Auto merge of #25065 - quantheory:fix_associated_const_ambiguity_mess…

…age, r=nikomatsakis

This fixes #24922 and #25017, and reduces the number of error messages that talk about "methods" when associated constants rather than methods are involved.

I will admit that I haven't thought very carefully about the error messages. My goal has been to make more of the messages technically correct in all situations, and to avoid ICEs. But in some cases we could probably talk specifically about "methods" rather than "items".

src/librustc_resolve/lib.rs

@@ -2528,15 +2528,18 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                                 // If anything ends up here entirely resolved,
                                 // it's an error. If anything ends up here
                                 // partially resolved, that's OK, because it may
-                                // be a `T::CONST` that typeck will resolve to
-                                // an inherent impl.
+                                // be a `T::CONST` that typeck will resolve.
                                 if path_res.depth == 0 {
                                     self.resolve_error(
                                         path.span,
                                         &format!("`{}` is not an enum variant, struct or const",
                                                  token::get_ident(
                                                      path.segments.last().unwrap().identifier)));
                                 } else {
+                                    let const_name = path.segments.last().unwrap()
+                                                         .identifier.name;
+                                    let traits = self.get_traits_containing_item(const_name);
+                                    self.trait_map.insert(pattern.id, traits);
                                     self.record_def(pattern.id, path_res);
                                 }
                             }

src/librustc_typeck/check/method/mod.rs

@@ -16,12 +16,10 @@ use middle::def;
 use middle::privacy::{AllPublic, DependsOn, LastPrivate, LastMod};
 use middle::subst;
 use middle::traits;
-use middle::ty::*;
-use middle::ty;
+use middle::ty::{self, AsPredicate, ToPolyTraitRef};
 use middle::infer;
 use util::ppaux::Repr;
 
-use std::rc::Rc;
 use syntax::ast::DefId;
 use syntax::ast;
 use syntax::codemap::Span;
@@ -39,7 +37,7 @@ pub enum MethodError {
     // Did not find an applicable method, but we did find various
     // static methods that may apply, as well as a list of
     // not-in-scope traits which may work.
-    NoMatch(Vec<CandidateSource>, Vec<ast::DefId>),
+    NoMatch(Vec<CandidateSource>, Vec<ast::DefId>, probe::Mode),
 
     // Multiple methods might apply.
     Ambiguity(Vec<CandidateSource>),
@@ -62,7 +60,7 @@ type ItemIndex = usize; // just for doc purposes
 pub fn exists<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                         span: Span,
                         method_name: ast::Name,
-                        self_ty: Ty<'tcx>,
+                        self_ty: ty::Ty<'tcx>,
                         call_expr_id: ast::NodeId)
                         -> bool
 {
@@ -92,11 +90,11 @@ pub fn exists<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 pub fn lookup<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                         span: Span,
                         method_name: ast::Name,
-                        self_ty: Ty<'tcx>,
-                        supplied_method_types: Vec<Ty<'tcx>>,
+                        self_ty: ty::Ty<'tcx>,
+                        supplied_method_types: Vec<ty::Ty<'tcx>>,
                         call_expr: &'tcx ast::Expr,
                         self_expr: &'tcx ast::Expr)
-                        -> Result<MethodCallee<'tcx>, MethodError>
+                        -> Result<ty::MethodCallee<'tcx>, MethodError>
 {
     debug!("lookup(method_name={}, self_ty={}, call_expr={}, self_expr={})",
            method_name.repr(fcx.tcx()),
@@ -115,9 +113,9 @@ pub fn lookup_in_trait<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                                  self_expr: Option<&ast::Expr>,
                                  m_name: ast::Name,
                                  trait_def_id: DefId,
-                                 self_ty: Ty<'tcx>,
-                                 opt_input_types: Option<Vec<Ty<'tcx>>>)
-                                 -> Option<MethodCallee<'tcx>>
+                                 self_ty: ty::Ty<'tcx>,
+                                 opt_input_types: Option<Vec<ty::Ty<'tcx>>>)
+                                 -> Option<ty::MethodCallee<'tcx>>
 {
     lookup_in_trait_adjusted(fcx, span, self_expr, m_name, trait_def_id,
                              0, false, self_ty, opt_input_types)
@@ -139,9 +137,9 @@ pub fn lookup_in_trait_adjusted<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                                           trait_def_id: DefId,
                                           autoderefs: usize,
                                           unsize: bool,
-                                          self_ty: Ty<'tcx>,
-                                          opt_input_types: Option<Vec<Ty<'tcx>>>)
-                                          -> Option<MethodCallee<'tcx>>
+                                          self_ty: ty::Ty<'tcx>,
+                                          opt_input_types: Option<Vec<ty::Ty<'tcx>>>)
+                                          -> Option<ty::MethodCallee<'tcx>>
 {
     debug!("lookup_in_trait_adjusted(self_ty={}, self_expr={}, m_name={}, trait_def_id={})",
            self_ty.repr(fcx.tcx()),
@@ -186,7 +184,9 @@ pub fn lookup_in_trait_adjusted<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     // Trait must have a method named `m_name` and it should not have
     // type parameters or early-bound regions.
     let tcx = fcx.tcx();
-    let (method_num, method_ty) = trait_method(tcx, trait_def_id, m_name).unwrap();
+    let (method_num, method_ty) = trait_item(tcx, trait_def_id, m_name)
+            .and_then(|(idx, item)| item.as_opt_method().map(|m| (idx, m)))
+            .unwrap();
     assert_eq!(method_ty.generics.types.len(subst::FnSpace), 0);
     assert_eq!(method_ty.generics.regions.len(subst::FnSpace), 0);
 
