Feature Request : Allowing users to specify install-layout

[asmodehn]

Referring to #562

One solution to this kind of problem could be to allow people to customize their installation layout without relying on specifying each directory independently.
After all, --target is like the old setuptools install-dir and then there used to be script-dir.
Although it make sense for setup tools to allow each directory independently for advanced users, the --target option might be trying to do something that is too detailed for pip's purpose.

Pip provides --prefix which allow users to specify where is the installation prefix, but in some cases that might not be enough (as it was with mine, dealing with old -but not obsolete- debian-based software framework), and users might want to customize where they install different parts of their package...

IMHO this situation could make sense :

• setuptools has all options to pass each directory separately (lib, scripts, headers, etc.) for heavy customization of package installation when needed. They can be used via pip --install-option on the exceptional situation when they are needed when setup.py install is called (and --develop-option for setup.py develop ref. Feature Request : Allowing users to specify develop-options #3602).
• pip has an option to pass the prefix and the layout (somehow defining the list of all directories relative to the prefix)

Passing the layout to pip would allow detailed customization by a user, while allowing pip to control how this is communicated to setuptools.
A very simple first version could be to just use/replicate the --install-layout option from setuptools.
Later on, more fancy customization could be allowed. The rules that make this layout valid or not might depend on the underlying install system (match a minimum required set of options that pip can pass to setuptools for example).

[dstufft]

Closing this, I don't believe this feature to be one we want to add. It is something that is likely too be a bit of a footgun for people and really should remain an internal detail inside of pip.