various cleanups to try to reduce the use of spans inside method resolution

compiler/rustc_hir_typeck/src/callee.rs

@@ -504,7 +504,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // method lookup.
             let Ok(pick) = self
             .probe_for_name(
-                call_expr.span,
                 Mode::MethodCall,
                 segment.ident,
                 IsSuggestion(true),

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -93,17 +93,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         call_expr_id: hir::HirId,
         allow_private: bool,
     ) -> bool {
-        let mode = probe::Mode::MethodCall;
         match self.probe_for_name(
-            method_name.span,
-            mode,
+            probe::Mode::MethodCall,
             method_name,
             IsSuggestion(false),
             self_ty,
             call_expr_id,
             ProbeScope::TraitsInScope,
         ) {
-            Ok(..) => true,
+            Ok(pick) => {
+                pick.maybe_emit_unstable_name_collision_hint(
+                    self.tcx,
+                    method_name.span,
+                    call_expr_id,
+                );
+                true
+            }
             Err(NoMatch(..)) => false,
             Err(Ambiguity(..)) => true,
             Err(PrivateMatch(..)) => allow_private,
@@ -125,10 +130,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) {
         let params = self
             .probe_for_name(
-                method_name.span,
                 probe::Mode::MethodCall,
                 method_name,
-                IsSuggestion(false),
+                IsSuggestion(true),
                 self_ty,
                 call_expr.hir_id,
                 ProbeScope::TraitsInScope,
@@ -175,7 +179,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         args: &'tcx [hir::Expr<'tcx>],
     ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
         let pick =
-            self.lookup_probe(span, segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
+            self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
 
         self.lint_dot_call_from_2018(self_ty, segment, span, call_expr, self_expr, &pick, args);
 
@@ -200,42 +204,38 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     .mk_ref(*region, ty::TypeAndMut { ty: *t_type, mutbl: mutability.invert() });
                 // We probe again to see if there might be a borrow mutability discrepancy.
                 match self.lookup_probe(
-                    span,
                     segment.ident,
                     trait_type,
                     call_expr,
                     ProbeScope::TraitsInScope,
                 ) {
-                    Ok(ref new_pick) if *new_pick != pick => {
+                    Ok(ref new_pick) if pick.differs_from(new_pick) => {
                         needs_mut = true;
                     }
                     _ => {}
                 }
             }
 
             // We probe again, taking all traits into account (not only those in scope).
-            let mut candidates = match self.lookup_probe(
-                span,
-                segment.ident,
-                self_ty,
-                call_expr,
-                ProbeScope::AllTraits,
-            ) {
-                // If we find a different result the caller probably forgot to import a trait.
-                Ok(ref new_pick) if *new_pick != pick => vec![new_pick.item.container_id(self.tcx)],
-                Err(Ambiguity(ref sources)) => sources
-                    .iter()
-                    .filter_map(|source| {
-                        match *source {
-                            // Note: this cannot come from an inherent impl,
-                            // because the first probing succeeded.
-                            CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
-                            CandidateSource::Trait(_) => None,
-                        }
-                    })
-                    .collect(),
-                _ => Vec::new(),
-            };
+            let mut candidates =
+                match self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::AllTraits) {
+                    // If we find a different result the caller probably forgot to import a trait.
+                    Ok(ref new_pick) if pick.differs_from(new_pick) => {
+                        vec![new_pick.item.container_id(self.tcx)]
+                    }
+                    Err(Ambiguity(ref sources)) => sources
+                        .iter()
+                        .filter_map(|source| {
+                            match *source {
+                                // Note: this cannot come from an inherent impl,
+                                // because the first probing succeeded.
+                                CandidateSource::Impl(def) => self.tcx.trait_id_of_impl(def),
+                                CandidateSource::Trait(_) => None,
+                            }
+                        })
+                        .collect(),
+                    _ => Vec::new(),
+                };
             candidates.retain(|candidate| *candidate != self.tcx.parent(result.callee.def_id));
 
             return Err(IllegalSizedBound(candidates, needs_mut, span));
@@ -247,23 +247,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     #[instrument(level = "debug", skip(self, call_expr))]
     pub fn lookup_probe(
         &self,
-        span: Span,
         method_name: Ident,
         self_ty: Ty<'tcx>,
         call_expr: &'tcx hir::Expr<'tcx>,
         scope: ProbeScope,
     ) -> probe::PickResult<'tcx> {
-        let mode = probe::Mode::MethodCall;
-        let self_ty = self.resolve_vars_if_possible(self_ty);
-        self.probe_for_name(
-            span,
-            mode,
+        let pick = self.probe_for_name(
+            probe::Mode::MethodCall,
             method_name,
             IsSuggestion(false),
             self_ty,
             call_expr.hir_id,
             scope,
-        )
+        )?;
+        pick.maybe_emit_unstable_name_collision_hint(self.tcx, method_name.span, call_expr.hir_id);
+        Ok(pick)
     }
 
     pub(super) fn obligation_for_method(
@@ -587,7 +585,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         let pick = self.probe_for_name(
-            span,
             probe::Mode::Path,
             method_name,
             IsSuggestion(false),
@@ -596,6 +593,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ProbeScope::TraitsInScope,
         )?;
 
+        pick.maybe_emit_unstable_name_collision_hint(self.tcx, span, expr_id);
+
         self.lint_fully_qualified_call_from_2018(
             span,
             method_name,