Add startless range (another part of #5085)

Ref #5093; close #5085

mrbgems/mruby-compiler/core/parse.y

@@ -1478,6 +1478,7 @@ heredoc_end(parser_state *p)
 %token tANDOP tOROP       /* && and || */
 %token tMATCH tNMATCH     /* =~ and !~ */
 %token tDOT2 tDOT3        /* .. and ... */
+%token tBDOT2 tBDOT3      /* (.. and (... */
 %token tAREF tASET        /* [] and []= */
 %token tLSHFT tRSHFT      /* << and >> */
 %token tCOLON2            /* :: */
@@ -1514,7 +1515,7 @@ heredoc_end(parser_state *p)
 %right '=' tOP_ASGN
 %left modifier_rescue
 %right '?' ':' tLABEL_TAG
-%nonassoc tDOT2 tDOT3
+%nonassoc tDOT2 tDOT3 tBDOT2 tBDOT3
 %left  tOROP
 %left  tANDOP
 %nonassoc  tCMP tEQ tEQQ tNEQ tMATCH tNMATCH
@@ -2194,6 +2195,10 @@ arg             : lhs '=' arg_rhs
                     {
                       $$ = new_dot2(p, $1, new_nil(p));
                     }
+                | tBDOT2 arg
+                    {
+                      $$ = new_dot2(p, new_nil(p), $2);
+                    }
                 | arg tDOT3 arg
                     {
                       $$ = new_dot3(p, $1, $3);
@@ -2202,6 +2207,10 @@ arg             : lhs '=' arg_rhs
                     {
                       $$ = new_dot3(p, $1, new_nil(p));
                     }
+                | tBDOT3 arg
+                    {
+                      $$ = new_dot3(p, new_nil(p), $2);
+                    }
                 | arg '+' arg
                     {
                       $$ = call_bin_op(p, $1, "+", $3);
@@ -5440,13 +5449,15 @@ parser_yylex(parser_state *p)
     return '-';
 
   case '.':
+    {
+      int is_beg = IS_BEG();
       p->lstate = EXPR_BEG;
       if ((c = nextc(p)) == '.') {
         if ((c = nextc(p)) == '.') {
-        return tDOT3;
+          return is_beg ? tBDOT3 : tDOT3;
         }
         pushback(p, c);
-      return tDOT2;
+        return is_beg ? tBDOT2 : tDOT2;
       }
       pushback(p, c);
       if (c >= 0 && ISDIGIT(c)) {
@@ -5454,6 +5465,7 @@ parser_yylex(parser_state *p)
       }
       p->lstate = EXPR_DOT;
       return '.';
+    }
 
     start_num:
   case '0': case '1': case '2': case '3': case '4':

src/range.c

@@ -32,7 +32,7 @@ r_check(mrb_state *mrb, mrb_value a, mrb_value b)
     return;
   }
 
-  if (mrb_nil_p(b)) return;
+  if (mrb_nil_p(a) || mrb_nil_p(b)) return;
 
   n = mrb_cmp(mrb, a, b);
   if (n == -2) {                /* can not be compared */
@@ -217,7 +217,13 @@ range_include(mrb_state *mrb, mrb_value range)
 
   beg = RANGE_BEG(r);
   end = RANGE_END(r);
-  if (r_le(mrb, beg, val)) {                   /* beg <= val */
+  if (mrb_nil_p(beg)) {
+    if (RANGE_EXCL(r) ? r_gt(mrb, end, val)    /* end >  val */
+                      : r_ge(mrb, end, val)) { /* end >= val */
+      return mrb_true_value();
+    }
+  }
+  else if (r_le(mrb, beg, val)) {              /* beg <= val */
     if (mrb_nil_p(end)) {
       return mrb_true_value();
     }
@@ -266,9 +272,14 @@ range_inspect(mrb_state *mrb, mrb_value range)
   mrb_value str;
   struct RRange *r = mrb_range_ptr(mrb, range);
 
+  if (!mrb_nil_p(RANGE_BEG(r))) {
     str  = mrb_inspect(mrb, RANGE_BEG(r));
     str  = mrb_str_dup(mrb, str);
     mrb_str_cat(mrb, str, "...", RANGE_EXCL(r) ? 3 : 2);
+  }
+  else {
+    str = mrb_str_new(mrb, "...", RANGE_EXCL(r) ? 3 : 2);
+  }
   if (!mrb_nil_p(RANGE_END(r))) {
     mrb_value str2 = mrb_inspect(mrb, RANGE_END(r));
     mrb_str_cat_str(mrb, str, str2);