[tarantool-patches] Re: [PATCH] lua: fix decimal comparison with box.NULL

[Serge Petrenko]

> 27 авг. 2019 г., в 15:25, Vladimir Davydov <vdavydov.dev at gmail.com> написал(а):
> 
> On Tue, Aug 27, 2019 at 03:10:47PM +0300, Serge Petrenko wrote:
>> 
>>> 27 авг. 2019 г., в 15:04, Vladimir Davydov <vdavydov.dev at gmail.com> написал(а):
>>> 
>>> On Tue, Aug 27, 2019 at 02:22:09PM +0300, Serge Petrenko wrote:
>>>> This problem is similar to the one fixed in commit
>>>> 3c6c1cc96a1a510493c21c472565d4063e403ba2 (lua:fix decimal comparison
>>>> with nil)
>>>> We should handle box.NULL the same way.
>>>> 
>>>> Closes #4454
>>>> ---
>>>> https://github.com/tarantool/tarantool/issues/4454
>>>> https://github.com/tarantool/tarantool/tree/sp/gh-4454-decimal-cmp-null
>>>> 
>>>> src/lua/decimal.c         |  3 ++-
>>>> test/app/decimal.result   | 30 ++++++++++++++++++++++++++++++
>>>> test/app/decimal.test.lua |  8 ++++++++
>>>> 3 files changed, 40 insertions(+), 1 deletion(-)
>>>> 
>>>> diff --git a/src/lua/decimal.c b/src/lua/decimal.c
>>>> index 23e50ba68..8905a0b9d 100644
>>>> --- a/src/lua/decimal.c
>>>> +++ b/src/lua/decimal.c
>>>> @@ -235,7 +235,8 @@ static int
>>>> ldecimal_eq(struct lua_State *L)
>>>> {
>>>> 	assert(lua_gettop(L) == 2);
>>>> -	if (lua_isnil(L, 1) || lua_isnil(L, 2)) {
>>>> +	if (lua_isnil(L, 1) || lua_isnil(L, 2) ||
>>>> +	    luaL_isnull(L, 1) || luaL_isnull(L, 2)) {
>>>> 		lua_pushboolean(L, false);
>>>> 		return 1;
>>>> 	}
>>>> diff --git a/test/app/decimal.result b/test/app/decimal.result
>>>> index 8251e13d8..90d0984b0 100644
>>>> --- a/test/app/decimal.result
>>>> +++ b/test/app/decimal.result
>>>> @@ -248,6 +248,36 @@ a <= nil
>>>> | ---
>>>> | - error: '[string "return a <= nil "]:1: attempt to compare decimal with nil'
>>>> | ...
>>>> +-- and with box.NULL
>>>> +--
>>>> +a == box.NULL
>>>> + | ---
>>>> + | - false
>>>> + | ...
>>>> +a ~= box.NULL
>>>> + | ---
>>>> + | - true
>>>> + | ...
>>>> +a > box.NULL
>>>> + | ---
>>>> + | - error: '[string "return a > box.NULL "]:1: expected decimal, number or string as
>>>> + |     1 argument'
>>>> + | ...
>>> 
>>> 1 argument?
>> 
>> 1st argument
>> 
>>> 
>>>> +a < box.NULL
>>>> + | ---
>>>> + | - error: '[string "return a < box.NULL "]:1: expected decimal, number or string as
>>>> + |     2 argument'
>>>> + | ...
>>> 
>>> 2 argument?
>> 
>> 2nd argument
> 
> But in both cases box.NULL is the second argument, isn't it?
> 
> Anyway, looks like it's a different issue, because I get the same
> confusing error message while trying to compare a decimal with, say,
> a string. We can fix it in a separate patch if we need to.

Ah, I see. Sorry for the misunderstanding.
Yes, here’s the reason for it:
(an extract from https://www.lua.org/manual/5.1/manual.html <https://www.lua.org/manual/5.1/manual.html>)
`a >= b is equivalent to b <= a. Note that, in the absence of a "le" metamethod, Lua tries the "lt", assuming that a <= b is equivalent to not (b < a).`
`a > b is equivalent to b < a.`

So, a > box.NULL actually calls `decimal_lt(box.NULL, a)`. That’s why argument numbers get messed up.
AFAIR you don’t have `__gt` and `__ge` metamethods in lua. I guess we should just get rid of argument numbers,
in error messages here, because I don’t see how this can be fixed otherwise.

> 
> Pushed the patch to the master branch as is.

Thanks!


--
Serge Petrenko
sergepetrenko at tarantool.org


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