The Alpine builder images install R-dev but never the graphics headers.
R's configure treats those as optional and does not fail when they are
absent, so the build succeeds and ships an R whose capabilities() reports
cairo, png, jpeg and tiff as FALSE. Installing the runtime libraries on
the target system afterwards cannot bring compiled-out devices back.
Note that --with-x=no was not the cause. R's bitmap and pangocairo checks
run independently of R_X11, and libpng was in fact found. capabilities("png")
needs a device backend, and with X11 off and cairo absent there was none,
which is why all four read FALSE. X11 stays off: these are headless images
and cairo covers png()/jpeg()/tiff()/svg().
- Install pkgconf, cairo-dev, pango-dev, fontconfig-dev, freetype-dev,
libpng-dev, jpeg-dev, tiff-dev and zlib-dev in every Alpine builder image.
- Pass --with-cairo, --with-libpng, --with-jpeglib and --with-libtiff
explicitly so the intent is visible next to --with-x=no.
- Assert REQUIRED_CAPABILITIES after make install, so a build that loses a
device fails instead of being packaged and uploaded. Opt-in per Dockerfile,
leaving the other platforms untouched.
- Add a FORCE_REBUILD escape hatch to the dedup step. Artifact filenames
carry only the R version, so the HEAD probe would otherwise keep skipping
every Alpine version and serving the stale broken binaries.
- Record the three gotchas in CLAUDE.md.
Verified by compiling R 4.5.1 in the patched alpine-322 image: jpeg, png,
tiff and cairo are TRUE, default bitmapType is cairo, and all four devices
render. The guard was exercised in both directions against that build.
