In the past couple of weeks, Ximin Luo worked on making R generate reproducible output. This is now mostly complete, and we're waiting on feedback from upstream about our patch. In the meantime, there are a few packages that remain unreproducible, but the issue probably lies in those specific packages rather than the R toolchain. Perhaps you can help out with them, after reading this!


R packages compile into a .rdb database format that contains the package's definitions, plus a .rdx index file for easy lookup in the .rdb file. Usually, there is a main rdb with the package contents, plus another rdb that stores the help data. There is also a paths.rds (same format as .rdx) that contains some more stuff.

One can actually read these files by hand using Rscript, see the diffoscope code in rdata.py. If you run that, you can see that path.rds contains some obvious paths, but the other files contain less obvious stuff, and in fact these scripts give identical output for the .rdb files, even though they are bitwise different. To get to the bottom of this, we'll have to use the R debugger.

Attached to this post is a script that smooths this process. I ran this against Debian's R packages, but it probably also works with other distros' R packages - try it and see.

You run it like ./r-mini-repro-test.sh $pkgdir $builddir and it will output some hashes for you; make sure to install the build dependencies first. You should manually vary both $pkgdir and $builddir to introduce the build-path variations; $builddir can be an arbitrary string but $pkgdir should point to the actual R package's source directory, so I just copy that to two locations and point the script at each of them in turn.

Now, we can begin debugging. Before I did this, we had 478 unreproducible R packages so the biggest problem was likely with R itself. I downloaded the source code of both R and a small example package (r-cran-tensor), then figured out how the R packages were actually being built. This resulted in me writing the script above, to speed up debugging. You can read about R's debugger here (no HTTPS), it's a bit primitive but it supports the basic stuff (step, continue, where, print/eval) and that was adequate for me.

Debugging R core

So let's take a small example with Debian R 3.4.0-1:

$ ../r-mini-repro-test.sh r-cran-tensor-1.5 123
[..]
* installing *source* package ‘tensor’ ...
** package ‘tensor’ successfully unpacked and MD5 sums checked
** R
** preparing package for lazy loading
** help
*** installing help indices
** building package indices
** testing if installed package can be loaded
* DONE (tensor)
[..]
c71a766429151a13e46039f3c37a14edc704004f410c34f8f37a2f098506421d  ./debian/123/usr/lib/R/site-library/tensor/R/tensor.rdx
736b5b4a885db71fb3fe2a538faeefe43c500c4080dbf2c75b97135b98401acd  ./debian/123/usr/lib/R/site-library/tensor/R/tensor.rdb
8a3f9616de7ee78a83b07395dd6ec43c5259d3f1b1b653d397808fc9fc5d96c2  ./debian/123/usr/lib/R/site-library/tensor/help/tensor.rdx
d1ac634987b24606a5da627ec073f45edce2bddf071391dd17c246a0a01eba63  ./debian/123/usr/lib/R/site-library/tensor/help/tensor.rdb
80796cc1a2cfcac40c394153f67617d575e103a405430b8483c2261a903db046  ./debian/123/usr/lib/R/site-library/tensor/help/paths.rds
$ ../r-mini-repro-test.sh r-cran-tensor-1.5 1234
[..]
5f081f4d6f9da1fbe06e374067e6636d926de4cdf09886058b15c5928c636c0d  ./debian/1234/usr/lib/R/site-library/tensor/R/tensor.rdx
7145669891e1b766ca0d8d89fa9c317af716e61a62650abe3a11a848240f1d57  ./debian/1234/usr/lib/R/site-library/tensor/R/tensor.rdb
8a3f9616de7ee78a83b07395dd6ec43c5259d3f1b1b653d397808fc9fc5d96c2  ./debian/1234/usr/lib/R/site-library/tensor/help/tensor.rdx
d1ac634987b24606a5da627ec073f45edce2bddf071391dd17c246a0a01eba63  ./debian/1234/usr/lib/R/site-library/tensor/help/tensor.rdb
80796cc1a2cfcac40c394153f67617d575e103a405430b8483c2261a903db046  ./debian/1234/usr/lib/R/site-library/tensor/help/paths.rds

The files are created by the ** preparing package for lazy loading and ** help steps. In retrospect this seems somewhat obvious from the output, but I had never done R before so I spent a while using strace to be sure; one can see that those files are indeed written to after those strings are printed.

