Track IsSuggestion in ProbeContext. Don't warn stability for suggestions.

Author: kennytm

src/librustc_typeck/check/method/probe.rs

@@ -39,6 +39,7 @@ 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)]
 pub struct IsSuggestion(pub bool);
 
 struct ProbeContext<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
@@ -66,6 +67,8 @@ struct ProbeContext<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
  /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used
  /// for error reporting
  unsatisfied_predicates: Vec<TraitRef<'tcx>>,
+
+ is_suggestion: IsSuggestion,
 }
 
 impl<'a, 'gcx, 'tcx> Deref for ProbeContext<'a, 'gcx, 'tcx> {
@@ -277,8 +280,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  // this creates one big transaction so that all type variables etc
  // that we create during the probe process are removed later
  self.probe(|_| {
- let mut probe_cx =
- ProbeContext::new(self, span, mode, method_name, return_type, Rc::new(steps));
+ let mut probe_cx = ProbeContext::new(
+ self, span, mode, method_name, return_type, Rc::new(steps), is_suggestion,
+ );
 
  probe_cx.assemble_inherent_candidates();
  match scope {
@@ -379,7 +383,8 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
  mode: Mode,
  method_name: Option<ast::Name>,
  return_type: Option<Ty<'tcx>>,
- steps: Rc<Vec<CandidateStep<'tcx>>>)
+ steps: Rc<Vec<CandidateStep<'tcx>>>,
+ is_suggestion: IsSuggestion)
  -> ProbeContext<'a, 'gcx, 'tcx> {
  ProbeContext {
  fcx,
@@ -395,6 +400,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
  allow_similar_names: false,
  private_candidate: None,
  unsatisfied_predicates: Vec::new(),
+ is_suggestion,
  }
  }
 
@@ -952,14 +958,12 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
  Some(&mut unstable_candidates),
  );
  if let Some(pick) = res {
- if !unstable_candidates.is_empty() && !self_ty.is_ty_var() {
+ if !self.is_suggestion.0 && !unstable_candidates.is_empty() {
  if let Ok(p) = &pick {
  // Emit a lint if there are unstable candidates alongside the stable ones.
  //
- // Note, we suppress warning if `self_ty` is TyVar (`_`), since every
- // possible candidates of every type will be considered, which leads to
- // bogus ambiguity like `str::rsplit` vs `[_]::rsplit`. This condition is
- // seen in `src/test/compile-fail/occurs-check-2.rs`.
+ // We suppress warning if we're picking the method only because it is a
+ // suggestion.
  self.emit_unstable_name_collision_hint(p, &unstable_candidates);
  }
  }
@@ -1265,7 +1269,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
  let steps = self.steps.clone();
  self.probe(|_| {
  let mut pcx = ProbeContext::new(self.fcx, self.span, self.mode, self.method_name,
- self.return_type, steps);
+ self.return_type, steps, IsSuggestion(true));
  pcx.allow_similar_names = true;
  pcx.assemble_inherent_candidates();
  pcx.assemble_extension_candidates_for_traits_in_scope(ast::DUMMY_NODE_ID)?;