[PATCH] python: Configure tox to skip missing interpreters

[Wainer dos Santos Moschetta <wainersm@redhat.com>]

Currently tox tests against the installed interpreters, however if any
supported interpreter is absent then it will return fail. It seems not
reasonable to expect developers to have all supported interpreters
installed on their systems. Luckily tox can be configured to skip
missing interpreters.

This changed the tox setup so that missing interpreters are skipped by
default. On the CI, however, we still want to enforce it tests
against all supported. This way on CI the
--skip-missing-interpreters=false option is passed to tox.

Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
---
Tested locally with `make check-tox` and where I only Python 3.6 and 3.9
installed.
Tested on CI: https://gitlab.com/wainersm/qemu/-/jobs/1390010988
Still on CI, but I deliberately removed Python 3.8: https://gitlab.com/wainersm/qemu/-/jobs/1390046531

 .gitlab-ci.d/static_checks.yml | 1 +
 python/Makefile                | 5 ++++-
 python/setup.cfg               | 1 +
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/.gitlab-ci.d/static_checks.yml b/.gitlab-ci.d/static_checks.yml
index b01f6ec231..96dbd9e310 100644
--- a/.gitlab-ci.d/static_checks.yml
+++ b/.gitlab-ci.d/static_checks.yml
@@ -43,6 +43,7 @@ check-python-tox:
     - make -C python check-tox
   variables:
     GIT_DEPTH: 1
+    QEMU_TOX_EXTRA_ARGS: --skip-missing-interpreters=false
   needs:
     job: python-container
   allow_failure: true
diff --git a/python/Makefile b/python/Makefile
index ac46ae33e7..fe27a3e12e 100644
--- a/python/Makefile
+++ b/python/Makefile
@@ -1,4 +1,5 @@
 QEMU_VENV_DIR=.dev-venv
+QEMU_TOX_EXTRA_ARGS ?=
 
 .PHONY: help
 help:
@@ -15,6 +16,8 @@ help:
 	@echo "    These tests use the newest dependencies."
 	@echo "    Requires: Python 3.6 - 3.10, and tox."
 	@echo "    Hint (Fedora): 'sudo dnf install python3-tox python3.10'"
+	@echo "    The variable QEMU_TOX_EXTRA_ARGS can be use to pass extra"
+	@echo "    arguments to tox".
 	@echo ""
 	@echo "make check-dev:"
 	@echo "    Run tests in a venv against your default python3 version."
@@ -87,7 +90,7 @@ check:
 
 .PHONY: check-tox
 check-tox:
-	@tox
+	@tox $(QEMU_TOX_EXTRA_ARGS)
 
 .PHONY: clean
 clean:
diff --git a/python/setup.cfg b/python/setup.cfg
index 11f71d5312..14bab90288 100644
--- a/python/setup.cfg
+++ b/python/setup.cfg
@@ -121,6 +121,7 @@ multi_line_output=3
 
 [tox:tox]
 envlist = py36, py37, py38, py39, py310
+skip_missing_interpreters = true
 
 [testenv]
 allowlist_externals = make
-- 
2.31.1