Add command to create a default config

Adds a "mkconfig" subcommand and helper to dump the default
configuration to a file or to stdout.

README.md

@@ -129,6 +129,14 @@ Pyrex is configured using a ini-style configuration file. The location of this
 file is specified by the `PYREXCONFFILE` environment variable. This environment
 variable must be set before the environment is initialized.
 
+If you do not yet have a config file, you can use the `mkconfig` command to use
+the default one and assign the `PYREXCONFFILE` variable in a single command
+like so:
+
+```shell
+$ export PYREXCONFFILE=`./meta-pyrex/mkconfig ./pyrex.ini`
+```
+
 The configuration file is the ini file format supported by Python's
 [configparser](https://docs.python.org/3/library/configparser.html) class, with
 the following notes:

ci/test.py

@@ -689,6 +689,23 @@ def test_pyrex_config(self):
         )
         self.assertEqual(s, "ABCDEFGHI")
 
+    def test_pyrex_mkconfig(self):
+        out_file = os.path.join(self.build_dir, "temp-pyrex.ini")
+        cmd = [os.path.join(PYREX_ROOT, "pyrex.py"), "mkconfig"]
+
+        output = self.assertSubprocess(
+            cmd + [out_file], capture=True, cwd=self.build_dir
+        )
+        self.assertEqual(output, out_file)
+
+        output = self.assertSubprocess(cmd, capture=True)
+        self.assertEqual(output, pyrex.read_default_config(False).rstrip())
+
+        with open(out_file, "r") as f:
+            self.assertEqual(f.read().rstrip(), output)
+
+        self.assertSubprocess(cmd + [out_file], cwd=self.build_dir, returncode=1)
+
 
 class PyrexImageType_oe(PyrexImageType_base):
     """

mkconfig

@@ -0,0 +1,18 @@
+#! /bin/sh
+#
+# Copyright 2019 Garmin Ltd. or its subsidiaries
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+"$(dirname "$0")/pyrex.py" mkconfig "$@"

pyrex.py

@@ -30,6 +30,7 @@
 import hashlib
 import json
 import tempfile
+import contextlib
 
 VERSION = "0.0.4"
 
@@ -761,6 +762,25 @@ def config_get(args):
         print(val)
         return 0
 
+    def mkconfig(args):
+        @contextlib.contextmanager
+        def get_output_file():
+            if args.output == "-":
+                yield sys.stdout
+            else:
+                with open(args.output, "w" if args.force else "x") as f:
+                    yield f
+                print(os.path.abspath(args.output))
+
+        try:
+            with get_output_file() as f:
+                f.write(read_default_config(False))
+        except FileExistsError:
+            sys.stderr.write("Refusing to overwrite existing file '%s'\n" % args.output)
+            return 1
+
+        return 0
+
     subparser_args = {}
     if sys.version_info >= (3, 7, 0):
         subparser_args["required"] = True
@@ -827,6 +847,23 @@ def config_get(args):
     )
     config_get_parser.set_defaults(func=config_get)
 
+    mkconfig_parser = subparsers.add_parser(
+        "mkconfig", help="Create a default Pyrex configuration"
+    )
+    mkconfig_parser.add_argument(
+        "-f",
+        "--force",
+        action="store_true",
+        help="Overwrite destination file if it already exists",
+    )
+    mkconfig_parser.add_argument(
+        "output",
+        default="-",
+        nargs="?",
+        help="Output file. Use '-' for standard out. Default is %(default)s",
+    )
+    mkconfig_parser.set_defaults(func=mkconfig)
+
     args = parser.parse_args()
 
     func = getattr(args, "func", None)