feat(pex): support cross builds of py_pex_binary targetting Linux

py/private/py_pex_binary.bzl

@@ -101,7 +101,6 @@ def _py_python_pex_impl(ctx):
     )
     args.add(binary[DefaultInfo].files_to_run.executable, format = "--executable=%s")
     args.add(ctx.attr.python_shebang, format = "--python-shebang=%s")
-    args.add(py_toolchain.python, format = "--python=%s")
 
     py_version = py_toolchain.interpreter_version_info
     args.add_all(

py/tests/py-pex-binary/BUILD.bazel

@@ -1,4 +1,6 @@
 load("@aspect_bazel_lib//lib:testing.bzl", "assert_contains")
+load("@aspect_bazel_lib//lib:transitions.bzl", "platform_transition_binary")
+load("@bazel_skylib//rules:build_test.bzl", "build_test")
 load("//py:defs.bzl", "py_binary", "py_pex_binary")
 
 # Test that both single-file modules (six) and multi-file modules (cowsay) work with py_pex_binary.
@@ -32,3 +34,43 @@ assert_contains(
     actual = "print_modules_pex.out",
     expected = "Mooo!,cowsay-6.1/cowsay/__init__.py,six-1.16.0/six.py",
 )
+
+# Cross-compilation to Linux can work.
+# TODO(https://github.com/aspect-build/rules_py/issues/625): support arbitrary cross-compilation.
+
+# At least one of these platforms is a cross-compile, no matter where we run.
+platform(
+    name = "arm64_linux",
+    constraint_values = [
+        "@platforms//os:linux",
+        "@platforms//cpu:aarch64",
+    ],
+)
+
+platform(
+    name = "amd64_linux",
+    constraint_values = [
+        "@platforms//os:linux",
+        "@platforms//cpu:x86_64",
+    ],
+)
+
+platform_transition_binary(
+    name = "print_modules_pex_arm64_linux",
+    binary = ":print_modules_pex",
+    target_platform = ":arm64_linux",
+)
+
+platform_transition_binary(
+    name = "print_modules_pex_amd64_linux",
+    binary = ":print_modules_pex",
+    target_platform = ":amd64_linux",
+)
+
+build_test(
+    name = "cross_builds",
+    targets = [
+        ":print_modules_pex_arm64_linux",
+        ":print_modules_pex_amd64_linux",
+    ],
+)

py/tools/pex/main.py

@@ -9,7 +9,6 @@
 
 import sys
 from pex.pex_builder import Check,PEXBuilder
-from pex.interpreter import PythonInterpreter
 from pex.interpreter_constraints import InterpreterConstraint
 from pex.layout import Layout
 from pex.dist_metadata import Distribution
@@ -37,13 +36,6 @@ def __call__(self, parser, namespace, value, option_str=None):
     "immediately and not save it to a file.",
 )
 
-parser.add_argument(
-    "--python",
-    dest="python",
-    required=True
-)
-
-
 parser.add_argument(
     "--python-version-constraint",
     dest="constraints",
@@ -128,7 +120,10 @@ def __call__(self, parser, namespace, value, option_str=None):
 
 
 pex_builder = PEXBuilder(
-    interpreter=PythonInterpreter.from_binary(options.python),
+    # Build the PEX artifact using the current interpreter; we know it works in cfg=exec
+    # because that's how we're already running. Interpreters inferred by other means might
+    # not work in cross-builds.
+    interpreter=None,
 )