use Flit as build system

This patch switches the build system from setuptools (using `setup.py`) to Flit
(using `pyproject.toml`).

.github/workflows/release.yml

@@ -11,9 +11,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v2
       - name: Install dependencies
-        run: python3 -m pip install setuptools wheel
+        run: python3 -m pip install flit
       - name: Build package
-        run: python3 setup.py sdist bdist_wheel
+        run: python3 -m flit build
       - name: Publish package to PyPI
         uses: pypa/[email protected]
         with:

.github/workflows/test.yaml

@@ -20,14 +20,14 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v2
       - name: Install build dependencies
-        run: python3 -m pip install setuptools wheel
+        run: python3 -m pip install flit
       - name: Build package
         id: build
         run: |
           # To make the wheels reproducible, set the timestamp of the (files in
           # the) generated wheels to the date of the commit.
           export SOURCE_DATE_EPOCH=`git show -s --format=%ct`
-          python3 setup.py sdist bdist_wheel
+          python3 -m flit build
           printf "::set-output name=wheel::%s" dist/*.whl
       - name: Upload package artifacts
         uses: actions/upload-artifact@v2
@@ -156,7 +156,7 @@ jobs:
           python3 -um pip install setuptools wheel
           python3 -um pip install --upgrade --upgrade-strategy eager .[docs]
       - name: Build docs
-        run: python3 setup.py build_sphinx --nitpicky --warning-is-error --keep-going
+        run: python3 -m sphinx -n -W --keep-going docs build/sphinx/html
   build-and-test-container-image:
     name: Build container image
     needs: build-python-package

pyproject.toml

@@ -0,0 +1,27 @@
+[project]
+name = "nutils"
+readme = "README.md"
+authors = [
+    { name = "Evalf", email = "[email protected]" },
+]
+requires-python = '~=3.7'
+dependencies = [
+    "appdirs~=1.0",
+    "bottombar~=2.0.2",
+    "numpy>=1.17",
+    "psutil~=5.0",
+    "stringly",
+    "treelog>=1.0b5",
+]
+dynamic = ["description", "version"]
+
+[project.optional-dependencies]
+docs = ["Sphinx>=1.8"]
+export_mpl = ["matplotlib>=1.3", "pillow>2.6"]
+matrix_mkl = ["mkl"]
+matrix_scipy = ["scipy>=0.13"]
+import_gmsh = ["meshio"]
+
+[build-system]
+requires = ["flit_core >=3.2,<4"]
+build-backend = "flit_core.buildapi"