commands: new submodule (MR 2252)

The current mechanism of invoking pmbootstrap actions can be a bit
confusing, and relies heavily on args being a big namespace with lots of
properties (which may or may not be valid depending on the context).

To aid in slowly removing args from the codebase, introduce a new
mechanism for running commands. This works by having a class for each
command, where the arguments are passed in as parameters to the
constructor.

No doubt this won't scale very far, but it's a skeleton we can continue
to build on as we migrate more commands over to not require args in
order to run.

Signed-off-by: Caleb Connolly <caleb@postmarketos.org>

pmb/commands/log.py

@@ -0,0 +1,42 @@
+# Copyright 2024 Caleb Connolly
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from __future__ import annotations
+from typing import Generator, List, Optional
+from pathlib import Path, PosixPath, PurePosixPath
+from pmb import commands
+from pmb.core.types import PathString
+from pmb.helpers import run
+from pmb.core import get_context
+from pmb import config
+
+class Log(commands.Command):
+    clear_log: bool
+    lines: int
+    
+    def __init__(self, clear_log: bool, lines: int):
+        self.clear_log = clear_log
+        self.lines = lines
+
+    def run(self):
+        context = get_context()
+        log_testsuite = config.work / "log_testsuite.txt"
+
+        if self.clear_log:
+            run.user(["truncate", "-s", "0", context.log])
+            run.user(["truncate", "-s", "0", log_testsuite])
+
+        cmd: List[PathString] = ["tail", "-n", str(self.lines), "-F"]
+
+        # Follow the testsuite's log file too if it exists. It will be created when
+        # starting a test case that writes to it (git -C test grep log_testsuite).
+        if log_testsuite.exists():
+            cmd += [log_testsuite]
+
+        # tail writes the last lines of the files to the terminal. Put the regular
+        # log at the end, so that output is visible at the bottom (where the user
+        # looks for an error / what's currently going on).
+        cmd += [context.log]
+
+        run.user(cmd, output="tui")
+