Add enter_trace_span!() that checks if tracing is enabled

Author: Stypox

compiler/rustc_const_eval/src/interpret/mod.rs

@@ -18,6 +18,7 @@ mod traits;
 mod util;
 mod validity;
 mod visitor;
+mod tracing_utils;
 
 #[doc(no_inline)]
 pub use rustc_middle::mir::interpret::*; // have all the `interpret` symbols in one place: here

compiler/rustc_const_eval/src/interpret/tracing_utils.rs

@@ -0,0 +1,18 @@
+/// This struct is needed to enforce `#[must_use]` on [tracing::span::EnteredSpan]
+/// while wrapping them in an `Option`.
+#[must_use]
+pub enum MaybeEnteredSpan {
+    Some(tracing::span::EnteredSpan),
+    None,
+}
+
+#[macro_export]
+macro_rules! enter_trace_span {
+    ($machine:ident, $($tt:tt)*) => {
+        if $machine::TRACING_ENABLED {
+            $crate::interpret::tracing_utils::MaybeEnteredSpan::Some(tracing::info_span!($($tt)*).entered())
+        } else {
+            $crate::interpret::tracing_utils::MaybeEnteredSpan::None
+        }
+    }
+}