make mut a keyword synonymous with mutable

first step towards issue #1273

29 files changed, 224 insertions, 206 deletions

diff --git a/src/comp/driver/driver.rs b/src/comp/driver/driver.rs
index 62cffd97099..53ba8c65bdf 100644
--- a/src/comp/driver/driver.rs
+++ b/src/comp/driver/driver.rs
@@ -159,7 +159,7 @@ fn compile_upto(sess: session, cfg: ast::crate_cfg,
          bind middle::tstate::ck::check_crate(ty_cx, crate));
     let mut_map =
         time(time_passes, "mutability checking",
-             bind middle::mut::check_crate(ty_cx, crate));
+             bind middle::mutbl::check_crate(ty_cx, crate));
     let (copy_map, ref_map) =
         time(time_passes, "alias checking",
              bind middle::alias::check_crate(ty_cx, crate));
diff --git a/src/comp/front/test.rs b/src/comp/front/test.rs
index 68119c93584..47cd3328755 100644
--- a/src/comp/front/test.rs
+++ b/src/comp/front/test.rs
@@ -256,7 +256,7 @@ fn mk_test_desc_vec_ty(cx: test_ctxt) -> @ast::ty {
     let test_desc_ty: ast::ty =
         nospan(ast::ty_path(test_desc_ty_path, cx.sess.next_node_id()));
 
-    let vec_mt: ast::mt = {ty: @test_desc_ty, mut: ast::imm};
+    let vec_mt: ast::mt = {ty: @test_desc_ty, mutbl: ast::m_imm};
 
     ret @nospan(ast::ty_vec(vec_mt));
 }
@@ -270,7 +270,7 @@ fn mk_test_desc_vec(cx: test_ctxt) -> @ast::expr {
     }
 
     ret @{id: cx.sess.next_node_id(),
-          node: ast::expr_vec(descs, ast::imm),
+          node: ast::expr_vec(descs, ast::m_imm),
           span: dummy_sp()};
 }
 
@@ -288,7 +288,7 @@ fn mk_test_desc_rec(cx: test_ctxt, test: test) -> @ast::expr {
          span: span};
 
     let name_field: ast::field =
-        nospan({mut: ast::imm, ident: "name", expr: @name_expr});
+        nospan({mutbl: ast::m_imm, ident: "name", expr: @name_expr});
 
     let fn_path = @nospan({global: false, idents: path, types: []});
 
@@ -300,7 +300,7 @@ fn mk_test_desc_rec(cx: test_ctxt, test: test) -> @ast::expr {
     let fn_wrapper_expr = mk_test_wrapper(cx, fn_expr, span);
 
     let fn_field: ast::field =
-        nospan({mut: ast::imm, ident: "fn", expr: fn_wrapper_expr});
+        nospan({mutbl: ast::m_imm, ident: "fn", expr: fn_wrapper_expr});
 
     let ignore_lit: ast::lit = nospan(ast::lit_bool(test.ignore));
 
@@ -310,7 +310,7 @@ fn mk_test_desc_rec(cx: test_ctxt, test: test) -> @ast::expr {
          span: span};
 
     let ignore_field: ast::field =
-        nospan({mut: ast::imm, ident: "ignore", expr: @ignore_expr});
+        nospan({mutbl: ast::m_imm, ident: "ignore", expr: @ignore_expr});
 
     let fail_lit: ast::lit = nospan(ast::lit_bool(test.should_fail));
 
@@ -320,7 +320,7 @@ fn mk_test_desc_rec(cx: test_ctxt, test: test) -> @ast::expr {
          span: span};
 
     let fail_field: ast::field =
-        nospan({mut: ast::imm, ident: "should_fail", expr: @fail_expr});
+        nospan({mutbl: ast::m_imm, ident: "should_fail", expr: @fail_expr});
 
     let desc_rec_: ast::expr_ =
         ast::expr_rec([name_field, fn_field, ignore_field, fail_field],
@@ -378,7 +378,7 @@ fn mk_test_wrapper(cx: test_ctxt,
 fn mk_main(cx: test_ctxt) -> @ast::item {
     let str_pt = @nospan({global: false, idents: ["str"], types: []});
     let str_ty = @nospan(ast::ty_path(str_pt, cx.sess.next_node_id()));
-    let args_mt: ast::mt = {ty: str_ty, mut: ast::imm};
+    let args_mt: ast::mt = {ty: str_ty, mutbl: ast::m_imm};
     let args_ty: ast::ty = nospan(ast::ty_vec(args_mt));
 
     let args_arg: ast::arg =
diff --git a/src/comp/metadata/astencode.rs b/src/comp/metadata/astencode.rs
index 167536907ec..71a95506a9d 100644
--- a/src/comp/metadata/astencode.rs
+++ b/src/comp/metadata/astencode.rs
@@ -483,28 +483,28 @@ impl ast_output for ast_ctxt {
                 self.tag(at_ty_bot) {||}
               }
 
-              ty_box({ty: ty, mut: m}) {
+              ty_box({ty: ty, mutbl: m}) {
                 self.tag(at_ty_box) {||
                     self.ty(ty);
                     self.mutbl(m);
                 }
               }
 
-              ty_uniq({ty: ty, mut: m}) {
+              ty_uniq({ty: ty, mutbl: m}) {
                 self.tag(at_ty_uniq) {||
                     self.ty(ty);
                     self.mutbl(m);
                 }
               }
 
-              ty_vec({ty: ty, mut: m}) {
+              ty_vec({ty: ty, mutbl: m}) {
                 self.tag(at_ty_vec) {||
                     self.ty(ty);
                     self.mutbl(m);
                 }
               }
 
-              ty_ptr({ty: ty, mut: m}) {
+              ty_ptr({ty: ty, mutbl: m}) {
                 self.tag(at_ty_ptr) {||
                     self.ty(ty);
                     self.mutbl(m);
diff --git a/src/comp/metadata/tydecode.rs b/src/comp/metadata/tydecode.rs
index c7d434b3c1c..9bd7ee75512 100644
--- a/src/comp/metadata/tydecode.rs
+++ b/src/comp/metadata/tydecode.rs
@@ -311,11 +311,11 @@ fn parse_ty(st: @pstate, conv: conv_did) -> ty::t {
 fn parse_mt(st: @pstate, conv: conv_did) -> ty::mt {
     let m;
     alt peek(st) {
-      'm' { next(st); m = ast::mut; }
-      '?' { next(st); m = ast::maybe_mut; }
-      _ { m = ast::imm; }
+      'm' { next(st); m = ast::m_mutbl; }
+      '?' { next(st); m = ast::m_const; }
+      _ { m = ast::m_imm; }
     }
-    ret {ty: parse_ty(st, conv), mut: m};
+    ret {ty: parse_ty(st, conv), mutbl: m};
 }
 
 fn parse_def(st: @pstate, conv: conv_did) -> ast::def_id {
@@ -356,7 +356,7 @@ fn parse_ty_fn(st: @pstate, conv: conv_did) -> ty::fn_ty {
     let inputs: [ty::arg] = [];
     while peek(st) != ']' {
         let mode = alt check peek(st) {
-          '&' { ast::by_mut_ref }
+          '&' { ast::by_mutbl_ref }
           '-' { ast::by_move }
           '+' { ast::by_copy }
           '=' { ast::by_ref }
diff --git a/src/comp/metadata/tyencode.rs b/src/comp/metadata/tyencode.rs
index e69b3888b6c..e1e0cd7d68b 100644
--- a/src/comp/metadata/tyencode.rs
+++ b/src/comp/metadata/tyencode.rs
@@ -85,10 +85,10 @@ fn enc_ty(w: io::writer, cx: @ctxt, t: ty::t) {
     }
 }
 fn enc_mt(w: io::writer, cx: @ctxt, mt: ty::mt) {
-    alt mt.mut {
-      imm { }
-      mut { w.write_char('m'); }
-      maybe_mut { w.write_char('?'); }
+    alt mt.mutbl {
+      m_imm { }
+      m_mutbl { w.write_char('m'); }
+      m_const { w.write_char('?'); }
     }
     enc_ty(w, cx, mt.ty);
 }
@@ -215,7 +215,7 @@ fn enc_ty_fn(w: io::writer, cx: @ctxt, ft: ty::fn_ty) {
     w.write_char('[');
     for arg: ty::arg in ft.inputs {
         alt ty::resolved_mode(cx.tcx, arg.mode) {
-          by_mut_ref { w.write_char('&'); }
+          by_mutbl_ref { w.write_char('&'); }
           by_move { w.write_char('-'); }
           by_copy { w.write_char('+'); }
           by_ref { w.write_char('='); }
diff --git a/src/comp/middle/alias.rs b/src/comp/middle/alias.rs
index 2ae8de9abcc..34caf927662 100644
--- a/src/comp/middle/alias.rs
+++ b/src/comp/middle/alias.rs
@@ -22,7 +22,7 @@ type invalid = {reason: invalid_reason,
                 node_id: node_id,
                 sp: span, path: @ast::path};
 
