create src/init.c for skeleton

[eddelbuettel]

This lets Rcpp.package.skeleton() create src/init.c (by making the required call).

Should compileAttributes() do that too?

[jjallaire]

Yes I think compileAttributes should do this as well, however I think it should also insert a preamble (similar to it's other auto-generated files) so that if the user creates their own src/init.c then we don't overwrite it.

[eddelbuettel]

I think I agree. And if/when it does, we need to remove it from here as well.

Also need to add .registration=TRUE to NAMESPACE as this PR does.

[codecov-io]

Codecov Report

Merging #692 into master will decrease coverage by 0.05%.
The diff coverage is 73.33%.

@@            Coverage Diff             @@
##           master     #692      +/-   ##
==========================================
- Coverage   89.77%   89.72%   -0.06%     
==========================================
  Files          66       66              
  Lines        3511     3523      +12     
==========================================
+ Hits         3152     3161       +9     
- Misses        359      362       +3

Impacted Files	Coverage Δ
R/Rcpp.package.skeleton.R	83.73% <73.33%> (-0.04%)	⬇️
R/RcppClass.R	77.01% <0%> (-1.15%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update abea6f2...fb27ed3. Read the comment docs.

[eddelbuettel]

@jjallaire I only glanced at src/attributes.cpp and R/Attributes.R and I am not sure how we can reuse.
Or should we just duplicate as

 looking for token 
 if not found
      abort 
 else 
      write token 
      append output from `tools::package_native_....()` 

[jjallaire]

I can take a look sometime later this week or next. The biggest issue I see is that if users have a file other than init.c which includes a package initialization function we'll be adding another one (which will break their compilation). Note this will happen on their local system rather than on CRAN so it's recoverable, but still ugly. Another possibility would be to scan for package init functions as part of our normal scanning and then only write init.c if there is no package init function.

[eddelbuettel]

Point well taken on files not-named init.c. We may well have to scan then. OTOH the good news is that I have been relying on the tools::package_native_routine_registration_skeleton() function for several months now with many uploads, and it just works. So this doesn't seem unsurmountable. Wish I had thought of this fairly clean way of integrating things earlier.

[eddelbuettel]

I'll fold this to tick off another micro-issue.