[llvm] [llvm] replace static_assert with std::enable_if_t in ilist_node_impl (PR #127722)

[Saleem Abdulrasool via llvm-commits]

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@@ -147,9 +149,8 @@ class ilist_node_impl
   ///
   /// This requires sentinel tracking to be explicitly enabled.  Use the
   /// ilist_sentinel_tracking<true> option to get this API.
-  bool isSentinel() const {
-    static_assert(OptionsT::is_sentinel_tracking_explicit,
-                  "Use ilist_sentinel_tracking<true> to enable isSentinel()");
+  template <typename T = OptionsT>
+  std::enable_if_t<T::is_sentinel_tracking_explicit, bool> isSentinel() const {
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compnerd wrote:

@MaskRay the bug is not in the compiler, it is in the code. The body of the function cannot be initialized generically - it is only possible if the options have explicit sentinel tracking due to the `static_assert`. The SFINAE is preserving the semantics of the `static_assert`. The alternative is to drop the `static_assert` and permit calling the function "accidentally" when the precondition doesn't hold.

https://github.com/llvm/llvm-project/pull/127722