safe transmute: tweak tracing

ref: https://github.com/rust-lang/rust/pull/92268#discussion_r925246903
ref: https://github.com/rust-lang/rust/pull/92268#discussion_r925250811
ref: https://github.com/rust-lang/rust/pull/92268#discussion_r925255782

compiler/rustc_transmute/src/layout/dfa.rs

@@ -103,7 +103,7 @@ where
         Self { transitions, start, accepting }
     }
 
-    #[tracing::instrument]
+    #[instrument(level = "DEBUG")]
     #[cfg_attr(feature = "rustc", allow(rustc::potential_query_instability))]
     pub(crate) fn from_nfa(nfa: Nfa<R>) -> Self {
         let Nfa { transitions: nfa_transitions, start: nfa_start, accepting: nfa_accepting } = nfa;

compiler/rustc_transmute/src/layout/tree.rs

@@ -76,7 +76,6 @@ where
     }
 
     /// A `Tree` whose layout is entirely padding of the given width.
-    #[tracing::instrument]
     pub(crate) fn padding(width_in_bytes: usize) -> Self {
         Self::Seq(vec![Self::uninit(); width_in_bytes])
     }
@@ -316,10 +315,7 @@ pub(crate) mod rustc {
                             tcx,
                         )?,
                         AdtKind::Enum => {
-                            tracing::trace!(
+                            tracing::trace!(?adt_def, "treeifying enum");
-                                adt_def = ?adt_def,
-                                "treeifying enum"
-                            );
                             let mut tree = Tree::uninhabited();
 
                             for (idx, discr) in adt_def.discriminants(tcx) {
@@ -398,13 +394,13 @@ pub(crate) mod rustc {
 
             // The layout of the variant is prefixed by the discriminant, if any.
             if let Some(discr) = discr {
-                tracing::trace!(discr = ?discr, "treeifying discriminant");
+                tracing::trace!(?discr, "treeifying discriminant");
                 let discr_layout = alloc::Layout::from_size_align(
                     layout_summary.discriminant_size,
                     clamp(layout_summary.discriminant_align),
                 )
                 .unwrap();
-                tracing::trace!(discr_layout = ?discr_layout, "computed discriminant layout");
+                tracing::trace!(?discr_layout, "computed discriminant layout");
                 variant_layout = variant_layout.extend(discr_layout).unwrap().0;
                 tree = tree.then(Self::from_disr(discr, tcx, layout_summary.discriminant_size));
             }
@@ -469,11 +465,7 @@ pub(crate) mod rustc {
             layout.align().abi.bytes().try_into().unwrap(),
         )
         .unwrap();
-        tracing::trace!(
+        tracing::trace!(?ty, ?layout, "computed layout for type");
-            ty = ?ty,
-            layout = ?layout,
-            "computed layout for type"
-        );
         Ok(layout)
     }
 }

compiler/rustc_transmute/src/lib.rs

@@ -8,6 +8,9 @@
 )]
 #![allow(dead_code, unused_variables)]
 
+#[macro_use]
+extern crate tracing;
+
 #[cfg(feature = "rustc")]
 pub(crate) use rustc_data_structures::fx::{FxHashMap as Map, FxHashSet as Set};
 

compiler/rustc_transmute/src/maybe_transmutable/mod.rs

@@ -64,7 +64,7 @@ mod rustc {
     impl<'tcx> MaybeTransmutableQuery<Ty<'tcx>, TyCtxt<'tcx>> {
         /// This method begins by converting `src` and `dst` from `Ty`s to `Tree`s,
         /// then computes an answer using those trees.
-        #[tracing::instrument(skip(self), fields(src = ?self.src, dst = ?self.dst))]
+        #[instrument(level = "DEBUG", skip(self), fields(src = ?self.src, dst = ?self.dst))]
         pub fn answer(self) -> Answer<<TyCtxt<'tcx> as QueryContext>::Ref> {
             let query_or_answer = self.map_layouts(|src, dst, scope, &context| {
                 // Convert `src` and `dst` from their rustc representations, to `Tree`-based
@@ -103,14 +103,14 @@ where
     /// This method begins by de-def'ing `src` and `dst`, and prunes private paths from `dst`,
     /// then converts `src` and `dst` to `Nfa`s, and computes an answer using those NFAs.
     #[inline(always)]
-    #[tracing::instrument(skip(self), fields(src = ?self.src, dst = ?self.dst))]
+    #[instrument(level = "DEBUG", skip(self), fields(src = ?self.src, dst = ?self.dst))]
     pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
         let assume_visibility = self.assume.visibility;
         let query_or_answer = self.map_layouts(|src, dst, scope, context| {
             // Remove all `Def` nodes from `src`, without checking their visibility.
             let src = src.prune(&|def| true);
 
-            tracing::trace!(src = ?src, "pruned src");
+            tracing::trace!(?src, "pruned src");
 
             // Remove all `Def` nodes from `dst`, additionally...
             let dst = if assume_visibility {
@@ -121,7 +121,7 @@ where
                 dst.prune(&|def| context.is_accessible_from(def, scope))
             };
 
-            tracing::trace!(dst = ?dst, "pruned dst");
+            tracing::trace!(?dst, "pruned dst");
 
             // Convert `src` from a tree-based representation to an NFA-based representation.
             // If the conversion fails because `src` is uninhabited, conclude that the transmutation
@@ -152,7 +152,7 @@ where
     ///
     /// This method converts `src` and `dst` to DFAs, then computes an answer using those DFAs.
     #[inline(always)]
-    #[tracing::instrument(skip(self), fields(src = ?self.src, dst = ?self.dst))]
+    #[instrument(level = "DEBUG", skip(self), fields(src = ?self.src, dst = ?self.dst))]
     pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
         let query_or_answer = self
             .map_layouts(|src, dst, scope, context| Ok((Dfa::from_nfa(src), Dfa::from_nfa(dst))));
@@ -192,7 +192,7 @@ where
     }
 
     #[inline(always)]
-    #[tracing::instrument(skip(self))]
+    #[instrument(level = "DEBUG", skip(self))]
     fn answer_memo(
         &self,
         cache: &mut Map<(dfa::State, dfa::State), Answer<<C as QueryContext>::Ref>>,

compiler/rustc_transmute/src/maybe_transmutable/query_context.rs

@@ -52,7 +52,7 @@ mod rustc {
 
         type Scope = Ty<'tcx>;
 
-        #[tracing::instrument(skip(self))]
+        #[instrument(level = "DEBUG", skip(self))]
         fn is_accessible_from(&self, def: Self::Def, scope: Self::Scope) -> bool {
             use layout::rustc::Def;
             use rustc_middle::ty;
@@ -82,7 +82,7 @@ mod rustc {
                 false
             };
 
-            tracing::trace!(ret = ?ret, "ret");
+            tracing::trace!(?ret, "ret");
             ret
         }