-enum unsafe_ty { contains(ty::t), mut_contains(ty::t), }
+enum unsafe_ty { contains(ty::t), mutbl_contains(ty::t), }
 
 type binding = @{node_id: node_id,
                  span: span,
@@ -183,9 +183,9 @@ fn add_bindings_for_let(cx: ctx, &bs: [binding], loc: @ast::local) {
             err(cx, loc.span, "a reference binding can't be \
                                rooted in a temporary");
         }
-        for proot in pattern_roots(cx.tcx, root.mut, loc.node.pat) {
+        for proot in pattern_roots(cx.tcx, root.mutbl, loc.node.pat) {
             let bnd = mk_binding(cx, proot.id, proot.span, root_var,
-                                 unsafe_set(proot.mut));
+                                 unsafe_set(proot.mutbl));
             // Don't implicitly copy explicit references
             bnd.copied = not_allowed;
             bs += [bnd];
@@ -228,7 +228,7 @@ fn check_call(cx: ctx, sc: scope, f: @ast::expr, args: [@ast::expr])
         let arg = args[i];
         let root = expr_root(cx, arg, false);
         alt ty::resolved_mode(cx.tcx, arg_t.mode) {
-          ast::by_mut_ref {
+          ast::by_mutbl_ref {
             alt path_def(cx, arg) {
               some(def) {
                 let dnum = ast_util::def_id_of_def(def).node;
@@ -242,14 +242,14 @@ fn check_call(cx: ctx, sc: scope, f: @ast::expr, args: [@ast::expr])
         let root_var = path_def_id(cx, root.ex);
         let arg_copied = alt ty::resolved_mode(cx.tcx, arg_t.mode) {
           ast::by_move | ast::by_copy { copied }
-          ast::by_mut_ref { not_allowed }
+          ast::by_mutbl_ref { not_allowed }
           ast::by_ref | ast::by_val { not_copied }
         };
         bindings += [@{node_id: arg.id,
                        span: arg.span,
                        root_var: root_var,
                        local_id: 0u,
-                       unsafe_tys: unsafe_set(root.mut),
+                       unsafe_tys: unsafe_set(root.mutbl),
                        mutable copied: arg_copied}];
         i += 1u;
     }
@@ -285,7 +285,7 @@ fn check_call(cx: ctx, sc: scope, f: @ast::expr, args: [@ast::expr])
             let i = 0u;
             for arg_t: ty::arg in arg_ts {
                 let mut_alias =
-                    (ast::by_mut_ref == ty::arg_mode(cx.tcx, arg_t));
+                    (ast::by_mutbl_ref == ty::arg_mode(cx.tcx, arg_t));
                 if i != j &&
                        ty_can_unsafely_include(cx, unsafe_ty, arg_t.ty,
                                                mut_alias) &&
@@ -339,14 +339,14 @@ fn check_alt(cx: ctx, input: @ast::expr, arms: [ast::arm], sc: scope,
             span: span};
         let binding_info: [info] = [];
         for pat in a.pats {
-            for proot in pattern_roots(cx.tcx, root.mut, pat) {
+            for proot in pattern_roots(cx.tcx, root.mutbl, pat) {
                 let canon_id = pat_id_map.get(proot.name);
                 alt vec::find(binding_info, {|x| x.id == canon_id}) {
-                  some(s) { s.unsafe_tys += unsafe_set(proot.mut); }
+                  some(s) { s.unsafe_tys += unsafe_set(proot.mutbl); }
                   none {
                       binding_info += [
                           {id: canon_id,
-                           mutable unsafe_tys: unsafe_set(proot.mut),
+                           mutable unsafe_tys: unsafe_set(proot.mutbl),
                            span: proot.span}];
                   }
                 }
@@ -369,20 +369,20 @@ fn check_for(cx: ctx, local: @ast::local, seq: @ast::expr, blk: ast::blk,
 
     // If this is a mutable vector, don't allow it to be touched.
     let seq_t = ty::expr_ty(cx.tcx, seq);
-    let cur_mut = root.mut;
+    let cur_mutbl = root.mutbl;
     alt ty::get(seq_t).struct {
       ty::ty_vec(mt) {
-        if mt.mut != ast::imm {
-            cur_mut = some(contains(seq_t));
+        if mt.mutbl != ast::m_imm {
+            cur_mutbl = some(contains(seq_t));
         }
       }
       _ {}
     }
     let root_var = path_def_id(cx, root.ex);
     let new_bs = sc.bs;
-    for proot in pattern_roots(cx.tcx, cur_mut, local.node.pat) {
+    for proot in pattern_roots(cx.tcx, cur_mutbl, local.node.pat) {
         new_bs += [mk_binding(cx, proot.id, proot.span, root_var,
-                              unsafe_set(proot.mut))];
+                              unsafe_set(proot.mutbl))];
     }
     visit::visit_block(blk, {bs: new_bs with sc}, v);
 }
@@ -493,36 +493,36 @@ fn path_def_id(cx: ctx, ex: @ast::expr) -> option<ast::node_id> {
 }
 
 fn ty_can_unsafely_include(cx: ctx, needle: unsafe_ty, haystack: ty::t,
-                           mut: bool) -> bool {
-    fn get_mut(cur: bool, mt: ty::mt) -> bool {
-        ret cur || mt.mut != ast::imm;
+                           mutbl: bool) -> bool {
+    fn get_mutbl(cur: bool, mt: ty::mt) -> bool {
+        ret cur || mt.mutbl != ast::m_imm;
     }
-    fn helper(tcx: ty::ctxt, needle: unsafe_ty, haystack: ty::t, mut: bool)
+    fn helper(tcx: ty::ctxt, needle: unsafe_ty, haystack: ty::t, mutbl: bool)
         -> bool {
         if alt needle {
           contains(ty) { ty == haystack }
-          mut_contains(ty) { mut && ty == haystack }
+          mutbl_contains(ty) { mutbl && ty == haystack }
         } { ret true; }
         alt ty::get(haystack).struct {
           ty::ty_enum(_, ts) {
             for t: ty::t in ts {
-                if helper(tcx, needle, t, mut) { ret true; }
+                if helper(tcx, needle, t, mutbl) { ret true; }
             }
             ret false;
           }
           ty::ty_box(mt) | ty::ty_ptr(mt) | ty::ty_uniq(mt) {
-            ret helper(tcx, needle, mt.ty, get_mut(mut, mt));
+            ret helper(tcx, needle, mt.ty, get_mutbl(mutbl, mt));
           }
           ty::ty_rec(fields) {
             for f: ty::field in fields {
-                if helper(tcx, needle, f.mt.ty, get_mut(mut, f.mt)) {
+                if helper(tcx, needle, f.mt.ty, get_mutbl(mutbl, f.mt)) {
                     ret true;
                 }
             }
             ret false;
           }
           ty::ty_tup(ts) {
-            for t in ts { if helper(tcx, needle, t, mut) { ret true; } }
+            for t in ts { if helper(tcx, needle, t, mutbl) { ret true; } }
             ret false;
           }
           ty::ty_fn({proto: ast::proto_bare, _}) { ret false; }
@@ -532,11 +532,11 @@ fn ty_can_unsafely_include(cx: ctx, needle: unsafe_ty, haystack: ty::t,
           // treated as opaque downstream, and is thus safe unless we
           // saw mutable fields, in which case the whole thing can be
           // overwritten.
-          ty::ty_param(_, _) { ret mut; }
+          ty::ty_param(_, _) { ret mutbl; }
           _ { ret false; }
         }
     }
-    ret helper(cx.tcx, needle, haystack, mut);
+    ret helper(cx.tcx, needle, haystack, mutbl);
 }
 
 fn def_is_local(d: ast::def) -> bool {
@@ -589,66 +589,66 @@ fn copy_is_expensive(tcx: ty::ctxt, ty: ty::t) -> bool {
 
 type pattern_root = {id: node_id,
                      name: ident,
-                     mut: option<unsafe_ty>,
+                     mutbl: option<unsafe_ty>,
                      span: span};
 
-fn pattern_roots(tcx: ty::ctxt, mut: option<unsafe_ty>, pat: @ast::pat)
+fn pattern_roots(tcx: ty::ctxt, mutbl: option<unsafe_ty>, pat: @ast::pat)
     -> [pattern_root] {
-    fn walk(tcx: ty::ctxt, mut: option<unsafe_ty>, pat: @ast::pat,
+    fn walk(tcx: ty::ctxt, mutbl: option<unsafe_ty>, pat: @ast::pat,
             &set: [pattern_root]) {
         alt normalize_pat(tcx, pat).node {
           ast::pat_wild | ast::pat_lit(_) | ast::pat_range(_, _) {}
           ast::pat_ident(nm, sub) {
-            set += [{id: pat.id, name: path_to_ident(nm), mut: mut,
+            set += [{id: pat.id, name: path_to_ident(nm), mutbl: mutbl,
                         span: pat.span}];
-            alt sub { some(p) { walk(tcx, mut, p, set); } _ {} }
+            alt sub { some(p) { walk(tcx, mutbl, p, set); } _ {} }
           }
           ast::pat_enum(_, ps) | ast::pat_tup(ps) {
-            for p in ps { walk(tcx, mut, p, set); }
+            for p in ps { walk(tcx, mutbl, p, set); }
           }
           ast::pat_rec(fs, _) {
             let ty = ty::node_id_to_type(tcx, pat.id);
             for f in fs {
-                let m = ty::get_field(ty, f.ident).mt.mut != ast::imm,
-                    c = if m { some(contains(ty)) } else { mut };
+                let m = ty::get_field(ty, f.ident).mt.mutbl != ast::m_imm,
+                    c = if m { some(contains(ty)) } else { mutbl };
                 walk(tcx, c, f.pat, set);
             }
           }
           ast::pat_box(p) {
             let ty = ty::node_id_to_type(tcx, pat.id);
             let m = alt ty::get(ty).struct {
-              ty::ty_box(mt) { mt.mut != ast::imm }
+              ty::ty_box(mt) { mt.mutbl != ast::m_imm }
               _ { tcx.sess.span_bug(pat.span, "box pat has non-box type"); }
             },
-                c = if m  {some(contains(ty)) } else { mut };
+                c = if m  {some(contains(ty)) } else { mutbl };
             walk(tcx, c, p, set);
           }
           ast::pat_uniq(p) {
             let ty = ty::node_id_to_type(tcx, pat.id);
             let m = alt ty::get(ty).struct {
-              ty::ty_uniq(mt) { mt.mut != ast::imm }
+              ty::ty_uniq(mt) { mt.mutbl != ast::m_imm }
               _ { tcx.sess.span_bug(pat.span, "uniq pat has non-uniq type"); }
             },
-                c = if m { some(contains(ty)) } else { mut };
+                c = if m { some(contains(ty)) } else { mutbl };
             walk(tcx, c, p, set);
           }
         }
     }
     let set = [];
-    walk(tcx, mut, pat, set);
+    walk(tcx, mutbl, pat, set);
     ret set;
 }
 
