Revamp Python build system to fix multiple build problems (#6)

* Revamp Python build system to fix multiple build problems

Use `pyproject.toml` to define build metadata. This enables the following
improvements:

* `pycocotools.mask` previously failed to load if the NumPy version was downgraded
  after `pycocotools` was installed, due to an ABI mismatch. This is fixed
  by using the oldest supported NumPy version for the current environment as
  the build dependency.

* Installing `pycocotools` no longer installs Cython as a dependency (it's
  not needed at runtime).

* `pycocotools` can now be installed without having `setuptools` in your
  environment.

All this is accomplished at the price of more strict system requirements:

* Required Python version is now 3.5+, primarily because that is what
  `oldest-supported-numpy` requires. Notably, this means that Python 2
  support is dropped.

* pip 10 or higher is required to install `pycocotools` from an sdist.

The setuptools requirement is bumped to 43, because setuptools includes
pyproject.toml in the sdist starting with this version. However, this has no
impact on users, since pip will automatically fetch the correct version.

Additionally, update the documentation to recommend using `pip` to install
the project, instead of running `setup.py` directly. This ensures that the
build result is the same as you would get by installing from an sdist. pip
21.1+ is required for this, because it uses the `in-tree-build` feature.

* Add tests to both installation methods

* Undo my change as CI is not running for PRs

Co-authored-by: Yuxin Wu <[email protected]>

.circleci/config.yml

@@ -9,8 +9,7 @@ jobs:
     steps:
       - checkout
       - run:
-          # TODO in-place pip install is not working
-          command: cd PythonAPI && python setup.py build_ext
+          command: python -m pip install --use-feature=in-tree-build ./PythonAPI
           name: Install From Source
 
   build-from-sdist:
@@ -19,8 +18,9 @@ jobs:
       - checkout
       - run:
           command: |
-            cd PythonAPI && python setup.py sdist
-            python -m pip install --progress-bar off dist/*.tar.gz
+            python -m pip install build
+            python -m build --sdist ./PythonAPI
+            python -m pip install --progress-bar off ./PythonAPI/dist/*.tar.gz
           name: Install From Distribution
       - run:
           command: |

PythonAPI/Makefile

@@ -5,5 +5,5 @@ all:
 
 install:
 	# install pycocotools to the Python site-packages
-	python setup.py build_ext install
+	python -m pip install --use-feature=in-tree-build .
 	rm -rf build

PythonAPI/pyproject.toml

@@ -0,0 +1,8 @@
+[build-system]
+requires = [
+    "cython>=0.27.3",
+    "oldest-supported-numpy",
+    "setuptools>=43.0.0",
+    "wheel",
+]
+build-backend = "setuptools.build_meta"

PythonAPI/setup.py

@@ -1,15 +1,8 @@
 """To compile and install locally run "python setup.py build_ext --inplace".
-To install library to Python site-packages run "python setup.py build_ext install"
+To install library to Python site-packages run "python -m pip install --use-feature=in-tree-build ."
 """
 import platform
-from setuptools import dist, setup, Extension
-
-setup_requires = [
-    'setuptools>=18.0',
-    'cython>=0.27.3',
-    'numpy',
-]
-dist.Distribution().fetch_build_eggs(setup_requires)
+from setuptools import setup, Extension
 
 import numpy as np
 
@@ -30,11 +23,10 @@
     license="FreeBSD",
     packages=['pycocotools'],
     package_dir={'pycocotools': 'pycocotools'},
-    setup_requires=setup_requires,
+    python_requires='>=3.5',
     install_requires=[
-        'setuptools>=18.0',
-        'cython>=0.27.3',
-        'matplotlib>=2.1.0'
+        'matplotlib>=2.1.0',
+        'numpy',
     ],
     version='2.0.3',
     ext_modules=ext_modules