How to find places where the rule is defined and which definition bazel uses in this specific package?
Say, I have gRPC installed and looking at grpc/examples/cpp/helloword/BUILD file. I can see a common rule for cpp builds: cc_binary. But this rule is not in grpc WORKSPACE file. Nor it in BUILD file. I do grep -rnw -e '"cc_binary"' and can't find it anywhere but /grpc/third_party/.. subdirectories. And this wouldn't make any sense for bazel to initiate this rule there.
I do finding the dependencies of a rule bazel query "deps(//examples/cpp/helloworld:cc_binary)" and strangely, it doesn't want to query the rules - only targets. I get:
ERROR: no such target '//examples/cpp/helloworld:cc_binary': target 'cc_binary' not declared in package 'examples/cpp/helloworld'
When I do bazel query 'kind(cc_binary, deps(//examples/cpp/helloworld:greeter_client))' I think I'm getting closer with this list:
//examples/cpp/helloworld:greeter_client @upb//upbc:protoc-gen-upbdefs @upb//upbc:protoc-gen-upb @com_google_protobuf//:protoc //src/compiler:grpc_cpp_plugin @bazel_tools//third_party/def_parser:def_parser
But how can it help me? Is there a way to do it?
In general, query --output=build will emit a comment indicating where a target's rule class is defined:
$ bazel query --output build //src/proto/grpc/core:stats_py_pb2
py_proto_library(
name = "stats_py_pb2",
deps = ["//src/proto/grpc/core:stats_descriptor"],
)
# Rule stats_py_pb2 instantiated at (most recent call last):
# grpc/src/proto/grpc/core/BUILD:35:17 in <toplevel>
# Rule py_proto_library defined at (most recent call last):
# grpc/bazel/python_rules.bzl:154:24 in <toplevel>
cc_binary is a builtin rule, implemented in Java within Bazel. Therefore, Bazel cannot provide a Starlark source for its definition:
$ bazel query --output build //examples/cpp/helloworld:greeter_client
cc_binary(
name = "greeter_client",
deps = ["//:grpc++", "//examples/protos:helloworld_cc_grpc"],
defines = ["BAZEL_BUILD"],
srcs = ["//examples/cpp/helloworld:greeter_client.cc"],
)
# Rule greeter_client instantiated at (most recent call last):
# grpc/examples/cpp/helloworld/BUILD:17:10 in <toplevel>