-// Wraps the expr_root in mut.rs to also handle roots that exist through
+// Wraps the expr_root in mutbl.rs to also handle roots that exist through
 // return-by-reference
 fn expr_root(cx: ctx, ex: @ast::expr, autoderef: bool)
-    -> {ex: @ast::expr, mut: option<unsafe_ty>} {
-    let base_root = mut::expr_root(cx.tcx, ex, autoderef);
+    -> {ex: @ast::expr, mutbl: option<unsafe_ty>} {
+    let base_root = mutbl::expr_root(cx.tcx, ex, autoderef);
     let unsafe_ty = none;
     for d in *base_root.ds {
-        if d.mut { unsafe_ty = some(contains(d.outer_t)); break; }
+        if d.mutbl { unsafe_ty = some(contains(d.outer_t)); break; }
     }
-    ret {ex: base_root.ex, mut: unsafe_ty};
+    ret {ex: base_root.ex, mutbl: unsafe_ty};
 }
 
 fn unsafe_set(from: option<unsafe_ty>) -> [unsafe_ty] {
diff --git a/src/comp/middle/debuginfo.rs b/src/comp/middle/debuginfo.rs
index d23fa4f5e8c..1349a43e7e0 100644
--- a/src/comp/middle/debuginfo.rs
+++ b/src/comp/middle/debuginfo.rs
@@ -587,21 +587,21 @@ fn create_ty(_cx: @crate_ctxt, _t: ty::t, _ty: @ast::ty)
           ty::ty_float(t) { ast::ty_float(t) }
           ty::ty_uint(t) { ast::ty_uint(t) }
           ty::ty_box(mt) { ast::ty_box({ty: t_to_ty(cx, mt.ty, span),
-                                        mut: mt.mut}) }
+                                        mutbl: mt.mutbl}) }
           ty::ty_uniq(mt) { ast::ty_uniq({ty: t_to_ty(cx, mt.ty, span),
-                                          mut: mt.mut}) }
+                                          mutbl: mt.mutbl}) }
           ty::ty_rec(fields) {
             let fs = [];
             for field in fields {
                 fs += [{node: {ident: field.ident,
                                mt: {ty: t_to_ty(cx, field.mt.ty, span),
-                                    mut: field.mt.mut}},
+                                    mutbl: field.mt.mutbl}},
                         span: span}];
             }
             ast::ty_rec(fs)
           }
           ty::ty_vec(mt) { ast::ty_vec({ty: t_to_ty(cx, mt.ty, span),
-                                        mut: mt.mut}) }
+                                        mutbl: mt.mutbl}) }
           _ {
             cx.tcx.sess.span_bug(span, "t_to_ty: Can't handle this type");
           }
diff --git a/src/comp/middle/kind.rs b/src/comp/middle/kind.rs
index 9a97fb71060..8c12807ae43 100644
--- a/src/comp/middle/kind.rs
+++ b/src/comp/middle/kind.rs
@@ -167,7 +167,7 @@ fn check_expr(e: @expr, cx: ctx, v: visit::vt<ctx>) {
         for arg_t in ty::ty_fn_args(ty::expr_ty(cx.tcx, f)) {
             alt ty::arg_mode(cx.tcx, arg_t) {
               by_copy { maybe_copy(cx, args[i]); }
-              by_ref | by_val | by_mut_ref | by_move { }
+              by_ref | by_val | by_mutbl_ref | by_move { }
             }
             i += 1u;
         }
diff --git a/src/comp/middle/last_use.rs b/src/comp/middle/last_use.rs
index a0e8388e824..69166d3ba7f 100644
--- a/src/comp/middle/last_use.rs
+++ b/src/comp/middle/last_use.rs
@@ -156,7 +156,7 @@ fn visit_expr(ex: @expr, cx: ctx, v: visit::vt<ctx>) {
               }
               _ {
                 alt ty::arg_mode(cx.tcx, arg_ts[i]) {
-                  by_mut_ref { clear_if_path(cx, arg, v, false); }
+                  by_mutbl_ref { clear_if_path(cx, arg, v, false); }
                   _ { v.visit_expr(arg, cx, v); }
                 }
               }
@@ -299,7 +299,7 @@ fn clear_def_if_path(cx: ctx, d: def, to: bool)
             clear_in_current(cx, def_id.node, to);
             some(def_id.node)
           }
-          by_ref | by_val | by_mut_ref {
+          by_ref | by_val | by_mutbl_ref {
             none
           }
         }
diff --git a/src/comp/middle/mut.rs b/src/comp/middle/mutbl.rs
index cf3388c7f40..7ba837f8231 100644
--- a/src/comp/middle/mut.rs
+++ b/src/comp/middle/mutbl.rs
@@ -5,7 +5,7 @@ import driver::session::session;
 
 enum deref_t { unbox(bool), field, index, }
 
-type deref = @{mut: bool, kind: deref_t, outer_t: ty::t};
+type deref = @{mutbl: bool, kind: deref_t, outer_t: ty::t};
 
 // Finds the root (the thing that is dereferenced) for the given expr, and a
 // vec of dereferences that were used on this root. Note that, in this vec,
@@ -18,15 +18,19 @@ fn expr_root(tcx: ty::ctxt, ex: @expr, autoderef: bool) ->
         while true {
             alt ty::get(t).struct {
               ty::ty_box(mt) {
-                ds += [@{mut: mt.mut == mut, kind: unbox(false), outer_t: t}];
+                ds += [@{mutbl: mt.mutbl == m_mutbl,
+                         kind: unbox(false),
+                         outer_t: t}];
                 t = mt.ty;
               }
               ty::ty_uniq(mt) {
-                ds += [@{mut: mt.mut == mut, kind: unbox(false), outer_t: t}];
+                ds += [@{mutbl: mt.mutbl == m_mutbl,
+                         kind: unbox(false),
+                         outer_t: t}];
                 t = mt.ty;
               }
               ty::ty_res(_, inner, tps) {
-                ds += [@{mut: false, kind: unbox(false), outer_t: t}];
+                ds += [@{mutbl: false, kind: unbox(false), outer_t: t}];
                 t = ty::substitute_type_params(tcx, tps, inner);
               }
               ty::ty_enum(did, tps) {
@@ -35,7 +39,7 @@ fn expr_root(tcx: ty::ctxt, ex: @expr, autoderef: bool) ->
                        vec::len(variants[0].args) != 1u {
                     break;
                 }
-                ds += [@{mut: false, kind: unbox(false), outer_t: t}];
+                ds += [@{mutbl: false, kind: unbox(false), outer_t: t}];
                 t = ty::substitute_type_params(tcx, tps, variants[0].args[0]);
               }
               _ { break; }
@@ -48,19 +52,19 @@ fn expr_root(tcx: ty::ctxt, ex: @expr, autoderef: bool) ->
         alt copy ex.node {
           expr_field(base, ident, _) {
             let auto_unbox = maybe_auto_unbox(tcx, ty::expr_ty(tcx, base));
-            let is_mut = false;
+            let is_mutbl = false;
             alt ty::get(auto_unbox.t).struct {
               ty::ty_rec(fields) {
                 for fld: ty::field in fields {
                     if str::eq(ident, fld.ident) {
-                        is_mut = fld.mt.mut == mut;
+                        is_mutbl = fld.mt.mutbl == m_mutbl;
                         break;
                     }
                 }
               }
               _ {}
             }
-            ds += [@{mut: is_mut, kind: field, outer_t: auto_unbox.t}];
+            ds += [@{mutbl: is_mutbl, kind: field, outer_t: auto_unbox.t}];
             ds += auto_unbox.ds;
             ex = base;
           }
@@ -69,12 +73,12 @@ fn expr_root(tcx: ty::ctxt, ex: @expr, autoderef: bool) ->
             alt ty::get(auto_unbox.t).struct {
               ty::ty_vec(mt) {
                 ds +=
-                    [@{mut: mt.mut == mut,
+                    [@{mutbl: mt.mutbl == m_mutbl,
                        kind: index,
                        outer_t: auto_unbox.t}];
               }
               ty::ty_str {
-                ds += [@{mut: false, kind: index, outer_t: auto_unbox.t}];
+                ds += [@{mutbl: false, kind: index, outer_t: auto_unbox.t}];
               }
               _ { break; }
             }
@@ -84,17 +88,20 @@ fn expr_root(tcx: ty::ctxt, ex: @expr, autoderef: bool) ->
           expr_unary(op, base) {
             if op == deref {
                 let base_t = ty::expr_ty(tcx, base);
-                let is_mut = false, ptr = false;
+                let is_mutbl = false, ptr = false;
                 alt ty::get(base_t).struct {
-                  ty::ty_box(mt) { is_mut = mt.mut == mut; }
-                  ty::ty_uniq(mt) { is_mut = mt.mut == mut; }
+                  ty::ty_box(mt) { is_mutbl = mt.mutbl == m_mutbl; }
+                  ty::ty_uniq(mt) { is_mutbl = mt.mutbl == m_mutbl; }
                   ty::ty_res(_, _, _) { }
                   ty::ty_enum(_, _) { }
-                  ty::ty_ptr(mt) { is_mut = mt.mut == mut; ptr = true; }
+                  ty::ty_ptr(mt) {
+                    is_mutbl = mt.mutbl == m_mutbl;
+                    ptr = true;
+                  }
                   _ { tcx.sess.span_bug(base.span, "Ill-typed base \
                         expression in deref"); }
                 }
-                ds += [@{mut: is_mut, kind: unbox(ptr && is_mut),
+                ds += [@{mutbl: is_mutbl, kind: unbox(ptr && is_mutbl),
                          outer_t: base_t}];
                 ex = base;
             } else { break; }
@@ -109,27 +116,27 @@ fn expr_root(tcx: ty::ctxt, ex: @expr, autoderef: bool) ->
     ret {ex: ex, ds: @ds};
 }
 
