packaging: ensure that --python is an absolute path when building on Windows

For whatever reason, even though only python2 is on PATH, passing `python.exe`
causes the later check that it's not py3 to bail out.

contrib/packaging/inno/build.py

@@ -1,48 +1,51 b''
 #!/usr/bin/env python3
 # build.py - Inno installer build script.
 #
 # Copyright 2019 Gregory Szorc <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 # This script automates the building of the Inno MSI installer for Mercurial.
 
 # no-check-code because Python 3 native.
 
 import argparse
 import os
 import pathlib
 import sys
 
 
 if __name__ == '__main__':
     parser = argparse.ArgumentParser()
 
     parser.add_argument('--python',
                         required=True,
                         help='path to python.exe to use')
     parser.add_argument('--iscc',
                         help='path to iscc.exe to use')
     parser.add_argument('--version',
                         help='Mercurial version string to use '
                              '(detected from __version__.py if not defined')
 
     args = parser.parse_args()
 
+    if not os.path.isabs(args.python):
+        raise Exception('--python arg must be an absolute path')
+
     if args.iscc:
         iscc = pathlib.Path(args.iscc)
     else:
         iscc = (pathlib.Path(os.environ['ProgramFiles(x86)']) / 'Inno Setup 5' /
             'ISCC.exe')
 
     here = pathlib.Path(os.path.abspath(os.path.dirname(__file__)))
     source_dir = here.parent.parent.parent
     build_dir = source_dir / 'build'
 
     sys.path.insert(0, str(source_dir / 'contrib' / 'packaging'))
 
     from hgpackaging.inno import build
 
     build(source_dir, build_dir, pathlib.Path(args.python), iscc,
           version=args.version)

contrib/packaging/wix/build.py

@@ -1,81 +1,84 b''
 #!/usr/bin/env python3
 # Copyright 2019 Gregory Szorc <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 # no-check-code because Python 3 native.
 
 """Code to build Mercurial WiX installer."""
 
 import argparse
 import os
 import pathlib
 import sys
 
 
 if __name__ == '__main__':
     parser = argparse.ArgumentParser()
 
     parser.add_argument('--name',
                         help='Application name',
                         default='Mercurial')
     parser.add_argument('--python',
                         help='Path to Python executable to use',
                         required=True)
     parser.add_argument('--sign-sn',
                         help='Subject name (or fragment thereof) of certificate '
                              'to use for signing')
     parser.add_argument('--sign-cert',
                         help='Path to certificate to use for signing')
     parser.add_argument('--sign-password',
                         help='Password for signing certificate')
     parser.add_argument('--sign-timestamp-url',
                         help='URL of timestamp server to use for signing')
     parser.add_argument('--version',
                         help='Version string to use')
     parser.add_argument('--extra-packages-script',
                         help=('Script to execute to include extra packages in '
                               'py2exe binary.'))
     parser.add_argument('--extra-wxs',
                         help='CSV of path_to_wxs_file=working_dir_for_wxs_file')
     parser.add_argument('--extra-features',
                         help=('CSV of extra feature names to include '
                               'in the installer from the extra wxs files'))
 
     args = parser.parse_args()
 
     here = pathlib.Path(os.path.abspath(os.path.dirname(__file__)))
     source_dir = here.parent.parent.parent
 
     sys.path.insert(0, str(source_dir / 'contrib' / 'packaging'))
 
     from hgpackaging.wix import (
         build_installer,
         build_signed_installer,
     )
 
     fn = build_installer
     kwargs = {
         'source_dir': source_dir,
         'python_exe': pathlib.Path(args.python),
         'version': args.version,
     }
 
+    if not os.path.isabs(args.python):
+        raise Exception('--python arg must be an absolute path')
+
     if args.extra_packages_script:
         kwargs['extra_packages_script'] = args.extra_packages_script
     if args.extra_wxs:
         kwargs['extra_wxs'] = dict(
             thing.split("=") for thing in args.extra_wxs.split(','))
     if args.extra_features:
         kwargs['extra_features'] = args.extra_features.split(',')
 
     if args.sign_sn or args.sign_cert:
         fn = build_signed_installer
         kwargs['name'] = args.name
         kwargs['subject_name'] = args.sign_sn
         kwargs['cert_path'] = args.sign_cert
         kwargs['cert_password'] = args.sign_password
         kwargs['timestamp_url'] = args.sign_timestamp_url
 
     fn(**kwargs)