Re: [vim/vim] fix: ":for" over a tuple leaks memory on every iteration (PR #20914)

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SamuelSchlesinger left a comment (vim/vim#20914)

Here's one you can verify from outside of the code, it is a bit more minimal: 

```vimscript
" Minimal reproduction of the ":for" over a tuple memory leak.
" The script uses nothing but :let, :while and :for.  Measure memory from
" the outside:
"
"   macOS:  /usr/bin/time -l ./vim -N -u NONE -i NONE -es -S tuple_leak_demo.vim
"   Linux:  /usr/bin/time -v ./vim -N -u NONE -i NONE -es -S tuple_leak_demo.vim
"
" Observed max RSS (macOS, 1,000,000 iterations):
"   unpatched:  93.0 MB   (~80 bytes leaked per iteration: the copied items)
"   patched:    12.8 MB
"
" Control: change the tuple (...) below into a list [...] and the unpatched
" max RSS drops to 12.7 MB, isolating the leak to the tuple code path.

let i = 0
while i < 1000000
  for x in ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'b')
  endfor
  let i += 1
endwhile
qa!
```

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<div style=3D"display: flex; flex-wrap: wrap; white-space: pre-wrap; align-=
items: center; "><img height=3D"20" width=3D"20" style=3D"border-radius:50%=
; margin-right: 4px;" decoding=3D"async" src=3D"https://avatars.githubuserc=
ontent.com/u/10200200" /><strong>SamuelSchlesinger</strong> left a comment =
<a href=3D"https://github.com/vim/vim/pull/20914#issuecomment-5157544718">(=
vim/vim#20914)</a></div>
<p dir=3D"auto">Here's one you can verify from outside of the code, it is a=
 bit more minimal:</p>
<div class=3D"highlight highlight-source-viml" dir=3D"auto"><pre class=3D"n=
otranslate"><span class=3D"pl-c"><span class=3D"pl-c">"</span> Minimal repr=
oduction of the ":for" over a tuple memory leak.</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span> The script uses nothing =
but :let, :while and :for.  Measure memory from</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span> the outside:</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span></span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span>   macOS:  /usr/bin/time =
-l ./vim -N -u NONE -i NONE -es -S tuple_leak_demo.vim</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span><span class=3D"pl-c1">   =
Linux:</span>  /usr/bin/time -v ./vim -N -u NONE -i NONE -es -S tuple_leak_=
demo.vim</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span></span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span> Observed max RSS (macOS,=
 1,000,000 iterations):</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span>   unpatched:  93.0 MB   =
(~80 bytes leaked per iteration: the copied items)</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span>   patched:    12.8 MB</s=
pan>
<span class=3D"pl-c"><span class=3D"pl-c">"</span></span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span><span class=3D"pl-c1"> Co=
ntrol:</span> change the tuple (...) below into a list [...] and the unpatc=
hed</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span> max RSS drops to 12.7 MB=
, isolating the leak to the tuple code path.</span>

<span class=3D"pl-k">let</span> <span class=3D"pl-c1">i</span> <span class=
=3D"pl-k">=3D</span> <span class=3D"pl-c1">0</span>
<span class=3D"pl-k">while</span> <span class=3D"pl-c1">i</span><span class=
=3D"pl-k"> &lt; </span><span class=3D"pl-c1">1000000</span>
  <span class=3D"pl-k">for</span> <span class=3D"pl-c1">x</span> <span clas=
s=3D"pl-k">in</span> (<span class=3D"pl-s"><span class=3D"pl-pds">'</span>a=
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa<span class=3D"pl-pds">'</=
span></span>, <span class=3D"pl-s"><span class=3D"pl-pds">'</span>b<span cl=
ass=3D"pl-pds">'</span></span>)
  <span class=3D"pl-k">endfor</span>
  <span class=3D"pl-k">let</span> <span class=3D"pl-c1">i</span> <span clas=
s=3D"pl-k">+=3D</span> <span class=3D"pl-c1">1</span>
<span class=3D"pl-k">endwhile</span>
<span class=3D"pl-c1">qa</span><span class=3D"pl-k">!</span></pre></div>

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