Then we can grep the R source code for these strings.

r-base-3.4.0$ grep -Ri "preparing package for lazy loading" src
src/library/tools/R/install.R:                starsmsg(stars, "preparing package for lazy loading")

Reading the file, we see that this happens in the tools:::.install_packages function, and reading it further we see that it calls makeLazyLoading then code2LazyLoadDB then makeLazyLoadDB. Seems promising, let's confirm it before chasing potential wild geese.

Important: In the rest of these command-line outputs I'll prepend what I input with >>> but this doesn't actually get printed by Rscript. So don't be surprised that you don't see these, when you're trying to recreate my steps.

Also I am a total R noob so possibly there are more elegant ways to do what I'm about to show you; this is what I came up with after 2-3 hours of research.

$ DEBUG=1 ../r-mini-repro-test.sh r-cran-tensor-1.5 123
enter (some or all of) the following into R:
[.. helpful commands ..]
+ R_DEFAULT_PACKAGES= LC_COLLATE=C /usr/lib/R/bin/R --no-restore --slave --args nextArg-lnextArgdebian/123/usr/lib/R/site-librarynextArg-dnextArg.nextArg--built-timestamp="Thu, 01 Jan 1970 00:00:00 +0000"
>>> debug(tools:::makeLazyLoadDB)
>>> tools:::.install_packages()
processing ‘.’
[..]
** preparing package for lazy loading
debugging in: makeLazyLoadDB(ns, dbbase, compress = compress)
debug: {
[.. source code of makeLazyLoadDB, not yet run ..]
}

OK so we just entered the function and it's paused, in a separate shell let's check what it's doing:

$ find r-cran-tensor-1.5 -name '*.rdb'
[ no output ]

So, no files have been written yet, which means none of the parent functions did anything, we are in the right function (or it's in a child). If we continue the function, we get:

>>> c
exiting from: makeLazyLoadDB(ns, dbbase, compress = compress)
** help
debugging in: makeLazyLoadDB(db, file.path(manOutDir, basename(outDir)))
debug: {
[.. source code of makeLazyLoadDB, not yet run ..]
}

$ find r-cran-tensor-1.5 -name '*.rdb'
r-cran-tensor-1.5/debian/123/usr/lib/R/site-library/tensor/R/tensor.rdb

Then continuing again:

>>> c
exiting from: makeLazyLoadDB(db, file.path(manOutDir, basename(outDir)))
*** installing help indices
** building package indices
** testing if installed package can be loaded
* DONE (tensor)

$ find r-cran-tensor-1.5 -name '*.rdb'
r-cran-tensor-1.5/debian/123/usr/lib/R/site-library/tensor/help/tensor.rdb
r-cran-tensor-1.5/debian/123/usr/lib/R/site-library/tensor/R/tensor.rdb

So it seems likely this function is the correct one. After reading the source code of makeLazyLoadDB, even though I don't understand the whole thing, it looks like possibly this part is the one that does the actual writing:

    for (i in seq_along(vars)) {
        key <- if (is.null(from) || is.environment(from))
            lazyLoadDBinsertVariable(vars[i], from, datafile,
                                     ascii, compress,  envhook)
        else lazyLoadDBinsertListElement(from, i, datafile, ascii,
                                         compress, envhook)
        assign(vars[i], key, envir = varenv)
    }

So let's step through it and see if the data contains any paths.

