[clang] [Clang] Disallow explicit object parameters in more contexts (PR #89078)

[via cfe-commits]

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@@ -7525,6 +7525,8 @@ def err_explicit_object_parameter_mutable: Error<
 def err_invalid_explicit_object_type_in_lambda: Error<
   "invalid explicit object parameter type %0 in lambda with capture; "
   "the type must be the same as, or derived from, the lambda">;
+def err_explicit_object_parameter_invalid: Error<
+  "an explicit object parameter is not allowed here">;
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Sirraide wrote:

I’d have to somehow figure out what ‘here’ is for that... is the `DeclaratorContext` enough to deduce that reliably, or is there some other way of knowing that?

Alternatively, something like ‘an explicit object parameter can only appear as the first argument in a member function’, would also be an option.

https://github.com/llvm/llvm-project/pull/89078