Quickly Build Package Repeatedly in R - c++

Question

I have a package I'm writing in R that has a boatload of complicated C++ code which takes a while to compile.
When I change the code, I'd like to quickly rebuild the package so I can test it. However, R CMD build seems to start from scratch each time, rather than using my code's makefiles to do only what is needed.
Is there a way to quickly do repeated builds of a package in R for testing?

Answer 1

I am a little overdue a short blog post on this, but I mentioned it a couple of times before: use ccache. It helps dramatically when the files don't change (ie when you just alter help pages), or when few files changes. Caching is a very clever trick, and package is robust.
On Ubuntu/Debian: sudo apt-get install ccache followed by e.g. this in your ~/.R/Makevars:
VER=
CCACHE=ccache
#CCACHE=
CC=$(CCACHE) gcc$(VER)
CXX=$(CCACHE) g++$(VER)
CXX11=$(CCACHE) g++$(VER)
CXX14=$(CCACHE) g++$(VER)
That also allows to switch between g++ versions. Changing it to clang++ is left as an exercise to the reader ;-)
Besides this, see the options to R CMD build and R CMD INSTALL to skip vignette and/or manual building to further speed up re-builds.
Illustration: Here is re-install of Rcpp itself (fresh from a git pull) where the first installation takes 21.9 seconds on my (decent) machine at work, the second then only takes 1.4 seconds thanks to ccache:
~/git/rcpp(master)$ time R CMD INSTALL .
* installing to library ‘/usr/local/lib/R/site-library’
* installing *source* package ‘Rcpp’ ...
** libs
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c Date.cpp -o Date.o
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c Module.cpp -o Module.o
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c Rcpp_init.cpp -o Rcpp_init.o
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c api.cpp -o api.o
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c attributes.cpp -o attributes.o
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c barrier.cpp -o barrier.o
g++ -shared -L/usr/lib/R/lib -Wl,-Bsymbolic-functions -Wl,-z,relro -o Rcpp.so Date.o Module.o Rcpp_init.o api.o attributes.o barrier.o -L/usr/lib/R/lib -lR
installing to /usr/local/lib/R/site-library/Rcpp/libs
** R
** inst
** preparing package for lazy loading
** help
*** installing help indices
** building package indices
** installing vignettes
** testing if installed package can be loaded
* DONE (Rcpp)
real 0m21.917s
user 0m21.388s
sys 0m2.304s
~/git/rcpp(master)$ ./cleanup
~/git/rcpp(master)$ time R CMD INSTALL .
* installing to library ‘/usr/local/lib/R/site-library’
* installing *source* package ‘Rcpp’ ...
** libs
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c Date.cpp -o Date.o
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c Module.cpp -o Module.o
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c Rcpp_init.cpp -o Rcpp_init.o
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c api.cpp -o api.o
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c attributes.cpp -o attributes.o
ccache g++ -I/usr/share/R/include -DNDEBUG -I../inst/include/ -fpic -g -O3 -Wall -pipe -pedantic -Wextra -Wno-empty-body -Wno-unused -c barrier.cpp -o barrier.o
g++ -shared -L/usr/lib/R/lib -Wl,-Bsymbolic-functions -Wl,-z,relro -o Rcpp.so Date.o Module.o Rcpp_init.o api.o attributes.o barrier.o -L/usr/lib/R/lib -lR
installing to /usr/local/lib/R/site-library/Rcpp/libs
** R
** inst
** preparing package for lazy loading
** help
*** installing help indices
** building package indices
** installing vignettes
** testing if installed package can be loaded
* DONE (Rcpp)
real 0m1.444s
user 0m1.380s
sys 0m1.452s
~/git/rcpp(master)$

Answer 2

Dirk's answer above pointed me in the right direction, but was insufficient. Since he has requested that I not append the final steps I required, I do so here.
My question could not have been answered without the following.
Dirk's answer did not work off the bat for me. If compilation still seems slow to you, try running:
ccache -s
The result will look a little like this
cache directory /home/myuser/.ccache
primary config /home/myuser/.ccache/ccache.conf
secondary config (readonly) /etc/ccache.conf
cache hit (direct) 0
cache hit (preprocessed) 0
cache miss 989
cache hit rate 0 %
called for link 12
preprocessor error 12
cleanups performed 16
files in cache 177
cache size 31.1 MB
max cache size 5.0 GB
Note that cache isn't getting hit, which means ccache isn't doing anything.
You can use:
export CCACHE_LOGFILE=ccache.log
R CMD build .
to do some debugging, though this wasn't helpful for me.
What fixed things was to run:
export CCACHE_NOHASHDIR=true
R CMD build .
As it turns out, ccache sometimes takes the location of a file into account. R CMD build . appears to build in a temporary directory, so the location of the files was changing each time.