$ DEBUG=1 ../r-mini-repro-test.sh r-cran-tensor-1.5 123
[..]
>>> debug(tools:::makeLazyLoadDB)
>>> tools:::.install_packages()
processing ‘.’
[..]
** preparing package for lazy loading
debugging in: makeLazyLoadDB(ns, dbbase, compress = compress)
debug: {
[.. source code of makeLazyLoadDB, not yet run ..]
}
>>>                                                                             # pressing <Enter> just means "step"
debug: ascii <- as.logical(ascii)                                               # this is the first line of the function
>>>                                                                             # keep stepping
[..]
>>>
debug: for (i in seq_along(vars)) {
[.. source code of the inside of the block, not yet run ..]
}
>>>
debug: key <- if (is.null(from) || is.environment(from)) lazyLoadDBinsertVariable(vars[i],
    from, datafile, ascii, compress, envhook) else lazyLoadDBinsertListElement(from,
    i, datafile, ascii, compress, envhook)
>>>
debug: lazyLoadDBinsertVariable(vars[i], from, datafile, ascii, compress,
    envhook)                                                                    # not yet run

If we look at the source code we see that it will try to insert the value of .Internal(getVarsFromFrame(vars[i], from, FALSE))[[1L]] into the file, so let's evaluate it:

>>> .Internal(getVarsFromFrame(vars[i], from, FALSE))[[1L]]
function (x, y)
tensor(x, y, 2, 2)
<environment: namespace:tensor>
>>> typeof(.Internal(getVarsFromFrame(vars[i], from, FALSE))[[1L]])
[1] "closure"
>>> environment(.Internal(getVarsFromFrame(vars[i], from, FALSE))[[1L]])        # get the environment of a closure
<environment: namespace:tensor>
>>> envlist(environment(.Internal(getVarsFromFrame(vars[i], from, FALSE))[[1L]])) # environment as an envlist, more detailed output
$`%*t%`
function (x, y)
tensor(x, y, 2, 2)
<environment: namespace:tensor>

$`%t*%`
function (x, y)
tensor(x, y, 1, 1)
<environment: namespace:tensor>

$`%t*t%`
function (x, y)
tensor(x, y, 1, 2)
<environment: namespace:tensor>

$.__NAMESPACE__.
<environment: 0x55eb55d00be0>

$.__S3MethodsTable__.
<environment: 0x55eb55d166e8>

$.packageName
[1] "tensor"

$tensor
function (A, B, alongA = integer(0), alongB = integer(0))
{
[.. function definition ..]
}
<environment: namespace:tensor>

Nothing obviously containing paths so far, let's keep stepping and dumping the objects

>>>
debug: assign(vars[i], key, envir = varenv)
>>>                                                                             # next iteration now
debug: key <- if (is.null(from) || is.environment(from)) lazyLoadDBinsertVariable(vars[i],
    from, datafile, ascii, compress, envhook) else lazyLoadDBinsertListElement(from,
    i, datafile, ascii, compress, envhook)
>>>
debug: lazyLoadDBinsertVariable(vars[i], from, datafile, ascii, compress,
    envhook)
>>> .Internal(getVarsFromFrame(vars[i], from, FALSE))[[1L]]
function (x, y)
tensor(x, y, 1, 1)
<environment: namespace:tensor>
>>>
[.. more stepping ..]
debug: lazyLoadDBinsertVariable(vars[i], from, datafile, ascii, compress,
    envhook)
>>> .Internal(getVarsFromFrame(vars[i], from, FALSE))[[1L]]
<environment: 0x55eb55d00be0>
>>> envlist(.Internal(getVarsFromFrame(vars[i], from, FALSE))[[1L]])
$S3methods
     [,1] [,2] [,3]

$dynlibs
NULL

$exports
<environment: 0x55eb55d0a4f8>

$imports
$imports$base
[1] TRUE


$lazydata
<environment: 0x55eb55d0a178>
attr(,"name")
[1] "lazydata:tensor"

$path
[1] "/mystupidbuildpath/r-tests/r-cran-tensor-1.5/debian/123/usr/lib/R/site-library/tensor"

$spec
    name  version
"tensor"    "1.5"

Oh, here we go. (In fact we could have got this earlier, it was part of the .__NAMESPACE__. key of the first environment that we examined.) Naturally, you'll sometimes miss stuff, and sometimes go down dead ends when doing something like this, perseverence is important.

