Make the scripts that aren't in public/ error out with a message

[pradyunsg]

Toward #61.

/cc @pypa/pip-committers, since I'd like to run this past other folks' eyes as well (and get a green tick or two) because this is changing something that'll affect a lot of users. I don't want to do something that can be this disruptive unilaterally.

[pradyunsg]

@pfmoore @uranusjr nudge.

[pfmoore]

Sorry, TBH I don't have time to do much more than a very superficial look at the moment. And I've not really been following what's going on with the moves in this repo. But from a quick skim, this looks OK.

[pradyunsg]

No worries, I'll quickly summarise what's up with this repository:

I rewrote the generation pipeline in #85, to be Python 3 based, and to not depend on invoke. It's also pretty now (because it uses rich). That was most of the code-related commotion in this repository. I also triaged the entire issue tracker, and trimmed any open issues / PRs that were resolved or addressed. All of that stuff is unrelated to this PR. :)

---

In #61, there's discussion about what we should do to make it easier to make a pip release that drops Python minor version support (eg: Python 3.5).

The main part of that plan is to change how we serve scripts from this repository. Now, we basically serve only the public/ folder in this repository, and those would go under bootstrap.pypa.io/pip/.

The important thing here is that it changes what url we serve our existing scripts on, from bootstrap.pypa.io/2.7/get-pip.py to bootstrap.pypa.io/pip/2.7/get-pip.py.

In exchange, it simplifies the server-side deployment setup and allows us to add additional files easily (add a public/3.6/get-pip.py in this repository). The main "issue" is that we're changing the URL, which results in churn for people (read: broken pipeline).

If the overall plan (of having a public folder in this repository and change old scripts with a message about the new location) is "not horrible" and the message in this PR's moved.py is "good enough", just let me know. I think that's all I am really asking for feedback on. :)

[pfmoore]

Ah right. I missed most of the rewrites because I don't follow this repo, so I only see direct pings. Strong +1 on having the "old Python" scripts served as bootstrap.pypa.io/pip/2.7/get-pip.py (with the main get-pip.py still at the top level) - essentially the same as virtualenv does it.

The message looks fine, too. I'm sure there will be some complaints that we're renaming at all, but 🤷

[uranusjr]

I took a quick look and everything seems fine to me. Can’t say I understand much about the whole process though, so take that as you will. I have an unrelated idea while looking at the code though, will file a separate issue for that.

Edit: turns out I’m not the only one thought about it (#88), so I’ll comment there instead.

[pradyunsg]

Let's do this.

[T2L]

@pradyunsg why not provide a simple 301 redirect to a new location rather than break everyone's pipelines?

[pradyunsg]

Because that would've broken pipelines too, and in a more subtle way with a bad error message. From #61 (comment):

We can't serve redirects from the current [url] since curl does not follow redirects by default.