[v2] configure: more resilient Python version capture

The current approach to capture the Python version is fragile, as it
was demonstrated by a very specific build of Python 3 on Fedora 29
that, under non-interactive shells would print multiline version
information.

The (badly) stripped version output would be sent to config-host.mak,
producing bad syntax and rendering the makefiles unusable.  Now, the
Python versions is printed by configure, but only a simple (and better
controlled variable) indicating whether the build system is using
Python 2 is kept on config-host.mak.

Signed-off-by: Cleber Rosa <crosa@redhat.com>

---
v2: Use python from '$python' variable instead of hardcoded 'python2'
---
 configure              | 5 +++--
 tests/Makefile.include | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

On Mon, Aug 26, 2019 at 11:58:32AM -0400, Cleber Rosa wrote:
> The current approach to capture the Python version is fragile, as it
> was demonstrated by a very specific build of Python 3 on Fedora 29
> that, under non-interactive shells would print multiline version
> information.
> 
> The (badly) stripped version output would be sent to config-host.mak,
> producing bad syntax and rendering the makefiles unusable.  Now, the
> Python versions is printed by configure, but only a simple (and better
> controlled variable) indicating whether the build system is using
> Python 2 is kept on config-host.mak.
> 
> Signed-off-by: Cleber Rosa <crosa@redhat.com>
> 
> ---
> v2: Use python from '$python' variable instead of hardcoded 'python2'
> ---
>  configure              | 5 +++--
>  tests/Makefile.include | 2 +-
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/configure b/configure
> index e44e454c43..95134c0180 100755
> --- a/configure
> +++ b/configure
> @@ -1864,7 +1864,7 @@ if ! $python -c 'import sys; sys.exit(sys.version_info < (2,7))'; then
>  fi
>  
>  # Preserve python version since some functionality is dependent on it
> -python_version=$($python -V 2>&1 | sed -e 's/Python\ //')
> +python_version=$($python -c 'import sys; print("%d.%d.%d" % (sys.version_info[0], sys.version_info[1], sys.version_info[2]))' 2>/dev/null)
>  
>  # Suppress writing compiled files
>  python="$python -B"
> @@ -6511,6 +6511,7 @@ if ! $python -c 'import sys; sys.exit(sys.version_info < (3,0))'; then
>    echo
>    echo "warning: Python 2 support is deprecated" >&2
>    echo "warning: Python 3 will be required for building future versions of QEMU" >&2
> +  python2="y"
>  fi
>  
>  config_host_mak="config-host.mak"
> @@ -7333,7 +7334,7 @@ echo "INSTALL_DATA=$install -c -m 0644" >> $config_host_mak
>  echo "INSTALL_PROG=$install -c -m 0755" >> $config_host_mak
>  echo "INSTALL_LIB=$install -c -m 0644" >> $config_host_mak
>  echo "PYTHON=$python" >> $config_host_mak
> -echo "PYTHON_VERSION=$python_version" >> $config_host_mak
> +echo "PYTHON2=$python2" >> $config_host_mak
>  echo "CC=$cc" >> $config_host_mak
>  if $iasl -h > /dev/null 2>&1; then
>    echo "IASL=$iasl" >> $config_host_mak
> diff --git a/tests/Makefile.include b/tests/Makefile.include
> index 49684fd4f4..f5ac09549c 100644
> --- a/tests/Makefile.include
> +++ b/tests/Makefile.include
> @@ -1135,7 +1135,7 @@ TESTS_RESULTS_DIR=$(BUILD_DIR)/tests/results
>  AVOCADO_SHOW=app
>  AVOCADO_TAGS=$(patsubst %-softmmu,-t arch:%, $(filter %-softmmu,$(TARGET_DIRS)))
>  
> -ifneq ($(findstring v2,"v$(PYTHON_VERSION)"),v2)
> +ifneq ($(PYTHON2),y)
>  $(TESTS_VENV_DIR): $(TESTS_VENV_REQ)
>  	$(call quiet-command, \
>              $(PYTHON) -m venv --system-site-packages $@, \
> -- 
> 2.21.0
> 
> 

Reviewed-by: Tony Nguyen <tony.nguyen@bt.com>

On Mon, Aug 26, 2019 at 11:58:32AM -0400, Cleber Rosa wrote:
> The current approach to capture the Python version is fragile, as it
> was demonstrated by a very specific build of Python 3 on Fedora 29
> that, under non-interactive shells would print multiline version
> information.
> 
> The (badly) stripped version output would be sent to config-host.mak,
> producing bad syntax and rendering the makefiles unusable.  Now, the
> Python versions is printed by configure, but only a simple (and better
> controlled variable) indicating whether the build system is using
> Python 2 is kept on config-host.mak.
> 
> Signed-off-by: Cleber Rosa <crosa@redhat.com>

Queued, thanks!