Treat warnings as errors but ignore warnings in googletest

Question

I have a C++ project where I want to use the -Wsign-conversion compile option. As build tool Bazel 0.28.1 is used. My self-written code does not generate warning of that type. The project uses Googletest. Unfortunately, Googletest generates this kind of warning, which breaks my build. Here are my files:

.bazelrc

build --cxxopt=-Werror           # Every warning is treated as an error.
build --cxxopt=-std=c++14
build --cxxopt=-Wsign-conversion # Warn for implicit conversions that may change the sign of an integer value

gtest.BUILD

cc_library(
    name = "main",
    srcs = glob(
        ["src/*.cc"],
        exclude = ["src/gtest-all.cc"]
    ),
    hdrs = glob([
        "include/**/*.h",
        "src/*.h"
    ]),
    copts = ["-Iexternal/gtest/include"],
    linkopts = ["-pthread"],
    visibility = ["//visibility:public"],
)

WORKSPACE

workspace(name = "GTestDemo")

load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")

git_repository(
    name = "googletest",
    remote = "https://github.com/google/googletest",
    #tag = "release-1.8.1",
    commit = "2fe3bd994b3189899d93f1d5a881e725e046fdc2", 
    shallow_since = "1535728917 -0400",
)

BUILD

cc_test(
    name = "tests",
    srcs = ["test.cpp"],
    copts = ["-Iexternal/gtest/include"],
    deps = [
            "@googletest//:gtest_main",
        ],
)

test.cpp

#include <iostream>

#include "gtest/gtest.h"

TEST(sample_test_case, sample_test)
{
    EXPECT_EQ(1, 1);
}

When I try to build the code the following error is shown:

Starting local Bazel server and connecting to it...
INFO: Analyzed target //:tests (21 packages loaded, 540 targets configured).
INFO: Found 1 target...
INFO: Deleting stale sandbox base /mnt/ramdisk/bazel-sandbox.be60b2910864108c1e29c6fce8ad6ea4
ERROR: /home/admin/.cache/bazel/_bazel_admin/cc9b56275ffa85d1a0fca263d1d708e4/external/googletest/BUILD.bazel:55:1: C++ compilation of rule '@googletest//:gtest' failed (Exit 1) gcc failed: error executing command /usr/bin/gcc -U_FORTIFY_SOURCE -fstack-protector -Wall -Wunused-but-set-parameter -Wno-free-nonheap-object -fno-omit-frame-pointer '-std=c++0x' -MD -MF ... (remaining 36 argument(s) skipped)

Use --sandbox_debug to see verbose messages from the sandbox
external/googletest/googletest/src/gtest-filepath.cc: In member function 'testing::internal::FilePath testing::internal::FilePath::RemoveFileName() const':
external/googletest/googletest/src/gtest-filepath.cc:168:45: error: conversion to 'std::__cxx11::basic_string<char>::size_type {aka long unsigned int}' from 'long int' may change the sign of the result [-Werror=sign-conversion]
     dir = std::string(c_str(), last_sep + 1 - c_str());
                                ~~~~~~~~~~~~~^~~~~~~~~
cc1plus: all warnings being treated as errors
Target //:tests failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 7.225s, Critical Path: 0.66s
INFO: 0 processes.
FAILED: Build did NOT complete successfully

Is there a possibility in Bazel to ignore warnings in 3rd-party-library such as googletest?

Answer 1

This is more of a GCC question.

"System headers" are immune from this kind of thing :

-Wsystem-headers : Print warning messages for constructs found in system header files. Warnings from system headers are normally suppressed , on the assumption that they usually do not indicate real problems and would only make the compiler output harder to read.

So, you can just pretend that the 3rd-party lib is a system header, using GCC's -isystem flag (instead of -I ):

copts = ["-isystem external/gtest/include"],

Answer 2

Bazel's --per_file_copt allows setting flags for all files except ones matching some regular expression. Something more like this in your .bazelrc should do what you're looking for:

# Warn for implicit conversions that may change the sign of an integer value,
# for C++ files not in googletest
build --per_file_copt=.*\.(cc|cpp),-googletest/.*@-Wsign-conversion

You'll need to update that to match any extensions you use for C++ files other than .cc and .cpp. The documentation for cc_library.srcs lists all the extensions Bazel uses, for reference.

I couldn't figure out how to match @googletest// in the flag, because I don't see a way to escape an @ there... However, I'm pretty sure it's matching against @googletest and not external/googletest or something, because /googletest doesn't match anything. Probably won't matter, but it is something to keep in mind if you have any other filenames with googletest in them.