The names are also a hint, after grepping the R source code for names like "S3methods" and "lazydata" we see that src/library/base/R/namespace.R is the only one that contains all of them, then reading that code in more depth reveals this.

After patching it, rebuilding r-base, installing this patched version, then running our tests again, we see that we've eliminated differences in the main rdb file but not the help rdb file. :(

In fact, after some more time stepping through the loop repeatedly and printing out all the objects, nothing obvious shows up. Time to re-read the source code of makeLazyLoadDB. We notice that all the lazyLoadDBinsert* functions have a hook parameter that we haven't been stepping through because it's in a separate function. So let's do that. Since it's an inner function, one has to call debug() inside makeLazyLoadDB:

$ DEBUG=1 ../r-mini-repro-test.sh r-cran-tensor-1.5 123
[..]
>>> debug(tools:::makeLazyLoadDB)
>>> tools:::.install_packages()
processing ‘.’
[..]
** preparing package for lazy loading
debugging in: makeLazyLoadDB(ns, dbbase, compress = compress)
debug: {
[.. source code of makeLazyLoadDB, not yet run ..]
}
>>> c
exiting from: makeLazyLoadDB(ns, dbbase, compress = compress)
** help
debugging in: makeLazyLoadDB(db, file.path(manOutDir, basename(outDir)))
debug: {
[.. source code of makeLazyLoadDB, not yet run ..]
}
[.. stepping through the function ..]
debug: envhook <- function(e) {
[.. function definition ..]
}
>>>                                                                             # step next, to define that function
[.. next statement, we don't care about it ..]
>>> debug(envhook)
[.. then keep stepping through makeLazyLoadDB ..]
>>>
debug: lazyLoadDBinsertVariable(vars[i], from, datafile, ascii, compress,
    envhook)
[.. then keep stepping through makeLazyLoadDB ..]
debug: lazyLoadDBinsertVariable(vars[i], from, datafile, ascii, compress,
    envhook)
[.. hook wasn't run for these previous iterations for some reason, but keep stepping ..]
[.. eventually we get ..]

debugging in: (function (e)
{
[.. function definition ..]
})(<environment>)                                                               # "(..)(<environment>)" is R's name for that function (actually a closure)
debug: {
[.. source code, not yet run ..]
}
>>> e
/mystupidbuildpath/r-tests/r-cran-tensor-1.5/man/tensor.Rd
>>> typeof(e)
[1] "environment"
>>> envlist(e)
$Enc
[1] "UTF-8"

$encoding
[1] ""

$filename
[1] "/mystupidbuildpath/r-tests/r-cran-tensor-1.5/man/tensor.Rd"

$timestamp
[1] "2002-01-16 11:51:14 CET"

$wd
[1] "/mystupidbuildpath/r-tests/r-cran-tensor-1.5"

After doing the same thing as before, i.e. grepping the R source code for "Enc" "timestamp" etc, we spot a few different places that are setting the wd field.

Then after some experimenting, we find that overwriting this in a different file (src/library/tools/R/parseRd.R) seems to work to get rid of this irreproducibility. (This may not be the best; our exact strategy is still being discussed with upstream, but at least we know which areas of the code are responsible.)

Exercise for the reader to figure out how to get rid of the paths.rds difference. After doing the previous two, this one is fairly easy.

These three issues allowed us to write a preliminary patch that enabled us to reproduce r-cran-tensor.

