pmbootstrap init: check for required programs (!1845)

Prepare to require "git" in a follow-up patch.

pmb/config/__init__.py

@@ -47,6 +47,11 @@ pmaports_min_version = "4"
 # see migrate_work_folder()).
 work_version = 3
 
+# Programs that pmbootstrap expects to be available from the host system. Keep
+# in sync with README.md, and try to keep the list as small as possible. The
+# idea is to run almost everything in Alpine chroots.
+required_programs = ["openssl", "ps"]
+
 # Keys saved in the config file (mostly what we ask in 'pmbootstrap init')
 config_keys = ["ccache_size", "device", "extra_packages", "hostname", "jobs",
                "kernel", "keymap", "nonfree_firmware", "nonfree_userland",

pmb/config/init.py

@@ -19,6 +19,7 @@ along with pmbootstrap.  If not, see <http://www.gnu.org/licenses/>.
 import logging
 import glob
 import os
+import shutil
 
 import pmb.config
 import pmb.config.pmaports
@@ -32,6 +33,17 @@ import pmb.parse.deviceinfo
 import pmb.parse._apkbuild
 
 
+def require_programs():
+    missing = []
+    for program in pmb.config.required_programs:
+        if not shutil.which(program):
+            missing.append(program)
+    if missing:
+        raise RuntimeError("Can't find all programs required to run"
+                           " pmbootstrap. Please install first: " +
+                           ", ".join(missing))
+
+
 def ask_for_work_path(args):
     """
     Ask for the work path, until we can create it (when it does not exist) and
@@ -345,6 +357,8 @@ def ask_for_ssh_keys(args):
 
 
 def frontend(args):
+    require_programs()
+
     # Work folder (needs to be first, so we can create chroots early)
     cfg = pmb.config.load(args)
     work, work_exists = ask_for_work_path(args)

test/test_config_init.py

@@ -0,0 +1,40 @@
+"""
+Copyright 2019 Oliver Smith
+
+This file is part of pmbootstrap.
+
+pmbootstrap is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+pmbootstrap 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 General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with pmbootstrap.  If not, see <http://www.gnu.org/licenses/>.
+"""
+import os
+import pytest
+import sys
+
+# Import from parent directory
+sys.path.insert(0, os.path.realpath(
+    os.path.join(os.path.dirname(__file__) + "/..")))
+import pmb.config.init
+
+
+def test_require_programs(monkeypatch):
+    func = pmb.config.init.require_programs
+
+    # Nothing missing
+    func()
+
+    # Missing program
+    invalid = "invalid-program-name-here-asdf"
+    monkeypatch.setattr(pmb.config, "required_programs", [invalid])
+    with pytest.raises(RuntimeError) as e:
+        func()
+    assert str(e.value).startswith("Can't find all programs")