Protobuf with Rust and Bazel

Berend Lange

unread,

Nov 3, 2025, 7:59:02 AM 11/3/25

to Protocol Buffers

The v4 version of protobuf does not compile with bazel unless its running with `--spawn-strategy=standalone` or `--spawn-strategy=local`.

see repo

https://github.com/berendjan/rust-bazel-starter.git

This be easily reproduced with MODULE.bazel
```
"""Rust-Temp"""

module(
name = "rust-temp",
version = "0.0.0",
)

bazel_dep(name = "rules_rust", version = "0.67.0") # https://github.com/bazelbuild/rules_rust/releases

crate = use_extension("@rules_rust//crate_universe:extensions.bzl", "crate")

crate.spec(package = "protobuf", version = "4.32.0-release")
crate.from_specs()
use_repo(crate, "crates")
```

BUILD.bazel
```
load("@rules_rust//rust:defs.bzl", "rust_binary")

rust_binary(
name = "test",
srcs = glob(["**/*.rs"]),
deps = [
"@crates//:protobuf",
],
)
```

main.rs
```rust

pub fn main () {

println ! ( "hello world" );

}

```

The error emitted:

```
ERROR: /home/berend/.cache/bazel/_bazel_berend/6b2aa4fe5e02f6a12410110ed2ccd580/external/rules_rust++crate+crates__protobuf-4.32.0-release/BUILD.bazel:27:13: Compiling Rust rlib protobuf v4.32.0-release (20 files) failed: (Exit 1): process_wrapper failed: error executing Rustc command (from target @@rules_rust++crate+crates__protobuf-4.32.0-release//:protobuf) bazel-out/k8-opt-exec-ST-d57f47055a04/bin/external/rules_rust+/util/process_wrapper/process_wrapper --env-file ... (remaining 35 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
error: couldn't read `external/rules_rust++crate+crates__protobuf-4.32.0-release/src/upb/lib.rs`: No such file or directory (os error 2)
--> external/rules_rust++crate+crates__protobuf-4.32.0-release/src/shared.rs:75:1
|
75 | mod upb;
| ^^^^^^^^

error: aborting due to 1 previous error

Target //:test failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 69.621s, Critical Path: 40.24s
INFO: 223 processes: 17 action cache hit, 134 internal, 89 linux-sandbox.
ERROR: Build did NOT complete successfully
```

Em Rauch

unread,

Nov 3, 2025, 8:06:17 AM 11/3/25

to Berend Lange, Protocol Buffers

Thanks for raising this. Do you mind opening an issue on github to triage/discuss?

Broadly we have test coverage running for two cases: bazel where you use proto_library and cargo where you use the cratesio crate. The two have a number of differences, most relevantly that when using bazel targets small / fine-grained crates are a good idea for build hygiene, whereas with cargo/cratesio comparatively 'fat' crates are the norm.

Just from the error message, it is possible that what you are hitting might stem from the fact that in our normal bazel build upb is a separate crate, but in the cratesio build it is just a mod within the same crate instead. _Though_ maybe thats a red herring.

(Just because you sent a separate 'test' message, FYI this list has to be moderated because of spam problems, so there's some delay between sending and the email going through for the moderation process to happen).

--
You received this message because you are subscribed to the Google Groups "Protocol Buffers" group.
To unsubscribe from this group and stop receiving emails from it, send an email to protobuf+u...@googlegroups.com .
To view this discussion visit https://groups.google.com/d/msgid/protobuf/1f369855-f6aa-4a47-b106-33126cd771d0n%40googlegroups.com .

Berend Lange

unread,

Nov 3, 2025, 9:34:32 AM 11/3/25

to Protocol Buffers

I opened an issue on github .
I was trying to use the new protoc-gen-rust-grpc plugin in bazel, should i be using a different setup with protobuf and udp imported as bazel rules? Is there an example available online?

Reply all

Reply to author

Forward