[RRFC] an ability for a package to indicate that it should always be installed as if --save-exact were specified

Motivation ("The Why")

Install an exact version of Prettier locally in your project. This makes sure that everyone in the project gets the exact same version of Prettier. Even a patch release of Prettier can result in slightly different formatting, so you wouldn’t want different team members using different versions and formatting each other’s changes back and forth.

-- from Prettier's docs, https://prettier.io/docs/en/install.html#summary

Example

Another example of where this can be really useful is packages whose authors explicitly acknowledge they don't follow semver.
For example, TypeScript. See https://github.com/microsoft/TypeScript/issues/14116

How

Current Behaviour

There is no way to do this.

Desired Behaviour

As a package maintainer, I should be able to specify "exactVersion": true (or "semver": false) in package.json, so that the users automatically get "my-package": "1.2.3" instead of "my-package": "^1.2.3" when they run npm install my-package.

References

• Related: https://github.com/npm/rfcs/pull/40

Review the desired behavior in this issue and the related RFC #40, focusing on package.json and the npm install flow described here. Done means a package maintainer can declare exactVersion (or an equivalent setting) and npm install records an exact version instead of a caret range.