feat: Allow stampable repotags for oci_tarball (#185)

Co-authored-by: Alex Eagle <[email protected]>

docs/tarball.md

@@ -41,6 +41,6 @@ Passing anything other than oci_image to the image attribute will lead to build
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="oci_tarball-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/docs/build-ref.html#name">Name</a> | required |  |
 | <a id="oci_tarball-image"></a>image |  Label of a directory containing an OCI layout, typically <code>oci_image</code>   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | required |  |
-| <a id="oci_tarball-repotags"></a>repotags |  List of repository+tags to apply to the loaded image   | List of strings | required |  |
+| <a id="oci_tarball-repotags"></a>repotags |  a file containing repotags, one per line.   | <a href="https://bazel.build/docs/build-ref.html#labels">Label</a> | optional | None |
 
 

oci/defs.bzl

@@ -8,7 +8,7 @@ load("//oci/private:structure_test.bzl", _structure_test = "structure_test")
 load("@bazel_skylib//lib:types.bzl", "types")
 load("@bazel_skylib//rules:write_file.bzl", "write_file")
 
-oci_tarball = _oci_tarball
+oci_tarball_rule = _oci_tarball
 oci_image_rule = _oci_image
 oci_image_index = _oci_image_index
 oci_push_rule = _oci_push
@@ -82,3 +82,31 @@ def oci_push(name, repotags = None, **kwargs):
         repotags = repotags,
         **kwargs
     )
+
+def oci_tarball(name, repotags = None, **kwargs):
+    """Macro wrapper around [oci_tarball_rule](#oci_tarball_rule).
+
+    Allows the repotags attribute to be a list of strings in addition to a text file.
+
+    Args:
+        name: name of resulting oci_tarball_rule
+        repotags: a list of repository:tag to specify when loading the image,
+            or a label of a file containing tags one-per-line.
+            See [stamped_tags](https://github.com/bazel-contrib/rules_oci/blob/main/examples/push/stamp_tags.bzl)
+            as one example of a way to produce such a file.
+        **kwargs: other named arguments to [oci_tarball_rule](#oci_tarball_rule).
+    """
+    if types.is_list(repotags):
+        tags_label = "_{}_write_tags".format(name)
+        write_file(
+            name = tags_label,
+            out = "_{}.tags.txt".format(name),
+            content = repotags,
+        )
+        repotags = tags_label
+
+    oci_tarball_rule(
+        name = name,
+        repotags = repotags,
+        **kwargs
+    )

oci/private/tarball.bzl

@@ -34,7 +34,12 @@ Passing anything other than oci_image to the image attribute will lead to build
 
 attrs = {
     "image": attr.label(mandatory = True, allow_single_file = True, doc = "Label of a directory containing an OCI layout, typically `oci_image`"),
-    "repotags": attr.string_list(mandatory = True, doc = "List of repository+tags to apply to the loaded image"),
+    "repotags": attr.label(
+        doc = """\
+            a file containing repotags, one per line.
+            """,
+        allow_single_file = [".txt"],
+    ),
     "_tarball_sh": attr.label(allow_single_file = True, default = "//oci/private:tarball.sh.tpl"),
     "_build_tar": attr.label(
         default = Label("@rules_pkg//pkg/private/tar:build_tar"),
@@ -75,22 +80,27 @@ def _tarball_impl(ctx):
 
     yq_bin = ctx.toolchains["@aspect_bazel_lib//lib:yq_toolchain_type"].yqinfo.bin
     executable = ctx.actions.declare_file("{}/tarball.sh".format(ctx.label.name))
+
+    substitutions = {
+        "{{yq}}": yq_bin.path,
+        "{{image_dir}}": image.path,
+        "{{blobs_dir}}": blobs.path,
+        "{{manifest_path}}": manifest.path,
+    }
+
+    if ctx.attr.repotags:
+        substitutions["{{tags}}"] = ctx.file.repotags.path
+
     ctx.actions.expand_template(
         template = ctx.file._tarball_sh,
         output = executable,
         is_executable = True,
-        substitutions = {
-            "{{yq}}": yq_bin.path,
-            "{{image_dir}}": image.path,
-            "{{blobs_dir}}": blobs.path,
-            "{{manifest_path}}": manifest.path,
-            "{{repotags}}": json.encode(ctx.attr.repotags),
-        },
+        substitutions = substitutions,
     )
 
     ctx.actions.run(
         executable = executable,
-        inputs = [image],
+        inputs = [image, ctx.file.repotags],
         outputs = [manifest, blobs],
         tools = [yq_bin],
         mnemonic = "OCITarball",

oci/private/tarball.sh.tpl

@@ -4,9 +4,14 @@ set -o pipefail -o errexit -o nounset
 readonly YQ="{{yq}}"
 readonly IMAGE_DIR="{{image_dir}}"
 readonly BLOBS_DIR="{{blobs_dir}}"
-readonly REPOTAGS='{{repotags}}'
+readonly TAGS_FILE="{{tags}}"
 readonly TARBALL_MANIFEST_PATH="{{manifest_path}}"
 
+REPOTAGS=()
+# read repotags file as array and prepend it to REPOTAGS array.
+IFS=$'\n' REPOTAGSFILE=($(cat "$TAGS_FILE"))
+REPOTAGS=(${REPOTAGSFILE[@]+"${REPOTAGSFILE[@]}"} ${REPOTAGS[@]+"${REPOTAGS[@]}"})
+
 MANIFEST_DIGEST=$(${YQ} eval '.manifests[0].digest | sub(":"; "/")' "${IMAGE_DIR}/index.json")
 MANIFEST_BLOB_PATH="${IMAGE_DIR}/blobs/${MANIFEST_DIGEST}"
 
@@ -23,7 +28,7 @@ for LAYER in $(${YQ} ".[]" <<< $LAYERS); do
 done
 
 config="blobs/${CONFIG_DIGEST}" \
-repotags="${REPOTAGS}" \
+repotags="${REPOTAGS:-[]}" \
 layers="${LAYERS}" \
 "${YQ}" eval \
         --null-input '.[0] = {"Config": env(config), "RepoTags": env(repotags), "Layers": env(layers) | map( "blobs/" + . + ".tar.gz") }' \