Remove by-mutable-ref mode from the compiler

and test cases. Closes #3513

Author: catamorphism

doc/rust.md

@@ -2784,14 +2784,12 @@ aside a copy of that value to refer to. If this is not semantically safe (for
 example, if the referred-to value contains mutable fields), it will reject the
 program. If the compiler deems copying the value expensive, it will warn.
 
-A function can be declared to take an argument by mutable reference. This
-allows the function to write to the slot that the reference refers to.
-
-An example function that accepts an value by mutable reference:
+A function with an argument of type `&mut T`, for some type `T`, can write to
+the slot that its argument refers to. An example of such a function is:
 
 ~~~~~~~~
-fn incr(&i: int) {
-    i = i + 1;
+fn incr(i: &mut int) {
+    *i = *i + 1;
 }
 ~~~~~~~~
 

src/libsyntax/ast.rs

@@ -574,7 +574,7 @@ impl<T:cmp::Eq> inferable<T> : cmp::Eq {
 
 // "resolved" mode: the real modes.
 #[auto_serialize]
-enum rmode { by_ref, by_val, by_mutbl_ref, by_move, by_copy }
+enum rmode { by_ref, by_val, by_move, by_copy }
 
 impl rmode : to_bytes::IterBytes {
     pure fn iter_bytes(+lsb0: bool, f: to_bytes::Cb) {

src/libsyntax/parse/obsolete.rs

@@ -22,7 +22,8 @@ pub enum ObsoleteSyntax {
     ObsoleteClassMethod,
     ObsoleteClassTraits,
     ObsoletePrivSection,
-    ObsoleteModeInFnType
+    ObsoleteModeInFnType,
+    ObsoleteByMutRefMode
 }
 
 impl ObsoleteSyntax : cmp::Eq {
@@ -94,6 +95,10 @@ impl parser : ObsoleteReporter {
                 "to use a (deprecated) mode in a fn type, you should \
                  give the argument an explicit name (like `&&v: int`)"
             ),
+            ObsoleteByMutRefMode => (
+                "by-mutable-reference mode",
+                "Declare an argument of type &mut T instead"
+            ),
         };
 
         self.report(sp, kind, kind_str, desc);

src/libsyntax/parse/parser.rs

@@ -20,13 +20,13 @@ use obsolete::{
     ObsoleteLowerCaseKindBounds, ObsoleteLet,
     ObsoleteFieldTerminator, ObsoleteStructCtor,
     ObsoleteWith, ObsoleteClassMethod, ObsoleteClassTraits,
-    ObsoleteModeInFnType
+    ObsoleteModeInFnType, ObsoleteByMutRefMode
 };
 use ast::{_mod, add, alt_check, alt_exhaustive, arg, arm, attribute,
              bind_by_ref, bind_by_implicit_ref, bind_by_value, bind_by_move,
              bitand, bitor, bitxor, blk, blk_check_mode, bound_const,
              bound_copy, bound_send, bound_trait, bound_owned, box, by_copy,
-             by_move, by_mutbl_ref, by_ref, by_val, capture_clause,
+             by_move, by_ref, by_val, capture_clause,
              capture_item, cdir_dir_mod, cdir_src_mod, cdir_view_item,
              class_immutable, class_mutable,
              crate, crate_cfg, crate_directive, decl, decl_item, decl_local,
@@ -570,9 +570,10 @@ impl parser {
 
     fn parse_arg_mode() -> mode {
         if self.eat(token::BINOP(token::AND)) {
-            self.span_fatal(copy self.last_span,
-                            ~"Obsolete syntax has no effect");
-            expl(by_mutbl_ref)
+            self.obsolete(copy self.span,
+                          ObsoleteByMutRefMode);
+            // Bogus mode, but doesn't matter since it's an error
+            expl(by_ref)
         } else if self.eat(token::BINOP(token::MINUS)) {
             expl(by_move)
         } else if self.eat(token::ANDAND) {

