Fail for blank target from auto (or engine) version file

[shadowspawn]

Pull Request

Problem

Using auto and engine will fallback to current if the found version file does not contain a target version. This could be due to an empty version file, but the more likely situation is a package.json with no engines field. This is a bit surprising and not particularly useful.

There is a technical argument for current if there is an engines field with a node field which is empty, but even then installing the current version of node is not all that useful.

And, like with dependencies, if you don't specify the version (or if you specify "*" as the version), then any version of node will do.

https://docs.npmjs.com/cli/v7/configuring-npm/package-json#engines

Resolves: #692

Solution

Display an error if the target version is missing (blank).

% echo "" >>  .node-version
% n auto
       found : /Users/john/Documents/Sandpits/n/issues/692/.node-version
        read : 

  Error: file found for auto did not contain target version of node

% rm .node-version

% npm init -y
% n engine
       found : /Users/john/Documents/Sandpits/n/issues/692/package.json
        read : 

  Error: did not find supported versions of node in 'engines' field of package.json

ChangeLog

• changed: display error if version missing in version file for auto and engine (rather than fallback to current)