I take it there is no interest in this?

(In reply to Dirk Eddelbuettel from comment #1)
> I take it there is no interest in this?

There's some, from me.
I think it would make sense _if_ we additionally returned a "Date" object
(possibly NA), and also we the function gets an option (i.e. optional argument which when flipped) takes the  'Built:' date if that's available.

Maybe some simple (R only, no C(++)) heurestics from anydate() could be used
for the  NN/NN/NN  and  NN/NN/NNNN dates?

I agree on Date being preferable, but see the analysis I included in the initial post: too few packages "do it right".

Now, over time CRAN could enforce this.

Heuristics are fine--what anytime and anydate do internally can be done in R as well. It "simply" tries a bunch of formats.

BTW Gabor Csardi has a package that ported the (much more powerful) Date parser from Linus himself (IIRC).  I can look that up.

But how do we return "either a Date or a character" ?

(In reply to Dirk Eddelbuettel from comment #3)
> I agree on Date being preferable, but see the analysis I included in the
> initial post: too few packages "do it right".

I know... and the new function could entice *some* to do better.
> 
> Now, over time CRAN could enforce this.
> 
> Heuristics are fine--what anytime and anydate do internally can be done in R
> as well. It "simply" tries a bunch of formats.

good.  
What I should have said in 'Comment 2' was that the 'Packaged: ' field should be looked at if the regular 'Date:' does not give a valid result; then maybe
a 'Date/Publication: ' as CRAN adds and only then a possible  'Built: ' field.

> 
> BTW Gabor Csardi has a package that ported the (much more powerful) Date
> parser from Linus himself (IIRC).  I can look that up.

and you'd propose that full parser to be added to R?

> 
> But how do we return "either a Date or a character" ?

I don't understand,
where did you cite the "............................" from?

Good comments, and good suggestion re alternate fields for fallback.  My last comment was mostly because I did not understand how you suggested to not return a character fallback if no Date was found.


But now with suggestion, a quick test:


packageDate <- function(pkg, lib.loc = NULL) {
    res <- suppressWarnings(packageDescription(pkg, lib.loc=lib.loc,
                                               fields = "Date"))

    if (is.na(res))
        stop(gettextf("package %s not found", sQuote(pkg)), domain = NA)

    res <- as.Date(res)
    if (!is.na(res)) return(res)

    for (fld in c("Date/Publication", "Built", "Packaged")) {
        res <- suppressWarnings(packageDescription(pkg, 
                                                   lib.loc=lib.loc, 
                                                   fields = fld))
        res <- as.Date(res)
        if (!is.na(res)) return(res)
    }

    res                                 # default NA value
}


Happy to update the formal diff with something like this.

The aforementioned package by Gabor is 'parsedate' but it also contains C code, and is on CRAN.   Maybe be overkill here.

(In reply to Dirk Eddelbuettel from comment #5)

and then you, DE, entered a better version into a completely unrelated bug
report (https://bugs.r-project.org/bugzilla/show_bug.cgi?id=16496)

Here it is, modified in the order of fields to be tried, according to my
own proposal above:

packageDate <- function(pkg, lib.loc = NULL) {
    for (fld in c("Date", "Packaged", "Date/Publication", "Built")) {
        res <- suppressWarnings(packageDescription(pkg, 
                                                   lib.loc=lib.loc, 
                                                   fields = fld))
        res <- as.Date(res)
        if (!is.na(res)) return(res)
    }
    res # default NA value
}

This looks quite good now in my view.
I don't like the use of suppressWarnings() and may want to add an argument
to packageDescription() instead.

Yes, sorry.  For me (Chrome, Linux) bugzilla jumps to a _different_ bug report of mine after I save an update.  

I think the suppressMessages() use was copied over from packageVersion.  In r-devel right now:

packageVersion <- function(pkg, lib.loc = NULL)
{
    res <- suppressWarnings(packageDescription(pkg, lib.loc=lib.loc,
                                               fields = "Version"))
    if (!is.na(res)) package_version(res) else
    stop(gettextf("package %s not found", sQuote(pkg)), domain = NA)
}

I am fine either way and happy to update the suggest patch (including the help
page mentioning that we now try multiple fields).