Add tracing instrumentation to method typeck

I was recently digging into how this code works, and this
instrumentation was helpful.

Author: tmandry

Diff for: compiler/rustc_typeck/src/check/method/confirm.rs

@@ -31,6 +31,7 @@ impl<'a, 'tcx> Deref for ConfirmContext<'a, 'tcx> {
     }
 }
 
+#[derive(Debug)]
 pub struct ConfirmResult<'tcx> {
     pub callee: MethodCallee<'tcx>,
     pub illegal_sized_bound: Option<Span>,

Diff for: compiler/rustc_typeck/src/check/method/mod.rs

@@ -102,6 +102,7 @@ pub enum CandidateSource {
 
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Determines whether the type `self_ty` supports a method name `method_name` or not.
+    #[instrument(level = "debug", skip(self))]
     pub fn method_exists(
         &self,
         method_name: Ident,
@@ -129,6 +130,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     }
 
     /// Adds a suggestion to call the given method to the provided diagnostic.
+    #[instrument(level = "debug", skip(self, err, call_expr))]
     crate fn suggest_method_call(
         &self,
         err: &mut DiagnosticBuilder<'a>,
@@ -177,6 +179,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// * `span`:                  the span for the method call
     /// * `call_expr`:             the complete method call: (`foo.bar::<T1,...Tn>(...)`)
     /// * `self_expr`:             the self expression (`foo`)
+    #[instrument(level = "debug", skip(self, call_expr, self_expr))]
     pub fn lookup_method(
         &self,
         self_ty: Ty<'tcx>,
@@ -204,6 +207,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         let result =
             self.confirm_method(span, self_expr, call_expr, self_ty, pick.clone(), segment);
+        debug!("result = {:?}", result);
 
         if let Some(span) = result.illegal_sized_bound {
             let mut needs_mut = false;
@@ -256,6 +260,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         Ok(result.callee)
     }
 
+    #[instrument(level = "debug", skip(self, call_expr))]
     pub fn lookup_probe(
         &self,
         span: Span,
@@ -286,6 +291,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     // FIXME(#18741): it seems likely that we can consolidate some of this
     // code with the other method-lookup code. In particular, the second half
     // of this method is basically the same as confirmation.
+    #[instrument(level = "debug", skip(self, span, opt_input_types))]
     pub fn lookup_method_in_trait(
         &self,
         span: Span,
@@ -409,6 +415,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         Some(InferOk { obligations, value: callee })
     }
 
+    #[instrument(level = "debug", skip(self))]
     pub fn resolve_ufcs(
         &self,
         span: Span,

Diff for: compiler/rustc_typeck/src/check/method/probe.rs

@@ -48,7 +48,7 @@ pub use self::PickKind::*;
 
 /// Boolean flag used to indicate if this search is for a suggestion
 /// or not. If true, we can allow ambiguity and so forth.
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 pub struct IsSuggestion(pub bool);
 
 struct ProbeContext<'a, 'tcx> {
@@ -219,6 +219,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// would result in an error (basically, the same criteria we
     /// would use to decide if a method is a plausible fit for
     /// ambiguity purposes).
+    #[instrument(level = "debug", skip(self, scope_expr_id))]
     pub fn probe_for_return_type(
         &self,
         span: Span,
@@ -264,6 +265,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .collect()
     }
 
+    #[instrument(level = "debug", skip(self, scope_expr_id))]
     pub fn probe_for_name(
         &self,
         span: Span,
@@ -770,7 +772,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         // will be reported by `object_safety.rs` if the method refers to the
         // `Self` type anywhere other than the receiver. Here, we use a
         // substitution that replaces `Self` with the object type itself. Hence,
-        // a `&self` method will wind up with an argument type like `&Trait`.
+        // a `&self` method will wind up with an argument type like `&dyn Trait`.
         let trait_ref = principal.with_self_ty(self.tcx, self_ty);
         self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| {
             let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);