Add a script to generate Python bundled provides

See https://src.fedoraproject.org/rpms/python-setuptools/pull-request/40

Strictly speaking, this is not an RPM generator, but:

 - it generates provides
 - it is tighly coupled with pythondistdeps.py

Usage:

 1. Run `$ /usr/lib/rpm/pythonbundles.py .../vendored.txt`

 2. Copy the output into the spec as a macro definition:

    %global bundled %{expand:
    Provides: bundled(python3dist(appdirs)) = 1.4.3
    Provides: bundled(python3dist(packaging)) = 16.8
    Provides: bundled(python3dist(pyparsing)) = 2.2.1
    Provides: bundled(python3dist(six)) = 1.15
    }

 3. Use the macro to expand the provides
 4. Verify the macro contents in %check:

    %check
    ...
    %{_rpmconfigdir}/pythonbundles.py src/_vendor/vendored.txt --compare-with '%{bundled}'

pythonbundles.py

@@ -0,0 +1,90 @@
+#!/usr/bin/python3 -B
+#                  (imports pythondistdeps from /usr/lib/rpm, hence -B)
+#
+# This program is free software.
+#
+# It is placed in the public domain or under the CC0-1.0-Universal license,
+# whichever is more permissive.
+#
+# Alternatively, it may be redistributed and/or modified under the terms of
+# the LGPL version 2.1 (or later) or GPL version 2 (or later).
+#
+# Use this script to generate bundled provides, e.g.:
+# ./pythonbundles.py setuptools-47.1.1/pkg_resources/_vendor/vendored.txt
+
+import pathlib
+import sys
+
+# inject parse_version import to pythondistdeps
+# not the nicest API, but :/
+from pkg_resources import parse_version
+import pythondistdeps
+pythondistdeps.parse_version = parse_version
+
+
+def generate_bundled_provides(path, namespace):
+    provides = set()
+
+    for line in path.read_text().splitlines():
+        line, _, comment = line.partition('#')
+        if comment.startswith('egg='):
+            # not a real comment
+            # e.g. git+https://github.com/monty/spam.git@master#egg=spam&...
+            egg, *_ = comment.strip().partition(' ')
+            egg, *_ = egg.strip().partition('&')
+            name = pythondistdeps.normalize_name(egg[4:])
+            provides.add(f'Provides: bundled({namespace}({name}))')
+            continue
+        line = line.strip()
+        if line:
+            name, _, version = line.partition('==')
+            name = pythondistdeps.normalize_name(name)
+            bundled_name = f"bundled({namespace}({name}))"
+            python_provide = pythondistdeps.convert(bundled_name, '==', version)
+            provides.add(f'Provides: {python_provide}')
+
+    return provides
+
+
+def compare(expected, given):
+    stripped = (l.strip() for l in given)
+    no_comments = set(l for l in stripped if not l.startswith('#'))
+    no_comments.discard('')
+    if expected == no_comments:
+        return True
+    extra_expected = expected - no_comments
+    extra_given = no_comments - expected
+    if extra_expected:
+        print('Missing expected provides:', file=sys.stderr)
+        for provide in sorted(extra_expected):
+            print(f'    - {provide}', file=sys.stderr)
+    if extra_given:
+        print('Redundant unexpected provides:', file=sys.stderr)
+        for provide in sorted(extra_given):
+            print(f'    + {provide}', file=sys.stderr)
+    return False
+
+
+if __name__ == '__main__':
+    import argparse
+
+    parser = argparse.ArgumentParser(prog=sys.argv[0],
+                                     formatter_class=argparse.ArgumentDefaultsHelpFormatter)
+    parser.add_argument('vendored', metavar='VENDORED.TXT',
+                        help='Upstream information about vendored libraries')
+    parser.add_argument('-c', '--compare-with', action='store',
+                        help='A string value to compare with and verify')
+    parser.add_argument('-n', '--namespace', action='store',
+                        help='What namespace of provides will used', default='python3dist')
+    args = parser.parse_args()
+
+    provides = generate_bundled_provides(pathlib.Path(args.vendored), args.namespace)
+
+    if args.compare_with:
+        given = args.compare_with.splitlines()
+        same = compare(provides, given)
+        if not same:
+            sys.exit(1)
+    else:
+        for provide in sorted(provides):
+            print(provide)