Add automatic provision of the --tag option to npm publish

[Avaq]

Closes #55

[davidchambers]

The "${options[publish-command]}" == 'npm publish' check doesn't sit well with me. Semantically, I believe we're trying to express the following:

if pre-release
  default-publish-command = npm publish --tag options[prerelease-label]
else
  default-publish-command = npm publish

if user-specified-publish-command
  publish-command = user-specified-publish-command
else
  publish-command = default-publish-command

The above could instead be expressed like so:

if user-specified-publish-command
  publish-command = user-specified-publish-command
else if pre-release
  publish-command = npm publish --tag options[prerelease-label]
else
  publish-command = npm publish

Rather than set the default value of publish-command conditionally, the code in this pull request updates the publish-command value if it is 'npm publish', regardless of whether the default value was used or whether the user specified 'npm publish' explicitly.

Although the subtle difference between the two approaches is unlikely to be significant in practice, I would find the code easier to understand if it only manipulated the default publish-command value.

[Avaq]

I knew you'd say that. I tried going for the suggested approach first, but found that in order to run this logic:

if user-specified-publish-command
  publish-command = user-specified-publish-command
else if pre-release
  publish-command = npm publish --tag options[prerelease-label]
else
  publish-command = npm publish

Two separate variables are needed (user-specified-publish-command and publish-command), which needed various changes to the code.

I figured by using the right wording in the documentation, I could get away with the current approach.

[davidchambers]

Could we leave options[publish-command] unset initially, and set it to the desired default value later if it remains unset?

[Avaq]

Sure :)
I thought you'd disapprove because of the mixed type, in that case.

[Avaq]

I just released a new beta version of Fluture using this version of xyz. I'm happy to report that it works as intended. :)

$ npm dist-tags ls fluture
beta: 12.0.0-beta.1
latest: 11.0.1

[Avaq]

Shall we merge and release this?

[davidchambers]

Shall we merge and release this?

Yes. Thank you for reminding me. v3.1.0 or v4.0.0?

[Avaq]

v3.1.0 or v4.0.0?

Technically I think this is a breaking change, because the behaviour changed. I would be surprised if anyone relies on prerelease packages being published with the latest tag, but I still think it's good to do a major bump, if only to give people a reason to look at what's changed.

[Avaq]

@davidchambers Would you like me to merge, and perhaps release, this?

[davidchambers]

Absolutely. In the future please let me know when you git push --force a change as I rely on GitHub notifications to know when action is required from me. I'm sorry to have left you hanging.

[Avaq]

Hi @davidchambers. Any plans to release this to npm? I've been using direct install from GitHub all this time.

[davidchambers]

https://github.com/davidchambers/xyz/releases/tag/v4.0.0

Sorry for the delay.