pyproject.toml is not PEP 517 compliant

[Jinnkunn]

Bug Description

The execution of 'maturin develop' can be flawless and error-free with maturin version 0.14.0. However, upgrading to maturin 0.15.0 will result in an error when running 'maturin develop'.

💥 maturin failed
  Caused by: pyproject.toml is invalid
  Caused by: pyproject.toml is not PEP 517 compliant: TOML parse error at line 1, column 1
  |
1 | [build-system]
  | ^
invalid type: sequence, expected string or map

Your maturin version (maturin --version)

0.15.0

Your Python version (python -V)

Python 3.9.6

Your pip version (pip -V)

pip 23.1.2

What bindings you're using

pyo3

Does cargo build work?

• Yes, it works

If on windows, have you checked that you aren't accidentally using unix path (those with the forward slash /)?

• Yes

Steps to Reproduce

Here is a sample structure I have in my pyproject.toml file. The ellipsis ("...") represents additional content that is not shown in the provided snippet.

[build-system]
requires = [ "maturin>=0.14", "numpy", "wheel", "patchelf",]
build-backend = "maturin"

[project]
name = "..."
license-files = [ "license.txt",]
requires-python = ">=3.8"
requires-dist = [ "maturin>=0.14", "...",]
dependencies = [ "packaging", "...",]
zip-safe = false
version = "..."
readme = "..."
description = "..."
classifiers = [ "...",]
[[project.authors]]
name = "..."
email = "..."

[project.urls]
homepage = "..."
documentation = "..."
repository = "..."

[project.optional-dependencies]
test = [ "coverage", "...",]
docs = [ "sphinx", "sphinx-rtd-theme",]
devel = []

[tool.maturin]
include = [ "...",]
bindings = "pyo3"
compatability = "manylinux2014"

[tool.pytest.ini_options]
testpaths = [ "...",]
addopts = "--color=yes --tb=native --cov-report term --cov-report html:docs/dist_coverage --cov=aisdb --doctest-modules --envfile .env"

RUST_LOG=maturin=debug maturin build

2023-05-18T01:12:41.314803Z DEBUG maturin::project_layout: Found pyproject.toml in working directory at ".../pyproject.toml"
💥 maturin failed
  Caused by: pyproject.toml is invalid
  Caused by: pyproject.toml is not PEP 517 compliant: TOML parse error at line 1, column 1
  |
1 | [build-system]
  | ^
invalid type: sequence, expected string or map

[messense]

cc @konstin, probably due to pep440_rs/pep508_rs integration?

[konstin]

It's the license-files key, i think the PEP has been updated in that regard: https://peps.python.org/pep-0639/#add-license-files-key . I've opened #1616 to fix the error message.