Rultor Merge Failure Due to Absence of ruff Command in maxonfjvipon/rultor-image-hs:master Image #1785

Rultor can no longer merge pull requests. Since #1637, the all target of the Makefile also runs ruff:

all: test hlint fourmolu ruff

ruff:
	ruff check .
	ruff format --check .

The merge script in .rultor.yml runs this target with make -j. It runs inside the image maxonfjvipon/rultor-image-hs:master, which has no ruff and no Python. The install step does not add ruff either:

install: |
  cabal --version
  ghc --version
  cabal update
  pdd -f /dev/null -v

So the merge of #1743 failed, even though all 3313 tests passed (log):

bash: line 1: ruff: command not found
make: *** [Makefile:50: ruff] Error 127
make: *** Waiting for unfinished jobs....

Every @rultor merge will fail the same way. A merge should run the same checks as make all on a laptop, and pass when they pass.

The image has curl and rultor runs as root. So the install step of .rultor.yml can download one pinned release binary of ruff into /usr/local/bin, and make -j will find it.