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fix(alpine): build R with cairo, png, jpeg and tiff graphics devices

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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.
This commit is contained in:
Patrick Schratz 2026-09-18 09:02:37 +02:00
commit c144a0c8b9
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7
CLAUDE.md
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@ -10,4 +10,11 @@ CI pipelines (Crow, in `.crow/`) that build R binaries and upload them to Backbl
## Gotchas
- **B2 requires authentication for the list-bucket API.** Anonymous GET only works for individual public-read objects — an empty bucket listing usually means missing credentials, not an empty bucket. This silently broke rebuild dedup once.
- **R's configure silently disables graphics devices when headers are missing.**
It never fails the build, so a missing `-dev` package yields a working 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; the binary has to be rebuilt.
`builder/build.sh` therefore asserts `REQUIRED_CAPABILITIES` (set per Dockerfile) after `make install`.
- **The `--with-x=no` on the Alpine images does not disable cairo.** R's bitmap and pangocairo checks run independently of `R_X11`, so `png()` and `svg()` work headless via cairo.
- **Artifact filenames carry only the R version, not the builder image.**
When a builder change alters the resulting binary, dedup would keep serving the stale artifact forever; set `FORCE_REBUILD` in `.crow/build.yaml` to rebuild and overwrite in place.
- When a pipeline fails, fetch the Crow logs yourself instead of asking the user to paste them, and monitor reruns in the background until green.