feat: track Decman configuration

system-config/modules/packages.py

@@ -0,0 +1,43 @@
+"""Package concern loading for Decman profiles."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import decman
+from decman.plugins import aur, pacman
+
+ROOT = Path(__file__).resolve().parents[1]
+PACKAGES = ROOT / "packages"
+
+
+def _names(path: Path) -> set[str]:
+    return {
+        line.strip()
+        for line in path.read_text(encoding="utf-8").splitlines()
+        if line.strip()
+    }
+
+
+class PackageConcern(decman.Module):
+    """One named concern backed by native and AUR package lists."""
+
+    def __init__(self, concern: str) -> None:
+        super().__init__(f"packages:{concern}")
+        self.concern = concern
+
+    @pacman.packages
+    def native_packages(self) -> set[str]:
+        return _names(PACKAGES / f"{self.concern}-repo.txt")
+
+    @aur.packages
+    def aur_packages(self) -> set[str]:
+        return _names(PACKAGES / f"{self.concern}-aur.txt")
+
+
+def configure_no_removal_guard() -> None:
+    """Keep Decman from pruning current dependency-orphans during adoption."""
+    if decman.pacman is None or decman.aur is None:
+        raise decman.SourceError("pacman and AUR plugins must be available")
+    decman.pacman.ignored_packages |= _names(PACKAGES / "ignored/repo-dependencies.txt")
+    decman.aur.ignored_packages |= _names(PACKAGES / "ignored/aur-dependencies.txt")