How to get bazel genrule to access transitive dependencies? - bazel

Question

I have the following in a BUILD file:
proto_library(
name = "proto_default_library",
srcs = glob(["*.proto"]),
visibility = ["//visibility:public"],
deps = [
"#go_googleapis//google/api:annotations_proto",
"#grpc_ecosystem_grpc_gateway//protoc-gen-openapiv2/options:options_proto",
],
)
genrule(
name = "generate-buf-image",
srcs = [
":buf_yaml",
":buf_breaking_image_json",
":protos",
],
exec_tools = [
":proto_default_library",
"//buf:generate-buf-image-sh",
"//buf:generate-buf-image",
],
outs = ["buf-image.json"],
cmd = "$(location //buf:generate-buf-image-sh) --buf-breaking-image-json=$(location :buf_breaking_image_json) $(location :protos) >$#",
)
While executing $(location //buf:generate-buf-image-sh), glob(["*.proto"]) of proto_default_library can be seen in the sandbox but the proto files of #go_googleapis//google/api:annotations_proto and #grpc_ecosystem_grpc_gateway//protoc-gen-openapiv2/options:options_proto cannot. The same goes for the dependencies of //buf:generate-buf-image-sh.
Do I need to explicitly list out all transitive dependencies so they can be processed by generate-buf-image? Is there a programmatic way to do that?

Answer 1

Since genrules are pretty generic, a genrule sees only the default provider of a target, which usually just has the main outputs of that target (e.g., for java_library, a jar of the classes of that library, for proto_library, the proto files of that library). So to get more detailed information, you would write a Starlark rule to access more specific providers. For example:
WORKSPACE:
load("#bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
http_archive(
name = "rules_proto",
sha256 = "66bfdf8782796239d3875d37e7de19b1d94301e8972b3cbd2446b332429b4df1",
strip_prefix = "rules_proto-4.0.0",
urls = [
"https://mirror.bazel.build/github.com/bazelbuild/rules_proto/archive/refs/tags/4.0.0.tar.gz",
"https://github.com/bazelbuild/rules_proto/archive/refs/tags/4.0.0.tar.gz",
],
)
load("#rules_proto//proto:repositories.bzl", "rules_proto_dependencies", "rules_proto_toolchains")
rules_proto_dependencies()
rules_proto_toolchains()
defs.bzl:
def _my_rule_impl(ctx):
output = ctx.actions.declare_file(ctx.attr.name + ".txt")
args = ctx.actions.args()
args.add(output)
inputs = []
for src in ctx.attr.srcs:
proto_files = src[ProtoInfo].transitive_sources
args.add_all(proto_files)
inputs.append(proto_files)
ctx.actions.run(
inputs = depset(transitive = inputs),
executable = ctx.attr._tool.files_to_run,
arguments = [args],
outputs = [output],
)
return DefaultInfo(files = depset([output]))
my_rule = rule(
implementation = _my_rule_impl,
attrs = {
"srcs": attr.label_list(providers=[ProtoInfo]),
"_tool": attr.label(default = "//:tool"),
},
)
ProtoInfo is here: https://bazel.build/rules/lib/ProtoInfo
BUILD:
load(":defs.bzl", "my_rule")
proto_library(
name = "proto_a",
srcs = ["proto_a.proto"],
deps = [":proto_b"],
)
proto_library(
name = "proto_b",
srcs = ["proto_b.proto"],
deps = [":proto_c"],
)
proto_library(
name = "proto_c",
srcs = ["proto_c.proto"],
)
my_rule(
name = "foo",
srcs = [":proto_a"],
)
sh_binary(
name = "tool",
srcs = ["tool.sh"],
)
proto_a.proto:
package my_protos_a;
message ProtoA {
optional int32 a = 1;
}
proto_b.proto:
package my_protos_b;
message ProtoB {
optional int32 b = 1;
}
proto_c.proto:
package my_protos_c;
message ProtoC {
optional int32 c = 1;
}
tool.sh:
output=$1
shift
echo input protos: $# > $output
$ bazel build foo
INFO: Analyzed target //:foo (40 packages loaded, 172 targets configured).
INFO: Found 1 target...
Target //:foo up-to-date:
bazel-bin/foo.txt
INFO: Elapsed time: 0.832s, Critical Path: 0.02s
INFO: 5 processes: 4 internal, 1 linux-sandbox.
INFO: Build completed successfully, 5 total actions
$ cat bazel-bin/foo.txt
input protos: proto_a.proto proto_b.proto proto_c.proto