feat: Transition oci_image_index into a macro with additional [name].digest target

docs/BUILD.bazel

@@ -18,7 +18,11 @@ stardoc_with_diff_test(
 
 stardoc_with_diff_test(
     name = "image_index",
-    bzl_library_target = "//oci/private:image_index",
+    bzl_library_target = "//oci:defs",
+    symbol_names = [
+        "oci_image_index_rule",
+        "oci_image_index",
+    ],
 )
 
 stardoc_with_diff_test(

examples/multi_architecture_image/BUILD.bazel

@@ -32,16 +32,8 @@ oci_image_index(
     ],
 )
 
-genrule(
-    name = "hash",
-    srcs = [":index"],
-    outs = ["sha256.sum"],
-    cmd = "$(JQ_BIN) -r '.manifests[0].digest' $(location :index)/index.json > $@",
-    toolchains = ["@jq_toolchains//:resolved_toolchain"],
-)
-
 assert_contains(
     name = "check_digest",
-    actual = ":hash",
+    actual = ":index.digest",
     expected = "sha256:a2b8ae94672721788b67874f27cf3574fada3ccccc69f483bcb43de653573fe0",
 )

oci/defs.bzl

@@ -19,7 +19,7 @@ load("//oci/private:push.bzl", _oci_push = "oci_push")
 
 oci_tarball_rule = _oci_tarball
 oci_image_rule = _oci_image
-oci_image_index = _oci_image_index
+oci_image_index_rule = _oci_image_index
 oci_push_rule = _oci_push
 
 def _write_nl_seperated_file(name, kind, elems, forwarded_kwargs):
@@ -33,6 +33,56 @@ def _write_nl_seperated_file(name, kind, elems, forwarded_kwargs):
     )
     return label
 
+def _digest(name, **kwargs):
+    # `oci_image_rule` and `oci_image_index_rule` produce a directory as default output.
+    # Label for the [name]/index.json file
+    directory_path(
+        name = "_{}_index_json".format(name),
+        directory = name,
+        path = "index.json",
+        **kwargs
+    )
+
+    copy_file(
+        name = "_{}_index_json_cp".format(name),
+        src = "_{}_index_json".format(name),
+        out = "_{}_index.json".format(name),
+        **kwargs
+    )
+
+    # Matches the [name].digest target produced by rules_docker container_image
+    jq(
+        name = name + ".digest",
+        args = ["--raw-output"],
+        srcs = ["_{}_index.json".format(name)],
+        filter = """.manifests[0].digest""",
+        out = name + ".json.sha256",  # path chosen to match rules_docker for easy migration
+        **kwargs
+    )
+
+def oci_image_index(name, **kwargs):
+    """Macro wrapper around [oci_image_index_rule](#oci_image_index_rule).
+
+    Produces a target `[name].digest`, whose default output is a file containing the sha256 digest of the resulting image.
+    This is the same output as for the `oci_image` macro.
+
+    Args:
+        name: name of resulting oci_image_index_rule
+        **kwargs: other named arguments to [oci_image_index_rule](#oci_image_index_rule) and
+            [common rule attributes](https://bazel.build/reference/be/common-definitions#common-attributes).
+    """
+    forwarded_kwargs = propagate_common_rule_attributes(kwargs)
+
+    oci_image_index_rule(
+        name = name,
+        **kwargs
+    )
+
+    _digest(
+        name = name,
+        **forwarded_kwargs
+    )
+
 def oci_image(
         name,
         created = None,
@@ -159,29 +209,8 @@ def oci_image(
         **kwargs
     )
 
-    # `oci_image_rule` produces a directory as default output.
-    # Label for the [name]/index.json file
-    directory_path(
-        name = "_{}_index_json".format(name),
-        directory = name,
-        path = "index.json",
-        **forwarded_kwargs
-    )
-
-    copy_file(
-        name = "_{}_index_json_cp".format(name),
-        src = "_{}_index_json".format(name),
-        out = "_{}_index.json".format(name),
-        **forwarded_kwargs
-    )
-
-    # Matches the [name].digest target produced by rules_docker container_image
-    jq(
-        name = name + ".digest",
-        args = ["--raw-output"],
-        srcs = ["_{}_index.json".format(name)],
-        filter = """.manifests[0].digest""",
-        out = name + ".json.sha256",  # path chosen to match rules_docker for easy migration
+    _digest(
+        name = name,
         **forwarded_kwargs
     )