Stale package build artifacts persist after pyproject.toml updates

[harlantc]

I'm confused about how setuptools chooses what to include when building from source. I'm working on creating packages with setuptools, and ran into an issue where I would make a change to a pyproject.toml, and not get the changes I expect, or do get the changes I expect, but also see the old config persist, even after wiping away the install location.

One instance of this occurred while I was trying to learn how to write a pyproject.toml, and I mistyped something.

[tool.setuptools.package-dir]
wrongname = "src/mypkg"

I then run pip install --prefix <path> -vv ., see I made a mistake, and update to:

[tool.setuptools.package-dir]
mypkg = "src/mypkg"

I deleted the install prefix and reran the installation. However, I see both wrongname and mypkg in the install site-packages. I'd understand wrongname sticking around if I hadn't cleaned the install dir, but it will reappear every time. I see there's a build/ dir created during the build step that is retaining the wrongname pkg, and when I delete that dir, it no longer shows up in my installs, but I would think the build should be refreshed every time pyproject.toml is changed.

Should I be deleting build/ myself before updating pyproject.toml, or is this a case where some flag for pip/setuptools that is helpful to ensure the build is always fresh? Would using python -m build be the correct workaround?

Again, I'm learning how this works, and this gotcha caused me a lot of frustration, as my changes did not have an obvious result.