pip install does not recognize missing extras in transitive dependecies

[Savlik]

Environment

• pip version: 19.1.1
• Python version: 3.7
• OS: Linux

Description
When one of the shared transitive dependency have an extra that depends on something and it is later in the installation order, the extra dependency is not installed. See how to reproduce for example.

Expected behavior
All transitive dependencies including extras should be install not depending on the installation order.

How to Reproduce
Sorry, my working example uses internal libraries and I do not know how to reproduce the bug using only public ones.

Lets say, I have four libraries libA, libB, libC and libD. The dependecies goes:

• libA -> libC
• libB -> libC[extra] -> libD

Now when I run pip install libA liB, only libraries libA, libB and libC will be installed, as if the libC[extra] dependency was lost.

Both pip install libB libA and pip install libA && pip install libB produces correct result and all four libraries will be installed.

Maybe related issue #4086

[pradyunsg]

This is basically #988.

[chrahunt]

@pradyunsg is it worth addressing this independent of #988 or should it wait for/be incorporated into that?

[pradyunsg]

We could but I'd personally really rather invest effort in a more comprehensive, complete fix.

[pradyunsg]

Closing this since I don't think there's any reason to track this specific instance passing.