treewide: add a Chroot type and adopt pathlib.Path (MR 2252)

Introduce a new module: pmb.core to contain explicitly typed pmbootstrap
API. The first component being Suffix and SuffixType. This explicitly
defines what suffixes are possible, future changes should aim to further
constrain this API (e.g. by validating against available device
codenames or architectures for buildroot suffixes).

Additionally, migrate the entire codebase over to using pathlib.Path.
This is a relatively new part of the Python standard library that uses a
more object oriented model for path handling. It also uses strong type
hinting and has other features that make it much cleaner and easier to
work with than pure f-strings. The Chroot class overloads the "/"
operator the same way the Path object does, allowing one to write paths
relative to a given chroot as:

builddir = chroot / "home/pmos/build"

The Chroot class also has a string representation ("native", or
"rootfs_valve-jupiter"), and a .path property for directly accessing the
absolute path (as a Path object).

The general idea here is to encapsulate common patterns into type hinted
code, and gradually reduce the amount of assumptions made around the
codebase so that future changes are easier to implement.

As the chroot suffixes are now part of the Chroot class, we also
implement validation for them, this encodes the rules on suffix naming
and will cause a runtime exception if a suffix doesn't follow the rules.

pmb/helpers/args.py

@@ -2,7 +2,9 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 import copy
 import os
+from pathlib import Path
 import pmb.config
+from pmb.core.types import PmbArgs
 import pmb.helpers.git
 
 """This file constructs the args variable, which is passed to almost all
@@ -29,7 +31,7 @@ import pmb.helpers.git
        Examples:
        args.aports ("$WORK/cache_git/pmaports", override with --aports)
        args.device ("samsung-i9100", "qemu-amd64" etc.)
-       args.work ("/home/user/.local/var/pmbootstrap", override with --work)
+       pmb.config.work ("/home/user/.local/var/pmbootstrap", override with --work)
 
     3. Parsed configs
        Similar to the cache above, specific config files get parsed and added
@@ -43,7 +45,7 @@ import pmb.helpers.git
 """
 
 
-def fix_mirrors_postmarketos(args):
+def fix_mirrors_postmarketos(args: PmbArgs):
     """Fix args.mirrors_postmarketos when it is supposed to be empty or the default value.
 
     In pmb/parse/arguments.py, we set the -mp/--mirror-pmOS argument to
@@ -65,7 +67,7 @@ def fix_mirrors_postmarketos(args):
         args.mirrors_postmarketos = []
 
 
-def check_pmaports_path(args):
+def check_pmaports_path(args: PmbArgs):
     """Make sure that args.aports exists when it was overridden by --aports.
 
     Without this check, 'pmbootstrap init' would start cloning the
@@ -76,7 +78,7 @@ def check_pmaports_path(args):
                          " not exist: " + args.aports)
 
 
-def replace_placeholders(args):
+def replace_placeholders(args: PmbArgs):
     """Replace $WORK and ~ (for path variables) in variables from any config.
 
     (user's config file, default config settings or config parameters specified on commandline)
@@ -87,15 +89,15 @@ def replace_placeholders(args):
             continue
         old = getattr(args, key)
         if isinstance(old, str):
-            setattr(args, key, old.replace("$WORK", args.work))
+            setattr(args, key, old.replace("$WORK", str(pmb.config.work)))
 
     # Replace ~ (path variables only)
     for key in ["aports", "config", "log", "work"]:
         if key in args:
-            setattr(args, key, os.path.expanduser(getattr(args, key)))
+            setattr(args, key, Path(getattr(args, key)).expanduser())
 
 
-def add_deviceinfo(args):
+def add_deviceinfo(args: PmbArgs):
     """Add and verify the deviceinfo (only after initialization)"""
     setattr(args, "deviceinfo", pmb.parse.deviceinfo(args))
     arch = args.deviceinfo["arch"]
@@ -106,7 +108,7 @@ def add_deviceinfo(args):
                          " <https://postmarketos.org/newarch>")
 
 
-def init(args):
+def init(args: PmbArgs):
     # Basic initialization
     fix_mirrors_postmarketos(args)
     pmb.config.merge_with_args(args)
@@ -127,7 +129,7 @@ def init(args):
     return args
 
 
-def update_work(args, work):
+def update_work(args: PmbArgs, work):
     """Update the work path in args.work and wherever $WORK was used."""
     # Start with the unmodified args from argparse
     args_new = copy.deepcopy(args.from_argparse)