"strict transitive dependency mode" not work ?

[daohu527]

Description of the bug:

Suppose there is the following dependency a->b->c, a contains the header file of c, but does not use anything, then a's build file depends on b, but not on c. Then this forms an implicit dependency, and bazel will not report a error!

What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

No response

Which operating system are you running Bazel on?

ubuntu 18.04

What is the output of bazel info release?

(11:37:20) INFO: Invocation ID: b93b0d49-edac-4215-9d9a-366bf997e477 release 3.7.1

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse master; git rev-parse HEAD ?

No response

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

No response

[sgowroji]

Hello @daohu527, Can you provide more details to reproduce the above problem. Thanks!

[daohu527]

I modified https://github.com/bazelbuild/examples/tree/main/cpp-tutorial/stage3 as an example.

as you see hello-world.cc contain lib/hello-time.h but no use it. and then hello-world deps on hello-greet, which deps on //lib:hello-time. In other words hello-world implicit deps on //lib:hello-time, but bazel will success build, which violates the strict transitive dependency mode.

additional, hello-world.cc use print_localtime will also success build.

cpp-tutorial/stage3/main/BUILD

load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library")

cc_library(
    name = "hello-greet",
    srcs = ["hello-greet.cc"],
    hdrs = ["hello-greet.h"],
    deps = [
        "//lib:hello-time",
    ],
)

cc_binary(
    name = "hello-world",
    srcs = ["hello-world.cc"],
    deps = [
        ":hello-greet",
    ],
)

cpp-tutorial/stage3/main/hello-world.cc

#include "lib/hello-time.h"
#include "main/hello-greet.h"
#include <iostream>
#include <string>

int main(int argc, char** argv) {
  std::string who = "world";
  if (argc > 1) {
    who = argv[1];
  }
  std::cout << get_greet(who) << std::endl;
  // print_localtime();
  return 0;
}

[fmeum]

Strict deps checking for C++ on that level of granularity requires passing the flag --features=layering_check as it may not work with all compilers. Does that give you the expected failure?

[daohu527]

yes, it thrown out an error like below.

main/hello-world.cc:1:10: error: module //main:hello-world does not depend on a module exporting 'lib/hello-time.h'
#include "lib/hello-time.h"

Then my question is, since bazel lets users use strict transitive dependency in best practice, why doesn't it check by default? link

[martis42]

@daohu527 This project of mine might be interesting for you: https://github.com/martis42/depend_on_what_you_use

It aims at linting the usage of headers in Bazel C++ targets compared to the targets dependency list.

It is still in an early phase, but maybe it can help you.

[daohu527]

@martis42 Thanks for your work, I will check out this project in detail !