[Tarantool-patches] [PATCH] error: add format string usage to form a CustomError message

[Vladislav Shpilevoy]

Hi! Thanks for the patch!

On 28/05/2020 10:31, Leonid Vasiliev wrote:
> For the CustomError the ability to create a message
> using a format string was added.
> 
> Closes #4903
> 
> @TarantoolBot document
> Title: Add format string usage to form a CustomError message
> When creating a ClientError error the predefined format
> (corresponding with the error code) is used.
> When creating a CustomError error a format string can be
> used to form the message.
> 
> ClientError:
> ```Lua
> box.error(code, reason args)
> ```
> 
> CustomError:
> ```Lua
> box.error(type, reason format string, reason args)
> ```

It would be good to provide an example here. And to state, that
client error case is not changed. Otherwise from the text above
it looks like you changed it to be 'the predefined format is used'.
But I will leave it to the doc team to ping you after this is
pushed.

Talking of the client error formatting correctness, it looks like
currently the documentation says:
https://www.tarantool.io/en/doc/2.3/reference/reference_lua/box_error/#lua-function.box.error

	When called with a Lua-table argument, the code and reason have any user-desired values. The result will be those values.

	Parameters:

	reason (string) – description of an error, defined by user
	code (integer) – numeric code for this error, defined by user

So in the site it is said, that 'reason' is defined by user, not be
a predefined internal format. The predefined format is used in
box.error(code, ...) syntax.

> ---
> https://github.com/tarantool/tarantool/issues/4903
> https://github.com/tarantool/tarantool/tree/lvasiliev/gh-4903-format-string-for-CustomError
> @ChangeLog Add format string usage to form a CustomError message