Test for GNU sed instead of macOS (#263)

Author: hugovk

build_docs.py

@@ -687,10 +687,25 @@ def build(self):
                 f"-D ogp_site_url={site_url}",
             )
 
+            def is_gnu_sed() -> bool:
+                """Check if we are using GNU sed."""
+                try:
+                    subprocess.run(
+                        ["sed", "--version"],
+                        stdout=subprocess.DEVNULL,
+                        stderr=subprocess.DEVNULL,
+                        check=True,
+                    )
+                    return True
+                except subprocess.CalledProcessError:
+                    return False
+                except FileNotFoundError:
+                    return False
+
             # Disable CPython switchers, we handle them now:
             run(
                 ["sed", "-i"]
-                + ([""] if sys.platform == "darwin" else [])
+                + ([] if is_gnu_sed() else [""])
                 + ["s/ *-A switchers=1//", self.checkout / "Doc" / "Makefile"]
             )
             self.versions.setup_indexsidebar(