mut tm = empty_tm();
         rustrt::rust_localtime(sec, nsec, &mut tm);
         tm