add llvm_enzyme to libcore

Author: ZuseZ4

library/core/Cargo.toml

@@ -38,4 +38,6 @@ check-cfg = [
     'cfg(target_has_reliable_f16_math)',
     'cfg(target_has_reliable_f128)',
     'cfg(target_has_reliable_f128_math)',
+    'cfg(llvm_enzyme)',
+
 ]

library/core/src/macros/mod.rs

@@ -1511,9 +1511,10 @@ pub(crate) mod builtin {
     /// If used on an input argument, a new shadow argument of the same type will be created,
     /// directly following the original argument.
     ///
-    /// ### Usage exammples:
+    /// ### Usage examples:
     ///
-    /// ```rust
+    #[cfg_attr(llvm_enzyme, doc = " ```rust")]
+    #[cfg_attr(not(llvm_enzyme), doc = " ```rust,compile_fail")]
     /// use std::autodiff::*;
     /// #[autodiff_forward(rb_fwd1, Dual, Const, Dual)]
     /// #[autodiff_forward(rb_fwd2, Const, Dual, Dual)]
@@ -1581,9 +1582,10 @@ pub(crate) mod builtin {
     /// `Const` should be used on non-float arguments, or float-based arguments as an optimization
     /// if we are not interested in computing the derivatives with respect to this argument.
     ///
-    /// ### Usage exammples:
+    /// ### Usage examples:
     ///
-    /// ```rust
+    #[cfg_attr(llvm_enzyme, doc = " ```rust")]
+    #[cfg_attr(not(llvm_enzyme), doc = " ```rust,compile_fail")]
     /// use std::autodiff::*;
     /// #[autodiff_reverse(rb_rev, Active, Active, Active)]
     /// fn rosenbrock(x: f64, y: f64) -> f64 {