fix: flip unused_inputs=1 by default (#432)

### Changes are visible to end-users: yes/no

- Searched for relevant documentation and updated as needed: yes
- Breaking change (forces users to change their own code or config): no
- Suggested release notes appear below: yes

### Test plan

- New test cases added

MODULE.bazel

@@ -8,7 +8,11 @@ module(
 
 # Lower-bound versions of direct dependencies.
 # When bumping, add a comment explaining what's required from the newer release.
-bazel_dep(name = "aspect_bazel_lib", version = "2.9.1") # py_image_layer requires 2.x for the `tar` rule.
+
+# py_image_layer requires 2.x for the `tar` rule.
+# py_image_layer needs compute_unused_inputs attribute
+# py_image_layer needs repo_mapping fix.
+bazel_dep(name = "aspect_bazel_lib", version = "2.9.4") 
 bazel_dep(name = "bazel_skylib", version = "1.4.2")
 bazel_dep(name = "rules_python", version = "0.29.0")
 bazel_dep(name = "platforms", version = "0.0.7")

py/private/BUILD.bazel

@@ -27,6 +27,7 @@ bzl_library(
     srcs = ["py_image_layer.bzl"],
     deps = [
         "@aspect_bazel_lib//lib:tar",
+        "@aspect_bazel_lib//lib:transitions",
     ],
 )
 

py/private/py_image_layer.bzl

@@ -31,16 +31,17 @@ oci_image(
 """
 
 load("@aspect_bazel_lib//lib:tar.bzl", "mtree_spec", "tar")
+load("@aspect_bazel_lib//lib:transitions.bzl", "platform_transition_filegroup")
 
 default_layer_groups = {
     # match *only* external pip like repositories that contain the string "site-packages"
-    "packages": "\\.runfiles/.*/site-packages",
+    "packages": "\\\\.runfiles/.*/site-packages",
     # match *only* external repositories that begins with the string "python"
     # e.g. this will match
     #   `/hello_world/hello_world_bin.runfiles/rules_python~0.21.0~python~python3_9_aarch64-unknown-linux-gnu/bin/python3`
     # but not match
     #   `/hello_world/hello_world_bin.runfiles/_main/python_app`
-    "interpreter": "\\.runfiles/python.*-.*/",
+    "interpreter": "\\\\.runfiles/.*python.*-.*/",
 }
 
 def _split_mtree_into_layer_groups(name, root, groups, group_names, **kwargs):
@@ -90,7 +91,7 @@ awk < $< 'BEGIN {
     )
 
 
-def py_image_layer(name, py_binary, root = None, layer_groups = {}, compress = "gzip", tar_args = ["--options", "gzip:!timestamp"], **kwargs):
+def py_image_layer(name, binary, root = "/", layer_groups = {}, compress = "gzip", tar_args = ["--options", "gzip:!timestamp"], compute_unused_inputs = 1, platform = None, **kwargs):
     """Produce a separate tar output for each layer of a python app
 
     > Requires `awk` to be installed on the host machine/rbe runner.
@@ -113,11 +114,13 @@ def py_image_layer(name, py_binary, root = None, layer_groups = {}, compress = "
 
     Args:
         name: base name for targets
-        py_binary: a py_binary target
+        binary: a py_binary target
         root: Path to where the layers should be rooted. If not specified, the layers will be rooted at the workspace root.
         layer_groups: Additional layer groups to create. They are used to group files into layers based on their path. In the form of: ```{"<name>": "regex_to_match_against_file_paths"}```
-        compress: Compression algorithm to use. Default is gzip. See: https://github.com/bazel-contrib/bazel-lib/blob/main/docs/tar.md#tar_rule
-        tar_args: Additional arguments to pass to the tar rule. Default is `["--options", "gzip:!timestamp"]`. See: https://github.com/bazel-contrib/bazel-lib/blob/main/docs/tar.md#tar_rule
+        compress: Compression algorithm to use. Default is gzip. See: https://github.com/bazel-contrib/bazel-lib/blob/main/docs/tar.md#tar_rule-compress
+        compute_unused_inputs: Whether to compute unused inputs. Default is 1. See: https://github.com/bazel-contrib/bazel-lib/blob/main/docs/tar.md#tar_rule-compute_unused_inputs
+        platform: The platform to use for the transition. Default is None. See: https://github.com/bazel-contrib/bazel-lib/blob/main/docs/transitions.md#platform_transition_binary-target_platform
+        tar_args: Additional arguments to pass to the tar rule. Default is `["--options", "gzip:!timestamp"]`. See: https://github.com/bazel-contrib/bazel-lib/blob/main/docs/tar.md#tar_rule-args
         **kwargs: attribute that apply to all targets expanded by the macro
 
