test(integration): reproduce cross-runtime py_binary launch breakage

.bazelignore

@@ -33,4 +33,5 @@ sphinxdocs
 tests/integration/compile_pip_requirements/bazel-compile_pip_requirements
 tests/integration/local_toolchains/bazel-local_toolchains
 tests/integration/py_cc_toolchain_registered/bazel-py_cc_toolchain_registered
+tests/integration/sys_executable_cross_runtime/bazel-module_under_test
 tests/integration/toolchain_target_settings/bazel-module_under_test

.bazelrc.deleted_packages

@@ -37,6 +37,7 @@ common --deleted_packages=tests/integration/pip_parse
 common --deleted_packages=tests/integration/pip_parse/empty
 common --deleted_packages=tests/integration/pip_parse_isolated
 common --deleted_packages=tests/integration/py_cc_toolchain_registered
+common --deleted_packages=tests/integration/sys_executable_cross_runtime
 common --deleted_packages=tests/integration/toolchain_target_settings
 common --deleted_packages=tests/modules/another_module
 common --deleted_packages=tests/modules/other

tests/integration/BUILD.bazel

@@ -97,6 +97,10 @@ rules_python_integration_test(
     py_main = "toolchain_target_settings_test.py",
 )
 
+rules_python_integration_test(
+    name = "sys_executable_cross_runtime_test",
+)
+
 py_library(
     name = "runner_lib",
     srcs = ["runner.py"],

tests/integration/sys_executable_cross_runtime/BUILD.bazel

@@ -0,0 +1,38 @@
+load("@rules_python//python:py_binary.bzl", "py_binary")
+load("@rules_shell//shell:sh_test.bzl", "sh_test")
+
+py_binary(
+    name = "child",
+    srcs = ["child.py"],
+    main = "child.py",
+    python_version = "3.11",
+)
+
+py_binary(
+    name = "parent",
+    srcs = ["parent.py"],
+    data = [":child"],
+    deps = ["@rules_python//python/runfiles"],
+    main = "parent.py",
+    python_version = "3.12",
+)
+
+sh_test(
+    name = "child_direct_test",
+    srcs = ["run_parent.sh"],
+    data = [":parent"],
+    env = {
+        "MODE": "direct",
+        "PARENT_BINARY": "$(rootpath :parent)",
+    },
+)
+
+sh_test(
+    name = "child_sys_executable_test",
+    srcs = ["run_parent.sh"],
+    data = [":parent"],
+    env = {
+        "MODE": "sys_executable",
+        "PARENT_BINARY": "$(rootpath :parent)",
+    },
+)

tests/integration/sys_executable_cross_runtime/MODULE.bazel

@@ -0,0 +1,20 @@
+module(name = "module_under_test")
+
+bazel_dep(name = "rules_shell", version = "0.6.1")
+bazel_dep(name = "rules_python", version = "0.0.0")
+local_path_override(
+    module_name = "rules_python",
+    path = "../../..",
+)
+
+python = use_extension("@rules_python//python/extensions:python.bzl", "python")
+python.defaults(python_version = "3.12")
+python.toolchain(
+    configure_coverage_tool = True,
+    python_version = "3.11",
+)
+python.toolchain(
+    configure_coverage_tool = True,
+    python_version = "3.12",
+)
+use_repo(python, "python_3_11", "python_3_12", "python_versions", "pythons_hub")

tests/integration/sys_executable_cross_runtime/child.py

@@ -0,0 +1,10 @@
+import re
+
+
+def main() -> None:
+    re.compile("child")
+    print("child completed")
+
+
+if __name__ == "__main__":
+    main()

tests/integration/sys_executable_cross_runtime/parent.py

@@ -0,0 +1,36 @@
+import os
+import subprocess
+import sys
+
+from python.runfiles import Runfiles
+
+
+def main() -> int:
+    assert len(sys.argv) == 2
+    mode = sys.argv[1]
+    runfiles = Runfiles.Create()
+    child = runfiles.Rlocation("_main/child")
+    assert child is not None
+
+    # Reproduce the broken contract: the parent exports its own runtime import
+    # paths, then starts the child launcher with sys.executable. The child
+    # launcher re-execs into its own interpreter, but the inherited PYTHONPATH
+    # still points at the parent's stdlib and site-packages.
+    os.environ["PYTHONPATH"] = os.pathsep.join(sys.path)
+
+    if mode == "sys_executable":
+        argv = [sys.executable, child]
+    elif mode == "direct":
+        argv = [child]
+    else:
+        raise RuntimeError(f"unknown launch mode: {mode}")
+
+    proc = subprocess.run(
+        argv,
+        check=False,
+    )
+    return proc.returncode
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

tests/integration/sys_executable_cross_runtime/run_parent.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+
+set -o errexit -o nounset -o pipefail
+
+"${PARENT_BINARY}" "${MODE}"