Simplify backtrace mechanism; fix #3633 #3634 #3644

Instead of preserving a backtrace in `mrb_state`, `mrb_exc_set`
keeps packed backtrace in an exception object. `#backtrace` unpacks
it to an array of strings.

include/mruby.h

@@ -152,12 +152,6 @@ struct mrb_context {
 
 struct mrb_jmpbuf;
 
-typedef struct {
-  const char *filename;
-  int lineno;
-  mrb_sym method_id;
-} mrb_backtrace_entry;
-
 typedef void (*mrb_atexit_func)(struct mrb_state*);
 
 #define MRB_STATE_NO_REGEXP 1
@@ -172,15 +166,9 @@ typedef struct mrb_state {
 
   struct mrb_context *c;
   struct mrb_context *root_c;
+  struct iv_tbl *globals;                 /* global variable table */
 
   struct RObject *exc;                    /* exception */
-  struct {
-    struct RObject *exc;
-    int n;
-    int n_allocated;
-    mrb_backtrace_entry *entries;
-  } backtrace;
-  struct iv_tbl *globals;                 /* global variable table */
 
   struct RObject *top_self;
   struct RClass *object_class;            /* Object class */

include/mruby/error.h

@@ -25,7 +25,6 @@ MRB_API void mrb_sys_fail(mrb_state *mrb, const char *mesg);
 MRB_API mrb_value mrb_exc_new_str(mrb_state *mrb, struct RClass* c, mrb_value str);
 #define mrb_exc_new_str_lit(mrb, c, lit) mrb_exc_new_str(mrb, c, mrb_str_new_lit(mrb, lit))
 MRB_API mrb_value mrb_make_exception(mrb_state *mrb, int argc, const mrb_value *argv);
-MRB_API mrb_value mrb_exc_backtrace(mrb_state *mrb, mrb_value exc);
 MRB_API mrb_value mrb_get_backtrace(mrb_state *mrb);
 MRB_API mrb_noreturn void mrb_no_method_error(mrb_state *mrb, mrb_sym id, mrb_value args, const char *fmt, ...);
 

src/error.c

@@ -163,8 +163,8 @@ exc_inspect(mrb_state *mrb, mrb_value exc)
   return str;
 }
 
-void mrb_save_backtrace(mrb_state *mrb);
-mrb_value mrb_restore_backtrace(mrb_state *mrb);
+void mrb_keep_backtrace(mrb_state *mrb, mrb_value exc);
+mrb_value mrb_unpack_backtrace(mrb_state *mrb, mrb_value backtrace);
 
 static mrb_value
 exc_get_backtrace(mrb_state *mrb, mrb_value exc)
@@ -175,17 +175,9 @@ exc_get_backtrace(mrb_state *mrb, mrb_value exc)
   attr_name = mrb_intern_lit(mrb, "backtrace");
   backtrace = mrb_iv_get(mrb, exc, attr_name);
   if (!mrb_array_p(backtrace)) {
-    if (mrb_obj_ptr(exc) == mrb->backtrace.exc && mrb->backtrace.n > 0) {
-      backtrace = mrb_restore_backtrace(mrb);
-      mrb->backtrace.n = 0;
-      mrb->backtrace.exc = 0;
-    }
-    else {
-      backtrace = mrb_exc_backtrace(mrb, exc);
-    }
+    backtrace = mrb_unpack_backtrace(mrb, backtrace);
     mrb_iv_set(mrb, exc, attr_name, backtrace);
   }
-
   return backtrace;
 }
 
@@ -224,7 +216,6 @@ exc_debug_info(mrb_state *mrb, struct RObject *exc)
   mrb_callinfo *ci = mrb->c->ci;
   mrb_code *pc = ci->pc;
 
-  mrb_obj_iv_set(mrb, exc, mrb_intern_lit(mrb, "ciidx"), mrb_fixnum_value((mrb_int)(ci - mrb->c->cibase)));
   while (ci >= mrb->c->cibase) {
     mrb_code *err = ci->err;
 
