Pip does not abort when asked to install non-existent extra

[ghost]

Environment

• pip version: doesn't matter
• Python version: doesn't matter
• OS: doesn't matter

Description

Suppose, you wanted to install azure[common]. Well, there isn't such a package. However, if you do this, azure package (seems like) will be installed.

Expected behavior

Error is shown to the user trying to install a nonexistent package.

How to Reproduce

Run pip install 'azure[common]'.

Output

A long wall of text indicating that things are being installed.

[RonnyPfannschmidt]

you requested the package azure with the extra common did you perhaps intend to install the package azure-common

[ghost]

What I wanted is a whole different story, not worth repeating here. The ticket is about something else though: extra package common doesn't exist for azure. When you ask setuptools to install this, it will tell you that there's no such thing, and it will install nothing. pip warns you that there is no such thing, but proceeds installing something I didn't ask for: azure (presumably). I'm never even told what's going to be installed.

[xavfernandez]

We could maybe add an option to abort installation on a missing extra but I'm not really convinced...

[ghost]

But this is not the only instance when pip installs unwanted garbage... I just gave it as an example.

Another example is when you have a previously installed dependency with a version incompatible with the currently installed dependency. pip will not abort in such case (as would virtually any other package manager in existence), but will print a message saying that versions are incompatible and will happily continue to install junk, all of which will later appear to be broken with very little hope of discovering the culprit, unless, somehow, you managed to stash the logs somewhere, and are ready to search through them for things that look suspicious.

To give you an example of this: try depending on azure-cli while also requiring prompt_toolkit >= 2.0.0. Lots of fun there...

What I'm looking for is not a solution to this single instance. I want pip to have a mode for not screwing up the environment, and to only allow screwing up the environment with special flags, like when you install a package, but ignore its dependencies etc.

[xavfernandez]

Let's keep the issue focused.

Another example is when you have a previously installed dependency with a version incompatible with the currently installed dependency.

The dependency resolution issue is #988.

with very little hope of discovering the culprit

pip check should easily give you the incompatible requirements.

[ghost]

pip check

That's trivial even without pip check... What's non-trivial about it is figuring out how it got there, not what the problem is.

[xavfernandez]

What's non-trivial about it is figuring out how it got there, not what the problem is.

That's trivial: someone installed something conflicting without looking at the logs ;) (or did not care).

[pradyunsg]

@wvxvw Your expected behavior is:

Error is shown to the user trying to install a nonexistent package.

However, the package does exist. It doesn't have the "common" extra here. Outside of an abort, what do you think would be a good way to work with this issue?

[pradyunsg]

@xavfernandez I changed the labels on this issue since it's really more about extras and not dependency resolution. Lemme know if you disagree. :)

[chrahunt]

There's a new topic #7122 that has some discussion on this same issue. I'll close this in favor of that one since it has more specific discussion related to the original issue.

@wvxvw if your concerns were not met with the previously-provided links please do not hesitate to create an issue!