10.0.0: temporary directory created before build trashes build

[kloczek]

test case for that is:

• clone repo
• execute in cloned directory mkdir temp; python3 -sBm build -w --no-isolation
  After that you may see something like below

+ /usr/bin/python3 -sBm build -w --no-isolation
* Getting build dependencies for wheel...
error: Multiple top-level packages discovered in a flat-layout: ['jaraco', 'SPECPARTS'].

To avoid accidental inclusion of unwanted files or directories,
setuptools will not proceed with this build.

If you are trying to create a single distribution with multiple packages
on purpose, you should not rely on automatic discovery.
Instead, consider the following options:

1. set up custom discovery (`find` directive with `include` or `exclude`)
2. use a `src-layout`
3. explicitly set `py_modules` or `packages` with a list of names

To find more information, look for "package discovery" on setuptools docs.

ERROR Backend subprocess exited when trying to invoke get_requires_for_build_wheel

[jaraco]

Duplicate with jaraco/skeleton#116.