Gazelle unable to build otel-collector

[NotANormalNerd]

Hey everyone.

we have the need to build an otel-collector with the following build-config.yaml

# All components:
# https://github.com/open-telemetry/opentelemetry-collector-releases/blob/main/distributions/otelcol-contrib/manifest.yaml
dist:
  name: otel-collector
  description: OTel Collector
extensions:
  - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/extension/basicauthextension v0.131.0
receivers:
  - gomod: go.opentelemetry.io/collector/receiver/otlpreceiver v0.131.0
  - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/receiver/prometheusreceiver v0.131.0
processors:
  - gomod: go.opentelemetry.io/collector/processor/batchprocessor v0.131.0
  - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/processor/transformprocessor v0.131.0
exporters:
  - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/exporter/fileexporter v0.131.0
  - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/exporter/syslogexporter v0.131.0
  - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/exporter/clickhouseexporter v0.131.0
  - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/exporter/rabbitmqexporter v0.131.0

This is our BUILD file

load("@rules_go//go:def.bzl", "go_binary", "go_library")

genrule(
    name = "get_go_modules",
    srcs = [
        "@otel_collector_custom_builder//file",
        ":builder-config.yaml",
    ],
    outs = [
        "components.go",
        "go.mod",
        "main.go",
        "main_others.go",
        # "go.sum",  # would be created with the ocbbuilder when omitting --skip-get-modules but this does not work within the sandbox
        # "main_windows.go",  # most likely only needed for Windows
    ],
    cmd = """
       $(location @otel_collector_custom_builder//file) \
           --skip-get-modules \
           --skip-compilation \
           --output-path $(RULEDIR) \
           --config $(location builder-config.yaml)
    """,
    visibility = ["//visibility:public"],
)

go_binary(
    name = "otelcol",
    embed = [":otel-collector_lib"],
    visibility = ["//visibility:public"],
)

go_library(
    name = "otel-collector_lib",
    srcs = [
        "components.go",
        "main.go",
        "main_others.go",
    ],
    importpath = "go.opentelemetry.io/collector/cmd/builder/non-free/packages/otel-collector",
    visibility = ["//visibility:private"],
    deps = [
        "@com_github_open_telemetry_opentelemetry_collector_contrib_exporter_clickhouseexporter//:clickhouseexporter",
        "@com_github_open_telemetry_opentelemetry_collector_contrib_exporter_fileexporter//:fileexporter",
        "@com_github_open_telemetry_opentelemetry_collector_contrib_exporter_syslogexporter//:syslogexporter",
        "@com_github_open_telemetry_opentelemetry_collector_contrib_extension_basicauthextension//:basicauthextension",
        "@com_github_open_telemetry_opentelemetry_collector_contrib_processor_transformprocessor//:transformprocessor",
        "@com_github_open_telemetry_opentelemetry_collector_contrib_receiver_prometheusreceiver//:prometheusreceiver",
        "@io_opentelemetry_go_collector_component//:component",
        "@io_opentelemetry_go_collector_confmap//:confmap",
        "@io_opentelemetry_go_collector_confmap_provider_envprovider//:envprovider",
        "@io_opentelemetry_go_collector_confmap_provider_fileprovider//:fileprovider",
        "@io_opentelemetry_go_collector_confmap_provider_httpprovider//:httpprovider",
        "@io_opentelemetry_go_collector_confmap_provider_httpsprovider//:httpsprovider",
        "@io_opentelemetry_go_collector_confmap_provider_yamlprovider//:yamlprovider",
        "@io_opentelemetry_go_collector_connector//:connector",
        "@io_opentelemetry_go_collector_exporter//:exporter",
        "@io_opentelemetry_go_collector_extension//:extension",
        "@io_opentelemetry_go_collector_otelcol//:otelcol",
        "@io_opentelemetry_go_collector_processor//:processor",
        "@io_opentelemetry_go_collector_processor_batchprocessor//:batchprocessor",
        "@io_opentelemetry_go_collector_receiver//:receiver",
        "@io_opentelemetry_go_collector_receiver_otlpreceiver//:otlpreceiver",
    ],
)

The rest of the setup is pretty much public on https://github.com/Checkmk/checkmk/tree/master
Like: https://github.com/Checkmk/checkmk/blob/master/bazel/module/gazelle/go.MODULE.bazel

Trying to get this to work is like playing whack a mole. Adding another exporter or other dependency is nearly impossible without having absolute knowledge of go, bazel and gazelle, which I don't.

I would absolutely appreciate if someone could try helping me get this to work or provide some pointers.

