chore: implement rudimentary CMake incremental build

We speed-up the build process for local development when CMake sources
are not changed in between build runs.

This reduces the build time from about 3 minutes to about 20 seconds.

Author: P403n1x87

setup.py

@@ -24,6 +24,7 @@
 from pathlib import Path  # isort: skip
 from pkg_resources import get_build_platform  # isort: skip
 from distutils.command.clean import clean as CleanCommand  # isort: skip
+from distutils.dep_util import newer_group
 
 
 try:
@@ -350,6 +351,35 @@ def build_extension(self, ext):
                 print(f"WARNING: An error occurred while building the extension: {e}")
 
     def build_extension_cmake(self, ext):
+        if os.getenv("DD_CMAKE_INCREMENTAL_BUILD", "0").lower() in ("1", "yes", "on", "true"):
+            # DEV: Rudimentary incremental build support. We copy the logic from
+            # setuptools' build_ext command, best effort.
+            full_path = Path(self.get_ext_fullpath(ext.name))
+            ext_path = Path(ext.source_dir, full_path.name)
+
+            # Collect all the source files within the source directory. We exclude
+            # Python sources and anything that does not have a suffix (most likely
+            # a binary file), or that has the same name as the extension binary.
+            sources = (
+                [
+                    _
+                    for _ in Path(ext.source_dir).rglob("**")
+                    if _.is_file() and _.name != full_path.name and _.suffix and _.suffix not in (".py", ".pyc", ".pyi")
+                ]
+                if ext.source_dir
+                else []
+            )
+            if not (self.force or newer_group([str(_.resolve()) for _ in sources], str(ext_path.resolve()), "newer")):
+                print(f"skipping '{ext.name}' CMake extension (up-to-date)")
+
+                # We need to copy the binary where setuptools expects it
+                full_path.parent.mkdir(parents=True, exist_ok=True)
+                shutil.copy(ext_path, full_path)
+
+                return
+            else:
+                print(f"building '{ext.name}' CMake extension")
+
         # Define the build and output directories
         output_dir = Path(self.get_ext_fullpath(ext.name)).parent.resolve()
         extension_basename = Path(self.get_ext_fullpath(ext.name)).name