Re: luaL_buffinit stack manipulation
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- Subject: Re: luaL_buffinit stack manipulation
- From: Andrew Gierth <andrew@...>
- Date: 2021年7月08日 12:33:42 +0100
>>>>> "Benoit" == Benoit Germain <bnt.germain@gmail.com> writes:
Benoit> Hello,
Benoit> I've just discovered that in Lua 5.4.3, luaL_buffinit pushes a
Benoit> light userdata on the stack, which it did not do in previous
Benoit> versions.
In previous versions, the luaL_Buffer functions would push a (full)
userdata, or in older versions possibly multiple full userdatas, onto
the stack at some unpredictable point. Hence the warnings about balanced
stack usage when using luaL_Buffer in the documentation.
This interface has been a _major_ cause of subtle bugs even for
experienced programmers (there are many examples in the list archives),
so there was a desire to at least have a way to check for those bugs.
5.4.3 compiled with asserts enabled will give an assert failure in at
least some cases of misuse; and it may be the ability to check this
assertion that prompted the "push a lightuserdata on the stack
immediately as a placeholder" change (it's part of the same commit).
The placeholder lightuserdata is replaced with a full userdata when the
initial buffer space in the luaL_Buffer is filled.
Benoit> However, the documentation for the function is [-0, +0, –] ,
Benoit> meaning we should not expect anything to be pushed on the
Benoit> stack, nor any error raised. Also, API incompatibility doesn't
Benoit> say anything about it either.
That may qualify as a documentation bug; [-0, +?, -] would be more
accurate.
--
Andrew.