proto_library for go requires `//third_party/go:protobuf` as dependency

[mateuszlewko]

I have the following rule for generating go from proto.

proto_library(
    name = "books_proto",
    srcs = ["books.proto"],
    labels = ["codegen"],
    languages = ["go"],
    visibility = ["PUBLIC"],
)

Building this rule correctly generates books.pb.go, however, building fails with the following error:

Build stopped after 60ms. 2 targets failed:
    //third_party/go:protobuf
Target //third_party/go:protobuf (referenced by //proto:_books_proto#go) doesn't exist
...
Couldn't find dependency //third_party/go:protobuf

I have protoc and protoc-gen-go installed and I don't have any custom configuration for proto or go rules. Do I have to add any rules to third_party/?

[peterebden]

Yep, you do. protoc and protoc-gen-go generate the code, //third_party/go;protobuf is a go_module that provides the google.golang.org/protobuf dependency for the generated code.

[mateuszlewko]

Thanks for quick response! I added the relevant rules:

go_mod_download(
    name = "protobuf_download",
    licences = ["BSD-3-Clause"],
    module = "github.com/golang/protobuf",
    version = "v1.5.2",
)

go_module(
    name = "protobuf",
    download = ":protobuf_download",
    exported_deps = [
        ":protobuf-go",
    ],
    install = ["..."],
    module = "github.com/golang/protobuf",
)

go_module(
    name = "protobuf-go",
    install = ["..."],
    module = "google.golang.org/protobuf",
    version = "v1.25.0",
    deps = [
        ":cmp",
    ],
)

go_module(
    name = "cmp",
    install = [
        "cmp/...",
    ],
    module = "github.com/google/go-cmp",
    version = "f144a35ed4ac538fae93fa3783175108738f71b9",
)

Unfortunately building "cmp" as a dependency fails with

Build stopped after 4.7s. 1 target failed: //third_party/go:_cmp#a_rule Error building target //third_party/go:_cmp#a_rule: exit status 1 find: /opt/homebrew/Cellar/go/1.18.1/libexec/pkg/darwin_amd64: No such file or directory

I'm on M1 Macbook. Any ideas how to fix / debug that?

[peterebden]

Hmmmm it's looking for darwin_amd64 and should be looking for darwin_arm64 on your machine (I assume that directory would exist). I'm not sure why it's doing that though.

What does plz query print //third_party/go:_cmp#a_rule produce?

[mateuszlewko]

Yes, the darwin_arm64 exists.

This is the output:

plz query print "//third_party/go:_cmp#a_rule"
# //third_party/go:_cmp#a_rule:
build_rule(
    name = '_cmp#a_rule',
    cmd = 'export GOPATH=$TMP_DIR && export GOROOT=$("$TOOLS_GO" env GOROOT) && find "$GOROOT"/pkg/darwin_amd64 -name "*.a" | sed -e s=^"$GOROOT"/pkg/darwin_amd64/== | sed -e s="\.a\$"== | xargs -I{} echo "packagefile {}="$GOROOT"/pkg/darwin_amd64/{}.a" | sort -u > goroot.importconfig && find . -name "*.importconfig" | xargs -I{} cat {} | sort -u >> importconfig && $TOOLS_PLEASE_GO install  --trim_path $TMP_DIR --src_root=$(location :_cmp#get) --module_name=github.com/google/go-cmp --importcfg=importconfig --go_tool=$TOOLS_GO --cc_tool=$TOOLS_CC --out=pkg/darwin_amd64 github.com/google/go-cmp/cmp/... && cat LD_FLAGS',
    srcs = ['//third_party/go:_cmp#get'],
    outs = ['pkg/darwin_amd64/github.com/google/go-cmp/cmp'],
    tools = {
        'cc': ['gcc'],
        'go': ['go'],
        'please_go': ['//_please:please_go'],
    },
    labels = [
        'link:plz-out/go',
        'go',
    ],
    building_description = 'Compiling...',
    needs_transitive_deps = True,
    build_timeout = 600,
    post_build = '<function _add_ld_flags>',
    requires = ['go'],
)

[peterebden]

Hmmmm right so it has picked up amd64 from somewhere; that should be coming from runtime.GOARCH, although it's a bit indirect.

Can you confirm whether this is actually the darwin_arm64 binary? I would expect it to have to be on an M1 but I'm not very familiar with them, wondering if there's some kind of emulation layer that could explain it...

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