[Rd] Control statements with condition with greater than one should give error (not just warning) [PATCH]

[Martin Maechler]

>>>>> Henrik Bengtsson <henrik.bengtsson at gmail.com>
>>>>>     on Fri, 3 Mar 2017 10:10:53 -0800 writes:

    > On Fri, Mar 3, 2017 at 9:55 AM, Hadley Wickham
    > <h.wickham at gmail.com> wrote:
    >>> But, how you propose a warning-to-error transition
    >>> should be made without wreaking havoc?  Just flip the
    >>> switch in R-devel and see CRAN and Bioconductor packages
    >>> break overnight?  Particularly Bioconductor devel might
    >>> become non-functional (since at times it requires
    >>> R-devel).  For my own code / packages, I would be able
    >>> to handle such a change, but I'm completely out of
    >>> control if one of the package I'm depending on does not
    >>> provide a quick fix (with the only option to remove
    >>> package tests for those dependencies).
    >> 
    >> Generally, a package can not be on CRAN if it has any
    >> warnings, so I don't think this change would have any
    >> impact on CRAN packages.  Isn't this also true for
    >> bioconductor?

    > Having a tests/warn.R file with:

    > warning("boom")

    > passes through R CMD check --as-cran unnoticed.  

Yes, indeed.. you are right Henrik  that many/most R warning()s would
not produce  R CMD check  'WARNING's ..

I think Hadley and I fell into the same mental pit of concluding
that such warning()s  from   if(<length-larger-one>)  ...
would not currently happen in CRAN / Bioc packages and hence
turning them to errors would not have a direct effect.

With your 2nd e-mail of saying that you'd propose such an option
only for a few releases of R you've indeed clarified your intent
to me.
OTOH, I would prefer using an environment variable (as you've
proposed as an alternative)  which is turned "active"  at the
beginning only manually or  for the  "CRAN incoming" checks of
the CRAN team (and bioconductor submission checks?)
and later for  '--as-cran'  etc until it eventually becomes the
unconditional behavior of R (and the env.variable is no longer used).

Martin