$ ./r-mini-repro-test.sh r-cran-tensor-1.5 123
[..]
bca9de1351ab265475cf6f1af3f6aff49bde1d209e8fafb33954caa8d90f3462  ./debian/123/usr/lib/R/site-library/tensor/R/tensor.rdx
ac7fffeb751ffc2d13c5317704b19787a7078446d97d1c6f259c93f282e04cef  ./debian/123/usr/lib/R/site-library/tensor/R/tensor.rdb
d989603340d1e8f14c35551ef379956653bf3b6e7b1868b4bf9a66d85820998e  ./debian/123/usr/lib/R/site-library/tensor/help/tensor.rdx
30e543cda9f97c202dc9c0291933940dfe71b94d352f66d8ed6c035c1a722b41  ./debian/123/usr/lib/R/site-library/tensor/help/tensor.rdb
e9f78ba2cca39a6face1ed88fce4bb718d911d567d01db49bc00a3011720ac50  ./debian/123/usr/lib/R/site-library/tensor/help/paths.rds
$ ./r-mini-repro-test.sh r-cran-tensor-1.5 1234
[..]
bca9de1351ab265475cf6f1af3f6aff49bde1d209e8fafb33954caa8d90f3462  ./debian/1234/usr/lib/R/site-library/tensor/R/tensor.rdx
ac7fffeb751ffc2d13c5317704b19787a7078446d97d1c6f259c93f282e04cef  ./debian/1234/usr/lib/R/site-library/tensor/R/tensor.rdb
d989603340d1e8f14c35551ef379956653bf3b6e7b1868b4bf9a66d85820998e  ./debian/1234/usr/lib/R/site-library/tensor/help/tensor.rdx
30e543cda9f97c202dc9c0291933940dfe71b94d352f66d8ed6c035c1a722b41  ./debian/1234/usr/lib/R/site-library/tensor/help/tensor.rdb
e9f78ba2cca39a6face1ed88fce4bb718d911d567d01db49bc00a3011720ac50  ./debian/1234/usr/lib/R/site-library/tensor/help/paths.rds
$ ./r-mini-repro-test.sh r-cran-tensor 1234
[..]
bca9de1351ab265475cf6f1af3f6aff49bde1d209e8fafb33954caa8d90f3462  ./debian/1234/usr/lib/R/site-library/tensor/R/tensor.rdx
ac7fffeb751ffc2d13c5317704b19787a7078446d97d1c6f259c93f282e04cef  ./debian/1234/usr/lib/R/site-library/tensor/R/tensor.rdb
d989603340d1e8f14c35551ef379956653bf3b6e7b1868b4bf9a66d85820998e  ./debian/1234/usr/lib/R/site-library/tensor/help/tensor.rdx
30e543cda9f97c202dc9c0291933940dfe71b94d352f66d8ed6c035c1a722b41  ./debian/1234/usr/lib/R/site-library/tensor/help/tensor.rdb
e9f78ba2cca39a6face1ed88fce4bb718d911d567d01db49bc00a3011720ac50  ./debian/1234/usr/lib/R/site-library/tensor/help/paths.rds

Testing the patch

Of course r-cran-tensor is just 1 package, so then we tested this patch on all 478 tagged R packages. Before the patch, all of these were unreproducible. Now 463/478 are reproducible, hurray!

The first version of the patch made 2 packages FTBFS ("fail to build from source"), r-bioc-biobase and r-cran-shinybs; this was fixed in a subsequent version of the patch. (Some other packages, r-cran-randomfields r-cran-randomfieldsutils, FTBFS even with an unpatched r-base, due to differences between 3.3.3 and 3.4.0 (#861333), and not because of our patch.)

Given the overwhelming proportion of packages that did reproduce, the other 14 packages that are still unreproducible, are quite probably due to issues in those specific packages. Only 2 of these are certainly due to build-path differences: r-cran-runit r-cran-rinside. This is because, we currently see they are reproducible in Debian testing but not Debian unstable. This is slightly misleading, the real reason is not testing vs unstable directly; rather the fact that we (at the time of writing) use the same build path when trying to reproduce Debian testing packages, and different paths for unstable. The other 12 are unreproducible in both testing and unstable, so it either suffers from a non-build-path issue as well as a build-path issue, or only a non-build-path issue.

