python: mkvenv: add ensuregroup command

Introduce a new subcommand that retrieves the packages to be installed
from a TOML file. This allows being more flexible in using the system
version of a package, while at the same time using a known-good version
when installing the package.  This is important for packages that
sometimes have backwards-incompatible changes or that depend on
specific versions of their dependencies.

Compared to JSON, TOML is more human readable and easier to edit.  A
parser is available in 3.11 but also available as a small (12k) package
for older versions, tomli.  While tomli is bundled with pip, this is only
true of recent versions of pip.  Of all the supported OSes pretty much
only FreeBSD has a recent enough version of pip while staying on Python
<3.11.  So we cannot use the same trick that is in place for distlib.

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

1 files changed, 17 insertions, 0 deletions

diff --git a/pythondeps.toml b/pythondeps.toml
new file mode 100644
index 0000000000..362f63ff2c
--- /dev/null
+++ b/pythondeps.toml
@@ -0,0 +1,17 @@
+# This file describes Python package requirements to be
+# installed in the pyvenv Python virtual environment.
+#
+# Packages are placed in groups, which are installed using
+# the ensuregroup subcommand of python/scripts/mkvenv.py.
+# Each group forms a TOML section and each entry in the
+# section is a TOML key-value list describing a package.
+# All fields are optional; valid fields are:
+#
+# - accepted: accepted versions when using a system package
+# - installed: fixed version to install in the virtual environment
+#              if a system package is not found; if not specified,
+#              the minimum and maximum
+# - canary: if specified, use this program name to present more
+#           precise error diagnostics to the user.  For example,
+#           'sphinx-build' can be used as a bellwether for the
+#           presence of 'sphinx' in the system.