[RFC PATCH v3 15/20] configure: add --enable-pypi and --disable-pypi

[John Snow <jsnow@redhat.com>]

In the event that there's no vendored source present and no sufficient
version of meson is found, we will attempt to connect to PyPI to install
the package ... only if '--disable-pypi' was not passed. This mechanism
is intended to replace the online functionality of the meson git submodule.

While --enable-pypi is the default, vendored source will always be
preferred when found, making PyPI a fallback. This should ensure that
configure-time venv building "just works" for almost everyone in almost
every circumstance.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 configure | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index e9947369b2..7421bb8364 100755
--- a/configure
+++ b/configure
@@ -623,6 +623,7 @@ check_py_version() {
 }
 
 python=
+pypi="enabled"
 first_python=
 if test -z "${PYTHON}"; then
     # A bare 'python' is traditionally python 2.x, but some distros
@@ -883,6 +884,10 @@ for opt do
   --with-git-submodules=*)
       git_submodules_action="$optarg"
   ;;
+  --disable-pypi) pypi="disabled"
+  ;;
+  --enable-pypi) pypi="enabled"
+  ;;
   --enable-plugins) if test "$mingw32" = "yes"; then
                         error_exit "TCG plugins not currently supported on Windows platforms"
                     else
@@ -1098,7 +1103,9 @@ target_python=$python
 # Defaults assumed for now:
 # - venv is cleared if it exists already;
 # - venv is allowed to use system packages;
-# - all setup is performed **offline**;
+# - all setup can be performed offline;
+# - missing packages may be fetched from PyPI,
+#   unless --disable-pypi is passed.
 # - pip is not installed into the venv when possible,
 #   but ensurepip is called as a fallback when necessary.
 
@@ -1114,7 +1121,13 @@ fi
 python="$python -B"
 
 
+mkvenv_flags=""
+if test "$pypi" = "enabled" ; then
+    mkvenv_flags="--online"
+fi
+
 if ! $python "${source_path}/python/scripts/mkvenv.py" ensure \
+     $mkvenv_flags \
      --dir "${source_path}/python/wheels" \
      "meson>=0.61.5" ;
 then
-- 
2.39.2