So, further investigation of each package is needed. This is where you can help. :)

Debugging R packages

To investigate why (for example) r-cran-runit doesn't reproduce despite our patches, we just do the above process again:

$ DEBUG=1 ../r-mini-repro-test.sh r-cran-runit
[..]
>>> debug(tools:::makeLazyLoadDB)
>>> tools:::.install_packages()
processing ‘.’
a directory
* build_help_types=
* DBG: 'R CMD INSTALL' now doing do_install()
* created lock directory ‘/mystupidbuildpath/r-tests/r-cran-runit/debian/r-cran-runit/usr/lib/R/site-library/00LOCK-r-cran-runit’
* installing *source* package ‘RUnit’ ...
** package ‘RUnit’ successfully unpacked and MD5 sums checked
** backing up earlier installation
** R
** inst
** preparing package for lazy loading
debugging in: makeLazyLoadDB(ns, dbbase, compress = compress)
debug: {
[.. source code of makeLazyLoadDB ..]
}

We know our irreproducibility is with the help files and not the main package, so c to skip this part:

>>> c
exiting from: makeLazyLoadDB(ns, dbbase, compress = compress)
** help
debugging in: makeLazyLoadDB(db, file.path(manOutDir, basename(outDir)))
debug: {
[.. source code of makeLazyLoadDB ..]
}

Examine the "from" object, grep the output for our builddir

>>> from
$`RUnit-internal`
[..]
$`RUnit-intro`
[..]
[.. etc ..]
[..]
$checkFuncs
\title{RUnit check [..]
[..]
  For a simple example see the provided test cases in
  /mystupidbuildpath/r-tests/r-cran-runit/debian/r-cran-runit/usr/lib/R/site-library/RUnit/examples/runitVirtualClassTest.r.
[..]

Found it, now we quit, patch the source code, and try again.

>>> Q
[..]
exit code 1
[.. hack hack hack ..]
$ ../r-mini-repro-test.sh r-cran-runit-0.4.31/ 123
[..]
01347305351a45bb88dab909c56942498e97f5edbe583cf6ab1327138914e315  ./debian/123/usr/lib/R/site-library/RUnit/R/RUnit.rdx
ecde40bdfac5b070acc30a0d5889d9d7f65418844d14312aceff6af5b9d0bf7a  ./debian/123/usr/lib/R/site-library/RUnit/R/RUnit.rdb
182d38ac5adc160eb9edd40d5bd7e27b95b756b8f14cee7d912ba4745ae81bdc  ./debian/123/usr/lib/R/site-library/RUnit/help/RUnit.rdx
f8a9f22acc9f937cb47a92f3979d619e83a791ad734796c2fcd9d0a34e1f11ca  ./debian/123/usr/lib/R/site-library/RUnit/help/RUnit.rdb
5c37672fdc1f325b8a3846f4eafd2624b246ec70ce01d197134fa1b97a9ee849  ./debian/123/usr/lib/R/site-library/RUnit/help/paths.rds
$ ../r-mini-repro-test.sh r-cran-runit-0.4.31/ 1234
[..]
01347305351a45bb88dab909c56942498e97f5edbe583cf6ab1327138914e315  ./debian/1234/usr/lib/R/site-library/RUnit/R/RUnit.rdx
ecde40bdfac5b070acc30a0d5889d9d7f65418844d14312aceff6af5b9d0bf7a  ./debian/1234/usr/lib/R/site-library/RUnit/R/RUnit.rdb
182d38ac5adc160eb9edd40d5bd7e27b95b756b8f14cee7d912ba4745ae81bdc  ./debian/1234/usr/lib/R/site-library/RUnit/help/RUnit.rdx
f8a9f22acc9f937cb47a92f3979d619e83a791ad734796c2fcd9d0a34e1f11ca  ./debian/1234/usr/lib/R/site-library/RUnit/help/RUnit.rdb
5c37672fdc1f325b8a3846f4eafd2624b246ec70ce01d197134fa1b97a9ee849  ./debian/1234/usr/lib/R/site-library/RUnit/help/paths.rds

Works! All finished. :) If yours doesn't, just repeat the above loop; hopefully eventually you'll get there.