Make most of the compiler aware of return-by-reference

tyencode/tydecode still don't know about it. return_ref will be extended to take
arguments anyway.

src/comp/metadata/tyencode.rs

@@ -218,7 +218,10 @@ fn enc_ty_fn(w: io::writer, cx: @ctxt, args: [ty::arg], out: ty::t,
         } else { w.write_char(';'); }
         enc_constr(w, cx, c);
     }
-    alt cf { noreturn. { w.write_char('!'); } _ { enc_ty(w, cx, out); } }
+    alt cf {
+      noreturn. { w.write_char('!'); }
+      _ { enc_ty(w, cx, out); }
+    }
 }
 
 // FIXME less copy-and-paste

src/comp/middle/ty.rs

@@ -279,7 +279,7 @@ type constr = constr_general<uint>;
 // Data structures used in type unification
 tag type_err {
     terr_mismatch;
-    terr_controlflow_mismatch;
+    terr_ret_style_mismatch(ast::ret_style, ast::ret_style);
     terr_box_mutability;
     terr_vec_mutability;
     terr_tuple_size(uint, uint);
@@ -1952,26 +1952,13 @@ mod unify {
                 _expected_constrs: [@constr], actual_constrs: [@constr]) ->
        result {
         if e_proto != a_proto { ret ures_err(terr_mismatch); }
-        alt expected_cf {
+        if actual_cf != ast::noreturn && actual_cf != expected_cf {
-          ast::return_val. { }
-          // ok
-          ast::noreturn. {
-            alt actual_cf {
-              ast::noreturn. {
-                // ok
-
-              }
-              _ {
             /* even though typestate checking is mostly
                responsible for checking control flow annotations,
                this check is necessary to ensure that the
                annotation in an object method matches the
                declared object type */
-
+            ret ures_err(terr_ret_style_mismatch(expected_cf, actual_cf));
-                ret ures_err(terr_controlflow_mismatch);
-              }
-            }
-          }
         }
         let t =
             unify_fn_common(cx, expected, actual, expected_inputs,
@@ -2470,9 +2457,16 @@ mod unify {
 fn type_err_to_str(err: ty::type_err) -> str {
     alt err {
       terr_mismatch. { ret "types differ"; }
-      terr_controlflow_mismatch. {
+      terr_ret_style_mismatch(expect, actual) {
-        ret "returning function used where non-returning function" +
+        fn to_str(s: ast::ret_style) -> str {
-                " was expected";
+            alt s {
+              ast::noreturn. { "non-returning" }
+              ast::return_val. { "return-by-value" }
+              ast::return_ref. { "return-by-reference" }
+            }
+        }
+        ret to_str(actual) + " function found where " + to_str(expect) +
+            " function was expected";
       }
       terr_box_mutability. { ret "boxed values differ in mutability"; }
       terr_vec_mutability. { ret "vectors differ in mutability"; }

src/comp/syntax/print/pprust.rs

@@ -1224,6 +1224,7 @@ fn print_fn_args_and_ret(s: ps, decl: ast::fn_decl, constrs: [@ast::constr]) {
     if decl.output.node != ast::ty_nil {
         space_if_not_bol(s);
         word_space(s, "->");
+        if decl.cf == ast::return_ref { word(s.s, "&"); }
         print_type(s, decl.output);
     }
 }
@@ -1419,9 +1420,11 @@ fn print_ty_fn(s: ps, proto: ast::proto, id: option::t<ast::ident>,
         space_if_not_bol(s);
         ibox(s, indent_unit);
         word_space(s, "->");
-        alt cf {
+        if cf == ast::noreturn {
-          ast::return_val. { print_type(s, output); }
+            word_nbsp(s, "!")
-          ast::noreturn. { word_nbsp(s, "!"); }
+        } else {
+            if cf == ast::return_ref { word(s.s, "&"); }
+            print_type(s, output);
         }
         end(s);
     }

src/comp/util/ppaux.rs

@@ -58,9 +58,12 @@ fn ty_to_str(cx: ctxt, typ: t) -> str {
         s += str::connect(strs, ", ");
         s += ")";
         if struct(cx, output) != ty_nil {
-            alt cf {
+            s += " -> ";
-              ast::noreturn. { s += " -> !"; }
+            if cf == ast::noreturn {
-              ast::return_val. { s += " -> " + ty_to_str(cx, output); }
+                s += "!";
+            } else {
+                if cf == ast::return_ref { s += "&"; }
+                s += ty_to_str(cx, output);
             }
         }
         s += constrs_str(constrs);