-// Actual mut-checking pass
+// Actual mutbl-checking pass
 
-type mut_map = std::map::hashmap<node_id, ()>;
-type ctx = {tcx: ty::ctxt, mut_map: mut_map};
+type mutbl_map = std::map::hashmap<node_id, ()>;
+type ctx = {tcx: ty::ctxt, mutbl_map: mutbl_map};
 
-fn check_crate(tcx: ty::ctxt, crate: @crate) -> mut_map {
-    let cx = @{tcx: tcx, mut_map: std::map::new_int_hash()};
+fn check_crate(tcx: ty::ctxt, crate: @crate) -> mutbl_map {
+    let cx = @{tcx: tcx, mutbl_map: std::map::new_int_hash()};
     let v = @{visit_expr: bind visit_expr(cx, _, _, _),
               visit_decl: bind visit_decl(cx, _, _, _)
               with *visit::default_visitor()};
     visit::visit_crate(*crate, (), visit::mk_vt(v));
-    ret cx.mut_map;
+    ret cx.mutbl_map;
 }
 
-enum msg { msg_assign, msg_move_out, msg_mut_ref, }
+enum msg { msg_assign, msg_move_out, msg_mutbl_ref, }
 
 fn mk_err(cx: @ctx, span: syntax::codemap::span, msg: msg, name: str) {
     cx.tcx.sess.span_err(span, alt msg {
       msg_assign { "assigning to " + name }
       msg_move_out { "moving out of " + name }
-      msg_mut_ref { "passing " + name + " by mutable reference" }
+      msg_mutbl_ref { "passing " + name + " by mutable reference" }
     });
 }
 
@@ -178,7 +185,7 @@ fn check_lval(cx: @ctx, dest: @expr, msg: msg) {
           some(name) { mk_err(cx, dest.span, msg, name); }
           _ { }
         }
-        cx.mut_map.insert(ast_util::def_id_of_def(def).node, ());
+        cx.mutbl_map.insert(ast_util::def_id_of_def(def).node, ());
       }
       _ {
         let root = expr_root(cx.tcx, dest, false);
@@ -186,12 +193,12 @@ fn check_lval(cx: @ctx, dest: @expr, msg: msg) {
             if msg != msg_move_out {
                 mk_err(cx, dest.span, msg, "non-lvalue");
             }
-        } else if !root.ds[0].mut {
+        } else if !root.ds[0].mutbl {
             let name =
                 alt root.ds[0].kind {
-                  mut::unbox(_) { "immutable box" }
-                  mut::field { "immutable field" }
-                  mut::index { "immutable vec content" }
+                  mutbl::unbox(_) { "immutable box" }
+                  mutbl::field { "immutable field" }
+                  mutbl::index { "immutable vec content" }
                 };
             mk_err(cx, dest.span, msg, name);
         }
@@ -227,7 +234,7 @@ fn check_call(cx: @ctx, f: @expr, args: [@expr]) {
     let i = 0u;
     for arg_t: ty::arg in arg_ts {
         alt ty::resolved_mode(cx.tcx, arg_t.mode) {
-          by_mut_ref { check_lval(cx, args[i], msg_mut_ref); }
+          by_mutbl_ref { check_lval(cx, args[i], msg_mutbl_ref); }
           by_move { check_lval(cx, args[i], msg_move_out); }
           by_ref | by_val | by_copy { }
         }
@@ -242,7 +249,7 @@ fn check_bind(cx: @ctx, f: @expr, args: [option<@expr>]) {
         alt arg {
           some(expr) {
             let o_msg = alt ty::resolved_mode(cx.tcx, arg_ts[i].mode) {
-              by_mut_ref { some("by mutable reference") }
+              by_mutbl_ref { some("by mutable reference") }
               by_move { some("by move") }
               _ { none }
             };
@@ -269,7 +276,7 @@ fn is_immutable_def(cx: @ctx, def: def) -> option<str> {
       def_arg(_, m) {
         alt ty::resolved_mode(cx.tcx, m) {
           by_ref | by_val { some("argument") }
-          by_mut_ref | by_move | by_copy { none }
+          by_mutbl_ref | by_move | by_copy { none }
         }
       }
       def_self(_) { some("self argument") }
diff --git a/src/comp/middle/trans/base.rs b/src/comp/middle/trans/base.rs
index 799eadcf69a..3b8bde61cb8 100644
--- a/src/comp/middle/trans/base.rs
+++ b/src/comp/middle/trans/base.rs
@@ -3987,7 +3987,7 @@ fn alloc_local(cx: @block_ctxt, local: @ast::local) -> @block_ctxt {
     };
     // Do not allocate space for locals that can be kept immediate.
     let ccx = bcx_ccx(cx);
-    if is_simple && !ccx.mut_map.contains_key(local.node.pat.id) &&
+    if is_simple && !ccx.mutbl_map.contains_key(local.node.pat.id) &&
        !ccx.last_uses.contains_key(local.node.pat.id) &&
        ty::type_is_immediate(t) {
         alt local.node.init {
@@ -4166,7 +4166,7 @@ fn copy_args_to_allocas(fcx: @fn_ctxt, bcx: @block_ctxt, args: [ast::arg],
         let argval = alt fcx.llargs.get(id) { local_mem(v) { v }
                                               _ { epic_fail() } };
         alt ty::resolved_mode(tcx, arg.mode) {
-          ast::by_mut_ref { }
+          ast::by_mutbl_ref { }
           ast::by_move | ast::by_copy { add_clean(bcx, argval, arg.ty); }
           ast::by_val {
             if !ty::type_is_immediate(arg.ty) {
@@ -4598,7 +4598,7 @@ fn create_main_wrapper(ccx: @crate_ctxt, sp: span, main_llfn: ValueRef,
         let unit_ty = ty::mk_str(ccx.tcx);
         let vecarg_ty: ty::arg =
             {mode: ast::expl(ast::by_val),
-             ty: ty::mk_vec(ccx.tcx, {ty: unit_ty, mut: ast::imm})};
+             ty: ty::mk_vec(ccx.tcx, {ty: unit_ty, mutbl: ast::m_imm})};
         // FIXME: mk_nil should have a postcondition
         let nt = ty::mk_nil(ccx.tcx);
         let llfty = type_of_fn(ccx, [vecarg_ty], nt, []);
@@ -5003,7 +5003,7 @@ fn write_abi_version(ccx: @crate_ctxt) {
 
 fn trans_crate(sess: session::session, crate: @ast::crate, tcx: ty::ctxt,
                output: str, emap: resolve::exp_map, amap: ast_map::map,
-               mut_map: mut::mut_map, copy_map: alias::copy_map,
+               mutbl_map: mutbl::mutbl_map, copy_map: alias::copy_map,
                last_uses: last_use::last_uses, impl_map: resolve::impl_map,
                method_map: typeck::method_map, dict_map: typeck::dict_map)
     -> (ModuleRef, link::link_meta) {
@@ -5080,7 +5080,7 @@ fn trans_crate(sess: session::session, crate: @ast::crate, tcx: ty::ctxt,
           type_sha1s: ty::new_ty_hash(),
           type_short_names: ty::new_ty_hash(),
           tcx: tcx,
-          mut_map: mut_map,
+          mutbl_map: mutbl_map,
           copy_map: copy_map,
           last_uses: last_uses,
           impl_map: impl_map,
diff --git a/src/comp/middle/trans/closure.rs b/src/comp/middle/trans/closure.rs
index 45e4bfadcbe..b6ef093d534 100644
--- a/src/comp/middle/trans/closure.rs
+++ b/src/comp/middle/trans/closure.rs
@@ -276,7 +276,7 @@ fn store_environment(
     // tuple.  This could be a ptr in uniq or a box or on stack,
     // whatever.
     let cbox_ty = tuplify_box_ty(tcx, cdata_ty);
-    let cboxptr_ty = ty::mk_ptr(tcx, {ty:cbox_ty, mut:ast::imm});
+    let cboxptr_ty = ty::mk_ptr(tcx, {ty:cbox_ty, mutbl:ast::m_imm});
     let llbox = cast_if_we_can(bcx, llbox, cboxptr_ty);
 
