Use write_source_files for oak_proto_rust copying

Change-Id: Iae9925e366f1494f8380ec9ab1bbfc0e31fea593

justfile

@@ -220,9 +220,6 @@ clang-tidy:
 bare_metal_crates_query := "bazel query 'attr(\"tags\", \"ci-build-for-x86_64-unknown-none\", //...)' | tr '\\n' ' '"
 
 bazel-ci:
-    # Make sure the generated prost files have been copied to the correct place.
-    bazel run oak_proto_rust:verify_generated
-
     # Test Oak as a dependency in the test workspace
     # Some dependencies aren't properly exposed yet, so just testing a subset of targets
     cd bazel/test_workspace && CARGO_BAZEL_REPIN=1 bazel build --config=unsafe-fast-presubmit @oak2//micro_rpc @oak2//oak_grpc_utils @oak2//oak_proto_rust

oak_proto_rust/BUILD

@@ -14,6 +14,7 @@
 # limitations under the License.
 #
 
+load("@aspect_bazel_lib//lib:write_source_files.bzl", "write_source_files")
 load("@rules_rust//cargo:defs.bzl", "cargo_build_script")
 load("@rules_rust//rust:defs.bzl", "rust_library")
 
@@ -87,20 +88,11 @@ cargo_build_script(
     ],
 )
 
-sh_binary(
-    name = "copy_generated",
-    srcs = [":copy_generated.sh"],
-    data = [
-        ":build",
-        ":oak_proto_rust",
-    ],
-)
-
-sh_binary(
-    name = "verify_generated",
-    srcs = [":verify_generated.sh"],
-    data = [
-        ":build",
-        ":oak_proto_rust",
-    ],
+# Prost build tools aren't available internally, so we copy the generated files
+# into the source tree for easy import. See README.md for more details.
+write_source_files(
+    name = "copy_generated_files",
+    files = {
+        "generated": "//oak_proto_rust:build",
+    },
 )

oak_proto_rust/README.md

@@ -11,13 +11,12 @@ This library is imported into some environments where Prost and/or build scripts
 are not available. To support building our Rust targets in these environmnets,
 we also include pre-generated Prost Rust code in the `generated` directory.
 
-A presubmit job will run the `oak_proto_rust:verify_generated` target to verify
-that all generated code also exists in the `generated` directory.
+The bazel `write_source_files` helps us with this. It creates a rule for copying
+the generated files, as well as a rule that verifies that they exist in the
+right place.
 
 If proto changes are made, you should run:
+`bazel run oak_proto_rust:copy_generated_files`
 
-`bazel run oak_proto_rust:copy_generated`
-
-to copy any added/modified files. Not that the script will not cover any
-_removed_ files, so take care to clean up any uneeded files if protos are
-removed at some point.
+If you forget, your presubmit will fail, with a message telling you to run that
+command.