@@ -288,10 +288,10 @@ pub fn lookup_in_trait_adjusted<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
         }
     }
 
-    let callee = MethodCallee {
-        origin: MethodTypeParam(MethodParam{trait_ref: trait_ref.clone(),
-                                            method_num: method_num,
-                                            impl_def_id: None}),
+    let callee = ty::MethodCallee {
+        origin: ty::MethodTypeParam(ty::MethodParam{trait_ref: trait_ref.clone(),
+                                                    method_num: method_num,
+                                                    impl_def_id: None}),
         ty: fty,
         substs: trait_ref.substs.clone()
     };
@@ -304,7 +304,7 @@ pub fn lookup_in_trait_adjusted<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 pub fn resolve_ufcs<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                               span: Span,
                               method_name: ast::Name,
-                              self_ty: Ty<'tcx>,
+                              self_ty: ty::Ty<'tcx>,
                               expr_id: ast::NodeId)
                               -> Result<(def::Def, LastPrivate), MethodError>
 {
@@ -322,41 +322,40 @@ pub fn resolve_ufcs<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
         _ => def::FromTrait(pick.item.container().id())
     };
     let def_result = match pick.item {
-        ImplOrTraitItem::MethodTraitItem(..) => def::DefMethod(def_id, provenance),
-        ImplOrTraitItem::ConstTraitItem(..) => def::DefAssociatedConst(def_id, provenance),
-        ImplOrTraitItem::TypeTraitItem(..) => {
+        ty::ImplOrTraitItem::MethodTraitItem(..) => def::DefMethod(def_id, provenance),
+        ty::ImplOrTraitItem::ConstTraitItem(..) => def::DefAssociatedConst(def_id, provenance),
+        ty::ImplOrTraitItem::TypeTraitItem(..) => {
             fcx.tcx().sess.span_bug(span, "resolve_ufcs: probe picked associated type");
         }
     };
     Ok((def_result, lp))
 }
 
 
-/// Find method with name `method_name` defined in `trait_def_id` and return it, along with its
-/// index (or `None`, if no such method).
-fn trait_method<'tcx>(tcx: &ty::ctxt<'tcx>,
-                      trait_def_id: ast::DefId,
-                      method_name: ast::Name)
-                      -> Option<(usize, Rc<ty::Method<'tcx>>)>
+/// Find item with name `item_name` defined in `trait_def_id` and return it, along with its
+/// index (or `None`, if no such item).
+fn trait_item<'tcx>(tcx: &ty::ctxt<'tcx>,
+                    trait_def_id: ast::DefId,
+                    item_name: ast::Name)
+                    -> Option<(usize, ty::ImplOrTraitItem<'tcx>)>
 {
     let trait_items = ty::trait_items(tcx, trait_def_id);
     trait_items
         .iter()
         .enumerate()
-        .find(|&(_, ref item)| item.name() == method_name)
-        .and_then(|(idx, item)| item.as_opt_method().map(|m| (idx, m)))
+        .find(|&(_, ref item)| item.name() == item_name)
+        .map(|(num, item)| (num, (*item).clone()))
 }
 
-fn impl_method<'tcx>(tcx: &ty::ctxt<'tcx>,
-                     impl_def_id: ast::DefId,
-                     method_name: ast::Name)
-                     -> Option<Rc<ty::Method<'tcx>>>
+fn impl_item<'tcx>(tcx: &ty::ctxt<'tcx>,
+                   impl_def_id: ast::DefId,
+                   item_name: ast::Name)
+                   -> Option<ty::ImplOrTraitItem<'tcx>>
 {
     let impl_items = tcx.impl_items.borrow();
     let impl_items = impl_items.get(&impl_def_id).unwrap();
     impl_items
         .iter()
         .map(|&did| ty::impl_or_trait_item(tcx, did.def_id()))
-        .find(|m| m.name() == method_name)
-        .and_then(|item| item.as_opt_method())
+        .find(|m| m.name() == item_name)
 }

src/librustc_typeck/check/method/probe.rs

@@ -136,7 +136,7 @@ pub fn probe<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     let steps = if mode == Mode::MethodCall {
         match create_steps(fcx, span, self_ty) {
             Some(steps) => steps,
-            None => return Err(MethodError::NoMatch(Vec::new(), Vec::new())),
+            None => return Err(MethodError::NoMatch(Vec::new(), Vec::new(), mode)),
         }
     } else {
         vec![CandidateStep {
@@ -866,7 +866,7 @@ impl<'a,'tcx> ProbeContext<'a,'tcx> {
                     }
                 }
             }).collect(),
-            Some(Err(MethodError::NoMatch(_, others))) => {
+            Some(Err(MethodError::NoMatch(_, others, _))) => {
                 assert!(others.is_empty());
                 vec![]
             }
@@ -877,7 +877,7 @@ impl<'a,'tcx> ProbeContext<'a,'tcx> {
             None => vec![],
         };
 
-        Err(MethodError::NoMatch(static_candidates, out_of_scope_traits))
+        Err(MethodError::NoMatch(static_candidates, out_of_scope_traits, self.mode))
     }
 
     fn pick_core(&mut self) -> Option<PickResult<'tcx>> {