Re: [PATCH 04/10] configure: protect against escaping venv when running Meson

[Daniel P . Berrangé]

On Wed, Feb 22, 2023 at 03:37:46PM +0100, Paolo Bonzini wrote:
> If neither --python nor --meson are specified, Meson's generated
> build.ninja will invoke Python script using the interpreter *that Meson
> itself is running under*; not the one identified by configure.
> 
> This is only an issue if Meson's Python interpreter is not "the first
> one in the path", which is the one that is used if --python is not
> specified.  A common case where this happen is when the "python3" binary
> comes from a virtual environment but Meson is not installed (with pip)
> in the virtual environment.  In this case (presumably) whoever set up
> the venv wanted to use the venv's Python interpreter to build QEMU,
> while Meson might use a different one, for example an enterprise
> distro's older runtime.
> 
> So, detect whether a virtual environment is setup, and if the virtual
> environment does not have Meson, use the meson submodule.  Meson will
> then run under the virtual environment's Python interpreter.

I fear this could be somewhat confusing to contributors. If I have
meson in my $PATH, at a sufficient version, it would be surprising
to find QEMU had been using a different version instead.

I can understand wanting to make it "just work", but should we
perhaps issue a warning from configure when we're intentionally
ignoring an otherwise valid meson installation ?

> 
> Reported-by: John Snow <jsnow@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  configure | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/configure b/configure
> index 00415f0b48d7..4d66a958023e 100755
> --- a/configure
> +++ b/configure
> @@ -1047,8 +1047,18 @@ fi
>  # Suppress writing compiled files
>  python="$python -B"
>  
> +has_meson() {
> +  if test "${VIRTUAL_ENV:+set}" = set; then
> +    # Ensure that Meson and Python come from the same virtual environment
> +    test -x "${VIRTUAL_ENV}/bin/meson" &&
> +      test "$(command -v meson)" -ef "${VIRTUAL_ENV}/bin/meson"
> +  else
> +    has meson
> +  fi
> +}
> +
>  if test -z "$meson"; then
> -    if test "$explicit_python" = no && has meson && version_ge "$(meson 
> --version)" 0.61.5; then
> +    if test "$explicit_python" = no && has_meson && version_ge "$(meson 
> --version)" 0.61.5; then
>          meson=meson
>      elif test "$git_submodules_action" != 'ignore' ; then
>          meson=git
> -- 
> 2.39.1
> 

With regards,
Daniel
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