sort case-insensitive to make RcppExports more deterministic

[jackwasey]

compileAttributes uses list.files which gives a locale-dependent ordering of the matched files. This differs between C and en-us.UTF-8, with C ordering putting upper-case file names first. This makes the code output to RcppExports.* different depending on the locale.

It was not obvious to me how to make this locale independent using base R, but at least ignoring case when calling list.files eliminates some of the discrepancies produced with these two widely used collations. People calling compileAttributes() from locales which are not ordered A-Z will see differences in the output order (and thus order of functions in the generated code).

[kevinushey]

A number of packages that have required locale-independent sorting have implemented a sort_c function, e.g. see what roxygen2 does here:

https://github.com/klutometis/roxygen/blob/bbf259ddee033a873426ded1e83cdd344b986595/R/util-locale.R#L1-L14

We could potentially do something similar in Rcpp -- explicitly set LC_COLLATE, sort the list of files, and then restore the old LC_COLLATE.

[kevinushey]

But if setting ignore.case is enough to handle the most common cases then I think that's sufficient.

[codecov-io]

Codecov Report

Merging #878 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #878   +/-   ##
=======================================
  Coverage   90.09%   90.09%           
=======================================
  Files          71       71           
  Lines        3271     3271           
=======================================
  Hits         2947     2947           
  Misses        324      324

Impacted Files	Coverage Δ
R/Attributes.R	90.66% <100%> (ø)	⬆️

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[jackwasey]

I'll leave it to your judgement: I agree this is a quick win which, at least for me, covers my fairly vanilla Ubuntu and Mac setups, which were producing different RcppExports code. I'm sure those case-insensitive windows users would also have bad interactions when also developing also on case-sensitive operating systems.

[eddelbuettel]

This is an easy win. We could always look into setting locale to C, sorting, then resetting as @kevinushey suggested. But until then this works for me.

[hadley]

Could we please change the locale here? That will also ensure consistency from system to system.

[eddelbuettel]

Quoting @jjallaire in the same thread :

A recent change in Rcpp (v0.12.18 from a couple of months ago) changed the sorting behavior to be more stable across locales/operating systems: #878

Net is that this should be a one-time issue and that the order will be better preserved across environments in the future.

[hadley]

That link is to this issue?

The problem with only ignoring the case is that you will still get a different default ordering in locales that don't order letters the same way as English. This means that collaborators with different locales will still generate different RcppExports.

[jjallaire]

@jackwasey or @kevinushey Do you see a way to change this so that we can completely stable ordering across all systems and locales?

[kevinushey]

We could set the locale to C temporarily and then sort the discovered files, e.g.

cppFiles <- list.files(srcDir, pattern = "\\.((c(c|pp)?)|(h(pp)?))$", ignore.case = TRUE)

locale <- Sys.getlocale(category = "LC_COLLATE")
Sys.setlocale(category = "LC_COLLATE", locale = "C")
cppFiles <- sort(cppFiles)
Sys.setlocale(category = "LC_COLLATE", locale = locale)

[jackwasey]

@kevinushey this looks good to me.