-Wmissing-designated-field-initializers complains even when the field has a default CTOR

[kcc]

cat ~/tmp/missing-designated-field-initializer-test.cpp
struct Foo {
  Foo(){}  // CTOR
};

struct Bar {
  int a{};
  Foo foo;
};

Bar getBar() {
  return {.a = 42};
}

~/LLVM-21.1.0-Linux-X64/bin/clang -c -Wmissing-designated-field-initializers  ~/tmp/missing-designated-field-initializer-test.cpp
.../tmp/missing-designated-field-initializer-test.cpp:11:18: warning: missing field 'foo' initializer [-Wmissing-designated-field-initializers]
   11 |   return {.a = 42};
      |                  ^
1 warning generated.

This warning would be extremely useful if foo didn't have a constructor, but in this case this warning is just a noise.

[keinflue]

I think this is intentional and was discussed before, see #83070.

[kcc]

Consistency with a 16-year old GCC functionality may not be a good enough reason.
This warning is very useful in case a field is left uninitialized.
And it is a noise in the example above.

A quick fix would be to add {} to field

As is, this warning is either going to be unused, or it will encourage adding unnecessary {} to otherwise correct code,
which by the way clang-tidy likes to complain about.

Maybe implement a new warning, -Wmissing-designated-field-initializers-for-uninitialized-fields-only?

[pinskia]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96868

Note the gcc bug is still open but not confirmed. I have not fully looked into the history yet either.