Louis Dionne b0fd9497af [libc++] Add a lightweight overridable assertion handler ... This patch adds a lightweight assertion handler mechanism that can be overriden at link-time in a fashion similar to `operator new`. This is a third take on https://llvm.org/D121123 (which allowed customizing the assertion handler at compile-time), and https://llvm.org/D119969 (which allowed customizing the assertion handler at runtime only). This approach is, I think, the best of all three explored approaches. Indeed, replacing the assertion handler in user code is ergonomic, yet we retain the ability to provide a custom assertion handler when deploying to older platforms that don't have a default handler in the dylib. As-is, this patch provides a pretty good amount of backwards compatibility with the previous debug mode: - Code that used to set _LIBCPP_DEBUG=0 in order to get basic assertions in their code will still get basic assertions out of the box, but those assertions will be using the new assertion handler support. - Code that was previously compiled with references to __libcpp_debug_function and friends will work out-of-the-box, no changes required. This is because we provide the same symbols in the dylib as we used to. - Code that used to set a custom __libcpp_debug_function will stop compiling, because we don't provide that declaration anymore. Users will have to migrate to the new way of setting a custom assertion handler, which is extremely easy. I suspect that pool of users is very limited, so breaking them at compile-time is probably acceptable. The main downside of this approach is that code being compiled with assertions enabled but deploying to an older platform where the assertion handler didn't exist yet will fail to compile. However users can easily fix the problem by providing a custom assertion handler and defining the _LIBCPP_AVAILABILITY_CUSTOM_ASSERTION_HANDLER_PROVIDED macro to let the library know about the custom handler. In a way, this is actually a feature because it avoids a load-time error that one would otherwise get when trying to run the code on the older target. Differential Revision: https://reviews.llvm.org/D121478		2022-03-23 15:35:46 -04:00
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caches	[libc++] Add a lightweight overridable assertion handler	2022-03-23 15:35:46 -04:00
Modules	[libc++] Do not install the C++ ABI library's headers as part of libc++'s build	2022-03-16 08:53:47 -04:00
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