bug#48579: 28.0.50; Spawning an emacs process using call-process results in inconsistent, behavior between GNU/Linux and macOS

[Daniel Mendler <mail@daniel-mendler.de>]

On 5/22/21 2:20 PM, Eli Zaretskii wrote:
>> Cc: alan@idiocy.org, 48579@debbugs.gnu.org
>> From: Daniel Mendler <mail@daniel-mendler.de>
>> Date: Sat, 22 May 2021 13:44:27 +0200
>>
>> Both GNU/Linux and macOS are Unixes, it is expected that Emacs behaves
>> in the same way on both platforms with regards to handling the current
>> directory. When Emacs is started via the command line or via forking
>> from another process, Emacs should inherit the default directory from
>> the parent process.
> 
> If this is what you think, then your concept of the default-directory
> is in direct contradiction with how Emacs works.  The cwd of the Emacs
> process is immaterial, and actually not even easily visible inside
> Emacs.  When a buffer visits a file, Emacs makes a point of behaving
> like that file's directory was its cwd.  For other buffers, my
> suggestion is to consider their default-directory to be indeterminate,
> and if you need it to have a specified value, you should force that by
> calling 'cd' or setting default-directory explicitly.  Anything else
> is bound to trip you some day, because it simply isn't how Emacs was
> designed to behave.

I am aware that the file visiting buffers have a different
default-directory. However the initial scratch buffer should inherit the
current working directory of the parent process. I don't see why some
"indeterminate" or "undefined" behavior is justified here.

> So when you say that Emacs should behave the same on these platforms,
> you should first ask yourself what is that "same behavior".  My answer
> is simple: you cannot predict what is the default-directory of a
> random buffer that doesn't visit a file.  In this sense, Emacs indeed
> works the same on all platforms.  Any other sense you may wish to
> assign to that is simply a basic mistake.

There is no technical roadblock preventing Emacs from determining the
current directory (at least on Unixes). The problem is that the Mac
Emacs port changes the directory according to its own standards.

Why do you call this "indeterminate", "undefined" or "random" behavior?
Are there other examples where buffers have random directories?

Daniel