mruby error messages should be directed to stderr

include/mruby.h

@@ -317,6 +317,7 @@ void mrb_name_error(mrb_state *mrb, mrb_sym id, const char *fmt, ...);
 void mrb_warn(mrb_state *mrb, const char *fmt, ...);
 void mrb_bug(mrb_state *mrb, const char *fmt, ...);
 void mrb_print_backtrace(mrb_state *mrb);
+void mrb_print_error(mrb_state *mrb);
 
 /* macros to get typical exception objects
    note:

mrbgems/mruby-bin-mruby/tools/mruby/mruby.c

@@ -198,8 +198,7 @@ main(int argc, char **argv)
       mrb_run(mrb, mrb_proc_new(mrb, mrb->irep[n]), mrb_top_self(mrb));
       n = 0;
       if (mrb->exc) {
-        mrb_print_backtrace(mrb);
-        p(mrb, mrb_obj_value(mrb->exc));
+        mrb_print_error(mrb);
         n = -1;
       }
     }
@@ -230,8 +229,7 @@ main(int argc, char **argv)
     mrbc_context_free(mrb, c);
     if (mrb->exc) {
       if (!mrb_undef_p(v)) {
-        mrb_print_backtrace(mrb);
-        p(mrb, mrb_obj_value(mrb->exc));
+        mrb_print_error(mrb);
       }
       n = -1;
     }

src/backtrace.c

@@ -17,7 +17,7 @@ mrb_print_backtrace(mrb_state *mrb)
   const char *filename, *method, *sep;
   int i, line;
 
-  printf("trace:\n");
+  fputs("trace:\n", stderr);
   ciidx = mrb_fixnum(mrb_obj_iv_get(mrb, mrb->exc, mrb_intern(mrb, "ciidx")));
   if (ciidx >= mrb->c->ciend - mrb->c->cibase)
     ciidx = 10; /* ciidx is broken... */
@@ -59,14 +59,14 @@ mrb_print_backtrace(mrb_state *mrb)
       const char *cn = mrb_class_name(mrb, ci->proc->target_class);
 
       if (cn) {
-        printf("\t[%d] %s:%d:in %s%s%s\n", i, filename, line, cn, sep, method);
+        fprintf(stderr, "\t[%d] %s:%d:in %s%s%s\n", i, filename, line, cn, sep, method);
       }
       else {
-        printf("\t[%d] %s:%d:in %s\n", i, filename, line, method);
+        fprintf(stderr, "\t[%d] %s:%d:in %s\n", i, filename, line, method);
       }
     }
     else {
-      printf("\t[%d] %s:%d\n", i, filename, line);
+      fprintf(stderr, "\t[%d] %s:%d\n", i, filename, line);
     }
   }
 #endif

src/print.c

@@ -34,6 +34,22 @@ mrb_p(mrb_state *mrb, mrb_value obj)
 #endif
 }
 
+void
+mrb_print_error(mrb_state *mrb)
+{
+#ifdef ENABLE_STDIO
+  mrb_value s;
+  
+  mrb_print_backtrace(mrb);
+  s = mrb_funcall(mrb, mrb_obj_value(mrb->exc), "inspect", 0);
+  if (mrb_string_p(s)) {
+    struct RString *str = mrb_str_ptr(s);
+    fwrite(str->ptr, str->len, 1, stderr);
+    putc('\n', stderr);
+  }
+#endif
+}
+
 void
 mrb_show_version(mrb_state *mrb)
 {

tasks/mrbgem_spec.rake

@@ -136,8 +136,7 @@ module MRuby
           unless rbfiles.empty?
             f.puts %Q[  mrb_load_irep(mrb, gem_mrblib_irep_#{funcname});]
             f.puts %Q[  if (mrb->exc) {]
-            f.puts %Q[    mrb_print_backtrace(mrb);]
-            f.puts %Q[    mrb_p(mrb, mrb_obj_value(mrb->exc));]
+            f.puts %Q[    mrb_print_error(mrb);]
             f.puts %Q[    exit(EXIT_FAILURE);]
             f.puts %Q[  }]
           end