     // If necessary, copy tydescs describing type parameters into the
@@ -905,7 +905,7 @@ fn trans_bind_thunk(ccx: @crate_ctxt,
                 bcx = take_ty(bcx, alloc, out_arg.ty);
                 val = alloc;
               }
-              ast::by_ref | ast::by_mut_ref | ast::by_move { }
+              ast::by_ref | ast::by_mutbl_ref | ast::by_move { }
             }
 
             // If the type is parameterized, then we need to cast the
diff --git a/src/comp/middle/trans/common.rs b/src/comp/middle/trans/common.rs
index d39759ad211..6398928e066 100644
--- a/src/comp/middle/trans/common.rs
+++ b/src/comp/middle/trans/common.rs
@@ -104,7 +104,7 @@ type crate_ctxt =
      type_sha1s: hashmap<ty::t, str>,
      type_short_names: hashmap<ty::t, str>,
      tcx: ty::ctxt,
-     mut_map: mut::mut_map,
+     mutbl_map: mutbl::mutbl_map,
      copy_map: alias::copy_map,
      last_uses: last_use::last_uses,
      impl_map: resolve::impl_map,
@@ -622,7 +622,7 @@ fn tuplify_box_ty(tcx: ty::ctxt, t: ty::t) -> ty::t {
 // descr is embedded in the box (ty::type vs ty::send_type).  This is useful
 // for unique closure boxes, hence the name "cbox_ty" (closure box type).
 fn tuplify_cbox_ty(tcx: ty::ctxt, t: ty::t, tydesc_t: ty::t) -> ty::t {
-    let ptr = ty::mk_ptr(tcx, {ty: ty::mk_nil(tcx), mut: ast::imm});
+    let ptr = ty::mk_ptr(tcx, {ty: ty::mk_nil(tcx), mutbl: ast::m_imm});
     ret ty::mk_tup(tcx, [ty::mk_uint(tcx), tydesc_t,
                          ptr, ptr,
                          t]);
diff --git a/src/comp/middle/trans/shape.rs b/src/comp/middle/trans/shape.rs
index 2ab8990ff98..2a4a2d423e2 100644
--- a/src/comp/middle/trans/shape.rs
+++ b/src/comp/middle/trans/shape.rs
@@ -782,7 +782,7 @@ fn dynamic_metrics(cx: @block_ctxt, t: ty::t) -> metrics {
 // nominal type that has pointers to itself in it.
 fn simplify_type(tcx: ty::ctxt, typ: ty::t) -> ty::t {
     fn nilptr(tcx: ty::ctxt) -> ty::t {
-        ty::mk_ptr(tcx, {ty: ty::mk_nil(tcx), mut: ast::imm})
+        ty::mk_ptr(tcx, {ty: ty::mk_nil(tcx), mutbl: ast::m_imm})
     }
     fn simplifier(tcx: ty::ctxt, typ: ty::t) -> ty::t {
         alt ty::get(typ).struct {
diff --git a/src/comp/middle/tstate/auxiliary.rs b/src/comp/middle/tstate/auxiliary.rs
index e6884d129fb..cd0cd7e11c3 100644
--- a/src/comp/middle/tstate/auxiliary.rs
+++ b/src/comp/middle/tstate/auxiliary.rs
@@ -1089,7 +1089,7 @@ fn callee_arg_init_ops(fcx: fn_ctxt, callee: node_id) -> [init_op] {
     vec::map(callee_modes(fcx, callee)) {|m|
         alt ty::resolved_mode(fcx.ccx.tcx, m) {
           by_move { init_move }
-          by_copy | by_ref | by_val | by_mut_ref { init_assign }
+          by_copy | by_ref | by_val | by_mutbl_ref { init_assign }
         }
     }
 }
diff --git a/src/comp/middle/tstate/pre_post_conditions.rs b/src/comp/middle/tstate/pre_post_conditions.rs
index a3fee3a5a75..326c768cabe 100644
--- a/src/comp/middle/tstate/pre_post_conditions.rs
+++ b/src/comp/middle/tstate/pre_post_conditions.rs
@@ -275,7 +275,7 @@ fn forget_args_moved_in(fcx: fn_ctxt, parent: @expr, modes: [mode],
     vec::iteri(modes) {|i,mode|
         alt ty::resolved_mode(fcx.ccx.tcx, mode) {
           by_move { forget_in_postcond(fcx, parent.id, operands[i].id); }
-          by_ref | by_val | by_mut_ref | by_copy { }
+          by_ref | by_val | by_mutbl_ref | by_copy { }
         }
     }
 }
diff --git a/src/comp/middle/ty.rs b/src/comp/middle/ty.rs
index e5f8fa26ee7..06823f4aa30 100644
--- a/src/comp/middle/ty.rs
+++ b/src/comp/middle/ty.rs
@@ -147,7 +147,7 @@ type method = {ident: ast::ident,
 
 type constr_table = hashmap<ast::node_id, [constr]>;
 
-type mt = {ty: t, mut: ast::mutability};
+type mt = {ty: t, mutbl: ast::mutability};
 
 
 // Contains information needed to resolve types and (in the future) look up
@@ -423,15 +423,18 @@ fn mk_enum(cx: ctxt, did: ast::def_id, tys: [t]) -> t {
 
 fn mk_box(cx: ctxt, tm: mt) -> t { mk_t(cx, ty_box(tm)) }
 
-fn mk_imm_box(cx: ctxt, ty: t) -> t { mk_box(cx, {ty: ty, mut: ast::imm}) }
+fn mk_imm_box(cx: ctxt, ty: t) -> t { mk_box(cx, {ty: ty,
+                                                  mutbl: ast::m_imm}) }
 
 fn mk_uniq(cx: ctxt, tm: mt) -> t { mk_t(cx, ty_uniq(tm)) }
 
-fn mk_imm_uniq(cx: ctxt, ty: t) -> t { mk_uniq(cx, {ty: ty, mut: ast::imm}) }
+fn mk_imm_uniq(cx: ctxt, ty: t) -> t { mk_uniq(cx, {ty: ty,
+                                                    mutbl: ast::m_imm}) }
 
 fn mk_ptr(cx: ctxt, tm: mt) -> t { mk_t(cx, ty_ptr(tm)) }
 
-fn mk_mut_ptr(cx: ctxt, ty: t) -> t { mk_ptr(cx, {ty: ty, mut: ast::mut}) }
+fn mk_mut_ptr(cx: ctxt, ty: t) -> t { mk_ptr(cx, {ty: ty,
+                                                  mutbl: ast::m_mutbl}) }
 
 fn mk_vec(cx: ctxt, tm: mt) -> t { mk_t(cx, ty_vec(tm)) }
 
@@ -541,16 +544,16 @@ fn fold_ty(cx: ctxt, fld: fold_mode, ty_0: t) -> t {
       ty_str | ty_type | ty_send_type | ty_opaque_closure_ptr(_) |
       ty_opaque_box {}
       ty_box(tm) {
-        ty = mk_box(cx, {ty: fold_ty(cx, fld, tm.ty), mut: tm.mut});
+        ty = mk_box(cx, {ty: fold_ty(cx, fld, tm.ty), mutbl: tm.mutbl});
       }
       ty_uniq(tm) {
-        ty = mk_uniq(cx, {ty: fold_ty(cx, fld, tm.ty), mut: tm.mut});
+        ty = mk_uniq(cx, {ty: fold_ty(cx, fld, tm.ty), mutbl: tm.mutbl});
       }
       ty_ptr(tm) {
-        ty = mk_ptr(cx, {ty: fold_ty(cx, fld, tm.ty), mut: tm.mut});
+        ty = mk_ptr(cx, {ty: fold_ty(cx, fld, tm.ty), mutbl: tm.mutbl});
       }
       ty_vec(tm) {
-        ty = mk_vec(cx, {ty: fold_ty(cx, fld, tm.ty), mut: tm.mut});
+        ty = mk_vec(cx, {ty: fold_ty(cx, fld, tm.ty), mutbl: tm.mutbl});
       }
       ty_enum(tid, subtys) {
         ty = mk_enum(cx, tid, vec::map(subtys, {|t| fold_ty(cx, fld, t) }));
@@ -565,7 +568,7 @@ fn fold_ty(cx: ctxt, fld: fold_mode, ty_0: t) -> t {
         let new_fields: [field] = [];
         for fl: field in fields {
             let new_ty = fold_ty(cx, fld, fl.mt.ty);
-            let new_mt = {ty: new_ty, mut: fl.mt.mut};
+            let new_mt = {ty: new_ty, mutbl: fl.mt.mutbl};
             new_fields += [{ident: fl.ident, mt: new_mt}];
         }
         ty = mk_rec(cx, new_fields);
@@ -922,12 +925,11 @@ fn type_allows_implicit_copy(cx: ctxt, ty: t) -> bool {
         alt sty {
           ty_param(_, _) { true }
           ty_vec(mt) {
-            mt.mut != ast::imm
+            mt.mutbl != ast::m_imm
           }
           ty_rec(fields) {
             for field in fields {
-                if field.mt.mut !=
-                    ast::imm {
+                if field.mt.mutbl != ast::m_imm {
                     ret true;
                 }
             }
@@ -1665,7 +1667,7 @@ mod unify {
         // If you're unifying on something mutable then we have to
         // be invariant on the inner type
         let newvariance = alt expected {
-          ast::mut {
+          ast::m_mutbl {
             variance_transform(variance, invariant)
           }
           _ {
@@ -1675,11 +1677,11 @@ mod unify {
 
