mruby-compiler: allow at-least-once loop behavior for mruby

mruby does not provide `begin ... end while cond` that behave at-least-once
loop, like CRuby does. It remains in TODO.md for long time. But finally we have
implemented the behavior.

TODO.md

@@ -9,5 +9,4 @@
 
 # Things to do (Things we need to consider)
 
-- `begin ... end while cond` to behave as CRuby
 - special variables ($1,$2..)

mrbgems/mruby-compiler/core/codegen.c

@@ -3679,12 +3679,13 @@ codegen(codegen_scope *s, node *tree, int val)
       if (!val) lp->reg = -1;
 
       /* Jump to body start on first iteration */
-      uint32_t body_start = genjmp2_0(s, OP_JMP, cursp(), NOVAL);
+      uint32_t body_start = genjmp_0(s, OP_JMP);
 
       /* pc0 is next target - condition check */
       lp->pc0 = new_label(s);
       codegen(s, tree->car, VAL);
       pop();
+      uint32_t pos = JMPLINK_START;
       if (nt == NODE_WHILE_MOD) {
         pos = genjmp2_0(s, OP_JMPNOT, cursp(), NOVAL);
       }

mrbgems/mruby-compiler/core/node.h

@@ -16,6 +16,8 @@ enum node_type {
   NODE_WHEN,
   NODE_WHILE,
   NODE_UNTIL,
+  NODE_WHILE_MOD,
+  NODE_UNTIL_MOD,
   NODE_ITER,
   NODE_FOR,
   NODE_BREAK,

mrbgems/mruby-compiler/core/parse.y

@@ -483,6 +483,22 @@ new_until(parser_state *p, node *a, node *b)
   return cons((node*)NODE_UNTIL, cons(a, b));
 }
 
+/* (:while_mod cond body) */
+static node*
+new_while_mod(parser_state *p, node *a, node *b)
+{
+  void_expr_error(p, a);
+  return cons((node*)NODE_WHILE_MOD, cons(a, b));
+}
+
+/* (:until_mod cond body) */
+static node*
+new_until_mod(parser_state *p, node *a, node *b)
+{
+  void_expr_error(p, a);
+  return cons((node*)NODE_UNTIL_MOD, cons(a, b));
+}
+
 /* (:for var obj body) */
 static node*
 new_for(parser_state *p, node *v, node *o, node *b)
@@ -1794,11 +1810,21 @@ stmt            : keyword_alias fsym {p->lstate = EXPR_FNAME;} fsym
                     }
                 | stmt modifier_while expr_value
                     {
-                      $$ = new_while(p, cond($3), $1);
+                      if ($1 && typen($1->car) == NODE_BEGIN) {
+                        $$ = new_while_mod(p, cond($3), $1);
+                      }
+                      else {
+                        $$ = new_while(p, cond($3), $1);
+                      }
                     }
                 | stmt modifier_until expr_value
                     {
-                      $$ = new_until(p, cond($3), $1);
+                      if ($1 && typen($1->car) == NODE_BEGIN) {
+                        $$ = new_until_mod(p, cond($3), $1);
+                      }
+                      else {
+                        $$ = new_until(p, cond($3), $1);
+                      }
                     }
                 | stmt modifier_rescue stmt
                     {
@@ -7283,6 +7309,26 @@ mrb_parser_dump(mrb_state *mrb, node *tree, int offset)
     mrb_parser_dump(mrb, tree->cdr, offset+2);
     break;
 
+  case NODE_WHILE_MOD:
+    printf("NODE_WHILE_MOD:\n");
+    dump_prefix(tree, offset+1);
+    printf("cond:\n");
+    mrb_parser_dump(mrb, tree->car, offset+2);
+    dump_prefix(tree, offset+1);
+    printf("body:\n");
+    mrb_parser_dump(mrb, tree->cdr, offset+2);
+    break;
+
+  case NODE_UNTIL_MOD:
+    printf("NODE_UNTIL_MOD:\n");
+    dump_prefix(tree, offset+1);
+    printf("cond:\n");
+    mrb_parser_dump(mrb, tree->car, offset+2);
+    dump_prefix(tree, offset+1);
+    printf("body:\n");
+    mrb_parser_dump(mrb, tree->cdr, offset+2);
+    break;
+
   case NODE_FOR:
     printf("NODE_FOR:\n");
     dump_prefix(tree, offset+1);