Re: [Tarantool-patches] [PATCH] box: rfc for stacked diagnostic area

[Nikita Pettik <korablev@tarantool.org>]

On 04 Feb 21:48, Vladislav Shpilevoy wrote:
> Thanks for the RFC.
> 
> It still does not conform with the template, but ok. I see that
> that ship has sailed already, some other RFCs also violate the
> template.
> 
> See 2 comments below.
> 
> >> 10. Are we not going to allow to link two existing errors? I imagine
> >> it could be simpler and more flexible for a user, than filling
> >> one big map in error.new().
> > 
> > Okay, I'm not against it:
> > 
> >  Another way to resolve this issue is to erase diagnostic area before
> > @@ -173,13 +158,23 @@ box.error.prev(error) == error.prev
> >  ```
> >  
> >  Furthermore, let's extend signature of `box.error.new()` with new (optional)
> > -argument - the 'reason' parent error object:
> > +argument - 'prev' - previous error object:
> >  
> >  ```
> >  e1 = box.error.new({code = 111, reason = "just cause"})
> >  e2 = box.error.new({code = 222, reason = "just cause x2", prev = e1})
> >  ```
> >  
> > +User may want to link already existing errors. To achieve this let's add
> > +`set_prev` method to error object or/and `link` to `box.error` so that one can
> > +join two errors:
> > +```
> > +e1 = box.error.new({code = 111, reason = "just cause"})
> > +e2 = box.error.new({code = 222, reason = "just cause x2"})
> > +...
> > +e2.set_prev(e1) -- e2.prev == e1
> > +box.error.link(e1, e2) -- e2.prev == e1
> > +```
> 
> 1. I don't think we need to change box.error global API. It would be
> enough to add new methods to error object. box.error.link() and
> box.error.prev() look redundant. What is a case, when they should
> be used instead of error object methods?
> 
> box.error.new() and last() exist because there is no other way to
> create an error, or to get a last one.

I've added both since was not sure which one is better.
Since you'd prefer avoid changing global interface (which is
reasonable argument) let's leave only e:set_prev():

diff --git a/doc/rfc/1148-stacked-diagnostics.md b/doc/rfc/1148-stacked-diagnostics.md
index d57e040ba..ed121770d 100644
--- a/doc/rfc/1148-stacked-diagnostics.md
+++ b/doc/rfc/1148-stacked-diagnostics.md
@@ -178,14 +178,12 @@ e2 = box.error.new({code = 222, reason = "just cause x2", prev = e1})
 ```
 
 User may want to link already existing errors. To achieve this let's add
-`set_prev` method to error object or/and `link` to `box.error` so that one can
-join two errors:
+`set_prev` method to error object so that one can join two errors:
 ```
 e1 = box.error.new({code = 111, reason = "just cause"})
 e2 = box.error.new({code = 222, reason = "just cause x2"})
 ...
 e2.set_prev(e1) -- e2.prev == e1
-box.error.link(e1, e2) -- e2.prev == e1
 ```
 ### Binary protocol