[clang] [LifetimeSafety] Warn on incorrectly placed `[[clang::lifetimebound]]` attributes (PR #196144)

[Utkarsh Saxena via cfe-commits]

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@@ -0,0 +1,80 @@
+// RUN: %clang_cc1 -fsyntax-only -Wlifetime-safety-lifetimebound-violation -verify %s
+
+#include "Inputs/lifetime-analysis.h"
+
+struct [[gsl::Owner]] MyObj {
+  int id;
+  ~MyObj() {}  // Non-trivial destructor
+};
+
+struct [[gsl::Pointer()]] View {
+  View(const MyObj &); // Borrows from MyObj
+  View();
+  void use() const;
+};
+
+bool cond();
+
+View not_lb(const MyObj &obj);
+
+View lb(const MyObj &obj [[clang::lifetimebound]]);
+
+View return_through_unannotated_passthrough(
+    const MyObj &obj [[clang::lifetimebound]]) { // expected-warning {{could not verify that the return value can be lifetime bound to 'obj'}}
+  return not_lb(obj);
+}
----------------
usx95 wrote:

For this PR, can you add a test where the lifetimebound is attached to unnamed param.

```cpp
View return_through_unannotated_passthrough(
  const MyObj & [[clang::lifetimebound]]) {
  return View();
}
```

Mostly concerned about the `ParmWithLifetimebound->getName()` to not crash.

https://github.com/llvm/llvm-project/pull/196144