tests: Use separate virtual environment for avocado

This reverts commits eea2d141179 ("Makefile: remove $(TESTS_PYTHON)",
2023-05-26) and 9c6692db550 ("tests: Use configure-provided pyvenv for
tests", 2023-05-18).

Right now, there is a conflict between wanting a ">=" constraint when
using a distro-provided package and wanting a "==" constraint when
installing Avocado from PyPI; this would provide the best of both worlds
in terms of resiliency for both distros that have required packages and
distros that don't.

The conflict is visible also for meson, where we would like to install
the latest 0.63.x version but also accept a distro 1.1.x version.
But it is worse for avocado, for two reasons:

1) we cannot use an "==" constraint to install avocado if the venv
includes a system avocado.  The distro will package plugins that have
"==" constraints on the version that is included in the distro, and, using
"pip install avocado==88.1" on a venv that includes system packages will
result in this error:

   ERROR: pip's dependency resolver does not currently take into account all the packages that are installed. This behaviour is the source of the following dependency conflicts.
   avocado-framework-plugin-varianter-yaml-to-mux 98.0 requires avocado-framework==98.0, but you have avocado-framework 88.1 which is incompatible.
   avocado-framework-plugin-result-html 98.0 requires avocado-framework==98.0, but you have avocado-framework 88.1 which is incompatible.
   make[1]: Leaving directory '/home/berrange/src/virt/qemu/build'

2) we cannot use ">=" either if the venv does _not_ include a system
avocado, because that would result in the installation of v101.0 which
is the one we've just reverted.

So the idea is to encode the dependencies as an (acceptable, locked)
tuple, like this hypothetical TOML that would be committed inside
python/ and used by mkvenv.py:

  [meson]
  meson = { minimum = "0.63.0", install = "0.63.3", canary = "meson" }

  [docs]
  # 6.0 drops support for Python 3.7
  sphinx = { minimum = "1.6", install = "<6.0", canary = "sphinx-build" }
  sphinx_rtd_theme = { minimum = "0.5" }

  [avocado]
  avocado-framework = { minimum = "88.1", install = "88.1", canary = "avocado" }

Once this is implemented, it would also be possible to install avocado in
pyvenv/ using "mkvenv.py ensure", thus using the distro package on Fedora
and CentOS Stream (the only distros where it's available).  But until
this is implemented, keep avocado in a separate venv.  There is still the
benefit of using a single python for meson custom_targets and for sphinx.

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

3 files changed, 12 insertions, 13 deletions

diff --git a/tests/Makefile.include b/tests/Makefile.include
index 8294a44816..9422ddaece 100644
--- a/tests/Makefile.include
+++ b/tests/Makefile.include
@@ -89,9 +89,10 @@ distclean-tcg: $(DISTCLEAN_TCG_TARGET_RULES)
 # Build up our target list from the filtered list of ninja targets
 TARGETS=$(patsubst libqemu-%.fa, %, $(filter libqemu-%.fa, $(ninja-targets)))
 
-TESTS_VENV_TOKEN=$(BUILD_DIR)/pyvenv/tests.group
+TESTS_VENV_DIR=$(BUILD_DIR)/tests/venv
 TESTS_VENV_REQ=$(SRC_PATH)/tests/requirements.txt
 TESTS_RESULTS_DIR=$(BUILD_DIR)/tests/results
+TESTS_PYTHON=$(TESTS_VENV_DIR)/bin/python3
 ifndef AVOCADO_TESTS
 	AVOCADO_TESTS=tests/avocado
 endif
@@ -107,10 +108,11 @@ else
 endif
 
 quiet-venv-pip = $(quiet-@)$(call quiet-command-run, \
-    $(PYTHON) -m pip -q --disable-pip-version-check $1, \
+    $(TESTS_PYTHON) -m pip -q --disable-pip-version-check $1, \
     "VENVPIP","$1")
 
