Migrate this to use slightly more constrainted monkeypatching

The primary benefit of this is that it'll work when you have a single project using both setuptools-rust as well as cffi.

setup.cfg

@@ -31,7 +31,8 @@ setup_requires = setuptools>=41; wheel; setuptools_scm[toml]>=3.4.3
 distutils.commands =
     check_rust=setuptools_rust.check:check_rust
     clean_rust=setuptools_rust:clean_rust
-    build_ext=setuptools_rust:build_ext
     build_rust=setuptools_rust:build_rust
     test_rust=setuptools_rust:test_rust
     tomlgen_rust=setuptools_rust:tomlgen_rust
+distutils.setup_keywords =
+    rust_extensions=setuptools_rust.setuptools_ext:rust_extensions

setuptools_rust/__init__.py

@@ -1,8 +1,6 @@
 from __future__ import print_function, absolute_import
 
-from . import patch
 from .build import build_rust
-from .build_ext import build_ext
 from .check import check_rust
 from .clean import clean_rust
 from .extension import RustExtension
@@ -16,10 +14,6 @@
     "Strip",
     "check_rust",
     "clean_rust",
-    "build_ext",
     "build_rust",
     "test_rust",
 )
-
-
-patch.monkey_patch_dist(build_ext)

setuptools_rust/patch.py

@@ -12,35 +12,8 @@
     wheel = False
 
 
+# XXX: Need to port the rest of this to setuptools_ext!
 def monkey_patch_dist(build_ext):
-    # allow to use 'rust_extensions' parameter for setup() call
-    Distribution.rust_extensions = ()
-
-    # replace setuptools build_ext
-    Distribution.orig_get_command_class = Distribution.get_command_class
-
-    def get_command_class(self, command):
-        if command == "build_ext":
-            if command not in self.cmdclass:
-                self.cmdclass[command] = build_ext
-
-        return self.orig_get_command_class(command)
-
-    Distribution.get_command_class = get_command_class
-
-    # use custom has_ext_modules
-    DistDistribution.orig_has_ext_modules = DistDistribution.has_ext_modules
-
-    def has_ext_modules(self):
-        return (
-            self.ext_modules
-            and len(self.ext_modules) > 0
-            or self.rust_extensions
-            and len(self.rust_extensions) > 0
-        )
-
-    DistDistribution.has_ext_modules = has_ext_modules
-
     # this is required because, install directly access distribution's
     # ext_modules attr to check if dist has ext modules
     install.orig_finalize_options = install.finalize_options
@@ -108,21 +81,3 @@ def finalize_options(self):
             self.orig_finalize_options()
 
         bdist_wheel.finalize_options = finalize_options
-
-    # clean rust project
-    def run_clean(self):
-        self.orig_run()
-
-        if not self.dry_run:
-            self.run_command("clean_rust")
-
-    clean.orig_run = clean.run
-    clean.run = run_clean
-
-    # check rust project
-    def run_check(self):
-        self.orig_run()
-        self.run_command("check_rust")
-
-    check.orig_run = check.run
-    check.run = run_check

setuptools_rust/setuptools_ext.py

@@ -0,0 +1,49 @@
+from distutils import log
+from distutils.command.check import check
+from distutils.command.clean import clean
+
+from setuptools.command.build_ext import build_ext
+
+
+def add_rust_extension(dist, rust_extension):
+    build_ext_base_class = dist.cmdclass.get('build_ext', build_ext)
+
+    class build_ext_rust_extension(build_ext_base_class):
+        def run(self):
+            if self.distribution.rust_extensions:
+                log.info("running build_rust")
+                build_rust = self.get_finalized_command("build_rust")
+                build_rust.inplace = self.inplace
+                build_rust.run()
+
+            build_ext_base_class.run(self)
+    dist.cmdclass['build_ext'] = build_ext_rust_extension
+
+    clean_base_class = dist.cmdclass.get('clean', clean)
+
+    class clean_rust_extension(clean_base_class):
+        def run(self):
+            clean_base_class.run(self)
+            if not self.dry_run:
+                self.run_command("clean_rust")
+    dist.cmdclass['clean'] = clean_rust_extension
+
+    check_base_class = dist.cmdclass.get('check', check)
+
+    class check_rust_extension(check_base_class):
+        def run(self):
+            check_base_class.run(self)
+            self.run_command("check_rust")
+    dist.cmdclass["check"] = check_rust_extension
+
+
+def rust_extensions(dist, attr, value):
+    assert attr == "rust_extensions"
+
+    orig_has_ext_modules = dist.has_ext_modules
+    dist.has_ext_modules = lambda: (
+        orig_has_ext_modules() or bool(dist.rust_extensions)
+    )
+
+    for rust_extension in value:
+        add_rust_extension(dist, rust_extension)