[bug] An error occurs on export-pkg of python-require package

[apyvovar]

Environment details

• Operating System+version: macOS 13.5.2
• Compiler+version: apple clang 14.0.3
• Conan version: 2.0.11
• Python version: 3.11.4

Steps to reproduce

For some cases, I have to build Conan package in specific build folder. So, I'm using corresponding --output-folder with this approach.

But there's a problem with python-require package. Running conan export-pkg command on python-require package results an error - A python-require cannot be export-pkg
Interesting note: Despite an error, looks like the package is actually exports to cache and an assertion fails later (conan list command show newly created package in cache).

Logs

conan_utils/2.0.2: Exported: conan_utils/2.0.2#d52343939be22b0ecd71de27769573ac (2023-09-25 15:07:33 UTC)
ERROR: Traceback (most recent call last):
  File "/opt/homebrew/lib/python3.11/site-packages/conan/cli/cli.py", line 272, in main
    cli.run(args)
  File "/opt/homebrew/lib/python3.11/site-packages/conan/cli/cli.py", line 172, in run
    command.run(self._conan_api, args[0][1:])
  File "/opt/homebrew/lib/python3.11/site-packages/conan/cli/command.py", line 125, in run
    info = self._method(conan_api, parser, *args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/lib/python3.11/site-packages/conan/cli/commands/export_pkg.py", line 52, in export_pkg
    assert conanfile.package_type != "python-require", "A python-require cannot be export-pkg"
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: A python-require cannot be export-pkg

ERROR: A python-require cannot be export-pkg

[memsharded]

Hi @apyvovar

Thanks for the report.

Indeed every stacktrace should be considered as a bug and fixed.

In this case it seems the fix would be a better error message, but the protection would still be there. A python_require is only a conanfile.py recipe, but it does not contain binaries, so it cannot be export-pkg. It can be conan export or even conan create (which is an alias to conan export for python_requires). But the conan export-pkg command is a very specific command to package pre-compiled binaries from user space, which doesn't make sense for python_requires packages.

We will check the behavior and messages, it probably should avoid the initial export completely, and fail earlier, but lets have a look.

[apyvovar]

Hello, @memsharded

Looks like the package is actually exported before an error. And it works properly.

Maybe, it makes more sense to handle python-require package as special case for export-pkg command for sake of consistency of package development flow, described in documentation (https://docs.conan.io/2/tutorial/developing_packages/local_package_development_flow.html) ? Feels like, this shouldn't cause much troubles.

[memsharded]

I am proposing #14819 for a better error message and avoiding the export.
The issue is that conan create and also export-pkg have associated other mechanisms like the export of binaries, running the test_package test, or storing the information in lockfiles or the --format=json. Trying to do the equivalent of a conan create for a python-require inside export-pkg will be quite dirty.