Yarn: CI mode

[arcanis]

We should have an official way of ensuring a project sanity. The CI mode would kick in if the CI environment variable is on, or if the --ci command line option is enabled. It would:

• Enable frozen-lockfile
• Bump all warnings to errors

[ajhool]

Just for clarity's sake, simply calling npm install --ci instead of yarn install will not work, correct? npm install --ci expects a package-lock.json and yarn won't provide that.

Is there a safe way to use npm install --ci while Yarn 2.0 sorts out this feature?

[kamontat]

@ajhool For npm, is npm ci

[thynson]

I want that yarn ci could be executed with only lock file without package.json, I've alread made a RFC(See https://github.com/yarnpkg/rfcs/pull/112), wish it could be implemented in Yarn 2.

[ianwalter]

I think maybe we could add these (or at least some of these) as well:

• --skip-integrity-check node_modules doesn't exist so this should be skipped (unless it doesn't make a difference)
• --non-interactive Fail if interactive is needed
• --no-progress Would be more appropriate I think for CI logs