Fixed string list concatenation error

[gentlegiantJGC]

I am using build to build my project and want to pass custom settings into the setup.py file.

The suggested way is to use the config-setting flag chained with your global-option flag however this errors if only one global option is defined because they pass it in as a string not a list of strings.

Your code tries concatenating a list of strings with a single string which causes an error.

Summary of changes

If config_settings["--global-option"] is a string wrap it in a list

[jaraco]

Can you provide an example of what usage results in a list and what usage results in a string, and what commands you run to get that behavior? Does setuptools need to accept both forms (list and string)? I believe the global-option is poorly-defined, so this might be a good time to evaluate a better way for Setuptools to solicit configuration.

In any case, it would also be nice to have a test for the desired behavior to capture that it's required and why.

[gentlegiantJGC]

This command does not work
python -m build -C--global-option=--find-libs=True

This command does work
python -m build -C--global-option=--find-libs=True -C--global-option=--find-libs=True

I am using the --config-setting argument in build (-C for short) which is parsing the command into a dictionary.

In the first case that is

{
    "--global-option": "--find-libs=True"
}

and in the second case is

{
    "--global-option": [
        "--find-libs=True",
        "--find-libs=True"
    ]
}

If it finds the same argument more than once it will convert it to a list and append subsequent values.

That dictionary gets passed onto setuptools where it pulls out the --global-option value which assumes it is a list. That is where the error happens.
https://github.com/pypa/setuptools/blob/main/setuptools/build_meta.py#L213

[jaraco]

My god, that syntax is atrocious (-C--global-option=--find-libs=True). Do we know where --global-option is defined outside of the setuptools implementation?

[gentlegiantJGC]

Yeh it isn't great.
Build just takes all the config settings and feeds them to the build system (in this case setuptools). They don't have a flag just for global option because I think that is a thing implemented by setuptools and they work with other build systems afaik.

Build parses the --config-setting here https://github.com/pypa/build/blob/main/src/build/__main__.py#L346
Setuptools parses the --global-option here https://github.com/pypa/setuptools/blob/main/setuptools/build_meta.py#L213

Edit:
Setuptools passes the global option values onto the build command so it must be a sequence of strings at that point.
The question is if you would be open to supporting a single string as input and converting it to the correct format.