Enable building abi3 shared objects

This depends on PyO3/pyo3#1125

Author: alex

.github/workflows/ci.yml

@@ -67,3 +67,47 @@ jobs:
           pip install --no-use-pep517 -e rust_with_cffi/
           pip install -r rust_with_cffi/requirements-dev.txt
           pytest rust_with_cffi/tests.py
+  test-abi3:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    steps:
+      - uses: actions/checkout@master
+      - name: Setup python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.6
+
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+
+      - name: Build package
+        run: pip install -e .
+
+      - name: Build an abi3 wheel
+        shell: bash
+        run: |
+          cd examples/rust_with_cffi/
+          python --version
+          python setup.py bdist_wheel --py-limited-api=cp35
+          ls -la dist/
+
+      # Now we switch to a differnet Python version and ensure we can install
+      # the wheel we just buitl.
+      - name: Setup python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.8
+
+      - name: Install abi3 wheel and run tests
+        shell: bash
+        run: |
+          cd examples/
+          python --version
+          pip install rust_with_cffi/dist/rust_with_cffi*.whl
+          python -c "from rust_with_cffi import rust; assert rust.rust_func() == 14"
+          python -c "from rust_with_cffi.cffi import lib; assert lib.cffi_func() == 15"

examples/rust_with_cffi/Cargo.lock

@@ -5,7 +5,7 @@ authors = ["Alex Gaynor <[email protected]>"]
 edition = "2018"
 
 [dependencies]
-pyo3 = { version = "0.12.1", features = ["extension-module"] }
+pyo3 = { git = "https://github.com/alex/pyo3", branch="abi3-link-python3", features = ["extension-module", "abi3"] }
 
 [lib]
 name = "rust_with_cffi"

examples/rust_with_cffi/Cargo.toml

@@ -21,7 +21,7 @@
         "Operating System :: MacOS :: MacOS X",
     ],
     packages=["rust_with_cffi"],
-    rust_extensions=[RustExtension("rust_with_cffi.rust")],
+    rust_extensions=[RustExtension("rust_with_cffi.rust", py_limited_api=True)],
     cffi_modules=["cffi_module.py:ffi"],
     install_requires=install_requires,
     setup_requires=setup_requires,

examples/rust_with_cffi/setup.py

@@ -285,7 +285,16 @@ def build_extension(self, ext):
 
                 ext.install_script(ext_path)
             else:
-                ext_path = build_ext.get_ext_fullpath(target_fname)
+                # Technically it's supposed to contain a
+                # `setuptools.Extension`, but in practice the only attribute it
+                # checks is `ext.py_limited_api`.
+                modpath = target_fname.split('.')[-1]
+                assert modpath not in build_ext.ext_map
+                build_ext.ext_map[modpath] = ext
+                try:
+                    ext_path = build_ext.get_ext_fullpath(target_fname)
+                finally:
+                    del build_ext.ext_map[modpath]
 
             try:
                 os.makedirs(os.path.dirname(ext_path))

setuptools_rust/build.py

@@ -47,6 +47,10 @@ class RustExtension:
       optional : bool
         if it is true, a build failure in the extension will not abort the
         build process, but instead simply not install the failing extension.
+      py_limited_api : bool
+        Same as `py_limited_api` on `setuptools.Extension`. Note that if you
+        set this to True, your extension must pass the appropriate feature
+        flags to pyo3 (ensuring that `abi3` feature is enabled).
     """
 
     def __init__(
@@ -64,6 +68,7 @@ def __init__(
         script=False,
         native=False,
         optional=False,
+        py_limited_api=False,
     ):
         if isinstance(target, dict):
             name = "; ".join("%s=%s" % (key, val) for key, val in target.items())
@@ -83,6 +88,10 @@ def __init__(
         self.script = script
         self.native = native
         self.optional = optional
+        self.py_limited_api = py_limited_api
+        # We pass this over to setuptools in one place, and it wants this
+        # attribute to exist.
+        self._links_to_dynamic = False
 
         if features is None:
             features = []