Rely on baze make variable location to find protobuf include paths.

Similar change was applied to oak_proto_rust.

The current approach assumes that protobuf is included under com_google_protobuf.
However, that might not be always the case as it might be protobuf~ if included from MODULE.bazel
or protobuf if included from WORKSPACE.

This change would allow repositories depending on `oak` not rename the imports.

Bug: b/344012112
Change-Id: I4bd43ca5dc236645e93e927c4771d3222cae3522

oak_containers_orchestrator/BUILD

@@ -92,6 +92,7 @@ cargo_build_script(
     ],
     build_script_env = {
         "PROTOC": "$(execpath @com_google_protobuf//:protoc)",
+        "DESCRIPTOR_PROTO_PATH": "$(location @com_google_protobuf//:descriptor_proto_srcs)",
     },
     crate_features = ["bazel"],
     data = [
@@ -100,7 +101,9 @@ cargo_build_script(
         "//proto/containers:orchestrator_crypto_proto",
         "//proto/key_provisioning:key_provisioning_proto",
         "//proto/session:messages_proto",
+        "@com_google_protobuf//:descriptor_proto_srcs",
         "@com_google_protobuf//:protoc",
+        "@com_google_protobuf//:well_known_type_protos",
     ],
     deps = [
         "//oak_grpc_utils",

oak_containers_orchestrator/build.rs

@@ -13,8 +13,38 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::path::PathBuf;
+
 use oak_grpc_utils::{generate_grpc_code, CodegenOptions};
 
+#[cfg(feature = "bazel")]
+fn get_included_protos() -> Vec<PathBuf> {
+    // The root of all Oak protos
+    let oak_proto_root = PathBuf::from("..");
+    // Rely on bazel make variable `location` to find protobuf include paths.
+    // We do this as protobuf might be imported under different names in the
+    // external directory based on the setup (BzlMod, WORKSPACE or others).
+    // Possible names are: com_google_protobuf, protobuf~, and protobuf.
+    // The goal is to allow dependent repositories to use this
+    // library without renaming their explicit import of protobuf library.
+    let protobuf_include_path = PathBuf::from(
+        std::env::var("DESCRIPTOR_PROTO_PATH")
+            .unwrap()
+            .replace("google/protobuf/descriptor.proto", ""),
+    );
+    vec![oak_proto_root, protobuf_include_path]
+}
+
+#[cfg(not(feature = "bazel"))]
+fn get_included_protos() -> Vec<PathBuf> {
+    // The root of all Oak protos, relative to this directory.
+    let oak_proto_root = PathBuf::from("..");
+
+    // In cargo mode, the protoc invocations already include the google
+    // protobufs, so we only need to provide the Oak proto root.
+    vec![oak_proto_root]
+}
+
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     // Generate gRPC code for Orchestrator services.
     generate_grpc_code(
@@ -28,13 +58,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
             "../proto/containers/hostlib_key_provisioning.proto",
             "../proto/session/messages.proto",
         ],
-        &[
-            "..",
-            // When building with Bazel, the build script doesn't automatically
-            // contain the information needed to find the well-known Google
-            // protos. So we need to include these paths here.
-            "../external/com_google_protobuf/src/google/protobuf/_virtual_imports/empty_proto",
-        ],
+        &get_included_protos(),
         CodegenOptions { build_server: true, build_client: true, ..Default::default() },
     )?;