[clang] Add Clang attribute to ensure that fields are initialized explicitly (PR #102040)

[Aaron Ballman via cfe-commits]

================
@@ -551,3 +551,32 @@ struct full_of_empty empty_test_2(void) {
   struct full_of_empty e;
   return e; // no-warning
 }
+
+struct with_explicit_field {
+  int x;
+  int y [[clang::requires_explicit_initialization]]; // #FIELD_Y
+};
+
+struct with_explicit_array {
+  [[clang::requires_explicit_initialization]] int arr[2]; // #FIELD_ARR
+};
+
+struct with_explicit_flex_array {
+  [[clang::requires_explicit_initialization]] int flex_arr[]; // #FIELD_FLEX_ARR
----------------
AaronBallman wrote:

This class should have another field that isn't a FAM, otherwise you get additional diagnostics.

https://github.com/llvm/llvm-project/pull/102040