feat: add a utility function that determines whether a part has slices

craft_parts/parts.py

@@ -99,12 +99,9 @@ def validate_root(cls, values: Dict[str, Any]) -> Dict[str, Any]:
             # This check is only relevant in deb systems.
             return values
 
-        def is_slice(name: str) -> bool:
-            return "_" in name
-
         # Detect a mixture of .deb packages and chisel slices.
         stage_packages = values.get("stage-packages", [])
-        has_slices = any(name for name in stage_packages if is_slice(name))
+        has_slices = part_has_slices(values)
         has_packages = any(name for name in stage_packages if not is_slice(name))
 
         if has_slices and has_packages:
@@ -642,6 +639,23 @@ def part_has_overlay(data: Dict[str, Any]) -> bool:
     return spec.has_overlay
 
 
+def part_has_slices(data: Dict[str, Any]) -> bool:
+    """Whether the part described by ``data`` has slices in its stage-packages.
+
+    :param data: The part data to query.
+    """
+    stage_packages = data.get("stage-packages", [])
+    return any(name for name in stage_packages if is_slice(name))
+
+
+def is_slice(name: str) -> bool:
+    """Whether the stage-package is a slice or a package.
+
+    :param name: name of the package.
+    """
+    return "_" in name
+
+
 def _get_part_spec(data: Dict[str, Any]) -> PartSpec:
     if not isinstance(data, dict):
         raise TypeError("value must be a dictionary")