[NotANormalNerd]

➜  otel-collector git:(otel/rabbitmq) ✗ bazel run @rules_go//go -- mod tidy -v 
INFO: Invocation ID: 4cfd11d9-4414-445d-a6c5-8005f29d6681
ERROR: /home/dennisschmalacker/.cache/bazel/_bazel_dennisschmalacker/19e564b0c5ebacf463295f111f7c198f/external/gazelle+/internal/bzlmod/go_deps.bzl:112:13: Traceback (most recent call last):
	File "/home/dennisschmalacker/.cache/bazel/_bazel_dennisschmalacker/19e564b0c5ebacf463295f111f7c198f/external/gazelle+/internal/bzlmod/go_deps.bzl", line 531, column 33, in _go_deps_impl
		_fail_on_unmatched_overrides(gazelle_overrides.keys(), module_resolutions, "gazelle_overrides")
	File "/home/dennisschmalacker/.cache/bazel/_bazel_dennisschmalacker/19e564b0c5ebacf463295f111f7c198f/external/gazelle+/internal/bzlmod/go_deps.bzl", line 112, column 13, in _fail_on_unmatched_overrides
		fail("Some {} did not target a Go module with a matching path: {}".format(
Error in fail: Some gazelle_overrides did not target a Go module with a matching path: github.com/prometheus/prometheus, go.opentelemetry.io/collector/pdata/xpdata, go.opentelemetry.io/collector/exporter, github.com/cncf/xds/go
ERROR: Analysis of target '@@rules_go+//go:go' failed; build aborted: error evaluating module extension @@gazelle+//:extensions.bzl%go_deps
INFO: Elapsed time: 0.176s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
ERROR: Build did NOT complete successfully
ERROR: Build failed. Not running target

Also there is a amazing cyclical dependency where I can't run mod tidy to create the go.sum, because it needs gazelle, but gazelle won't run because it needs the overwrites to be in go.sum.
Please, for the love of god, tell me we have some wrong configuration somewhere and it is not actually gazelle to blame here.

[NotANormalNerd]

Coming back to this.

It should be possible to build a project like Open Telemetry Collector in Bazel/Gazelle, without as much hassle as it is now.

https://opentelemetry.io/docs/collector/custom-collector/ Opentelemetry offers a command line program that will build the collector binary for you, without any hiccups.

So doing that manually should not be more work than using the cli program.

ocb --skip-compilation --skip-get-modules --config builder.config to generate the go.files from the config should be enough to create the binary in Bazel. (Without having to gazelle_override a bunch of dependencies.)

[dzbarsky]

I've been building otel collector in bazel just fine for years. I do it by manually maintaining the code generated by the OCB. I don't think trying to make OCB itself work is worth the effort, because you still need to handwrite build targets that assume what the generated code will look like

[NotANormalNerd]

I do it by manually maintaining the code generated by the OCB

Exactly what I want to avoid. I am not a go developer. I have no clue of how go works, how it compiles, what the ecosystem is.
I am a simple man: Here is my go files, that were bestowed upon me by business requirements and there is my build system that is bestowed upon me by our devops team.

I don't understand why gazelle_overrides need to be existing in the first place and why they are such as hassle for (what seems to me) like a straightforward thing like this.
Compiling a go program in bazel should not be more hassle than compiling it by hand, which right now, it is.

[dzbarsky]

I agree that the gazelle overrides are unfortunate. I recommend setting things up like so:

# This maps more closely to how vanilla go pulls in modules.
# See https://github.com/bazelbuild/bazel-gazelle/pull/1888
go_deps.gazelle_default_attributes(
    build_file_generation = "clean",
    directives = [
        "gazelle:proto disable",
    ],
)

This really should be the default behavior for gazelle and there is now consensus among the maintainers to change this in an upcoming major version bump.

Beyond that, the issue you are likely fighting is that since your Go sources are generated on the fly, Gazelle is unable to read them to generate your BUILD rules, so you probably have to tweak things by hand. You are really going against the grain of how the tooling is designed to be used. When you venture off the golden path, I think it's reasonable for you to need to invest a bit of time into understanding how the tooling works at a bit of a deeper level.

As I recommended above, if you want an easy experience, I highly recommend running the OCB binary outside Bazel, and committing the sources. Then you can just bazel run //:gazelle && go mod tidy && bazel mod tidy and let the tools do all the work. Here's an example I whipped up with your config. Hopefully it should be pretty clear how to evolve components.go to add new dependencies as needed, even if you don't know Go. But if that's too challenging, you can always re-run OCB or even ask an LLM to update the generated code for you :)

Compiling a go program in bazel should not be more hassle than compiling it by hand, which right now, it is.
The native Go tooling is really really good (and inspired by Bazel) so it's not surprising that wrapping it in Bazel is a slightly worse experience. But just to spell out the obvious, you're not just compiling a go program - you are compiling a code generator to emit source code, with dependencies that are unknown to the build system at runtime, and then trying to compile that generated code. I don't think Go native tooling can even do this in a single command, so you're really comparing apples and oranges.