How are VC switches supposed to work?

How are VC switches supposed to work?

[Glenn Morris]

VC switches don't work as they are documented to work.
If someone can confirm that they work correctly, I will try to update
the many incorrect pieces of documentation. If on the other hand the
documentation is correct then the code needs fixing.

The documentation says that switches are appended. For example:

C-h v vc-diff-switches
C-h f vc-cvs-register
The Emacs manual "Examining And Comparing Old Revisions"

all say that it works, eg, as: vc-cvs-diff-switches +
vc-diff-switches + diff-switches.


In practice, (almost) everywhere uses the vc-switches function to
process switches. This does no appending, it simply returns the first
non-nil element.

For example:

(setq vc-cvs-diff-switches "-a"
      vc-diff-switches "-b"
      diff-switches "-c")

(vc-switches 'CVS 'diff)
  -> '("-a")


The situation was basically the same (ie inconsistent) in Emacs 22 AFAICS.

Re: How are VC switches supposed to work?

[Stefan Monnier]

> VC switches don't work as they are documented to work.
> If someone can confirm that they work correctly, I will try to update
> the many incorrect pieces of documentation. If on the other hand the
> documentation is correct then the code needs fixing.

> The documentation says that switches are appended. For example:

> C-h v vc-diff-switches
> C-h f vc-cvs-register
> The Emacs manual "Examining And Comparing Old Revisions"

> all say that it works, eg, as: vc-cvs-diff-switches +
> vc-diff-switches + diff-switches.


> In practice, (almost) everywhere uses the vc-switches function to
> process switches. This does no appending, it simply returns the first
> non-nil element.

> For example:

> (setq vc-cvs-diff-switches "-a"
>       vc-diff-switches "-b"
>       diff-switches "-c")

> (vc-switches 'CVS 'diff)
> -> '("-a")

> The situation was basically the same (ie inconsistent) in Emacs 22 AFAICS.

I can't remember all the details, but I do remember that appending is
not good enough because you may have switches in diff-switches that are
not accepted by some backends.


        Stefan

Re: How are VC switches supposed to work?

[Glenn Morris]

Stefan Monnier wrote:

> I can't remember all the details, but I do remember that appending is
> not good enough because you may have switches in diff-switches that are
> not accepted by some backends.

Yes; now that I think about it, that is probably enough reason to kill
the "append" approach. Thanks.