Access __file__ global in Early bind function (package.py)

[vanridal]

Sometimes it can be quite useful to access the location of a package file in a Early bind function
Maybe you want to find a relative file to read in, like a python requirments.txt or a VERSION token file

In the global preprocess, the DeveloperPackage object as a filepath attribute,
Unfortunately in Early bind function the this object does not, I thought to add the attribute to the this object but then this will add this path attribute to the built package file, which i think is undesirable.

I think the best option is to support the standard global variable __file__

As this will not be added to the final build package file

[beatreichenbach]

I might be misunderstanding but for anything during build, can you not just use any of the REZ_BUILD_* environment variables?
https://rez.readthedocs.io/en/3.0.0/environment.html#build-environment-variables

For your use case specifically, you'd use REZ_BUILD_SOURCE_PATH.

[vanridal]

This is for an early bind function in a package.py, those variables wont exist yet.

My use case was around the version property and I actually solved my use case for this issue, I was a bit overzealous with submitting it. So used to using __file__ as a reliable way to get a python file

As im using it for building packages, i can use os.getcwd() but I decided to keep the issue open, as I could think of some use cases where os.getcwd() wouldn't work, for a loose example you had some manually created dynamic package in your repo, or even if at some point rez supported calling rez-build with a arg to the package.py instead of cwd.

Also I think ensuring the existence of the __file__ is more pythonic as it is a standard global variable.
Its also easily implemented with a single line of code

I created a pull request for it, and ive been using my commit with the rez 3.2.1 with no discovered ill effects. The maintainers may do with it with what they wish.