On 16/04/2018 1:06 PM, Martin Morgan wrote:

On 04/16/2018 12:31 PM, Duncan Murdoch wrote:
On 16/04/2018 12:06 PM, Martin Maechler wrote:
Duncan Murdoch <murdoch.dun...@gmail.com>
      on Mon, 16 Apr 2018 11:52:10 -0400 writes:

      > On 16/04/2018 11:35 AM, Ramon Diaz-Uriarte wrote:
      >> Dear All,
      >> Two recent threads in the bioconductor devel mailing list
      >> (https://stat.ethz.ch/pipermail/bioc-devel/2018-April/013156.html
      >> and
      >> https://stat.ethz.ch/pipermail/bioc-devel/2018-April/013259.html)
      >> are related to packages that have different names of html
      >> files in different operating systems.
      >> For example, parallel has a file called mclapply in
      >> Linux. So using, from the Rd file of another package,
      >> \link[parallel]{mclapply} works fine under Linux, but
      >> does not under Windows, because there is no mclapply.html
      >> file in Windows (there is a mcdummies file).
      >> Is there any recommended way to proceed in these cases?
      >> Yes, section 2.5 of Writing R Extensions indicates that
      >> \link[pkg]{foo} and \link[pkg:bar]{foo} are rarely
      >> needed; so the simplest way to proceed would be to avoid
      >> \link[pkg]{foo} and \link[pkg:bar]{foo}. I am asking for
      >> the cases where, as noted in 2.5, "more than one package
      >> offers help on a topic".

      > You could make the links conditional on the OS.  For example,

      > #ifdef windows
      > See \link[parallel]{mcdummies}.
      > #endif
      > #ifdef unix
      > See \link[parallel]{mclapply}.
      > #endif

      > The other possibility (useful if there are major differences
between the
      > platforms) is to have two copies of the help file, one in
man/unix, one
      > in man/windows, but that doesn't seem appropriate from your

      > Duncan Murdoch

and mid-term, I really think R and (CRAN, Bioc, ...) packages
should not do what we (R core) did here.
Rather,  \alias{mclapply}  should exist both for windows and
non-windows, and hence \link{mclapply}  would just work.

\alias{mclapply} does exist...

I forget whether that would work here:  parallel being a base package
(used by the package in question?) might mean it would be found without
the [parallel] in the link.  But in general, links to other packages
using [pkg] go to the *filename*, not to the alias.  This oddity happens
because we want the links to work even if the referenced package is
installed later than the Rd file is processed.

People are quite concerned about fixing the 'WARNING' this generates.
However from the text

    file link 'mclapply' in package 'parallel' does not exist and so has
been  treated as a topic

the help pages are actually constructed correctly, finding the page on
which the topic (aka alias) 'mclapply' is defined. This contrasts with a
completely incorrect link (e.g., \link[stats]{mclapply}) generating a

    missing file link

and unable to link to the mclapply topic.

Perhaps the WARNING from \link[parallel]{mclapply} should be a NOTE?

There are other oddities in the threads that Ramon indicates

    - WARNINGs from \link[foo]{bar} that should really be
\link[foo:baz]{bar} often only appear on Windows (parallel's use of
mcdummies is a special case here). Shouldn't they be
platform-independent? An example is


where as.MAList is defined in a file called asmalist.Rd so
\link[limma]{as.MAList} is incorrect. It generates a warning only on our
Windows machine (tokay2) not Linux or Mac. I had some recollection of
Windows-specific help system behavior, but I think this dates back to
the .chm days...

Yes, that looks like an issue in the Linux checks.

    - There were a spate of independent posts about this, suggesting that
this is relatively new phenomenon (though it could also be that
maintainers have been busy preparing their packages for the next
release, so are now noticing the problem...)

The fact that cross-package links go to files rather than aliases is very old, but the checks may be newer.

    - It doesn't seem like good practice to link to the file name, which
seems an internal aspect of a package, rather than to the alias, which
seems at least for symbols to be a user-facing public aspect of the package.

I agree, but as I said, this is very old. It was old when I wrote the Rd parser. I vaguely recall that the possibility of a change was considered and rejected, but I'm not sure about that.

Changing it to use only topics would likely cause problems for people who are not getting warnings now. Perhaps it would be sensible to switch from filename to topic without a warning if the referenced package is available for checking, only issuing the warning if the check machine can't verify that the link is good.

Duncan Murdoch

    - And finally I did make an svn commit related to this, so am
sensitive to blundering here

R-devel/src/library/tools/R$ svn log -c74129
r74129 | morgan | 2018-01-17 16:52:53 -0500 (Wed, 17 Jan 2018) | 10 lines

correct warning when \link[base]{foo} is incorrect

- now "missing file link" rather than "file link 'foo' in package 'base'
    does not exist and will be treated as a topic" (foo is _not_ a topic
    in base; the link to foo.html is missing)
- vice-versa for \link[base]{rbind} (rbind _is_ a topic in base,
documented in
    cbind.html, and will be resolved by the help system)
- see https://stat.ethz.ch/pipermail/r-devel/2009-October/055287.html and


    - There is a possibility that some of the oddities are Bioc
build-system specific, and I really have not had a chance to dig to the
bottom of this to my satisfaction.


The reason the file was named "mclapply" in man/unix but "mcdummies" in
man/windows was likely to save some time:  there are several aliases
documented in that one file on Windows, but they are in separate files
on Unix.

Duncan Murdoch

Martin Maechler

      >> Thanks,
      >> R.

      >> --
      >> Ramon Diaz-Uriarte
      >> Department of Biochemistry, Lab B-25
      >> Facultad de Medicina
      >> Universidad Autónoma de Madrid
      >> Arzobispo Morcillo, 4
      >> 28029 Madrid
      >> Spain

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