Hello! I hope everyone's had a great start to 2018! :) A few months back, while working on pip, I had noticed an oddity about extras. Installing a package with extras would not store information about the fact that the extras were requested. This means, later, it is not possible to know which extra-based optional dependencies of a package have to be considered when verifying that the packages are compatible with each other. This information is relavant for resolution/validation since without it, it is not possible to know which the extra-requirements to care about. As an example, installing ``requests[security]`` and then uninstalling ``PyOpenSSL`` leaves you in a state where you don't really satisfy what was asked for but there's no way to detect that either. Thus, obviously, I'm interested in making pip to be able to store this information. As I understand, this is done needs to be specified in a PEP and/or on PyPUG's specification page. To that end, here's seeding proposal for the discussion: a new `extras-requested.txt` file in the .dist-info directory, storing the extra names in a one-per-line format. Cheers! Pradyun