[Tarantool-patches] [PATCH v2 1/2] lua: introduce table.equals method

[Oleg Babin]

Thanks for your fixes. Seems I found one more issue.

```

mt = {__eq = function(a, b) return a.a == b.a end}

t1 = setmetatable({a = 3}, mt)

t2 = setmetatable({a = 3}, mt)

tarantool> t1 == t2 -- metamethod is triggered
---
- true
...

tarantool> t1 == {a = 3} -- tables have different metatables
---
- false
...

tarantool> {a = 3} == t1
---
- false
...

tarantool> table.equals(t1, t2) -- OK
---
- true
...

tarantool> table.equals(t1, {a = 3}) -- Seems also ok
---
- false
...

tarantool> table.equals({a = 3}, t1) -- It's strange
---
- true
...

```


Seems you can use two tables if they have the same metatable.

Probably here it's described better 
https://stackoverflow.com/questions/32637684/equality-operator-on-mixed-types-in-lua



On 13.08.2021 13:22, Serge Petrenko wrote:
>
>
> 13.08.2021 08:30, Oleg Babin пишет:
>> Thanks for your patch.
>>
>>
>> It seems it works in quite strange way:
>>
>> ```
>>
>> tarantool> table.equals({a = box.NULL}, {})
>> ---
>> - true
>> ...
>>
>> tarantool> table.equals({}, {a = box.NULL})
>> ---
>> - false
>> ...
>>
>> ```
>>
>>
>> I can change arguments order to get different result. Expected false 
>> in both cases.
>>
>> For tap it was considered as buggy behaviour 
>> https://github.com/tarantool/tarantool/issues/4125
>>
>>
>
> ====================================
>
> Good catch! Thanks!
>
> Check out the diff:
>
> diff --git a/src/lua/table.lua b/src/lua/table.lua
> index 5f35a30f6..3d5e69e97 100644
> --- a/src/lua/table.lua
> +++ b/src/lua/table.lua
> @@ -63,7 +63,7 @@ end
>  -- @return true when the two tables are equal (false otherwise).
>  local function table_equals(a, b)
>      if type(a) ~= 'table' or type(b) ~= 'table' then
> -        return a == b
> +        return type(a) == type(b) and a == b
>      end
>      local mt = getmetatable(a)
>      if mt and mt.__eq then
> diff --git a/test/app-tap/table.test.lua b/test/app-tap/table.test.lua
> index a3c9aa123..ec81593f3 100755
> --- a/test/app-tap/table.test.lua
> +++ b/test/app-tap/table.test.lua
> @@ -8,7 +8,7 @@ yaml.cfg{
>      encode_invalid_as_nil  = true,
>  }
>  local test = require('tap').test('table')
> -test:plan(38)
> +test:plan(40)
>
>  do -- check basic table.copy (deepcopy)
>      local example_table = {
> @@ -227,6 +227,10 @@ do -- check table.equals
>      test:ok(table.equals({}, {}), "table.equals for empty tables")
>      test:is(table.equals({}, {1}), false, "table.equals with one 
> empty table")
>      test:is(table.equals({1}, {}), false, "table.equals with one 
> empty table")
> +    test:is(table.equals({key = box.NULL}, {key = nil}), false,
> +            "table.equals for box.NULL and nil")
> +    test:is(table.equals({key = nil}, {key = box.NULL}), false,
> +            "table.equals for box.NULL and nil")
>      local tbl_a = {
>          first = {
>              1,
>
> ====================================
>> On 13.08.2021 02:30, Serge Petrenko via Tarantool-patches wrote:
>>> Introduce table.equals for comparing tables.
>>> The method respects __eq metamethod, if provided.
>>>
>>> Needed-for #5894
>>> ---
>>>
>