[BUG] Build succeeds when no packages are found by find_packages

setuptools version

setuptools==60.1.0

Python version

3.9

OS

Manjaro Linux

Additional environment information

No response

Description

Incorrectly configuring project that uses packages = find: leads to no packages being found. However build still succeeds without any warnings or errors and generates wheel without any code.

Leaving packages empty also works but I don't know if it is intentional or not. On the other hand when using packages = find: I expect something to be found so I consider this a bug.

Expected behavior

A warning or an error during build

How to Reproduce

1. Create project with src-structure

myproject
- pyproject.toml
- setup.cfg
- src
- - mypackage
- - - __init__.py
- - - app.py

2. Edit setup.cfg to contain:

[metadata]
name = myproject
version = 1.0.0

[options]
packages = find:
package_dir =
    = src

;[options.packages.find]
;where = src ; leave this commented so no packages are found

3. Run build
4. Check that no packages are in the generated wheel

Output

$ python -m build
* Creating venv isolated environment...
* Installing packages in isolated environment... (setuptools, wheel)
* Getting dependencies for sdist...
running egg_info
writing manifest file 'src/myproject.egg-info/SOURCES.txt'
* Building sdist...
running sdist
running egg_info
writing manifest file 'src/myproject.egg-info/SOURCES.txt'
warning: sdist: standard file not found: should have one of README, README.rst, README.txt, README.md

running check
warning: check: missing required meta-data: url

warning: check: missing meta-data: either (author and author_email) or (maintainer and maintainer_email) should be supplied

creating myproject-1.0.0
creating myproject-1.0.0/src
creating myproject-1.0.0/src/myproject.egg-info
copying pyproject.toml -> myproject-1.0.0
copying setup.cfg -> myproject-1.0.0
copying src/myproject.egg-info/PKG-INFO -> myproject-1.0.0/src/myproject.egg-info
copying src/myproject.egg-info/SOURCES.txt -> myproject-1.0.0/src/myproject.egg-info
copying src/myproject.egg-info/dependency_links.txt -> myproject-1.0.0/src/myproject.egg-info
copying src/myproject.egg-info/top_level.txt -> myproject-1.0.0/src/myproject.egg-info
Creating tar archive
removing 'myproject-1.0.0' (and everything under it)
* Building wheel from sdist
* Creating venv isolated environment...
* Installing packages in isolated environment... (setuptools, wheel)
* Getting dependencies for wheel...
running egg_info
writing manifest file 'src/myproject.egg-info/SOURCES.txt'
* Installing packages in isolated environment... (wheel)
* Building wheel...
running bdist_wheel
running build
running install
running install_egg_info
running egg_info
writing manifest file 'src/myproject.egg-info/SOURCES.txt'
Copying src/myproject.egg-info to build/bdist.linux-x86_64/wheel/myproject-1.0.0-py3.9.egg-info
running install_scripts
Successfully built myproject-1.0.0.tar.gz and myproject-1.0.0-py3-none-any.whl

$ # check wheel content
$ unzip dist/myproject-1.0.0-py3-none-any.whl 
Archive:  dist/myproject-1.0.0-py3-none-any.whl
  inflating: myproject-1.0.0.dist-info/METADATA  
  inflating: myproject-1.0.0.dist-info/WHEEL  
  inflating: myproject-1.0.0.dist-info/top_level.txt  
  inflating: myproject-1.0.0.dist-info/RECORD  

Code of Conduct

• I agree to follow the PSF Code of Conduct

Start with the setup.cfg package-discovery configuration using packages = find: and the commented [options.packages.find] section, then reproduce the behavior with python -m build. Trace how setuptools handles an empty package result and verify the completed behavior by inspecting the generated wheel for a warning or error and the expected package contents.