     Returns:
@@ -130,7 +133,7 @@ def py_image_layer(name, py_binary, root = None, layer_groups = {}, compress = "
     # into fine-grained layers for better pull, push and remote cache performance.
     mtree_spec(
         name = name + ".manifest",
-        srcs = [py_binary],
+        srcs = [binary],
         **kwargs
     )
 
@@ -141,17 +144,32 @@ def py_image_layer(name, py_binary, root = None, layer_groups = {}, compress = "
     _split_mtree_into_layer_groups(name, root, groups, group_names, **kwargs)
 
     # Finally create layers using the tar rule
-    result = []
+    srcs = []
     for group_name in group_names:
         tar_target = "_{}_{}".format(name, group_name)
         tar(
             name = tar_target,
-            srcs = [py_binary],
+            srcs = [binary],
             mtree = "{}.{}.manifest.spec".format(name, group_name),
             compress = compress,
+            compute_unused_inputs = compute_unused_inputs,
             args = tar_args,
             **kwargs
         )
-        result.append(tar_target)
+        srcs.append(tar_target)
+
+    if platform:
+        platform_transition_filegroup(
+            name = name,
+            srcs = srcs,
+            target_platform = platform,
+            **kwargs
+        )
+    else:
+        native.filegroup(
+            name = name,
+            srcs = srcs,
+            **kwargs
+        )
 
-    return result
+    return srcs

py/repositories.bzl

@@ -33,9 +33,9 @@ def rules_py_dependencies():
     # py_image_layer requires 2.x for the `tar` rule.
     http_archive(
         name = "aspect_bazel_lib",
-        sha256 = "f93d386d8d0b0149031175e81df42a488be4267c3ca2249ba5321c23c60bc1f0",
-        strip_prefix = "bazel-lib-2.9.1",
-        url = "https://github.com/bazel-contrib/bazel-lib/releases/download/v2.9.1/bazel-lib-v2.9.1.tar.gz",
+        sha256 = "349aabd3c2b96caeda6181eb0ae1f14f2a1d9f3cd3c8b05d57f709ceb12e9fb3",
+        strip_prefix = "bazel-lib-2.9.4",
+        url = "https://github.com/bazel-contrib/bazel-lib/releases/download/v2.9.4/bazel-lib-v2.9.4.tar.gz",
     )
 
     http_archive(

py/tests/py_image_layer/BUILD.bazel

@@ -0,0 +1,29 @@
+load("//py:defs.bzl", "py_image_layer", "py_binary")
+load("asserts.bzl", "assert_tar_listing")
+
+platform(
+    name = "linux_amd64",
+    constraint_values = [
+        "@platforms//os:linux",
+        "@platforms//cpu:x86_64",
+    ],
+)
+
+
+# Case 1: Basic usage
+py_binary(
+    name = "my_app_bin",
+    srcs = ["main.py"],
+)
+
+py_image_layer(
+    name = "my_app_layers",
+    binary = ":my_app_bin",
+    platform = ":linux_amd64",
+)
+
+assert_tar_listing(
+    name = "my_app_layers_test",
+    actual = [":my_app_layers"],
+    expected = ":my_app_layers.listing",
+)

py/tests/py_image_layer/asserts.bzl

@@ -0,0 +1,21 @@
+load("@aspect_bazel_lib//lib:write_source_files.bzl", "write_source_file")
+
+# buildifier: disable=function-docstring
+def assert_tar_listing(name, actual, expected):
+    actual_listing = "_{}_listing".format(name)
+    native.genrule(
+        name = actual_listing,
+        srcs = actual,
+        testonly = True,
+        outs = ["_{}.listing".format(name)],
+        cmd = 'echo $(SRCS) | TZ="UTC" LC_ALL="en_US.UTF-8" xargs -n 1 $(BSDTAR_BIN) --exclude "*/_repo_mapping" --exclude "**/tools/venv_bin/**" -tvf > $@'.format(actual),
+        toolchains = ["@bsd_tar_toolchains//:resolved_toolchain"],
+    )
+
+    write_source_file(
+        name = name,
+        in_file = actual_listing,
+        out_file = expected,
+        testonly = True,
+        tags = ["skip-on-bazel6"],
+    )

py/tests/py_image_layer/main.py

@@ -0,0 +1 @@
+print("Hello!!")