Enable experimental_tarball_format for container_bundle. (#1938)

Resolves TODO. Seems to improve build time.

Co-authored-by: aptenodytes-forsteri <aptenodytesforstericodes@gmail.com>

container/bundle.bzl

@@ -73,10 +73,7 @@ def _container_bundle_impl(ctx):
         ctx,
         images,
         ctx.outputs.tar_output,
-        # Experiment: currently only support experimental_tarball_format in
-        # container_image for testing optimization.
-        # TODO(#1695): Update this.
-        "legacy",
+        ctx.attr.experimental_tarball_format,
         stamp = stamp,
     )
 
@@ -109,6 +106,19 @@ container_bundle_ = rule(
             mandatory = False,
         ),
         "tar_output": attr.output(),
+        "experimental_tarball_format": attr.string(
+            values = [
+                "legacy",
+                "compressed",
+            ],
+            default = "legacy",
+            doc = ("The tarball format to use when producing an image .tar file. " +
+                   "Defaults to \"legacy\", which contains uncompressed layers. " +
+                   "If set to \"compressed\", the resulting tarball will contain " +
+                   "compressed layers, but is only loadable by newer versions of " +
+                   "docker. This is an experimental attribute, which is subject " +
+                   "to change or removal: do not depend on its exact behavior."),
+        ),
     }, _layer_tools),
     executable = True,
     toolchains = ["@io_bazel_rules_docker//toolchains/docker:toolchain_type"],

docs/container.md

@@ -8,8 +8,8 @@ Load these from `@io_bazel_rules_docker//container:container.bzl`.
 ## container_bundle
 
 <pre>
-container_bundle(<a href="#container_bundle-name">name</a>, <a href="#container_bundle-extract_config">extract_config</a>, <a href="#container_bundle-image_target_strings">image_target_strings</a>, <a href="#container_bundle-image_targets">image_targets</a>, <a href="#container_bundle-images">images</a>,
-                 <a href="#container_bundle-incremental_load_template">incremental_load_template</a>, <a href="#container_bundle-stamp">stamp</a>, <a href="#container_bundle-tar_output">tar_output</a>)
+container_bundle(<a href="#container_bundle-name">name</a>, <a href="#container_bundle-experimental_tarball_format">experimental_tarball_format</a>, <a href="#container_bundle-extract_config">extract_config</a>, <a href="#container_bundle-image_target_strings">image_target_strings</a>,
+                 <a href="#container_bundle-image_targets">image_targets</a>, <a href="#container_bundle-images">images</a>, <a href="#container_bundle-incremental_load_template">incremental_load_template</a>, <a href="#container_bundle-stamp">stamp</a>, <a href="#container_bundle-tar_output">tar_output</a>)
 </pre>
 
 A rule that aliases and saves N images into a single `docker save` tarball.
@@ -20,6 +20,7 @@ A rule that aliases and saves N images into a single `docker save` tarball.
 | Name  | Description | Type | Mandatory | Default |
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="container_bundle-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/docs/build-ref.html#name">Name</a> | required |  |
+| <a id="container_bundle-experimental_tarball_format"></a>experimental_tarball_format |  The tarball format to use when producing an image .tar file. Defaults to "legacy", which contains uncompressed layers. If set to "compressed", the resulting tarball will contain compressed layers, but is only loadable by newer versions of docker. This is an experimental attribute, which is subject to change or removal: do not depend on its exact behavior.   | String | optional | "legacy" |
 | <a id="container_bundle-extract_config"></a>extract_config |  -   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | //container/go/cmd/extract_config:extract_config |
 | <a id="container_bundle-image_target_strings"></a>image_target_strings |  -   | List of strings | optional | [] |
 | <a id="container_bundle-image_targets"></a>image_targets |  -   | <a href="https://bazel.build/docs/build-ref.html#labels">List of labels</a> | optional | [] |

tests/container/BUILD

@@ -988,6 +988,7 @@ container_image(
 # would take substantially longer for this target.
 container_bundle(
     name = "container_bundle_with_install_pkgs",
+    experimental_tarball_format = "compressed",
     images = {
         "install_pkgs_1:latest": ":test_install_pkgs",
         "install_pkgs_2:latest": ":test_install_git_for_reproducibility_1",