<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/133715>133715</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            modernize-use-designated-initializers Clang-Tidy check reports std::array when IgnoreSingleElementAggregates is false
        </td>
    </tr>

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

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

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

<pre>
    With code like:
```c++
#include <array>

std::array small_primes{2, 3, 5, 7};
```
it issues the following (see [Compiler Explorer](https://godbolt.org/z/fEoYch83q)):
```none
[<source>:3:24: warning: use designated initializer list to initialize 'array<int, 4>' [modernize-use-designated-initializers]](javascript:;)
    3 | std::array small_primes{2, 3, 5, 7};
      |                        ^~~~~~~~~~~~
 |                         .[0]= .[1]= .[2]= .[3]=
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/15.0.1/../../../../include/c++/15.0.1/array:102:5: note: aggregate type is defined here
  102 |     struct array
      | ^
1 warning generated.
```

Interestingly, the suggestion to use `.[i]=` is completely wrong:
```c++
#include <array>

std::array small_primes{.[0] = 2, .[1] = 3, .[2] = 5, .[3] = 7};
```
as the `.` there causes compilation error ([Compiler Explorer](https://godbolt.org/z/xM6T58h1v)):
```none
<source>:3:26: error: expected a field designator, such as '.field = 4'
    3 | std::array small_primes{.[0] = 2, .[1] = 3, .[2] = 5, .[3] = 7};
      | ^
1 error generated.
Compiler returned: 1
```

Finally, use of the same without `.`:
```c++
#include <array>

std::array small_primes{[0] = 2, [1] = 3, [2] = 5, [3] = 7};
```
results in other issues ([Compiler Explorer](https://godbolt.org/z/hdb5ePrb3)):
```none
<source>:3:25: warning: array designators are a C99 extension [-Wc99-designator]
    3 | std::array small_primes{[0] = 2, [1] = 3, [2] = 5, [3] = 7};
      | ^~~
<source>:3:25: error: array designator cannot initialize non-array type 'std::array<enable_if_t<is_same_v<int, int> && is_same_v<int, int> && is_same_v<int, int>, int>, 1 + sizeof...(_Up)>' (aka 'array<int, 1 + sizeof...(_Up)>')
<source>:3:34: error: array designator cannot initialize non-array type 'std::array<enable_if_t<is_same_v<int, int> && is_same_v<int, int> && is_same_v<int, int>, int>, 1 + sizeof...(_Up)>' (aka 'array<int, 1 + sizeof...(_Up)>')
    3 | std::array small_primes{[0] = 2, [1] = 3, [2] = 5, [3] = 7};
      |                                  ^
<source>:3:43: error: array designator cannot initialize non-array type 'std::array<enable_if_t<is_same_v<int, int> && is_same_v<int, int> && is_same_v<int, int>, int>, 1 + sizeof...(_Up)>' (aka 'array<int, 1 + sizeof...(_Up)>')
    3 | std::array small_primes{[0] = 2, [1] = 3, [2] = 5, [3] = 7};
      | ^
<source>:3:52: error: array designator cannot initialize non-array type 'std::array<enable_if_t<is_same_v<int, int> && is_same_v<int, int> && is_same_v<int, int>, int>, 1 + sizeof...(_Up)>' (aka 'array<int, 1 + sizeof...(_Up)>')
    3 | std::array small_primes{[0] = 2, [1] = 3, [2] = 5, [3] = 7};
      | ^
<source>:3:59: warning: missing field '_M_elems' initializer [-Wmissing-designated-field-initializers]
    3 | std::array small_primes{[0] = 2, [1] = 3, [2] = 5, [3] = 7};
      | ^
2 warnings and 4 errors generated.
Compiler returned: 1
```
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzsWF1v4jgX_jXm5giU2HECF1wEWqS5GOmV3lmN9gqZ5JB4xtis7bSlF_vbVyeBlpbOR2dntbNSIxRcYzt5PnyOT1UIurGIcyYXTF6NVBdb5-eqVruNqjuvRhtXH-YfdWyhcjWC0Z-RiZIlJcuT4VMxvqBPUjIutK1MVyMwsVTeqwMT1_RDUoZY0zxR9t0QdsqY9d7rHQZWLDjjSxB0k3QrWHHFxOL8KSwpdQQdQocBYouwdca4W20bYHwaEIHJxdLt9tqgh-u7vXEePZNXjE_bGPeBns5XjK8aV2-ciRPnG8ZX94yvttfu96qdij8Yn9HnKT7rLNLfcsHEMrjOV0ioRCmYKHnGRAm3ylttG2p2AaFGYlVFrEFbHbUy-h49GB0iRHfWB4wXR5qW2kaCntHavCA0O1ejt_oex13A8eOi47NFAyHsQX5SNypUXu9jz_OCgCQlAIAAVizhBwWA_qIFvnAxef3n40UzvjIYJkwuEnphcdW307M2P2uLod2bauX2kfFVdRR3jCdx-aqpqnGwah9aR0OM3gydjK_upvk6z8ZG2-5u3NiO8VUqJ8kkZXw1mVzejs6lBx0NfTbhKFKZJpyJUpLQ1kXaCaCaxmOjIkI87BF0gBq32mINLXrsGUwT_kBKiL6rIgwLntPLJO2U9OQlaNCiJ7knz7YBS8p3NqLHELVtzIH0og0RuqahPmfJZORDlifEpT5ymSf0dkSjwYjmALfe9ab92bv5JDKQmr2zTlL3PeLUw0898tQjTj0vRwA1bP0eV55Q2yNUqgs44NJG9fjRe-cpLvx4TLh7n3-Q0za9-WpMeCEg5GSK_gX6xt0eKwoECrYaTf0QG5wnzKGrWlCB4sBk-J3AZ4wXr9i7P5XuS0MOZD6x4wOnHmPnLdLbQXrp05W2ygwOJT-67WBUtUO41bF1XTxp-Q-48IKVC1IuOPm2Az2GzsQA2oIj-50y0t_yWltvJP7Pb8RrvSafJZ-Bh0eLBVAeQcFyNgO8i2gD7Q4mF-OP1Ww2PvOivHqF4X4as0_M1iePL6J82FHPMUKlrHXxPKtaZ8fDsD4kM148xcPEEq3aGFzr7TpS7g1rMuX65jEP05e4BsZzxnP48QFPWykwvoCg79FtJ5R2puvf9r3kQ9LnU_VZvXAq-Pq8IdW_QJ3I3qj7Hur-ReN_8xrC8AviZuJN3F9c3C9qJ_mbdv9Z7WbPsu5Oh0An9uMBjhfr92s0uAsE_7wA7BPvcfR5PddPvKjqfgH0_AQzgLI1ZINjw2sPg6N6LuqZmKkRztMiExnPZ3k-aueKb7KNLGQ-yxOUvMhmRZqlgk8LgcUsS0d6zhMuEyHSVKR5kk-mlSxwWm15VstMyCnLEtwpbSbG3OzoSDXqD2TzVIgilSOjNmhC_98NziujbDOOuj4wTmyM_JxmjTddE1iWUHkeHteJOhqcf1cNDst-5Q-6PkDVYvUZPO6dj-G5brctWnjXWOfx_1S74bXBHdpYnmrIQBXaVpmAo86b-bODo45tt5lUbkelrrk5fY333n3Cigrg4TRKleuA_2bO_woAAP__TosXEQ">