Re: [PATCH] Disable VC when Emacs is noninteractive -batch

[Stephen J. Turnbull]

Richard Stallman writes:

  stephen wrote:

 >     IMO, if VC's hooks are active in batch mode, that's a bug.
 > 
 > I don't see why.

Because they change the behavior of Emacs depending on, for example,
whether the working file differs from the repository file.

 >     You don't want programs that are *implicitly* sensitive to
 >     environment state active in batch mode.
 > 
 > I don't follow at all.  If "environment state" means the file system,
 > we certainly don't expect commands that operate on files to be
 > insensitive to that.

VC, however, uses metadata that most programs are not aware of.  This
can make a program that is deterministic when VC is not loaded
nondeterministic when it is loaded.  That's a bad thing if no human is
there to say "Whoa!  M-x undo!"

 >       (I'm sure there are good reasons for using VC
 >     noninteractively, although I personally don't use it in batch mode.
 >     But such programs should call VC functions explicitly.)
 > 
 > VC only does anything when you call VC functions explicitly.
 > Unless it has a bug.

That's clearly not true, for some value of "does anything": VC
installs hooks which are called for various file and buffer
operations.