bug#40407: [PATCH] slow ENCODE_FILE and DECODE_FILE

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Sat, 4 Apr 2020 00:32:21 +0200
> Cc: 40407@debbugs.gnu.org
> 
> Since string mutation is so rare, I doubt it has caused any real trouble. 
> Now, do we fix it by inverting the sense of the argument, or by renaming it 
> to COPY? I'm fairly neutral, but there are arguments in either way, both in 
> terms of performance and correctness. And what about internal calls to 
> code_convert_string?
> 
> There are 193 calls to {encode, decode}-coding-string in the Emacs tree, and 
> only 14 of them pass a non-nil value to NOCOPY. I'd be inclined to keep the 
> semantics but rename the argument to COPY, on the grounds that no-copy is a 
> better default; then change those 14 calls to pass nil instead, since that 
> obviously was the intent.

After looking at this for some time, I think the problem is rarely if
ever seen.  The only function which has the NOCOPY sense inverted is
code_convert_string, and it only does that when the CODING_SYSTEM
argument is nil, which should almost never happen.  So I think it's OK
to change code_convert_string on master to use NOCOPY in its correct
sense.