Preserve file permissions when extracting runfiles zip

In Python rules, the Python stub script is responsible for extracting the runfiles from the zip file when --build_python_zip is used. However, there's a bug in the standard Python library (https://bugs.python.org/issue15795) that causes file permissions to be lost when extracting zips. This causes runfiles to not be marked executable, which is a problem when the py_runtime is an in-build runtime (issue #5104).

This change updates the stub script to workaround the bug by directly chmodding extracted files with their intended mode. It also adds a regression test combining a custom py_runtime with --build_python_zip.

Fixes #5104, unblocks #7375.

RELNOTES: Fixed an issue where some `py_runtime`s were incompatible with using `--build_python_zip` (#5104).
PiperOrigin-RevId: 246195931

src/main/java/com/google/devtools/build/lib/bazel/rules/python/python_stub_template.txt

@@ -99,13 +99,38 @@ def FindModuleSpace():
 
   raise AssertionError('Cannot find .runfiles directory for %s' % sys.argv[0])
 
+def ExtractZip(zip_path, dest_dir):
+  """Extracts the contents of a zip file, preserving the unix file mode bits.
+
+  These include the permission bits, and in particular, the executable bit.
+
+  Ideally the zipfile module should set these bits, but it doesn't. See:
+  https://bugs.python.org/issue15795.
+
+  Args:
+      zip_path: The path to the zip file to extract
+      dest_dir: The path to the destination directory
+  """
+  zip_path = GetWindowsPathWithUNCPrefix(zip_path)
+  dest_dir = GetWindowsPathWithUNCPrefix(dest_dir)
+  with zipfile.ZipFile(zip_path) as zf:
+    for info in zf.infolist():
+      zf.extract(info, dest_dir)
+      # UNC-prefixed paths must be absolute/normalized. See
+      # https://docs.microsoft.com/en-us/windows/desktop/fileio/naming-a-file#maximum-path-length-limitation
+      file_path = os.path.abspath(os.path.join(dest_dir, info.filename))
+      # The Unix st_mode bits (see "man 7 inode") are stored in the upper 16
+      # bits of external_attr. Of those, we set the lower 12 bits, which are the
+      # file mode bits (since the file type bits can't be set by chmod anyway).
+      attrs = info.external_attr >> 16
+      if attrs != 0:  # Rumor has it these can be 0 for zips created on Windows.
+        os.chmod(file_path, attrs & 0o7777)
+
 # Create the runfiles tree by extracting the zip file
 def CreateModuleSpace():
-  ZIP_RUNFILES_DIRECTORY_NAME = "runfiles"
   temp_dir = tempfile.mkdtemp("", "Bazel.runfiles_")
-  zf = zipfile.ZipFile(GetWindowsPathWithUNCPrefix(os.path.dirname(__file__)))
-  zf.extractall(GetWindowsPathWithUNCPrefix(temp_dir))
-  return os.path.join(temp_dir, ZIP_RUNFILES_DIRECTORY_NAME)
+  ExtractZip(os.path.dirname(__file__), temp_dir)
+  return os.path.join(temp_dir, "runfiles")
 
 # Returns repository roots to add to the import path.
 def GetRepositoriesImports(module_space, import_all):

src/test/shell/bazel/python_version_test.sh

@@ -188,6 +188,47 @@ EOF
   expect_log "File contents: abcdefg"
 }
 
+# Regression test for #5104. This test ensures that it's possible to use
+# --build_python_zip in combination with a py_runtime (as opposed to not using
+# a py_runtime, i.e., the legacy --python_path mechanism).
+#
+# Note that with --incompatible_use_python_toolchains flipped, we're always
+# using a py_runtime, so in that case this amounts to a test that
+# --build_python_zip works at all.
+#
+# The specific issue #5104 was caused by file permissions being lost when
+# unzipping runfiles, which led to an unexecutable runtime.
+function test_build_python_zip_works_with_py_runtime() {
+  mkdir -p test
+
+  cat > test/BUILD << EOF
+py_binary(
+    name = "pybin",
+    srcs = ["pybin.py"],
+)
+
+py_runtime(
+    name = "mock_runtime",
+    interpreter = ":mockpy.sh",
+    python_version = "PY3",
+)
+EOF
+  cat > test/pybin.py << EOF
+# This doesn't actually run because we use a mock Python runtime that never
+# executes the Python code.
+print("I am pybin!")
+EOF
+  cat > test/mockpy.sh <<EOF
+#!/bin/bash
+echo "I am mockpy!"
+EOF
+  chmod u+x test/mockpy.sh
+
+  bazel run //test:pybin --python_top=//test:mock_runtime --build_python_zip \
+      &> $TEST_log || fail "bazel run failed"
+  expect_log "I am mockpy!"
+}
+
 function test_pybin_can_have_different_version_pybin_as_data_dep() {
   mkdir -p test