[clang] [LifetimeSafety] Warn on inapplicable `[[clang::lifetimebound]]` when return type can not carry a lifetime (PR #203767)

[Utkarsh Saxena via cfe-commits]

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@@ -11048,6 +11048,11 @@ def warn_lifetime_safety_inapplicable_lifetimebound
       InGroup<LifetimeSafetyInapplicableLifetimebound>,
       DefaultIgnore;
 
+def warn_lifetime_safety_inapplicable_lifetimebound_return
+    : Warning<"'lifetimebound' attribute has no effect on this function because return type %0 cannot carry a lifetime. The attribute only applies when the return type is a reference type, pointer type, or non-owner record type">,
+      InGroup<LifetimeSafetyInapplicableLifetimebound>,
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usx95 wrote:

I would prefer having a separate sub diaggroup allowing incremental adoption. It can still be under `LifetimeSafetyInapplicableLifetimebound`.

https://github.com/llvm/llvm-project/pull/203767