@@ -245,36 +236,9 @@ exc_debug_info(mrb_state *mrb, struct RObject *exc)
   }
 }
 
-static mrb_bool
-have_backtrace(mrb_state *mrb, struct RObject *exc)
-{
-  return !mrb_nil_p(mrb_obj_iv_get(mrb, exc, mrb_intern_lit(mrb, "backtrace")));
-}
-
 void
 mrb_exc_set(mrb_state *mrb, mrb_value exc)
 {
-  if (!mrb->gc.out_of_memory && mrb->backtrace.n > 0) {
-    mrb_value target_exc = mrb_nil_value();
-    int ai;
-
-    ai = mrb_gc_arena_save(mrb);
-    if ((mrb->exc && !have_backtrace(mrb, mrb->exc))) {
-      target_exc = mrb_obj_value(mrb->exc);
-    }
-    else if (!mrb_nil_p(exc) && mrb->backtrace.exc) {
-      target_exc = mrb_obj_value(mrb->backtrace.exc);
-      mrb_gc_protect(mrb, target_exc);
-    }
-    if (!mrb_nil_p(target_exc)) {
-      mrb_value backtrace;
-      backtrace = mrb_restore_backtrace(mrb);
-      set_backtrace(mrb, target_exc, backtrace);
-    }
-    mrb_gc_arena_restore(mrb, ai);
-  }
-
-  mrb->backtrace.n = 0;
   if (mrb_nil_p(exc)) {
     mrb->exc = 0;
   }
@@ -282,7 +246,7 @@ mrb_exc_set(mrb_state *mrb, mrb_value exc)
     mrb->exc = mrb_obj_ptr(exc);
     if (!mrb->gc.out_of_memory) {
       exc_debug_info(mrb, mrb->exc);
-      mrb_save_backtrace(mrb);
+      mrb_keep_backtrace(mrb, exc);
     }
   }
 }

src/gc.c

@@ -735,8 +735,6 @@ obj_free(mrb_state *mrb, struct RBasic *obj, int end)
 
   case MRB_TT_EXCEPTION:
     mrb_gc_free_iv(mrb, (struct RObject*)obj);
-    if ((struct RObject*)obj == mrb->backtrace.exc)
-      mrb->backtrace.exc = 0;
     break;
 
   case MRB_TT_CLASS:
@@ -870,8 +868,6 @@ root_scan_phase(mrb_state *mrb, mrb_gc *gc)
   mrb_gc_mark(mrb, (struct RBasic*)mrb->top_self);
   /* mark exception */
   mrb_gc_mark(mrb, (struct RBasic*)mrb->exc);
-  /* mark backtrace */
-  mrb_gc_mark(mrb, (struct RBasic*)mrb->backtrace.exc);
   /* mark pre-allocated exception */
   mrb_gc_mark(mrb, (struct RBasic*)mrb->nomem_err);
   mrb_gc_mark(mrb, (struct RBasic*)mrb->stack_err);

src/kernel.c

@@ -872,7 +872,6 @@ mrb_f_raise(mrb_state *mrb, mrb_value self)
     /* fall through */
   default:
     exc = mrb_make_exception(mrb, argc, a);
-    mrb_obj_iv_set(mrb, mrb_obj_ptr(exc), mrb_intern_lit(mrb, "lastpc"), mrb_cptr_value(mrb, mrb->c->ci->pc));
     mrb_exc_raise(mrb, exc);
     break;
   }

src/state.c

@@ -246,7 +246,6 @@ mrb_close(mrb_state *mrb)
 
   /* free */
   mrb_gc_free_gv(mrb);
-  mrb_free_backtrace(mrb);
   mrb_free_context(mrb, mrb->root_c);
   mrb_free_symtbl(mrb);
   mrb_alloca_free(mrb);

src/vm.c

@@ -1741,8 +1741,6 @@ RETRY_TRY_BLOCK:
 
       L_RAISE:
         ci0 = ci = mrb->c->ci;
-        mrb_obj_iv_ifnone(mrb, mrb->exc, mrb_intern_lit(mrb, "lastpc"), mrb_cptr_value(mrb, pc));
-        mrb_obj_iv_ifnone(mrb, mrb->exc, mrb_intern_lit(mrb, "ciidx"), mrb_fixnum_value(ci - mrb->c->cibase));
         eidx = ci->eidx;
         if (ci == mrb->c->cibase) {
           if (ci->ridx == 0) goto L_STOP;