fix: make oci_tarball work with disjoint output root

Author: thesayyn

examples/assertion/BUILD.bazel

@@ -1,6 +1,7 @@
 load("@aspect_bazel_lib//lib:tar.bzl", "tar")
+load("@aspect_bazel_lib//lib:transitions.bzl", "platform_transition_filegroup")
 load("@bazel_skylib//rules:build_test.bzl", "build_test")
-load("//oci:defs.bzl", "oci_image")
+load("//oci:defs.bzl", "oci_image", "oci_tarball")
 
 # Case 1: image name containing a capital case.
 oci_image(
@@ -46,12 +47,60 @@ oci_image(
     ],
 )
 
+# Case 4: Transition an oci_image and feed to oci_tarball
+oci_image(
+    name = "case4",
+    architecture = "arm64",
+    os = "linux",
+)
+
+platform_transition_filegroup(
+    name = "case4_transition",
+    srcs = [":case4"],
+    target_platform = "//examples:linux_arm64",
+)
+
+oci_tarball(
+    name = "case4_tarball",
+    image = ":case4_transition",
+    repo_tags = ["case4:example"],
+)
+
+filegroup(
+    name = "case4_tarball_tar",
+    srcs = [":case4_tarball"],
+    output_group = "tarball",
+)
+
+# Case 5:
+
+# Case 4: An oci_image directly fed into oci_tarball
+oci_image(
+    name = "case5",
+    architecture = "arm64",
+    os = "linux",
+)
+
+oci_tarball(
+    name = "case5_tarball",
+    image = ":case5",
+    repo_tags = ["case5:example"],
+)
+
+filegroup(
+    name = "case5_tarball_tar",
+    srcs = [":case5_tarball"],
+    output_group = "tarball",
+)
+
 # build them as test.
 build_test(
     name = "test",
     targets = [
         ":imagE",
         ":case2",
         ":case3",
+        ":case4_tarball_tar",
+        ":case5_tarball_tar",
     ],
 )

oci/private/tarball.bzl

@@ -113,7 +113,6 @@ def _tarball_impl(ctx):
         "{{jq_path}}": jq.bin.path,
         "{{tar}}": bsdtar.tarinfo.binary.path,
         "{{image_dir}}": image.path,
-        "{{bindir}}": ctx.bin_dir.path,
         "{{output}}": mtree_spec.path,
         "{{json_out}}": image_json.path,
     }
@@ -148,7 +147,7 @@ def _tarball_impl(ctx):
         output = exe,
         substitutions = {
             "{{TAR}}": bsdtar.tarinfo.binary.short_path,
-            "{{mtree_path}}": mtree_spec.short_path,
+            "{{mtree_path}}": mtree_spec.path,
             "{{loader}}": ctx.file.loader.path if ctx.file.loader else "",
         },
         is_executable = True,
@@ -160,10 +159,8 @@ def _tarball_impl(ctx):
     tar_inputs = depset(direct = mtree_outputs, transitive = [mtree_inputs])
     tar_args = ctx.actions.args()
     tar_args.add_all(["--create", "--no-xattr", "--no-mac-metadata"])
-    tar_args.add_all(["--cd", ctx.bin_dir.path])
     tar_args.add("--file", tarball)
-    # To reference our mtree spec file, we have to undo the --cd by removing three path segments
-    tar_args.add(mtree_spec, format = "@../../../%s")
+    tar_args.add(mtree_spec, format = "@%s")
     ctx.actions.run(
         executable = bsdtar.tarinfo.binary,
         inputs = tar_inputs,

oci/private/tarball.sh.tpl

@@ -17,7 +17,7 @@ readonly OUTPUT="{{output}}"
 function add_to_tar() {
     content=$1
     tar_path=$2
-    echo >>"${OUTPUT}" "${tar_path} uid=0 gid=0 mode=0755 time=1672560000 type=file content=${content#{{bindir}}/}"
+    echo >>"${OUTPUT}" "${tar_path} uid=0 gid=0 mode=0755 time=1672560000 type=file content=${content}"
 }
 
 MANIFEST_DIGEST=$(${JQ} -r '.manifests[0].digest | sub(":"; "/")' "${INDEX_FILE}" | tr  -d '"')

oci/private/tarball_run.sh.tpl

@@ -13,6 +13,31 @@ else
     exit 1
 fi
 
+
+# The execroot detection code is copied from https://github.com/aspect-build/rules_js/blob/d4ac7025a83192d011b7dd7447975a538e34c49b/js/private/js_binary.sh.tpl#L169-L217
+if [[ "$PWD" == *"/bazel-out/"* ]]; then
+    bazel_out_segment="/bazel-out/"
+elif [[ "$PWD" == *"/BAZEL-~1/"* ]]; then
+    bazel_out_segment="/BAZEL-~1/"
+elif [[ "$PWD" == *"/bazel-~1/"* ]]; then
+    bazel_out_segment="/bazel-~1/"
+fi
+
+if [[ "${bazel_out_segment:-}" ]]; then
+    # We are in runfiles and we don't yet know the execroot
+    rest="${PWD#*"$bazel_out_segment"}"
+    index=$((${#PWD} - ${#rest} - ${#bazel_out_segment}))
+    if [ ${index} -lt 0 ]; then
+        echo "No 'bazel-out' folder found in path '${PWD}'" >&2
+        exit 1
+    fi
+    EXECROOT="${PWD:0:$index}"
+else
+    # We are in execroot or in some other context all or a manually run oci_tarball.
+    EXECROOT="${PWD}"
+fi
+
+
 "$CONTAINER_CLI" load --input <(
-    {{TAR}} --create --no-xattr --no-mac-metadata @"{{mtree_path}}"
+    {{TAR}} --cd "$EXECROOT" --create --no-xattr --no-mac-metadata @"{{mtree_path}}"
 )