fix(pypi): build the environment on the fly

At some point when we started using pipstar, we silently started
building the python environment with system python interpreter. This is
fine because the environment in those code paths would be unused, but
this would break if python was not present on the machine.

This PR fixes this by creating the environment on the fly with a little
bit of code duplication.

Fixes #3712

Author: aignas

CHANGELOG.md

@@ -126,6 +126,8 @@ Other changes:
   )
   ```
   Fixes [#3676](https://github.com/bazel-contrib/rules_python/issues/3676).
+* (pypi) Fixes wheel extraction on hosts without python installed,
+  Fixes [#3712](https://github.com/bazel-contrib/rules_python/issues/3712).
 
 {#v2-0-0-added}
 ### Added

python/private/pypi/whl_library.bzl

@@ -306,9 +306,6 @@ def _whl_library_impl(rctx):
     extra_pip_args = []
     extra_pip_args.extend(rctx.attr.extra_pip_args)
 
-    # Manually construct the PYTHONPATH since we cannot use the toolchain here
-    environment = _create_repository_execution_environment(rctx, python_interpreter, logger = logger)
-
     whl_path = None
     sdist_filename = None
     if rctx.attr.whl_file:
@@ -377,7 +374,8 @@ def _whl_library_impl(rctx):
             python = python_interpreter,
             op = op_tmpl.format(name = rctx.attr.name, requirement = rctx.attr.requirement.split(" ", 1)[0]),
             arguments = args,
-            environment = environment,
+            # Manually construct the PYTHONPATH since we cannot use the toolchain here
+            environment = _create_repository_execution_environment(rctx, python_interpreter, logger = logger),
             srcs = rctx.attr._python_srcs,
             quiet = rctx.attr.quiet,
             timeout = rctx.attr.timeout,
@@ -414,7 +412,8 @@ def _whl_library_impl(rctx):
             python_interpreter = python_interpreter,
             args = args,
             whl_path = whl_path,
-            environment = environment,
+            # Manually construct the PYTHONPATH since we cannot use the toolchain here
+            environment = _create_repository_execution_environment(rctx, python_interpreter, logger = logger),
             logger = logger,
         )