sharp installs libvips and the code defines the cache using:

const cachePath = function () {
  const npmCachePath = env.npm_config_cache || /* istanbul ignore next */
    (env.APPDATA ? path.join(env.APPDATA, 'npm-cache') : path.join(os.homedir(), '.npm'));
  mkdirSync(npmCachePath);
  const libvipsCachePath = path.join(npmCachePath, '_libvips');
  mkdirSync(libvipsCachePath);
  return libvipsCachePath;
};

That npm_config_cache environment variable should be exposed by npm from the its cache setting. Using Fresh we have:

$ npm config list
; "env" config from environment

cache = "/cache" 
update-notifier = false 

That is because the CI images have XDG_CACHE_HOME=/cache.

On https://github.com/yarnpkg/yarn/issues/1632 , there is an explanation from 2016 about that npm_config_:

Configuration parameters are put in the environment with the npm_config_ prefix. For instance, you can view the effective root config by checking the npm_config_root environment variable.

And surely if I try:

"scripts": {
    "foo": "node -p process.env.npm_config_cache"
}

There is no such environment variable, however printing the whole env I see:

NPM_CONFIG_cache: '/cache',
NPM_CONFIG_update_notifier: 'false',

Those are the config from the environment. All the other ones are in all lower case:

  npm_config_user_agent: 'npm/9.8.0 node/v20.5.0 linux x64 workspaces/false',
  npm_node_execpath: '/usr/bin/node',
  npm_config_noproxy: '',
  npm_package_json: '/query-builder/package.json',
....

While the sharp caching system expects npm_config_cache our CI have npm exposes NPM_CONFIG_cache and the code end up falling back to use the non existent home directory.

After digging into the npm code I eventually found the mixed cased comes from the Docker images!!!

dockerfiles/node18-test/Dockerfile.template:ENV NPM_CONFIG_cache=$XDG_CACHE_HOME
dockerfiles/node18-test/Dockerfile.template:ENV NPM_CONFIG_update_notifier=false
dockerfiles/node20-test/Dockerfile.template:ENV NPM_CONFIG_cache=$XDG_CACHE_HOME
dockerfiles/node20-test/Dockerfile.template:ENV NPM_CONFIG_update_notifier=false
dockerfiles/node22-test/Dockerfile.template:ENV NPM_CONFIG_cache=$XDG_CACHE_HOME
dockerfiles/node22-test/Dockerfile.template:ENV NPM_CONFIG_update_notifier=false

That got carried over since January 2019 change https://gerrit.wikimedia.org/r/c/integration/config/+/482527/12/dockerfiles/node10-test/Dockerfile.template (that is for T212602 which is when we implemented not writing to HOME).

Why are they in mixed case? I have no idea but I guess we can change them to be all lower case.

Change #1055257 had a related patch set uploaded (by Hashar; author: Hashar):

[integration/config@master] dockerfiles: change NPM_CONFIG_cache to all lower case

https://gerrit.wikimedia.org/r/1055257

Change #1055257 merged by jenkins-bot:

[integration/config@master] dockerfiles: change NPM_CONFIG_cache to all lower case

https://gerrit.wikimedia.org/r/1055257

Change #1055429 had a related patch set uploaded (by Hashar; author: Hashar):

[integration/config@master] jjb: switch jobs to set NPM_CONFIG_cache to lower case

https://gerrit.wikimedia.org/r/1055429

Interestingly that would have been fixed byhaving HOME=/tmp (T365871) but https://gerrit.wikimedia.org/r/c/integration/config/+/1037453 did not update all the jobs ;/

Mentioned in SAL (#wikimedia-releng) [2024-07-19T13:38:18Z] <hashar> Updating Jenkins jobs for "NPM_CONFIG_cache to lower case" | https://gerrit.wikimedia.org/r/c/integration/config/+/1055429 | T370427

Change #1055429 merged by jenkins-bot:

[integration/config@master] jjb: switch jobs to set NPM_CONFIG_cache to lower case

https://gerrit.wikimedia.org/r/1055429