         if expected == actual { ret some((expected, newvariance)); }
         if variance == covariant {
-            if expected == ast::maybe_mut {
+            if expected == ast::m_const {
                 ret some((actual, newvariance));
             }
         } else if variance == contravariant {
-            if actual == ast::maybe_mut {
+            if actual == ast::m_const {
                 ret some((expected, newvariance));
             }
         }
@@ -1960,7 +1962,7 @@ mod unify {
             alt get(actual).struct {
               ty_box(actual_mt) {
                 let (mutt, var) = alt unify_mut(
-                    expected_mt.mut, actual_mt.mut, variance) {
+                    expected_mt.mutbl, actual_mt.mutbl, variance) {
                   none { ret ures_err(terr_box_mutability); }
                   some(mv) { mv }
                 };
@@ -1968,7 +1970,7 @@ mod unify {
                     cx, expected_mt.ty, actual_mt.ty, var);
                 alt result {
                   ures_ok(result_sub) {
-                    let mt = {ty: result_sub, mut: mutt};
+                    let mt = {ty: result_sub, mutbl: mutt};
                     ret ures_ok(mk_box(cx.tcx, mt));
                   }
                   _ { ret result; }
@@ -1981,7 +1983,7 @@ mod unify {
             alt get(actual).struct {
               ty_uniq(actual_mt) {
                 let (mutt, var) = alt unify_mut(
-                    expected_mt.mut, actual_mt.mut, variance) {
+                    expected_mt.mutbl, actual_mt.mutbl, variance) {
                   none { ret ures_err(terr_box_mutability); }
                   some(mv) { mv }
                 };
@@ -1989,7 +1991,7 @@ mod unify {
                     cx, expected_mt.ty, actual_mt.ty, var);
                 alt result {
                   ures_ok(result_mt) {
-                    let mt = {ty: result_mt, mut: mutt};
+                    let mt = {ty: result_mt, mutbl: mutt};
                     ret ures_ok(mk_uniq(cx.tcx, mt));
                   }
                   _ { ret result; }
@@ -2002,7 +2004,7 @@ mod unify {
             alt get(actual).struct {
               ty_vec(actual_mt) {
                 let (mutt, var) = alt unify_mut(
-                    expected_mt.mut, actual_mt.mut, variance) {
+                    expected_mt.mutbl, actual_mt.mutbl, variance) {
                   none { ret ures_err(terr_vec_mutability); }
                   some(mv) { mv }
                 };
@@ -2010,7 +2012,7 @@ mod unify {
                     cx, expected_mt.ty, actual_mt.ty, var);
                 alt result {
                   ures_ok(result_sub) {
-                    let mt = {ty: result_sub, mut: mutt};
+                    let mt = {ty: result_sub, mutbl: mutt};
                     ret ures_ok(mk_vec(cx.tcx, mt));
                   }
                   _ { ret result; }
@@ -2023,7 +2025,7 @@ mod unify {
             alt get(actual).struct {
               ty_ptr(actual_mt) {
                 let (mutt, var) = alt unify_mut(
-                    expected_mt.mut, actual_mt.mut, variance) {
+                    expected_mt.mutbl, actual_mt.mutbl, variance) {
                   none { ret ures_err(terr_vec_mutability); }
                   some(mv) { mv }
                 };
@@ -2031,7 +2033,7 @@ mod unify {
                     cx, expected_mt.ty, actual_mt.ty, var);
                 alt result {
                   ures_ok(result_sub) {
-                    let mt = {ty: result_sub, mut: mutt};
+                    let mt = {ty: result_sub, mutbl: mutt};
                     ret ures_ok(mk_ptr(cx.tcx, mt));
                   }
                   _ { ret result; }
@@ -2086,9 +2088,10 @@ mod unify {
                 while i < expected_len {
                     let expected_field = expected_fields[i];
                     let actual_field = actual_fields[i];
-                    let (mutt, var) = alt unify_mut(
-                        expected_field.mt.mut, actual_field.mt.mut, variance)
-                        {
+                    let u_mut = unify_mut(expected_field.mt.mutbl,
+                                          actual_field.mt.mutbl,
+                                          variance);
+                    let (mutt, var) = alt u_mut {
                       none { ret ures_err(terr_record_mutability); }
                       some(mv) { mv }
                     };
@@ -2103,7 +2106,7 @@ mod unify {
                                    actual_field.mt.ty, var);
                     alt result {
                       ures_ok(rty) {
-                        let mt = {ty: rty, mut: mutt};
+                        let mt = {ty: rty, mutbl: mutt};
                         result_fields += [{mt: mt with expected_field}];
                       }
                       _ { ret result; }
diff --git a/src/comp/middle/typeck.rs b/src/comp/middle/typeck.rs
index 4094b6eddbd..a54a376be2d 100644
--- a/src/comp/middle/typeck.rs
+++ b/src/comp/middle/typeck.rs
@@ -115,7 +115,7 @@ fn ty_param_bounds_and_ty_for_def(fcx: @fn_ctxt, sp: span, defn: ast::def) ->
                 fcx.ccx.tcx,
                 {
                     ty: ty::mk_mach_uint(fcx.ccx.tcx, ast::ty_u8),
-                    mut: ast::imm
+                    mutbl: ast::m_imm
                 })
         };
       }
@@ -259,7 +259,7 @@ fn ast_ty_to_ty(tcx: ty::ctxt, mode: mode, &&ast_ty: @ast::ty) -> ty::t {
 
     tcx.ast_ty_to_ty_cache.insert(ast_ty, none::<ty::t>);
     fn ast_mt_to_mt(tcx: ty::ctxt, mode: mode, mt: ast::mt) -> ty::mt {
-        ret {ty: ast_ty_to_ty(tcx, mode, mt.ty), mut: mt.mut};
+        ret {ty: ast_ty_to_ty(tcx, mode, mt.ty), mutbl: mt.mutbl};
     }
     fn instantiate(tcx: ty::ctxt, sp: span, mode: mode,
                    id: ast::def_id, args: [@ast::ty]) -> ty::t {
@@ -2057,9 +2057,11 @@ fn check_expr_with_unifier(fcx: @fn_ctxt, expr: @ast::expr, unify: unifier,
         bot = check_expr(fcx, oper);
         let oper_t = expr_ty(tcx, oper);
         alt unop {
-          ast::box(mut) { oper_t = ty::mk_box(tcx, {ty: oper_t, mut: mut}); }
-          ast::uniq(mut) {
-            oper_t = ty::mk_uniq(tcx, {ty: oper_t, mut: mut});
+          ast::box(mutbl) {
+            oper_t = ty::mk_box(tcx, {ty: oper_t, mutbl: mutbl});
+          }
+          ast::uniq(mutbl) {
+            oper_t = ty::mk_uniq(tcx, {ty: oper_t, mutbl: mutbl});
           }
           ast::deref {
             alt structure_of(fcx, expr.span, oper_t) {
@@ -2358,10 +2360,10 @@ fn check_expr_with_unifier(fcx: @fn_ctxt, expr: @ast::expr, unify: unifier,
         }
         write_ty(tcx, id, t_1);
       }
-      ast::expr_vec(args, mut) {
+      ast::expr_vec(args, mutbl) {
         let t: ty::t = next_ty_var(fcx);
         for e: @ast::expr in args { bot |= check_expr_with(fcx, e, t); }
-        let typ = ty::mk_vec(tcx, {ty: t, mut: mut});
+        let typ = ty::mk_vec(tcx, {ty: t, mutbl: mutbl});
         write_ty(tcx, id, typ);
       }
       ast::expr_tup(elts) {
@@ -2381,7 +2383,7 @@ fn check_expr_with_unifier(fcx: @fn_ctxt, expr: @ast::expr, unify: unifier,
         for f: ast::field in fields {
             bot |= check_expr(fcx, f.node.expr);
             let expr_t = expr_ty(tcx, f.node.expr);
-            let expr_mt = {ty: expr_t, mut: f.node.mut};
+            let expr_mt = {ty: expr_t, mutbl: f.node.mutbl};
             // for the most precise error message,
             // should be f.node.expr.span, not f.span
             fields_t +=
@@ -2894,7 +2896,7 @@ fn check_item(ccx: @crate_ctxt, it: @ast::item) {
 fn arg_is_argv_ty(_tcx: ty::ctxt, a: ty::arg) -> bool {
     alt ty::get(a.ty).struct {
       ty::ty_vec(mt) {
-        if mt.mut != ast::imm { ret false; }
+        if mt.mutbl != ast::m_imm { ret false; }
         alt ty::get(mt.ty).struct {
           ty::ty_str { ret true; }
           _ { ret false; }
diff --git a/src/comp/rustc.rc b/src/comp/rustc.rc
index 8958b1530b8..bf4113cf395 100644
--- a/src/comp/rustc.rc
+++ b/src/comp/rustc.rc
@@ -34,7 +34,7 @@ mod middle {
     mod check_alt;
     mod check_const;
     mod lint;
-    mod mut;
+    mod mutbl;
     mod alias;
     mod last_use;
     mod block_use;
diff --git a/src/comp/syntax/ast.rs b/src/comp/syntax/ast.rs
index deaf70c41fb..3a365e58bbd 100644
--- a/src/comp/syntax/ast.rs
+++ b/src/comp/syntax/ast.rs
@@ -121,7 +121,7 @@ enum pat_ {
     pat_range(@expr, @expr),
 }
 
