Add "flit info --version" command

References pypa#262

flit/__init__.py

@@ -79,6 +79,14 @@ def main(argv=None):
         help="Prepare pyproject.toml for a new package"
     )
 
+    parser_info = subparsers.add_parser('info',
+        help="Retrieve metadata information from the project",
+    )
+    parser_info.add_argument(
+        '--version', default=False, action='store_true', dest='show_version',
+        help="Print the version number of the project to stdout"
+    )
+
     args = ap.parse_args(argv)
 
     cf = args.ini_file
@@ -99,6 +107,11 @@ def main(argv=None):
 
     log.debug("Parsed arguments %r", args)
 
+    if args.subcmd == 'info' and args.show_version:
+        from .info import get_version
+        print(get_version(args.ini_file))
+        sys.exit(0)
+
     if args.logo:
         from .logo import clogo
         print(clogo.format(version=__version__))

flit/info.py

@@ -0,0 +1,20 @@
+"""
+This module contains code for the "info" subcommand
+"""
+
+
+def get_version(ini_path):
+    # type: (str) -> str
+    """
+    This will return the package version as a string.
+
+    :param ini_path: The filename of the main config-file
+        (flit.ini/pyproject.toml)
+    """
+    from . import inifile
+    from .common import Module, make_metadata
+    ini_info = inifile.read_pkg_ini(ini_path)
+    module = Module(ini_info['module'], ini_path.parent)
+    metadata = make_metadata(module, ini_info)
+    output = metadata.version
+    return output

tests/test_command.py

@@ -11,3 +11,12 @@ def test_flit_usage():
     out, _ = p.communicate()
     assert 'Build wheel' in out.decode('utf-8', 'replace')
     assert p.poll() == 1
+
+def test_flit_version():
+    import flit
+    version = flit.__version__
+
+    p = Popen([sys.executable, '-m', 'flit', 'info', '--version'],
+               stdout=PIPE, stderr=STDOUT)
+    out, _ = p.communicate()
+    assert out.decode('utf-8', 'replace').strip() == version