[BUG] setuptools.build_meta proceeds with no setup.py or setup.cfg

[godlygeek]

setuptools version

setuptools==58.1.0

Python version

Python 3.9

OS

Linux

Additional environment information

No response

Description

Running pip install . in a directory that contains nothing but a pyproject.toml with these contents:

[build-system]
requires = ["setuptools", "wheel"]
build-backend = "setuptools.build_meta"

successfully installs a distribution containing no modules or packages and no useful metadata:

$ cat /tmp/39/lib/python3.9/site-packages/UNKNOWN-0.0.0.dist-info/METADATA
Metadata-Version: 2.1
Name: UNKNOWN
Version: 0.0.0
Summary: UNKNOWN
Home-page: UNKNOWN
License: UNKNOWN
Platform: UNKNOWN

UNKNOWN

Expected behavior

I would expect the build backend to fail, due to it lacking any useful configuration, rather than succeeding in building a package that is empty except for placeholder metadata.

This may be a duplicate of #2329, but that one was specifically scoped to build_meta:__legacy__, and all of the discussion was about the legacy backend. In this case, you can see that the same issue occurs even with the PEP 517 backend.

How to Reproduce

See description

Output

See description

Code of Conduct

• I agree to follow the PSF Code of Conduct

[jaraco]

There's a lot of context and conversation in #2329, so I'm going to re-scope #2329 to include this concern.