src/libsyntax/print/pprust.rs

@@ -1688,7 +1688,6 @@ fn print_fn_block_args(s: ps, decl: ast::fn_decl,
 
 fn mode_to_str(m: ast::mode) -> ~str {
     match m {
-      ast::expl(ast::by_mutbl_ref) => ~"&",
       ast::expl(ast::by_move) => ~"-",
       ast::expl(ast::by_ref) => ~"&&",
       ast::expl(ast::by_val) => ~"++",

src/rustc/metadata/tydecode.rs

@@ -394,7 +394,6 @@ fn parse_arg(st: @pstate, conv: conv_did) -> ty::arg {
 
 fn parse_mode(st: @pstate) -> ast::mode {
     let m = ast::expl(match next(st) {
-        '&' => ast::by_mutbl_ref,
         '-' => ast::by_move,
         '+' => ast::by_copy,
         '=' => ast::by_ref,

src/rustc/metadata/tyencode.rs

@@ -333,7 +333,6 @@ fn enc_arg(w: io::Writer, cx: @ctxt, arg: ty::arg) {
 
 fn enc_mode(w: io::Writer, cx: @ctxt, m: mode) {
     match ty::resolved_mode(cx.tcx, m) {
-      by_mutbl_ref => w.write_char('&'),
       by_move => w.write_char('-'),
       by_copy => w.write_char('+'),
       by_ref => w.write_char('='),

src/rustc/middle/borrowck/check_loans.rs

@@ -529,7 +529,7 @@ impl check_loan_ctxt {
                 ast::by_move => {
                     self.check_move_out(*arg);
                 }
-                ast::by_mutbl_ref | ast::by_ref |
+                ast::by_ref |
                 ast::by_copy | ast::by_val => {
                 }
             }

src/rustc/middle/borrowck/gather_loans.rs

@@ -115,10 +115,6 @@ fn req_loans_in_expr(ex: @ast::expr,
         let scope_r = ty::re_scope(ex.id);
         for vec::each2(args, arg_tys) |arg, arg_ty| {
             match ty::resolved_mode(self.tcx(), arg_ty.mode) {
-              ast::by_mutbl_ref => {
-                let arg_cmt = self.bccx.cat_expr(*arg);
-                self.guarantee_valid(arg_cmt, m_mutbl, scope_r);
-              }
               ast::by_ref => {
                 let arg_cmt = self.bccx.cat_expr(*arg);
                 self.guarantee_valid(arg_cmt, m_imm,  scope_r);

src/rustc/middle/kind.rs

@@ -323,7 +323,7 @@ fn check_expr(e: @expr, cx: ctx, v: visit::vt<ctx>) {
         for ty::ty_fn_args(ty::expr_ty(cx.tcx, f)).each |arg_t| {
             match ty::arg_mode(cx.tcx, *arg_t) {
               by_copy => maybe_copy(cx, args[i], None),
-              by_ref | by_val | by_mutbl_ref | by_move => ()
+              by_ref | by_val | by_move => ()
             }
             i += 1u;
         }
@@ -335,7 +335,7 @@ fn check_expr(e: @expr, cx: ctx, v: visit::vt<ctx>) {
             Some(ref mme) => {
                 match ty::arg_mode(cx.tcx, mme.self_arg) {
                     by_copy => maybe_copy(cx, lhs, None),
-                    by_ref | by_val | by_mutbl_ref | by_move => ()
+                    by_ref | by_val | by_move => ()
                 }
             }
             _ => ()
@@ -465,14 +465,7 @@ fn check_imm_free_var(cx: ctx, def: def, sp: span) {
             cx.tcx.sess.span_err(sp, msg);
         }
       }
-      def_arg(_, mode) => {
-        match ty::resolved_mode(cx.tcx, mode) {
-          by_ref | by_val | by_move | by_copy => { /* ok */ }
-          by_mutbl_ref => {
-            cx.tcx.sess.span_err(sp, msg);
-          }
-        }
-      }
+      def_arg(*) => { /* ok */ }
       def_upvar(_, def1, _, _) => {
         check_imm_free_var(cx, *def1, sp);
       }