"unmet peer dependency" warning shown for transitive dependency that npm accepts

[edmorley]

Hi!

Do you want to request a feature or report a bug? A bug.

STR:

1. Clone https://github.com/edmorley/yarn-unmet-peerdependency-testcase
2. From the repo root, run: rm -rf node_modules/ && yarn install
3. And then: rm -rf node_modules/ && npm install

Expected:

• unmet peer dependency warnings aren't shown for dependencies that are installed transitively.
• yarn and npm errors/warnings are roughly the same for the same package.json.

Actual: The yarn output (example) includes:

warning "eslint-config-airbnb-base@12.0.2" has unmet peer dependency "eslint@^4.8.0".
warning "eslint-plugin-import@2.7.0" has unmet peer dependency "eslint@2.x - 4.x".

...whereas the NPM output (example) contains no such warnings.

To save having to dig through the repo, the testcase's package.json contains:

  "dependencies": {
    "neutrino": "7.1.0",
    "neutrino-preset-airbnb-base": "7.1.0"
}

...and the relevant child package's dependencies are as follows:

// neutrino-preset-airbnb-base
// https://github.com/mozilla-neutrino/neutrino-dev/blob/v7.1.0/packages/neutrino-preset-airbnb-base/package.json
  "dependencies": {
    ...
    "eslint-config-airbnb-base": "^12.0.1",
    "eslint-plugin-import": "^2.7.0",
    "neutrino-middleware-eslint": "^7.1.0"
  },

// neutrino-middleware-eslint
// https://github.com/mozilla-neutrino/neutrino-dev/blob/v7.1.0/packages/neutrino-middleware-eslint/package.json
  "dependencies": {
    ...
    "eslint": "^4.7.2",
    ...
  },

Please mention your node.js, yarn and operating system version. yarn 1.2.0 / npm 5.4.2 node 8.6.0 Windows 10 x64 using MSYS2 bash.

Many thanks :-)

[edmorley]

This also reproduces with yarn 1.2.1.

[BYK]

This doesn't seem like a bug to me. neutrino-preset-airbnb-base does not list anything related to eslint in its dependencies and I get the following warnings when I try:

warning "neutrino-preset-airbnb-base > eslint-config-airbnb-base@12.0.2" has unmet peer dependency "eslint@^4.8.0".
warning "neutrino-preset-airbnb-base > eslint-plugin-import@2.7.0" has unmet peer dependency "eslint@2.x - 4.x".

This plugin and the config are direct dependencies of neutrino-preset-airbnb-base so there should be an ESLint dependency listed compatible with these ranges in the same tree. That means either at the project root or inside neutrino-preset-airbnb-base itself. I'm guessing NPM doesn't complain about this since neutrino lists ESLint as a dependency and and it gets hoisted up to the project root. That said this is not guaranteed at all cases (hoisting is never guaranteed), so Yarn's warning is correct.

[edmorley]

But neutrino-preset-airbnb-base lists neutrino-middleware-eslint as a dependency, which does depend on eslint. I know this relies on hoisting to work, but this is the intended use-case - these are handy wrappers around common configuration, where the user isn't meant to have to install additional dependencies at the top level, nor do we want neutrino-preset-airbnb-base to use a different eslint version from neutrino-middleware-eslint. (And in fact, neither neutrino-preset-airbnb-base nor neutrino-middleware-eslint will directly use eslint, the neutrino main package will).

Is this just a workflow not very well supported by peerDependencies at the moment?

[edmorley]

Perhaps a middle ground would be for yarn to only warn in this case if it wasn't hoisting? Since if hoisting occurs then it's not actually an issue - and for Neutrino (and other ecosystems that use a similar plugin system), the hoisting is actually necessary/expected otherwise nothing would work.

[mpolichette]

@edmorley any chance you found a resolution to this issue? I'm using neutrino as well and it is frustrating to get a bunch of warnings we don't technically control.

[edmorley]

@mpolichette I haven't sadly.

@BYK, what do you think about:

Perhaps a middle ground would be for yarn to only warn in this case if it wasn't hoisting? Since if hoisting occurs then it's not actually an issue - and for Neutrino (and other ecosystems that use a similar plugin system), the hoisting is actually necessary/expected otherwise nothing would work.

[mpolichette]

I think this is supposed to be fixed in v1.4.0... https://github.com/yarnpkg/yarn/pull/5088

[edmorley]

This issue is about cases where the dep isn't at root level intentionally, but will be after hoisting. So isn't fixed in the latest release.

[billybonks]

and for Neutrino (and other ecosystems that use a similar plugin system), the hoisting is actually necessary/expected otherwise nothing would work.

i seem to agree with this statement.