Fallback to yarn when npm isn't installed

[dandv]

• ESLint Version:
  4.0.0
• Node Version:
  v7.10.0
• npm Version:
  None! Due to some issues with npm, I'm testing a yarn-only development flow.

What did you do? Please include the actual source code causing the issue.

yarn add --dev eslint
./node_modules/.bin/eslint --init

What did you expect to happen?
It would be great if eslint didn't rely on npm to be installed, and ran yarn if npm was not found.

What actually happened? Please include the actual, raw output from ESLint.

$ node_modules/.bin/eslint --init
? How would you like to configure ESLint? Use a popular style guide
? Which style guide do you want to follow? Airbnb
? Do you use React? No
? What format do you want your config file to be in? JavaScript
Installing eslint-plugin-import, eslint-config-airbnb-base
/bin/sh: 1: npm: not found
Command failed: npm i --save-dev eslint-plugin-import eslint-config-airbnb-base
Error: Command failed: npm i --save-dev eslint-plugin-import eslint-config-airbnb-base
    at checkExecSyncError (child_process.js:481:13)
    at Object.execSync (child_process.js:521:13)
    at Object.installSyncSaveDev (/z/prg/js/node_modules/eslint/lib/util/npm-util.js:56:18)
    at installModules (/z/prg/js/node_modules/eslint/lib/config/config-initializer.js:99:17)
    at getConfigForStyleGuide (/z/prg/js/node_modules/eslint/lib/config/config-initializer.js:277:5)
    at inquirer.prompt.then.earlyAnswers (/z/prg/js/node_modules/eslint/lib/config/config-initializer.js:357:22)

[not-an-aardvark]

Thanks for reporting. How did you end up with Node installed without npm being installed? Since npm is bundled with Node, I would have expected it to be a safe bet to assume it was installed.

[dandv]

@not-an-aardvark: I've uninstalled npm on purpose, to see how development would go with yarn alone. Haven't had a problem until now, and all operations have been much faster.

[platinumazure]

Is it possible to bundle either npm or yarn as a dependency (without massively increasing the size of the published package)? Are there APIs we could call directly instead of relying on the presence of an executable in the user's path?

[not-an-aardvark]

I think it might be easiest to just assume that npm is present, and print a useful error message if it's not. Given that npm is bundled with node, I suspect it's quite rare for users to not have npm installed. So we could do everything else, and then tell the user in an error message that "to finish the setup, you need to install these packages somehow."

[dandv]

Agree with @not-an-aardvark. I'm in the minority right now, but I suspect as yarn gets a larger foothold, others might disable npm as well. That will take a while though.

[not-an-aardvark]

Fixed in #9169.