partitions: add utility to make partition compatible filepaths

Signed-off-by: Callahan Kovacs <[email protected]>

craft_parts/utils/partition_utils.py

@@ -0,0 +1,67 @@
+# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4 -*-
+#
+# Copyright 2023 Canonical Ltd.
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License version 3 as published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Partition helpers."""
+
+import re
+from pathlib import Path
+from typing import Union
+
+from craft_parts.features import Features
+
+
+# XXX: for context, you can see where this function in the prototype:
+# https://github.com/mr-cal/craft-parts/commit/e2d15f1bb1da3207463ad3015b68509537b007c3
+
+
+def get_partition_compatible_filepath(filepath: Union[Path, str]) -> Union[Path, str]:
+    """Get a filepath compatible with the partitions feature.
+
+    If the filepath begins with a partition, then the parentheses are stripped from the
+    the partition. For example, `(default)/file` is converted to `default/file`.
+
+    If the filepath does not begin with a partition, the `default` partition is
+    prepended. For example, `file` is converted to `default/file`.
+
+    :param filepath: The filepath to modify.
+
+    :returns: A filepath that is compatible with the partitions feature.
+    """
+    if not Features().enable_partitions:
+        return filepath
+
+    # XXX: I think this is the correct thing to do. The default globs should not be
+    # modified (which comes from craft_parts/parts.py lines 55-58)
+    if filepath == "*":
+        return filepath
+
+    # XXX: I know there is at least one problem with this regex: `(default)` and
+    # `(default)/` are treated differently
+    match = re.match("^\\((?P<partition>[a-z]+)\\)/(?P<filepath>.*)", str(filepath))
+    if match:
+        partition = match.group("partition")
+        everything_else = match.group("filepath")
+    else:
+        partition = "default"
+        everything_else = filepath
+
+    new_filepath = Path(partition, everything_else)
+
+    # XXX: craft-parts calls this function in different places. Sometimes the filepath
+    # is a string and something it is a Path object. I decided to make this function
+    # handle both scenarios but I wonder if this approach will create
+    # type-checking issues in the future.
+    return str(new_filepath) if isinstance(filepath, str) else new_filepath