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

[Erich Keane via cfe-commits]

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@@ -1472,3 +1472,56 @@ template<typename T> struct Outer {
   };
 };
 Outer<int>::Inner outerinner;
+
+void aggregate() {
+  struct NonAgg {
+    NonAgg() { }
+    [[clang::requires_explicit_initialization]] int f;  // expected-warning {{'requires_explicit_initialization' attribute is ignored in non-aggregate type 'NonAgg'}}
+  };
+  NonAgg nonagg;  // no-warning
+  (void)nonagg;
+
+  struct S {
+    [[clang::requires_explicit_initialization]] int x; // expected-note 7{{'x' declared here}}
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erichkeane wrote:

And here, throughout file.

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