[clang-tidy] Check request: bugprone-avoid-dangling-in-std-filesystem

[denzor200]

Needs a check that will find usage of invalidated references to something that was owned by std::filesystem::directory_iterator before the invalidation. Since std::filesystem::directory_iterator's increment has to invalidate all copies of the previous value of *this(look at https://en.cppreference.com/w/cpp/filesystem/directory_iterator/increment ), this check will suggest to make a copy instead of taking a reference.

BEFORE

namespace fs = std::filesystem;
fs::directory_iterator it("sandbox");
fs::directory_iterator end;
while (it != end) {
    const fs::directory_entry& dir_entry = *it;
    const fs::path& dir_path = it->path();
    ++it;
    std::cout << dir_entry;                         // UB
    std::cout << " (" << dir_path << ")" << '\n';   // UB
}

AFTER

namespace fs = std::filesystem;
fs::directory_iterator it("sandbox");
fs::directory_iterator end;
while (it != end) {
    const fs::directory_entry dir_entry = *it;
    const fs::path dir_path = it->path();
    ++it;
    std::cout << dir_entry;
    std::cout << " (" << dir_path << ")" << '\n';
}

https://godbolt.org/z/3Wzoq4rP4

All of the above applies to std::filesystem::recursive_directory_iterator as well.

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: Denis Mikhailov (denzor200)

Needs a check that will find usage of invalidated references to something that was owned by std::filesystem::directory_iterator before the invalidation. Since std::filesystem::directory_iterator's increment has to invalidate all copies of the previous value of *this(look at https://en.cppreference.com/w/cpp/filesystem/directory_iterator/increment ), this check will suggest to make a copy instead of taking a reference.

BEFORE

namespace fs = std::filesystem;
fs::directory_iterator it("sandbox");
fs::directory_iterator end;
while (it != end) {
    const fs::directory_entry& dir_entry = *it;
    const fs::path& dir_path = it->path();
    ++it;
    std::cout << dir_entry;                         // UB
    std::cout << " (" << dir_path << ")" << '\n';   // UB
}

AFTER

namespace fs = std::filesystem;
fs::directory_iterator it("sandbox");
fs::directory_iterator end;
while (it != end) {
    const fs::directory_entry dir_entry = *it;
    const fs::path dir_path = it->path();
    ++it;
    std::cout << dir_entry;
    std::cout << " (" << dir_path << ")" << '\n';
}

https://godbolt.org/z/3Wzoq4rP4

All of the above applies to std::filesystem::recursive_directory_iterator as well.