Re: [Tarantool-patches] [PATCH luajit] test: adapt test checking reversed function

["Максим Корякшин via Tarantool-patches" <tarantool-patches@dev.tarantool.org>]

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Hi! Thanks for the comments. 
 
I agree that it is strange to add this test, as long as it does not test
anything, so I propose to remove it.
 
Best regards,
Maxim Kokryashkin
 
> 
>>Hi, Maxim!
>>
>>Thanks for the patch!
>>
>>Please consider my comments below.
>>
>>On 30.09.21, Maxim Kokryashkin wrote:
>>> The first fiber in Tarantool has only 512Kb of the stack which is not enough to
>>> handle such a deep call chain.
>>> The test is adapted to Tarantool by decreasing the string length.
>>>
>>> Closes tarantool/tarantool#5782
>>> Part of tarantool/tarantool#5845
>>> Part of tarantool/tarantool#4473
>>
>>Looks like it should be 5870 instead 4473. Also, 5845 is already
>>closed.
>>
>>> ---
>>
>>Please show the Tarantool branch as well, to show that problem is gone.
>>
>>> GitHub branch:  https://github.com/tarantool/luajit/tree/fckxorg/gh-5782-adapt-deep-nest-gsub-PUC-Rio
>>> Issue:  https://github.com/tarantool/tarantool/issues/5782
>>>
>>> test/PUC-Rio-Lua-5.1-tests/pm.lua | 9 ++++-----
>>> 1 file changed, 4 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/test/PUC-Rio-Lua-5.1-tests/pm.lua b/test/PUC-Rio-Lua-5.1-tests/pm.lua
>>> index e364ff9d..7da3ef4a 100644
>>> --- a/test/PUC-Rio-Lua-5.1-tests/pm.lua
>>> +++ b/test/PUC-Rio-Lua-5.1-tests/pm.lua
>>> @@ -206,12 +206,11 @@ function rev (s)
>>> return string.gsub(s, "(.)(.+)", function (c,s1) return rev(s1)..c end)
>>> end
>>>
>>> -local x = string.rep('012345', 10)
>>> --- FIXME: The first Tarantool's fiber has only 512Kb of stack.
>>> --- It is not enough for this recursive call.
>>> +-- This test is adapted to match the stack size (512Kb) of the first fiber in
>>> +-- Tarantool.
>>> -- See also  https://github.com/tarantool/tarantool/issues/5782 .
>>> --- The test is disabled for Tarantool binary.
>>> --- assert(rev(rev(x)) == x)
>>> +local x = string.rep('01234', 10)
>>> +assert(rev(rev(x)) == x)
>>
>>The patch is looks OK to me, but the main problem is still here:
>>LuaJIT is badly managing C stack overflow. The same chunk rases an error
>>for Lua 5.1, but crashes for LuaJIT.
>>
>>| $ luajit -e 'local function rev (s) return string.gsub(s, "(.)(.+)", function (c,s1) return rev(s1)..c end) end local x = string.rep("0", 1000) rev(x)'
>>| Segmentation fault
>>
>>| $ lua -e 'local function rev (s) return string.gsub(s, "(.)(.+)", function (c,s1) return rev(s1)..c end) end local x = string.rep("0", 1000) rev(x)'
>>| lua: C stack overflow
>>| stack traceback:
>>| [C]: in function 'gsub'
>>| (command line):1: in function 'rev'
>>| (command line):1: in function <(command line):1>
>>| [C]: in function 'gsub'
>>| (command line):1: in function 'rev'
>>| (command line):1: in function <(command line):1>
>>| [C]: in function 'gsub'
>>| (command line):1: in function 'rev'
>>| (command line):1: in function <(command line):1>
>>| [C]: in function 'gsub'
>>| ...
>>| [C]: in function 'gsub'
>>| (command line):1: in function 'rev'
>>| (command line):1: in function <(command line):1>
>>| [C]: in function 'gsub'
>>| (command line):1: in function 'rev'
>>| (command line):1: in function <(command line):1>
>>| [C]: in function 'gsub'
>>| (command line):1: in function 'rev'
>>| (command line):1: in main chunk
>>| [C]: ?
>>
>>So I suppose it is strange to add test that tests nothing.
>>
>>Thoughts?
>>
>>>
>>>
>>> -- gsub with tables
>>> --
>>> 2.33.0
>>>
>>
>>--
>>Best regards,
>>Sergey Kaplun
> 

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