fix: Normalize main script path in Python bootstrap (#2925)

Use `os.path.normpath()` to resolve `_main/../repo/` to `repo/` and
convert forward
slashes to backward slashes on Windows.

This fixes an issue where `_main` doesn't exist within runfiles and in
turn the
later assertion that the path to main exists fails (~L542). This
happens,
for example, when packaging a `py_binary` from a foreign repo into a
tar/container.

---------

Co-authored-by: Richard Levasseur <[email protected]>
Co-authored-by: Richard Levasseur <[email protected]>

Author: mering

CHANGELOG.md

@@ -91,6 +91,7 @@ END_UNRELEASED_TEMPLATE
   also retrieved from the URL as opposed to only the `--hash` parameter. Fixes
   [#2363](https://github.com/bazel-contrib/rules_python/issues/2363).
 * (pypi) `whl_library` now infers file names from its `urls` attribute correctly.
+* (py_test, py_binary) Allow external files to be used for main
 
 {#v0-0-0-added}
 ### Added

internal_dev_deps.bzl

@@ -68,10 +68,10 @@ def rules_python_internal_deps():
     http_archive(
         name = "rules_pkg",
         urls = [
-            "https://mirror.bazel.build/github.com/bazelbuild/rules_pkg/releases/download/0.7.0/rules_pkg-0.7.0.tar.gz",
-            "https://github.com/bazelbuild/rules_pkg/releases/download/0.7.0/rules_pkg-0.7.0.tar.gz",
+            "https://mirror.bazel.build/github.com/bazelbuild/rules_pkg/releases/download/1.0.1/rules_pkg-1.0.1.tar.gz",
+            "https://github.com/bazelbuild/rules_pkg/releases/download/1.0.1/rules_pkg-1.0.1.tar.gz",
         ],
-        sha256 = "8a298e832762eda1830597d64fe7db58178aa84cd5926d76d5b744d6558941c2",
+        sha256 = "d20c951960ed77cb7b341c2a59488534e494d5ad1d30c4818c736d57772a9fef",
     )
 
     http_archive(

python/private/python_bootstrap_template.txt

@@ -499,8 +499,12 @@ def Main():
   # The magic string percent-main-percent is replaced with the runfiles-relative
   # filename of the main file of the Python binary in BazelPythonSemantics.java.
   main_rel_path = '%main%'
-  if IsWindows():
-    main_rel_path = main_rel_path.replace('/', os.sep)
+  # NOTE: We call normpath for two reasons:
+  # 1. Transform Bazel `foo/bar` to Windows `foo\bar`
+  # 2. Transform `_main/../foo/main.py` to simply `foo/main.py`, which
+  #    matters if `_main` doesn't exist (which can occur if a binary
+  #    is packaged and needs no artifacts from the main repo)
+  main_rel_path = os.path.normpath(main_rel_path)
 
   if IsRunningFromZip():
     module_space = CreateModuleSpace()

tests/bootstrap_impls/BUILD.bazel

@@ -1,5 +1,3 @@
-load("@rules_shell//shell:sh_test.bzl", "sh_test")
-
 # Copyright 2023 The Bazel Authors. All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,6 +11,8 @@ load("@rules_shell//shell:sh_test.bzl", "sh_test")
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+load("@rules_pkg//pkg:tar.bzl", "pkg_tar")
+load("@rules_shell//shell:sh_test.bzl", "sh_test")
 load("//tests/support:py_reconfig.bzl", "py_reconfig_binary", "py_reconfig_test")
 load("//tests/support:sh_py_run_test.bzl", "sh_py_run_test")
 load("//tests/support:support.bzl", "SUPPORTS_BOOTSTRAP_SCRIPT")
@@ -158,4 +158,24 @@ py_reconfig_test(
     target_compatible_with = SUPPORTS_BOOTSTRAP_SCRIPT,
 )
 
+pkg_tar(
+    name = "external_binary",
+    testonly = True,
+    srcs = ["@other//:external_main"],
+    include_runfiles = True,
+    tags = ["manual"],  # Don't build as part of wildcards
+)
+
+sh_test(
+    name = "external_binary_test",
+    srcs = ["external_binary_test.sh"],
+    data = [":external_binary"],
+    # For now, skip this test on Windows because it fails for reasons
+    # other than the code path being tested.
+    target_compatible_with = select({
+        "@platforms//os:windows": ["@platforms//:incompatible"],
+        "//conditions:default": [],
+    }),
+)
+
 relative_path_test_suite(name = "relative_path_tests")

tests/bootstrap_impls/external_binary_test.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+set -euxo pipefail
+
+tmpdir="${TEST_TMPDIR}/external_binary"
+mkdir -p "${tmpdir}"
+tar xf "tests/bootstrap_impls/external_binary.tar" -C "${tmpdir}"
+test -x "${tmpdir}/external_main"
+output="$("${tmpdir}/external_main")"
+test "$output" = "token"

tests/modules/other/BUILD.bazel

@@ -0,0 +1,14 @@
+load("@rules_python//tests/support:py_reconfig.bzl", "py_reconfig_binary")
+
+package(
+    default_visibility = ["//visibility:public"],
+)
+
+py_reconfig_binary(
+    name = "external_main",
+    srcs = [":external_main.py"],
+    # We're testing a system_python specific code path,
+    # so force using that bootstrap
+    bootstrap_impl = "system_python",
+    main = "external_main.py",
+)

tests/modules/other/external_main.py

@@ -0,0 +1 @@
+print("token")