python: mkvenv: remove ensure command

This was used to bootstrap the venv with a TOML parser, after which
ensuregroup is used.  Now that we expect it to be present as a system
package (either tomli or, for Python 3.11, tomllib), it is not needed
anymore.

Note that this means that, when implemented, the hypothetical "isolated"
mode that does not use any system packages will only work with Python
3.11+.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

python/scripts/mkvenv.py

@@ -13,7 +13,6 @@
     create    create a venv
     post_init
               post-venv initialization
-    ensure    Ensure that the specified package is installed.
     ensuregroup
               Ensure that the specified package group is installed.
 
@@ -36,18 +35,6 @@
 
 --------------------------------------------------
 
-usage: mkvenv ensure [-h] [--online] [--dir DIR] dep_spec...
-
-positional arguments:
-  dep_spec    PEP 508 Dependency specification, e.g. 'meson>=0.61.5'
-
-options:
-  -h, --help  show this help message and exit
-  --online    Install packages from PyPI, if necessary.
-  --dir DIR   Path to vendored packages where we may install from.
-
---------------------------------------------------
-
 usage: mkvenv ensuregroup [-h] [--online] [--dir DIR] file group...
 
 positional arguments:
@@ -726,57 +713,6 @@ def _do_ensure(
     return None
 
 
-def ensure(
-    dep_specs: Sequence[str],
-    online: bool = False,
-    wheels_dir: Optional[Union[str, Path]] = None,
-    prog: Optional[str] = None,
-) -> None:
-    """
-    Use pip to ensure we have the package specified by @dep_specs.
-
-    If the package is already installed, do nothing. If online and
-    wheels_dir are both provided, prefer packages found in wheels_dir
-    first before connecting to PyPI.
-
-    :param dep_specs:
-        PEP 508 dependency specifications. e.g. ['meson>=0.61.5'].
-    :param online: If True, fall back to PyPI.
-    :param wheels_dir: If specified, search this path for packages.
-    :param prog:
-        If specified, use this program name for error diagnostics that will
-        be presented to the user. e.g., 'sphinx-build' can be used as a
-        bellwether for the presence of 'sphinx'.
-    """
-
-    if not HAVE_DISTLIB:
-        raise Ouch("a usable distlib could not be found, please install it")
-
-    # Convert the depspecs to a dictionary, as if they came
-    # from a section in a pythondeps.toml file
-    group: Dict[str, Dict[str, str]] = {}
-    for spec in dep_specs:
-        name = distlib.version.LegacyMatcher(spec).name
-        group[name] = {}
-
-        spec = spec.strip()
-        pos = len(name)
-        ver = spec[pos:].strip()
-        if ver:
-            group[name]["accepted"] = ver
-
-        if prog:
-            group[name]["canary"] = prog
-            prog = None
-
-    result = _do_ensure(group, online, wheels_dir)
-    if result:
-        # Well, that's not good.
-        if result[1]:
-            raise Ouch(result[0])
-        raise SystemExit(f"\n{result[0]}\n\n")
-
-
 def _parse_groups(file: str) -> Dict[str, Dict[str, Any]]:
     if not HAVE_TOMLLIB:
         if sys.version_info < (3, 11):
@@ -888,39 +824,6 @@ def _add_ensuregroup_subcommand(subparsers: Any) -> None:
     )
 
 
-def _add_ensure_subcommand(subparsers: Any) -> None:
-    subparser = subparsers.add_parser(
-        "ensure", help="Ensure that the specified package is installed."
-    )
-    subparser.add_argument(
-        "--online",
-        action="store_true",
-        help="Install packages from PyPI, if necessary.",
-    )
-    subparser.add_argument(
-        "--dir",
-        type=str,
-        action="store",
-        help="Path to vendored packages where we may install from.",
-    )
-    subparser.add_argument(
-        "--diagnose",
-        type=str,
-        action="store",
-        help=(
-            "Name of a shell utility to use for "
-            "diagnostics if this command fails."
-        ),
-    )
-    subparser.add_argument(
-        "dep_specs",
-        type=str,
-        action="store",
-        help="PEP 508 Dependency specification, e.g. 'meson>=0.61.5'",
-        nargs="+",
-    )
-
-
 def main() -> int:
     """CLI interface to make_qemu_venv. See module docstring."""
     if os.environ.get("DEBUG") or os.environ.get("GITLAB_CI"):
@@ -944,7 +847,6 @@ def main() -> int:
 
     _add_create_subcommand(subparsers)
     _add_post_init_subcommand(subparsers)
-    _add_ensure_subcommand(subparsers)
     _add_ensuregroup_subcommand(subparsers)
 
     args = parser.parse_args()
@@ -957,13 +859,6 @@ def main() -> int:
             )
         if args.command == "post_init":
             post_venv_setup()
-        if args.command == "ensure":
-            ensure(
-                dep_specs=args.dep_specs,
-                online=args.online,
-                wheels_dir=args.dir,
-                prog=args.diagnose,
-            )
         if args.command == "ensuregroup":
             ensure_group(
                 file=args.file,