-enum mutability { mut, imm, maybe_mut, }
+enum mutability { m_mutbl, m_imm, m_const, }
 
 enum proto {
     proto_bare,    // native fn
@@ -173,7 +173,7 @@ enum inferable<T> {
 }
 
 // "resolved" mode: the real modes.
-enum rmode { by_ref, by_val, by_mut_ref, by_move, by_copy }
+enum rmode { by_ref, by_val, by_mutbl_ref, by_move, by_copy }
 
 // inferable mode.
 type mode = inferable<rmode>;
@@ -205,7 +205,7 @@ enum decl_ { decl_local([@local]), decl_item(@item), }
 
 type arm = {pats: [@pat], guard: option<@expr>, body: blk};
 
-type field_ = {mut: mutability, ident: ident, expr: @expr};
+type field_ = {mutbl: mutability, ident: ident, expr: @expr};
 
 type field = spanned<field_>;
 
@@ -316,7 +316,7 @@ enum lit_ {
 
 // NB: If you change this, you'll probably want to change the corresponding
 // type structure in middle/ty.rs as well.
-type mt = {ty: @ty, mut: mutability};
+type mt = {ty: @ty, mutbl: mutability};
 
 type ty_field_ = {ident: ident, mt: mt};
 
diff --git a/src/comp/syntax/ast_util.rs b/src/comp/syntax/ast_util.rs
index 3511cd91853..cd508aae90b 100644
--- a/src/comp/syntax/ast_util.rs
+++ b/src/comp/syntax/ast_util.rs
@@ -66,8 +66,8 @@ pure fn lazy_binop(b: binop) -> bool {
 
 fn unop_to_str(op: unop) -> str {
     alt op {
-      box(mt) { if mt == mut { ret "@mutable "; } ret "@"; }
-      uniq(mt) { if mt == mut { ret "~mutable "; } ret "~"; }
+      box(mt) { if mt == m_mutbl { ret "@mut "; } ret "@"; }
+      uniq(mt) { if mt == m_mutbl { ret "~mut "; } ret "~"; }
       deref { ret "*"; }
       not { ret "!"; }
       neg { ret "-"; }
diff --git a/src/comp/syntax/ext/build.rs b/src/comp/syntax/ext/build.rs
index 4d0cfa75a14..5d615c4305d 100644
--- a/src/comp/syntax/ext/build.rs
+++ b/src/comp/syntax/ext/build.rs
@@ -61,7 +61,7 @@ fn mk_call(cx: ext_ctxt, sp: span, fn_path: [ast::ident],
 // e = expr, t = type
 fn mk_vec_e(cx: ext_ctxt, sp: span, exprs: [@ast::expr]) ->
    @ast::expr {
-    let vecexpr = ast::expr_vec(exprs, ast::imm);
+    let vecexpr = ast::expr_vec(exprs, ast::m_imm);
     ret @{id: cx.next_id(), node: vecexpr, span: sp};
 }
 fn mk_rec_e(cx: ext_ctxt, sp: span,
@@ -72,7 +72,7 @@ fn mk_rec_e(cx: ext_ctxt, sp: span,
         let ident = field.ident;
         let val = field.ex;
         let astfield =
-            {node: {mut: ast::imm, ident: ident, expr: val}, span: sp};
+            {node: {mutbl: ast::m_imm, ident: ident, expr: val}, span: sp};
         astfields += [astfield];
     }
     let recexpr = ast::expr_rec(astfields, option::none::<@ast::expr>);
diff --git a/src/comp/syntax/ext/qquote.rs b/src/comp/syntax/ext/qquote.rs
index 6afb3fa3f75..6d2a9e04d72 100644
--- a/src/comp/syntax/ext/qquote.rs
+++ b/src/comp/syntax/ext/qquote.rs
@@ -231,7 +231,7 @@ fn finish<T: qq_helper>
                                 [mk_str(cx,sp, loc.file.name),
                                  mk_uint(cx,sp, loc.line),
                                  mk_uint(cx,sp, loc.col)]),
-                        mk_unary(cx,sp, ast::box(ast::imm),
+                        mk_unary(cx,sp, ast::box(ast::m_imm),
                                  mk_str(cx,sp, str2)),
                         mk_access_(cx,sp,
                                    mk_access_(cx,sp, session_call(), "opts"),
diff --git a/src/comp/syntax/ext/simplext.rs b/src/comp/syntax/ext/simplext.rs
index df281640210..b8f9dd2c140 100644
--- a/src/comp/syntax/ext/simplext.rs
+++ b/src/comp/syntax/ext/simplext.rs
@@ -682,7 +682,7 @@ fn add_new_extension(cx: ext_ctxt, sp: span, arg: ast::mac_arg,
     let clauses: [@clause] = [];
     for arg: @expr in args {
         alt arg.node {
-          expr_vec(elts, mut) {
+          expr_vec(elts, mutbl) {
             if vec::len(elts) != 2u {
                 cx.span_fatal((*arg).span,
                               "extension clause must consist of [" +
diff --git a/src/comp/syntax/fold.rs b/src/comp/syntax/fold.rs
index 878b26fa84c..d161d27c020 100644
--- a/src/comp/syntax/fold.rs
+++ b/src/comp/syntax/fold.rs
@@ -337,7 +337,7 @@ fn wrap<T>(f: fn@(T, ast_fold) -> T)
 fn noop_fold_expr(e: expr_, fld: ast_fold) -> expr_ {
     fn fold_field_(field: field, fld: ast_fold) -> field {
         ret {node:
-                 {mut: field.node.mut,
+                 {mutbl: field.node.mutbl,
                   ident: fld.fold_ident(field.node.ident),
                   expr: fld.fold_expr(field.node.expr)},
              span: field.span};
@@ -434,7 +434,7 @@ fn noop_fold_expr(e: expr_, fld: ast_fold) -> expr_ {
 fn noop_fold_ty(t: ty_, fld: ast_fold) -> ty_ {
     let fold_mac = bind fold_mac_(_, fld);
     fn fold_mt(mt: mt, fld: ast_fold) -> mt {
-        {ty: fld.fold_ty(mt.ty), mut: mt.mut}
+        {ty: fld.fold_ty(mt.ty), mutbl: mt.mutbl}
     }
     fn fold_field(f: ty_field, fld: ast_fold) -> ty_field {
         {node: {ident: fld.fold_ident(f.node.ident),
diff --git a/src/comp/syntax/parse/parser.rs b/src/comp/syntax/parse/parser.rs
index 01f04433908..1e21dff0b34 100644
--- a/src/comp/syntax/parse/parser.rs
+++ b/src/comp/syntax/parse/parser.rs
@@ -150,7 +150,7 @@ fn bad_expr_word_table() -> hashmap<str, ()> {
                  "export", "fail", "fn", "for", "if",  "iface", "impl",
                  "import", "let", "log", "mod", "mutable", "native", "pure",
                  "resource", "ret", "trait", "type", "unchecked", "unsafe",
-                 "while, crust"] {
+                 "while", "crust", "mut"] {
         words.insert(word, ());
     }
     words
@@ -293,18 +293,18 @@ fn parse_ty_methods(p: parser) -> [ast::ty_method] {
 }
 
 fn parse_mt(p: parser) -> ast::mt {
-    let mut = parse_mutability(p);
+    let mutbl = parse_mutability(p);
     let t = parse_ty(p, false);
-    ret {ty: t, mut: mut};
+    ret {ty: t, mutbl: mutbl};
 }
 
 fn parse_ty_field(p: parser) -> ast::ty_field {
     let lo = p.span.lo;
-    let mut = parse_mutability(p);
+    let mutbl = parse_mutability(p);
     let id = parse_ident(p);
     expect(p, token::COLON);
     let ty = parse_ty(p, false);
-    ret spanned(lo, ty.span.hi, {ident: id, mt: {ty: ty, mut: mut}});
+    ret spanned(lo, ty.span.hi, {ident: id, mt: {ty: ty, mutbl: mutbl}});
 }
 
 // if i is the jth ident in args, return j
@@ -486,7 +486,7 @@ fn parse_ty(p: parser, colons_before_params: bool) -> @ast::ty {
 
 fn parse_arg_mode(p: parser) -> ast::mode {
     if eat(p, token::BINOP(token::AND)) {
-        ast::expl(ast::by_mut_ref)
+        ast::expl(ast::by_mutbl_ref)
     } else if eat(p, token::BINOP(token::MINUS)) {
         ast::expl(ast::by_move)
     } else if eat(p, token::ANDAND) {
@@ -693,11 +693,13 @@ fn parse_path_and_ty_param_substs(p: parser, colons: bool) -> @ast::path {
 
 fn parse_mutability(p: parser) -> ast::mutability {
     if eat_word(p, "mutable") {
-        ast::mut
+        ast::m_mutbl
+    } else if eat_word(p, "mut") {
+        ast::m_mutbl
     } else if eat_word(p, "const") {
-        ast::maybe_mut
+        ast::m_const
     } else {
-        ast::imm
+        ast::m_imm
     }
 }
 
