feat: support passing label to load command (#441)

Co-authored-by: Sahin Yort <[email protected]>

oci/private/tarball.bzl

@@ -39,6 +39,15 @@ attrs = {
         allow_single_file = [".txt"],
         mandatory = True,
     ),
+    "command": attr.label(
+        doc = """\
+            target for a container cli tool (i.e. docker or podman or other) that will be used to load the image into the local engine when using 'bazel run //my/image'.",
+            """,
+        allow_single_file = True,
+        mandatory = False,
+        executable = True,
+        cfg = "target",
+    ),
     "_run_template": attr.label(
         default = Label("//oci/private:tarball_run.sh.tpl"),
         doc = """ \
@@ -90,12 +99,16 @@ def _tarball_impl(ctx):
         output = exe,
         substitutions = {
             "{{image_path}}": tarball.short_path,
+            "{{command}}": ctx.file.command.path if ctx.file.command else "",
         },
         is_executable = True,
     )
+    runfiles = [tarball]
+    if ctx.file.command:
+        runfiles.append(ctx.file.command)
 
     return [
-        DefaultInfo(files = depset([tarball]), runfiles = ctx.runfiles(files = [tarball]), executable = exe),
+        DefaultInfo(files = depset([tarball]), runfiles = ctx.runfiles(files = runfiles), executable = exe),
     ]
 
 oci_tarball = rule(

oci/private/tarball_run.sh.tpl

@@ -2,13 +2,15 @@
 set -o pipefail -o errexit -o nounset
 
 readonly IMAGE="{{image_path}}"
-if command -v docker &> /dev/null; then
+if [ -e "{{command}}" ]; then
+    CONTAINER_CLI="{{command}}"
+elif command -v docker &> /dev/null; then
     CONTAINER_CLI="docker"
 elif command -v podman &> /dev/null; then
     CONTAINER_CLI="podman"
 else
     echo >&2 "Neither docker or podman could be found."
-    echo >&2 "If you wish to use another container runtime, please comment on https://github.com/bazel-contrib/rules_oci/issues/295."
+    echo >&2 "If you wish to use another container runtime, you can pass an executable to the 'command' attribute."
     exit 1
 fi