Debugging protoc-gen-connect-go?

[guw]

I have a Bazel setup that is using the protoc-gen-connect-go as a plug-in in the go proto compiler. It currently fails but there is zero output.

Are there any docs or someone has a few tips how to get some output to see what is going on?

The setup was working but we need to change the Go dependencies. Thus, I suspect a missing dependency somewhere. But I don't get a good error message at all.

This is how the compiler is defined:

go_proto_compiler(
    name = "connect_go_proto_compiler",
    plugin = "@com_connectrpc_connect//cmd/protoc-gen-connect-go:protoc-gen-connect-go",
    suffix = ".connect.go",
    options = [
        # This is needed so that the package name for the connectrpc generated go file
        # matches the package name for the protoc generated go file.
        "package_suffix=",
    ],
    visibility = ["//visibility:public"],
    deps = ["@com_connectrpc_connect//:go_default_library"],
)

The error is:

ERROR: ...BUILD.bazel:3:18: Generating into bazel-out/.../foo failed: (Exit 1): go-protoc-bin failed: error executing GoProtocGen command (from target //foo:foo_connect_go_proto) 
...
foo
"bazel-out/.../foo/foo.connect.go" expected from plugin "bazel-out/.../protoc-gen-connect-go" but not created

From testing with an invalid options I do at least know the plug-in is properly called. I would get output such as:

protoc-gen-connect-go: no such flag -verbose
--connect-go_out: protoc-gen-connect-go: Plugin failed with status code 1.
2025/05/16 10:09:40 error running protoc: exit status 1

[sfc-gh-gwagenknecht]

I figured out what's causing the problem. rules_go seems to have enforcement in place to check whether something was actually generated.

This prevents generation for some proto files:

connect-go/cmd/protoc-gen-connect-go/main.go

Lines 141 to 143 in a34cd27

	if len(file.Services) == 0 {
	return
	}

Would it be worth to consider this an error?

[guw]

In a previous version rules_go would generate and empty file if a plug-in did not output anything. In version 0.54.0 this was broken.
bazel-contrib/rules_go#4317