Update docs and docstrings.

docs/docs.md

@@ -72,6 +72,31 @@ Create a tarball and an OCI descriptor for it
 | <a id="oci_image_layer-symlinks"></a>symlinks |  Dictionary of symlink -> target entries to place in the tarball   | <a href="https://bazel.build/rules/lib/dict">Dictionary: String -> String</a> | optional |  `{}`  |
 
 
+<a id="oci_image_layout"></a>
+
+## oci_image_layout
+
+<pre>
+oci_image_layout(<a href="#oci_image_layout-name">name</a>, <a href="#oci_image_layout-manifest">manifest</a>)
+</pre>
+
+Writes an OCI Image Index and related blobs to an OCI Image Format
+directory. See https://github.com/opencontainers/image-spec/blob/main/image-layout.md
+for the specification of the OCI Image Format directory.
+
+All blobs must be provided in the manifest's OCILayout provider, in the
+files attribute. If blobs are missing, creation of the OCI Image Layout
+will fail.
+
+**ATTRIBUTES**
+
+
+| Name  | Description | Type | Mandatory | Default |
+| :------------- | :------------- | :------------- | :------------- | :------------- |
+| <a id="oci_image_layout-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
+| <a id="oci_image_layout-manifest"></a>manifest |  An OCILayout index to be written to the OCI Image Format directory.   | <a href="https://bazel.build/concepts/labels">Label</a> | optional |  `None`  |
+
+
 <a id="oci_push"></a>
 
 ## oci_push

oci/oci_image_layout.bzl

@@ -48,26 +48,12 @@ oci_image_layout = rule(
     doc = """
         Writes an OCI Image Index and related blobs to an OCI Image Format
         directory. See https://github.com/opencontainers/image-spec/blob/main/image-layout.md
-        for the specification of the OCI Image Format directory. Local blobs are
-        used where available, and if a referenced blob is not present, it is
-        fetched from the provided OCI repository and placed in the output.
+        for the specification of the OCI Image Format directory.
 
-        In order for this rule to work correctly in its current state, the
-        following flags must be provided to bazel:
-        --spawn_strategy=local
-
-        The spawn_strategy flag must be set to local because currently,
-        oci_image_index is only declaring the new JSON files it creates as
-        outputs; it's not declaring any manifests or layers from the images as
-        outputs. By default, Bazel only permits rules to access specifically
-        declared outputs of the rule's direct dependencies. In order for this
-        rule to access the transitive set of outputs of all dependencies, we
-        must disable bazel's sandboxing by setting spawn_strategy=local.
+        All blobs must be provided in the manifest's OCILayout provider, in the
+        files attribute. If blobs are missing, creation of the OCI Image Layout
+        will fail.
     """,
-    # TODO(kim.mason): Fix oci_image/oci_image_index so they explicitly declare
-    # outputs that include everything needed to build the image.
-    # TODO(kim.mason): Make it so that Docker credential helpers are available
-    # to oci_image_layout without making the system PATH available.
     implementation = _oci_image_layout_impl,
     attrs = {
         "manifest": attr.label(