fix(pypi): generate namespace package initializers without a shell

news/wheel-namespace-initializers.fixed.md

@@ -0,0 +1 @@
+(pypi) Wheel namespace package initializers no longer require a shell or `cp` on the execution platform.

python/private/pypi/BUILD.bazel

@@ -229,7 +229,7 @@ bzl_library(
 bzl_library(
     name = "namespace_pkgs",
     srcs = ["namespace_pkgs.bzl"],
-    deps = ["@bazel_skylib//rules:copy_file"],
+    deps = ["@bazel_skylib//rules:expand_template"],
 )
 
 bzl_library(

python/private/pypi/namespace_pkgs.bzl

@@ -1,6 +1,6 @@
 """Utilities to get where we should write namespace pkg paths."""
 
-load("@bazel_skylib//rules:copy_file.bzl", "copy_file")
+load("@bazel_skylib//rules:expand_template.bzl", "expand_template")
 
 _ext = struct(
     py = ".py",
@@ -59,16 +59,16 @@ def get_files(*, srcs, ignored_dirnames = [], root = None):
 
     return sorted([d for d in dirs if d not in ignored])
 
-def create_inits(*, srcs, ignored_dirnames = [], root = None, copy_file = copy_file, **kwargs):
+def create_inits(*, srcs, ignored_dirnames = [], root = None, write_init = expand_template, **kwargs):
     """Create init files and return the list to be included `py_library` srcs.
 
     Args:
         srcs: {type}`src` a list of files to be passed to {bzl:obj}`py_library`
             as `srcs` and `data`. This is usually a result of a {obj}`glob`.
         ignored_dirnames: {type}`str` a list of patterns to ignore.
         root: {type}`str` the prefix to use as the root.
-        copy_file: the `copy_file` rule to copy files in build context.
-        **kwargs: passed to {obj}`copy_file`.
+        write_init: rule that generates an initializer from the namespace template.
+        **kwargs: passed to `write_init`.
 
     Returns:
         {type}`list[str]` to be included as part of `py_library`.
@@ -78,11 +78,14 @@ def create_inits(*, srcs, ignored_dirnames = [], root = None, copy_file = copy_f
         src = "{}/__init__.py".format(out)
         ret.append(src)
 
-        copy_file(
+        # With no substitutions, Bazel writes the initializer verbatim. Skylib's
+        # copy_file would require a shell and cp on the Unix execution platform.
+        write_init(
             # For the target name, use a number instead of trying to convert an output
             # path into a valid label.
             name = "_cp_{}_namespace".format(i),
-            src = _TEMPLATE,
+            template = _TEMPLATE,
+            substitutions = {},
             out = src,
             **kwargs
         )

tests/pypi/namespace_pkgs/namespace_pkgs_tests.bzl

@@ -167,33 +167,36 @@ def _test_create_inits(env):
         "nested/root/foo/buu/__init__.py",
         "nested/root/foo/buu/bii.py",
     ]
-    copy_file_calls = []
+    write_init_calls = []
     template = Label("//python/private/pypi:namespace_pkg_tmpl.py")
 
     got = create_inits(
         srcs = srcs,
         root = "nested/root",
-        copy_file = lambda **kwargs: copy_file_calls.append(kwargs),
+        write_init = lambda **kwargs: write_init_calls.append(kwargs),
     )
     env.expect.that_collection(got).contains_exactly([
         call["out"]
-        for call in copy_file_calls
+        for call in write_init_calls
     ])
-    env.expect.that_collection(copy_file_calls).contains_exactly([
+    env.expect.that_collection(write_init_calls).contains_exactly([
         {
             "name": "_cp_0_namespace",
             "out": "nested/root/foo/__init__.py",
-            "src": template,
+            "substitutions": {},
+            "template": template,
         },
         {
             "name": "_cp_1_namespace",
             "out": "nested/root/foo/bar/__init__.py",
-            "src": template,
+            "substitutions": {},
+            "template": template,
         },
         {
             "name": "_cp_2_namespace",
             "out": "nested/root/foo/bee/__init__.py",
-            "src": template,
+            "substitutions": {},
+            "template": template,
         },
     ])