<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/138732>138732</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang-tidy] Check request: modernize-use-std-tie-to-decompose-result
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang-tidy
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          denzor200
      </td>
    </tr>
</table>

<pre>
    Needs a check that will find creations of a tuple-like which was assigned from a returned value. The check will show warning to change it to use `std::tie`.
Also the check will provide fix-it in the case when it's possible to deduce names for future "tied" variables.

BEFORE:
```
iterator it;
bool succeed;
const auto results = mapping.try_emplace("hello!");      // WARNING AND FIX-IT
it = results.first;
succeed = results.second; // deduced 'it' and 'succeed'
```

AFTER:
```
iterator it;
bool succeed;
std::tie(it, succeed) = mapping.try_emplace("hello!"); // use 'it' and 'succeed'
```

The check will respect original order of default constructors, copy constructors, and assignment operators for a not built-in type and will not provide a fix-it that will broke the order - only warning will be emited:
```
const auto results = mapping.try_emplace("hello!"); // WARNING
const iterator& it = results.first; // only copy constructor being called
                                    // but with `std::tie` we would call default constructor, copy constructor and then assignment operator
const bool succeed = results.second;
```

Another example with a built-in type:
```
const auto pos = get_position(); // WARNING AND FIX-IT
const float x = pos.first;
const float y = pos.second;
```

Keep in mind that the check will not provide fix-it in the case when it's impossible to deduce names - just a warning would be enough:
```
const auto results = mapping.try_emplace("hello!");      // WARNING
if (results.second) {
    handle_inserted(results.first);
}
// no name deduced
```

In the case when it's impossible to use `std::tie` no warning must be provided:
```
const auto results = mapping.try_emplace("hello!");
handle_inserted(results);
```

</pre>
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