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

[via cfe-commits]

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@@ -3141,6 +3148,10 @@ def warn_attribute_ignored_no_calls_in_stmt: Warning<
   "statement">,
   InGroup<IgnoredAttributes>;
 
+def warn_attribute_needs_aggregate : Warning<
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higher-performance wrote:

Interesting, thanks for the context. From my standpoint, I haven't looked at most of those, but `err_using_if_exists_on_ctor` has a small but crucial difference: the error is a syntactic one that is *directly* caused by the same declaration that is being annotated. Other hand, whether `warn_attribute_needs_aggregate` is triggered depends on a semantic property of the class that is wholistic (caused by other members/aspects of the class) and *not* caused by the annotated field.

But yeah, happy to hear what Aaron thinks.

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