Fixed errors with non-absolute labels

[UebelAndre]

This fixes the following errors when building post #1159

Repository rule http_archive defined at:
  /private/var/tmp/_bazel_user/c4900dc498759a5aae30fdfe5c69c114/external/bazel_tools/tools/build_defs/repo/http.bzl:336:31: in <toplevel>
ERROR: Analysis of target '//docs:cargo_bazel_rustdoc' failed; build aborted: no such package 'rust/settings': BUILD file not found in any of the following directories. Add a BUILD file to a directory to mark it as a package.
 - /Users/user/Code/cargo-bazel/rust/settings

[UebelAndre]

#1159 (comment)

Bisected to this commit, when trying to upgrade rules_rust. This triggered the following error for me:

    //proto/protobuf:protobuf_prost_generated (782077f4a782b271e6081e5d253d233307fbb065ebd24cbeda52275882be7e2c)
    //tools/prostgen:prostgen (ad7becf1f627c98f4c44ac49f5991ab41aa98662628ab4c26b029d7fb1035392)
.-> @rules_rust//util/process_wrapper:process_wrapper (ad7becf1f627c98f4c44ac49f5991ab41aa98662628ab4c26b029d7fb1035392)
|   @rules_rust//util/process_wrapper:process_wrapper_impl (ad7becf1f627c98f4c44ac49f5991ab41aa98662628ab4c26b029d7fb1035392)
|   @rules_rust//util/process_wrapper:process_wrapper_bin (ad7becf1f627c98f4c44ac49f5991ab41aa98662628ab4c26b029d7fb1035392)
`-- @rules_rust//util/process_wrapper:process_wrapper (ad7becf1f627c98f4c44ac49f5991ab41aa98662628ab4c26b029d7fb1035392)

Where the protobuf:protobuf_prost_generated target depends on the prostgen tool. This was in the host configuration. If I switched that to the exec configuration, the error went away, but it does seem like there's potentially a problem for rules that expected to be run on host.

This is also impacting this PR: https://buildkite.com/bazel/rules-rust-rustlang/builds/5643#51bcff38-d1a6-48ce-bad2-7b660b8b63a5

(19:03:32) ERROR: /workdir/util/process_wrapper/BUILD.bazel:37:12: in rust_binary rule //util/process_wrapper:process_wrapper_bin: cycle in dependency graph:
    //cargo/cargo_build_script_runner:bin_test
    //cargo/cargo_build_script_runner:cargo_build_script_runner
    //cargo/cargo_build_script_runner:cargo_build_script_output_parser
    //util/process_wrapper:process_wrapper
    //util/process_wrapper:process_wrapper_impl
.-> //util/process_wrapper:process_wrapper_bin
|   //util/process_wrapper:process_wrapper
|   //util/process_wrapper:process_wrapper_impl
`-- //util/process_wrapper:process_wrapper_bin

[UebelAndre]

@dfreese do you have a solution to the error in #1185 (comment) ?

[dfreese]

@dfreese do you have a solution to the error in #1185 (comment) ?

nothing concrete beyond what I mentioned in that initial comment, which I don't think directly translates. I'm trying to work on a minimally reproducible test case, but was running into the issue this PR addresses.

[dfreese]

@UebelAndre this is the smallest test case I could get that demonstrates the failure.

BUILD:

load("@rules_cc//cc:defs.bzl", "cc_test")
load("@rules_rust//rust:defs.bzl", "rust_binary", "rust_library", "rust_test")

package(default_visibility = ["//visibility:private"])

# Passes
# cc_binary(
#     name = "code_generation",
#     srcs = ["code_generation.cc"],
# )
# Fails
rust_binary(
    name = "code_generation",
    srcs = ["code_generation.rs"],
)

genrule(
    name = "generated",
    srcs = [],
    outs = ["generated.h"],
    cmd = "$(location :code_generation) > $@",
    # Irrelevant to the failure, but checked both with and without.
    stamp = True,
    tools = [":code_generation"],
)

cc_test(
    name = "test_value",
    srcs = [
        "generated.h",
        "test_value.cc",
    ],
    visibility = ["//visibility:public"],
)

code_generation.rs:

fn main() {
    println!("constexpr int kTestValue = 42;");
}

code_generation.cc:

#include <iostream>

int main() {
  std::cout << "constexpr int kTestValue = 42;" << std::endl;
  return 0;
}

test_value.cc:

#include "generated.h"
int main() { return kTestValue == 42 ? 0 : 1; }

# load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

# Updated 2022-03-11.  Main last updated 2022-03-11.
# http_archive(
#     name = "rules_rust",
#     sha256 = "ba638848794ff0698425e23f3cdc7c1c3cd3c1911fda720c80accbef4f0a48b6",
#     strip_prefix = "rules_rust-5e6ad9f638b5334a70ee914b63f080140020b3c4",
#     urls = [
#         "https://github.com/bazelbuild/rules_rust/archive/5e6ad9f638b5334a70ee914b63f080140020b3c4.tar.gz",
#     ],
# )

# Local repository applying PR #1185 
local_repository(
    name = "rules_rust",
    path = "../rules_rust",
)

load("@rules_rust//rust:repositories.bzl", "rules_rust_dependencies", "rust_register_toolchains")

rules_rust_dependencies()

rust_register_toolchains()

With that I see the following error. It looks the same on version 4.0.0 and 4.2.1.

someone@somewhere:~/cycle_example$ bazel-5.0.0 test //...
ERROR: /home/viz/.cache/bazel/_bazel_viz/1e97f2cc96b4e28933552bb1116a0892/external/rules_rust/util/process_wrapper/BUILD.bazel:7:6: in alias rule @rules_rust//util/process_wrapper:process_wrapper: cycle in dependency graph:
    //:generated (28ff57593ba01d914893f9cd455c859110ce813ccf3771961541220915f453dc)
    //:code_generation (ad7becf1f627c98f4c44ac49f5991ab41aa98662628ab4c26b029d7fb1035392)
.-> @rules_rust//util/process_wrapper:process_wrapper (ad7becf1f627c98f4c44ac49f5991ab41aa98662628ab4c26b029d7fb1035392)
|   @rules_rust//util/process_wrapper:process_wrapper_impl (ad7becf1f627c98f4c44ac49f5991ab41aa98662628ab4c26b029d7fb1035392)
|   @rules_rust//util/process_wrapper:process_wrapper_bin (ad7becf1f627c98f4c44ac49f5991ab41aa98662628ab4c26b029d7fb1035392)
`-- @rules_rust//util/process_wrapper:process_wrapper (ad7becf1f627c98f4c44ac49f5991ab41aa98662628ab4c26b029d7fb1035392)
ERROR: Analysis of target '//:generated' failed; build aborted
INFO: Elapsed time: 0.258s
INFO: 0 processes.
FAILED: Build did NOT complete successfully (1 packages loaded, 3 targets configured)
FAILED: Build did NOT complete successfully (1 packages loaded, 3 targets configured)

[dfreese]

I put together this #1187, which fixes both problems, I think.

[UebelAndre]

This change was addressed by #1187