add minVersion function

[kellyselden]

I'm trying to decide which range is "newer" when automatically updating package.json here and here. The scenario is

• my dep is "a": "^2.0.2"
• upstream was updated "a": "^1.4.0" => "a": "^2.0.0"

I want to be smart and say, even though the dep was updated, mine is more recent, so ignore the change. My pseudocode is if myDepRange < newDepRange then update.

Getting the lowest possible version in a range seems like a good way to compare two ranges for newest. I currently am doing:

function minVersion(range) {
  return new Range(range).set[0][0].semver.version;
}

But I feel like I'm reaching into too much private API. I would like add this function upstream to this library.

[coveralls]

Coverage increased (+0.02%) to 98.045% when pulling 1e13894 on kellyselden:minVersion into ec6f97a on npm:master.

[jaydenseric]

I would really like this too, to be able to derive the minimum supported Node.js version from the range in package.json engines. This is useful for configuring @babel/preset-env to transpile and polyfill for the minimum supported Node.js version.

To easily do this in my own packages I make the assumption the range is always a single semver prefixed with >=, so I can just strip it off with substring(2) to get a min version.

@babel/preset-env will eventually look at engines.node to do this automatically, so a more robust solution that can take arbitrary, complicated ranges will be useful.

[isaacs]

I think this will return an incorrect value in the following cases:

minVersion('1.2.3 || 1.0.0') // expect 1.0.0, get 1.2.3
minVersion('<=1.2.3 >1.0.0') // expect 1.0.1, get 1.2.3
minVersion('>1.2.3') // expect 1.2.4, get 1.2.3
minVersion('>1.2.3-alpha') // <-- this one is probably impossible? 1.2.3-alpha is incorrect tho

[coreyfarrell]

I was working on a patch for this before I saw this PR. #241 deals with these edge cases and includes testing for them situations. minVersion('>1.2.3-alpha') is not impossible, I believe the correct result is 1.2.3-alpha.0 which is less than 1.2.3-beta.

[isaacs]

I think that this might be theoretically impossible. You could get the minimum of a given set of versions that satisfies a given range. But what you can't do is (usually) specify the minimum version that would satisfy a range. Consider >1.2.3-alpha which would be satisfied by 1.2.3-beta or 1.2.3-alpha.0 or 1.2.3-alphb.

[jaydenseric]

The no-unsupported-features rule of eslint-plugin-node would probably benefit from this too. It seems they changed their approach from attempting to determine a min version.

[coreyfarrell]

semver.minVersion was implemented by #241 and released in semver@5.7.0. Sorry for bypassing this PR, I created/submitted the patch before I saw this.