Need vc-make-backup-files-when-linked

Need vc-make-backup-files-when-linked

[Neal Becker]

It is commonly recommended to use cp -al to make local clones when using 
mercurial.  emacs will not break the hard  links when files are edited, 
because vc-make-backup-files is usually nil.

We should have vc-make-backup-files-when-linked, which defaults to t, so that 
emacs will normally break the links.  This is the behavior users will 
expect.

Re: Need vc-make-backup-files-when-linked

[Miles Bader]

Neal Becker <ndbecker2@gmail.com> writes:
> It is commonly recommended to use cp -al to make local clones when using 
> mercurial.  emacs will not break the hard  links when files are edited, 
> because vc-make-backup-files is usually nil.

I think the default setting of `vc-make-backup-files' (nil) is quite
dangerous for another reason too:  backup files and commits often do not
have the same granularity, and if a user happens to edit for a long
period of time before committing, there's a good chance they'll get
screwed.

This is especially true with source-control systems like CVS or
Subversion that do not allow cheap/undoable local commits, but even for
more modern systems, I don't think Emacs should be making such a
dangerous assumptions (that they commit often, and so do not need Emacs
backup files) about the users' work habits.

Even in the case where a user has commited some changes, I don't think
one can simply assume that the repository contents obviates the need for
backup files -- for instance, I've grovelled through old emacs backup
files trying to find some changes I had made a few days, but erased
before commiting...

-Miles

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