@@ -707,7 +709,7 @@ fn parse_field(p: parser, sep: token::token) -> ast::field {
     let i = parse_ident(p);
     expect(p, sep);
     let e = parse_expr(p);
-    ret spanned(lo, e.span.hi, {mut: m, ident: i, expr: e});
+    ret spanned(lo, e.span.hi, {mutbl: m, ident: i, expr: e});
 }
 
 fn mk_expr(p: parser, lo: uint, hi: uint, node: ast::expr_) -> @ast::expr {
@@ -786,7 +788,7 @@ fn parse_bottom_expr(p: parser) -> pexpr {
         ret mk_pexpr(p, lo, hi, ast::expr_tup(es));
     } else if p.token == token::LBRACE {
         p.bump();
-        if is_word(p, "mutable") ||
+        if is_word(p, "mut") || is_word(p, "mutable") ||
                is_plain_ident(p) && p.look_ahead(1u) == token::COLON {
             let fields = [parse_field(p, token::COLON)];
             let base = none;
@@ -832,11 +834,11 @@ fn parse_bottom_expr(p: parser) -> pexpr {
         ret pexpr(parse_block_expr(p, lo, ast::unsafe_blk));
     } else if p.token == token::LBRACKET {
         p.bump();
-        let mut = parse_mutability(p);
+        let mutbl = parse_mutability(p);
         let es =
             parse_seq_to_end(token::RBRACKET, seq_sep(token::COMMA),
                              parse_expr, p);
-        ex = ast::expr_vec(es, mut);
+        ex = ast::expr_vec(es, mutbl);
     } else if p.token == token::POUND_LT {
         p.bump();
         let ty = parse_ty(p, false);
@@ -971,7 +973,7 @@ fn parse_syntax_ext_naked(p: parser, lo: uint) -> @ast::expr {
             };
         let hi = es.span.hi;
         e = some(mk_expr(p, es.span.lo, hi,
-                         ast::expr_vec(es.node, ast::imm)));
+                         ast::expr_vec(es.node, ast::m_imm)));
     }
     let b = none;
     if p.token == token::LBRACE {
@@ -1578,6 +1580,9 @@ fn parse_local(p: parser, allow_init: bool) -> @ast::local {
 }
 
 fn parse_let(p: parser) -> @ast::decl {
+    if eat_word(p, "mut") {
+        /* TODO */
+    }
     let lo = p.span.lo;
     let locals = [parse_local(p, true)];
     while eat(p, token::COMMA) {
@@ -1587,10 +1592,10 @@ fn parse_let(p: parser) -> @ast::decl {
 }
 
 fn parse_instance_var(p:parser) -> ast::class_member {
-    let is_mut = ast::class_immutable;
+    let is_mutbl = ast::class_immutable;
     expect_word(p, "let");
-    if eat_word(p, "mutable") {
-            is_mut = ast::class_mutable;
+    if eat_word(p, "mut") || eat_word(p, "mutable") {
+            is_mutbl = ast::class_mutable;
     }
     if !is_plain_ident(p) {
         p.fatal("expecting ident");
@@ -1598,7 +1603,7 @@ fn parse_instance_var(p:parser) -> ast::class_member {
     let name = parse_ident(p);
     expect(p, token::COLON);
     let ty = parse_ty(p, false);
-    ret ast::instance_var(name, ty, is_mut, p.get_id());
+    ret ast::instance_var(name, ty, is_mutbl, p.get_id());
 }
 
 fn parse_stmt(p: parser, first_item_attrs: [ast::attribute]) -> @ast::stmt {
diff --git a/src/comp/syntax/print/pprust.rs b/src/comp/syntax/print/pprust.rs
index 23cea66e8db..343b4500a3d 100644
--- a/src/comp/syntax/print/pprust.rs
+++ b/src/comp/syntax/print/pprust.rs
@@ -318,10 +318,10 @@ fn print_type(s: ps, &&ty: @ast::ty) {
       ast::ty_uniq(mt) { word(s.s, "~"); print_mt(s, mt); }
       ast::ty_vec(mt) {
         word(s.s, "[");
-        alt mt.mut {
-          ast::mut { word_space(s, "mutable"); }
-          ast::maybe_mut { word_space(s, "const"); }
-          ast::imm { }
+        alt mt.mutbl {
+          ast::m_mutbl { word_space(s, "mut"); }
+          ast::m_const { word_space(s, "const"); }
+          ast::m_imm { }
         }
         print_type(s, mt.ty);
         word(s.s, "]");
@@ -331,7 +331,7 @@ fn print_type(s: ps, &&ty: @ast::ty) {
         word(s.s, "{");
         fn print_field(s: ps, f: ast::ty_field) {
             cbox(s, indent_unit);
-            print_mutability(s, f.node.mt.mut);
+            print_mutability(s, f.node.mt.mutbl);
             word(s.s, f.node.ident);
             word_space(s, ":");
             print_type(s, f.node.mt.ty);
@@ -785,10 +785,10 @@ fn print_expr(s: ps, &&expr: @ast::expr) {
     let ann_node = node_expr(s, expr);
     s.ann.pre(ann_node);
     alt expr.node {
-      ast::expr_vec(exprs, mut) {
+      ast::expr_vec(exprs, mutbl) {
         ibox(s, indent_unit);
         word(s.s, "[");
-        if mut == ast::mut {
+        if mutbl == ast::m_mutbl {
             word(s.s, "mutable");
             if vec::len(exprs) > 0u { nbsp(s); }
         }
@@ -799,7 +799,7 @@ fn print_expr(s: ps, &&expr: @ast::expr) {
       ast::expr_rec(fields, wth) {
         fn print_field(s: ps, field: ast::field) {
             ibox(s, indent_unit);
-            if field.node.mut == ast::mut { word_nbsp(s, "mutable"); }
+            if field.node.mutbl == ast::m_mutbl { word_nbsp(s, "mutable"); }
             word(s.s, field.node.ident);
             word_space(s, ":");
             print_expr(s, field.node.expr);
@@ -1274,7 +1274,7 @@ fn print_fn_block_args(s: ps, decl: ast::fn_decl) {
 
 fn mode_to_str(m: ast::mode) -> str {
     alt m {
-      ast::expl(ast::by_mut_ref) { "&" }
+      ast::expl(ast::by_mutbl_ref) { "&" }
       ast::expl(ast::by_move) { "-" }
       ast::expl(ast::by_ref) { "&&" }
       ast::expl(ast::by_val) { "++" }
@@ -1436,16 +1436,16 @@ fn print_op_maybe_parens(s: ps, expr: @ast::expr, outer_prec: int) {
     if add_them { pclose(s); }
 }
 
-fn print_mutability(s: ps, mut: ast::mutability) {
-    alt mut {
-      ast::mut { word_nbsp(s, "mutable"); }
-      ast::maybe_mut { word_nbsp(s, "const"); }
-      ast::imm {/* nothing */ }
+fn print_mutability(s: ps, mutbl: ast::mutability) {
+    alt mutbl {
+      ast::m_mutbl { word_nbsp(s, "mutable"); }
+      ast::m_const { word_nbsp(s, "const"); }
+      ast::m_imm {/* nothing */ }
     }
 }
 
 fn print_mt(s: ps, mt: ast::mt) {
-    print_mutability(s, mt.mut);
+    print_mutability(s, mt.mutbl);
     print_type(s, mt.ty);
 }
 
diff --git a/src/comp/util/ppaux.rs b/src/comp/util/ppaux.rs
index 03bbeb0d538..2d253a1c3a9 100644
--- a/src/comp/util/ppaux.rs
+++ b/src/comp/util/ppaux.rs
@@ -53,12 +53,11 @@ fn ty_to_str(cx: ctxt, typ: t) -> str {
         ret f.ident + ": " + mt_to_str(cx, f.mt);
     }
     fn mt_to_str(cx: ctxt, m: mt) -> str {
-        let mstr;
-        alt m.mut {
-          ast::mut { mstr = "mutable "; }
-          ast::imm { mstr = ""; }
-          ast::maybe_mut { mstr = "const "; }
-        }
+        let mstr = alt m.mutbl {
+          ast::m_mutbl { "mut " }
+          ast::m_imm { "" }
+          ast::m_const { "const " }
+        };
         ret mstr + ty_to_str(cx, m.ty);
     }
     fn parameterized(cx: ctxt, base: str, tps: [ty::t]) -> str {
diff --git a/src/fuzzer/fuzzer.rs b/src/fuzzer/fuzzer.rs
index de5be53dc73..b0a47e4051b 100644
--- a/src/fuzzer/fuzzer.rs
+++ b/src/fuzzer/fuzzer.rs
@@ -50,8 +50,10 @@ fn common_exprs() -> [ast::expr] {
      dse(ast::expr_lit(@dsl(ast::lit_nil))),
      dse(ast::expr_lit(@dsl(ast::lit_bool(false)))),
      dse(ast::expr_lit(@dsl(ast::lit_bool(true)))),
-     dse(ast::expr_unary(ast::box(ast::imm), @dse(ast::expr_lit(@dsl(ast::lit_bool(true)))))),
-     dse(ast::expr_unary(ast::uniq(ast::imm), @dse(ast::expr_lit(@dsl(ast::lit_bool(true))))))
+     dse(ast::expr_unary(ast::box(ast::m_imm),
+                         @dse(ast::expr_lit(@dsl(ast::lit_bool(true)))))),
+     dse(ast::expr_unary(ast::uniq(ast::m_imm),
+                         @dse(ast::expr_lit(@dsl(ast::lit_bool(true))))))
     ]
 }