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The clang-tidy packaged in ubuntu 20.04 (10.0.0) seems to be choking on a fairly simple block of code that involves structured bindings and move operations:

#include <memory>
#include <tuple>

struct T {
  ~T() {
    if(ptr != nullptr) { // clang-tidy is convinced ptr is uninitialized when the tuple is destroyed.

    }
  }

  T(T&& rhs) : ptr(rhs.ptr) {
    rhs.ptr = nullptr;
  }

  // Be very explicit for the sake of the MCVE.
  T() = default;
  T(const T&) = delete;
  T& operator=(T&&) = delete;
  T& operator=(const T&) = delete;

  int* ptr = nullptr;
};

std::tuple<T, T> foo();

void bar() {
  auto [a, b] = foo();

  T x = std::move(a);
  T y = std::move(b);
}

void baz() {
  auto a_b = foo();
  auto& a = std::get<0>(a_b);
  auto& b = std::get<1>(a_b);

  T x = std::move(a);
  T y = std::move(b);
}

Clang-tidy is flagging bar() with:

warning: The left operand of '!=' is a garbage value [clang-analyzer-core.UndefinedBinaryOperatorResult] if(ptr != nullptr) {

Whereas baz() is just fine.

I would rather not turn off that test altogether, and adding a NOLINT on that comparison line is... iffy at best, especially since it lives in an unrelated library. (as in the library has no idea these objects will end up in a tuple).

So my question is: Is there some way to fix this while keeping the structured binding? Or alternatively, is clang-tidy actually right here, and I am horribly misunderstanding how structured bindings work?

FWIW, clang-tidy is being invoked through cmake like so:

set(CMAKE_CXX_CLANG_TIDY clang-tidy;--format-style=file)
  • 2
    I think it's a bug. You can make this example even more [compact](https://cppinsights.io/lnk?code=I2luY2x1ZGUgPHR1cGxlPgoKc3RydWN0IFQgewogIH5UKCkgeyBpZiAocHRyKSB7fSB9CiAgYm9vbCBwdHIgPSB0cnVlOwp9OwoKaW50IG1haW4oKSB7CiAgYXV0byBbYSwgYl0gPSBzdGQ6OnR1cGxlPFQsIFQ+e307CiAgYi5wdHIgPSB0cnVlOwp9&insightsOptions=cpp17&std=cpp17&rev=1.0) and clang-tidy still fails. The link also shows that `baz` and `bar` are basically the same. – local-ninja Jul 04 '20 at 18:40
  • Well, yes... `baz()` is intentionally equivalent to demonstrate that it's specifically the use of the structured binding that confuses clang-tidy. –  Jul 05 '20 at 00:35

0 Answers0