[clang] [clang] Warn [[clang::lifetimebound]] misusages on types (PR #118281)

[Ilya Biryukov via cfe-commits]

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@@ -9,11 +9,20 @@ namespace usage_invalid {
     ~A() [[clang::lifetimebound]]; // expected-error {{cannot be applied to a destructor}}
     static int *static_class_member() [[clang::lifetimebound]]; // expected-error {{static member function has no implicit object parameter}}
     int *explicit_object(this A&) [[clang::lifetimebound]]; // expected-error {{explicit object member function has no implicit object parameter}}
-    int not_function [[clang::lifetimebound]]; // expected-error {{only applies to parameters and implicit object parameters}}
-    int [[clang::lifetimebound]] also_not_function; // expected-error {{cannot be applied to types}}
+    int attr_on_var [[clang::lifetimebound]]; // expected-error {{only applies to parameters and implicit object parameters}}
+    int [[clang::lifetimebound]] attr_on_int; // expected-error {{cannot be applied to types}}
+    int * [[clang::lifetimebound]] attr_on_int_ptr; // expected-error {{cannot be applied to types}}
+    int * [[clang::lifetimebound]] * attr_on_int_ptr_ptr; // expected-error {{cannot be applied to types}}
+    int (* [[clang::lifetimebound]] attr_on_func_ptr)(); // expected-error {{cannot be applied to types}}
     void void_return_member() [[clang::lifetimebound]]; // expected-error {{'lifetimebound' attribute cannot be applied to an implicit object parameter of a function that returns void; did you mean 'lifetime_capture_by(X)'}}
   };
   int *attr_with_param(int &param [[clang::lifetimebound(42)]]); // expected-error {{takes no arguments}}
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ilya-biryukov wrote:

Could we add some tests for things that aren't working yet?
Now that we have a much wider coverage than before, it also makes more sense to list the cases we don't yet have covered. Some that come to mind are:

```cpp
// Uses in function types, but not on the functions declarations.
// We fail to diagnose those don't have "implicit object paramter".
int (*a)(int) [[clang::lifetimebound]];
int (*(*b)(int) [[clang::lifetimebound]])(int);
struct X{};
int (X::*c)(int) [[clang::lifetimebound]];
```

https://github.com/llvm/llvm-project/pull/118281