-$(TESTS_VENV_TOKEN): $(TESTS_VENV_REQ)
+$(TESTS_VENV_DIR): $(TESTS_VENV_REQ)
+	$(call quiet-command, $(PYTHON) -m venv $@, VENV, $@)
 	$(call quiet-venv-pip,install -e "$(SRC_PATH)/python/")
 	$(call quiet-venv-pip,install -r $(TESTS_VENV_REQ))
 	$(call quiet-command, touch $@)
@@ -119,7 +121,7 @@ $(TESTS_RESULTS_DIR):
 	$(call quiet-command, mkdir -p $@, \
             MKDIR, $@)
 
-check-venv: $(TESTS_VENV_TOKEN)
+check-venv: $(TESTS_VENV_DIR)
 
 FEDORA_31_ARCHES_TARGETS=$(patsubst %-softmmu,%, $(filter %-softmmu,$(TARGETS)))
 FEDORA_31_ARCHES_CANDIDATES=$(patsubst ppc64,ppc64le,$(FEDORA_31_ARCHES_TARGETS))
@@ -129,7 +131,7 @@ FEDORA_31_DOWNLOAD=$(filter $(FEDORA_31_ARCHES),$(FEDORA_31_ARCHES_CANDIDATES))
 # download one specific Fedora 31 image
 get-vm-image-fedora-31-%: check-venv
 	$(call quiet-command, \
-             $(PYTHON) -m avocado vmimage get \
+             $(TESTS_PYTHON) -m avocado vmimage get \
              --distro=fedora --distro-version=31 --arch=$*, \
 	"AVOCADO", "Downloading avocado tests VM image for $*")
 
@@ -138,7 +140,7 @@ get-vm-images: check-venv $(patsubst %,get-vm-image-fedora-31-%, $(FEDORA_31_DOW
 
 check-avocado: check-venv $(TESTS_RESULTS_DIR) get-vm-images
 	$(call quiet-command, \
-            $(PYTHON) -m avocado \
+            $(TESTS_PYTHON) -m avocado \
             --show=$(AVOCADO_SHOW) run --job-results-dir=$(TESTS_RESULTS_DIR) \
             $(if $(AVOCADO_TAGS),, --filter-by-tags-include-empty \
 			--filter-by-tags-include-empty-key) \
@@ -161,7 +163,7 @@ check:
 check-build: run-ninja
 
 check-clean:
-	rm -rf $(TESTS_RESULTS_DIR)
+	rm -rf $(TESTS_VENV_DIR) $(TESTS_RESULTS_DIR)
 
 clean: check-clean clean-tcg
 distclean: distclean-tcg
diff --git a/tests/requirements.txt b/tests/requirements.txt
index 07e713ef5a..0ba561b6bd 100644
--- a/tests/requirements.txt
+++ b/tests/requirements.txt
@@ -1,9 +1,6 @@
 # Add Python module requirements, one per line, to be installed
-# in the qemu build_dir/pyvenv Python virtual environment. For more info,
+# in the tests/venv Python virtual environment. For more info,
 # refer to: https://pip.pypa.io/en/stable/user_guide/#id1
-#
-# Note that qemu.git/python/ is implicitly installed to this venv when
-# 'make check-venv' is run, and will persist until configure is run
-# again.
+# Note that qemu.git/python/ is always implicitly installed.
 avocado-framework==88.1
 pycdlib==1.11.0
diff --git a/tests/vm/Makefile.include b/tests/vm/Makefile.include
index f0f5d32fb0..c2a8ca1c17 100644
--- a/tests/vm/Makefile.include
+++ b/tests/vm/Makefile.include
@@ -5,7 +5,7 @@ ifeq ($(realpath $(SRC_PATH)),$(realpath .))
 VM_PYTHON = PYTHONPATH=$(SRC_PATH)/python /usr/bin/env python3
 VM_VENV =
 else
-VM_PYTHON = $(PYTHON)
+VM_PYTHON = $(TESTS_PYTHON)
 VM_VENV = check-venv
 endif