Not possible to use both otelmetrichttp and otelmetricgrpc

[pellared]

FYI. it looks like its no longer possible to have both otelmetrichttp and otelmetricgrpc in the same binary. I'm not sure how common this is, but go.opentelemetry.io/contrib/exporters/autoexport is an example.

$ git clone https://github.com/open-telemetry/opentelemetry-go-contrib.git
$ cd opentelemetry-go-contrib/exporters/autoexport/
$ go get go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp@main
go: upgraded go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.25.0 => v1.25.1-0.20240422142149-b34cfc47c4e0
go: added go.opentelemetry.io/proto/slim/otlp v1.2.0
$ go get go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc@main
go: downloading go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.25.1-0.20240422142149-b34cfc47c4e0
go: upgraded go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.25.0 => v1.25.1-0.20240422142149-b34cfc47c4e0
$ go test ./...
panic: proto: file "opentelemetry/proto/common/v1/common.proto" is already registered
	previously from: "go.opentelemetry.io/proto/otlp/common/v1"
	currently from:  "go.opentelemetry.io/proto/slim/otlp/common/v1"
See https://protobuf.dev/reference/go/faq#namespace-conflict

Originally posted by @gregoryfranklin in #2579 (comment)

[pellared]

This has be double-check before making a new release as it can be a blocker.

[MrAlias]

Please coordinate with @XSAM who is working on #5250

[pellared]

Most probably we will have to revert these two PRs:

• otlpmetrichttp: Use go.opentelemetry.io/proto/slim/otlp #5222
• otlploghttp: Use go.opentelemetry.io/proto/slim/otlp #5216

@gregoryfranklin, thanks for reporting the issue ❤️

[XSAM]

I have checked the protobuf codes regarding this behavior. The implementation prevents importing go.opentelemetry.io/proto/otlp and go.opentelemetry.io/proto/slim at the same time.

https://github.com/protocolbuffers/protobuf-go/blob/e4ad8f9dfc8bc3184ebb70c296bd63955343e903/reflect/protoregistry/registry.go#L126-L133

Though we could use go build -ldflags "-X google.golang.org/protobuf/reflect/protoregistry.conflictPolicy=warn" to change the conflict policy and probably pass this check, it requires our end-users to do this, which is not acceptable.

Plan for the release

Rollback these two PRs:

• otlpmetrichttp: Use go.opentelemetry.io/proto/slim/otlp #5222
• otlploghttp: Use go.opentelemetry.io/proto/slim/otlp #5216

After the release

We might need to deprecate package go.opentelemetry.io/proto/slim, as it is not compatible with go.opentelemetry.io/proto/otlp, which provides grpc support. And it makes the package somewhat unusable.