Rollup of 6 pull requests

src/librustc/error_codes.rs

@@ -1700,6 +1700,27 @@ To understand better how closures work in Rust, read:
 https://doc.rust-lang.org/book/ch13-01-closures.html
 "##,
 
+E0566: r##"
+Conflicting representation hints have been used on a same item.
+
+Erroneous code example:
+
+```
+#[repr(u32, u64)] // warning!
+enum Repr { A }
+```
+
+In most cases (if not all), using just one representation hint is more than
+enough. If you want to have a representation hint depending on the current
+architecture, use `cfg_attr`. Example:
+
+```
+#[cfg_attr(linux, repr(u32))]
+#[cfg_attr(not(linux), repr(u64))]
+enum Repr { A }
+```
+"##,
+
 E0580: r##"
 The `main` function was incorrectly declared.
 
@@ -2097,7 +2118,6 @@ rejected in your own crates.
     E0490, // a value of type `..` is borrowed for too long
     E0495, // cannot infer an appropriate lifetime due to conflicting
            // requirements
-    E0566, // conflicting representation hints
     E0623, // lifetime mismatch where both parameters are anonymous regions
     E0628, // generators cannot have explicit parameters
     E0631, // type mismatch in closure arguments

src/librustc/hir/mod.rs

@@ -1053,6 +1053,13 @@ impl Mutability {
             MutImmutable => MutImmutable,
         }
     }
+
+    pub fn invert(self) -> Self {
+        match self {
+            MutMutable => MutImmutable,
+            MutImmutable => MutMutable,
+        }
+    }
 }
 
 #[derive(Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Hash, HashStable)]

src/librustc/traits/error_reporting.rs

@@ -453,21 +453,17 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
     }
 
-    fn find_similar_impl_candidates(&self,
-                                    trait_ref: ty::PolyTraitRef<'tcx>)
-                                    -> Vec<ty::TraitRef<'tcx>>
-    {
-        let simp = fast_reject::simplify_type(self.tcx,
-                                              trait_ref.skip_binder().self_ty(),
-                                              true);
+    fn find_similar_impl_candidates(
+        &self,
+        trait_ref: ty::PolyTraitRef<'tcx>,
+    ) -> Vec<ty::TraitRef<'tcx>> {
+        let simp = fast_reject::simplify_type(self.tcx, trait_ref.skip_binder().self_ty(), true);
         let all_impls = self.tcx.all_impls(trait_ref.def_id());
 
         match simp {
             Some(simp) => all_impls.iter().filter_map(|&def_id| {
                 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
-                let imp_simp = fast_reject::simplify_type(self.tcx,
-                                                          imp.self_ty(),
-                                                          true);
+                let imp_simp = fast_reject::simplify_type(self.tcx, imp.self_ty(), true);
                 if let Some(imp_simp) = imp_simp {
                     if simp != imp_simp {
                         return None
@@ -482,10 +478,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
     }
 
-    fn report_similar_impl_candidates(&self,
-                                      impl_candidates: Vec<ty::TraitRef<'tcx>>,
-                                      err: &mut DiagnosticBuilder<'_>)
-    {
+    fn report_similar_impl_candidates(
+        &self,
+        impl_candidates: Vec<ty::TraitRef<'tcx>>,
+        err: &mut DiagnosticBuilder<'_>,
+    ) {
         if impl_candidates.is_empty() {
             return;
         }
@@ -720,10 +717,18 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                             // which is somewhat confusing.
                             err.help(&format!("consider adding a `where {}` bound",
                                               trait_ref.to_predicate()));
-                        } else if !have_alt_message {
-                            // Can't show anything else useful, try to find similar impls.
-                            let impl_candidates = self.find_similar_impl_candidates(trait_ref);
-                            self.report_similar_impl_candidates(impl_candidates, &mut err);
+                        } else {
+                            if !have_alt_message {
+                                // Can't show anything else useful, try to find similar impls.
+                                let impl_candidates = self.find_similar_impl_candidates(trait_ref);
+                                self.report_similar_impl_candidates(impl_candidates, &mut err);
+                            }
+                            self.suggest_change_mut(
+                                &obligation,
+                                &mut err,
+                                &trait_ref,
+                                points_at_arg,
+                            );
                         }
 
                         // If this error is due to `!: Trait` not implemented but `(): Trait` is
@@ -1081,9 +1086,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 
                     let substs = self.tcx.mk_substs_trait(trait_type, &[]);
                     let new_trait_ref = ty::TraitRef::new(trait_ref.def_id, substs);
-                    let new_obligation = Obligation::new(ObligationCause::dummy(),
-                                                         obligation.param_env,
-                                                         new_trait_ref.to_predicate());
+                    let new_obligation = Obligation::new(
+                        ObligationCause::dummy(),
+                        obligation.param_env,
+                        new_trait_ref.to_predicate(),
+                    );
 
                     if self.predicate_may_hold(&new_obligation) {
                         let sp = self.tcx.sess.source_map()
@@ -1105,6 +1112,71 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
     }
 
+    /// Check if the trait bound is implemented for a different mutability and note it in the
+    /// final error.
+    fn suggest_change_mut(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+        err: &mut DiagnosticBuilder<'tcx>,
+        trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
+        points_at_arg: bool,
+    ) {
+        let span = obligation.cause.span;
+        if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
+            let refs_number = snippet.chars()
+                .filter(|c| !c.is_whitespace())
+                .take_while(|c| *c == '&')
+                .count();
+            if let Some('\'') = snippet.chars()
+                .filter(|c| !c.is_whitespace())
+                .skip(refs_number)
+                .next()
+            { // Do not suggest removal of borrow from type arguments.
+                return;
+            }
+
+            if let ty::Ref(region, t_type, mutability) = trait_ref.skip_binder().self_ty().kind {
+                let trait_type = match mutability {
+                    hir::Mutability::MutMutable => self.tcx.mk_imm_ref(region, t_type),
+                    hir::Mutability::MutImmutable => self.tcx.mk_mut_ref(region, t_type),
+                };
+
+                let substs = self.tcx.mk_substs_trait(&trait_type, &[]);
+                let new_trait_ref = ty::TraitRef::new(trait_ref.skip_binder().def_id, substs);
+                let new_obligation = Obligation::new(
+                    ObligationCause::dummy(),
+                    obligation.param_env,
+                    new_trait_ref.to_predicate(),
+                );
+
+                if self.evaluate_obligation_no_overflow(
+                    &new_obligation,
+                ).must_apply_modulo_regions() {
+                    let sp = self.tcx.sess.source_map()
+                        .span_take_while(span, |c| c.is_whitespace() || *c == '&');
+                    if points_at_arg &&
+                        mutability == hir::Mutability::MutImmutable &&
+                        refs_number > 0
+                    {
+                        err.span_suggestion(
+                            sp,
+                            "consider changing this borrow's mutability",
+                            "&mut ".to_string(),
+                            Applicability::MachineApplicable,
+                        );
+                    } else {
+                        err.note(&format!(
+                            "`{}` is implemented for `{:?}`, but not for `{:?}`",
+                            trait_ref,
+                            trait_type,
+                            trait_ref.skip_binder().self_ty(),
+                        ));
+                    }
+                }
+            }
+        }
+    }
+
     fn suggest_semicolon_removal(
         &self,
         obligation: &PredicateObligation<'tcx>,

src/librustc/traits/query/evaluate_obligation.rs

@@ -56,7 +56,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     // Helper function that canonicalizes and runs the query. If an
     // overflow results, we re-run it in the local context so we can
     // report a nice error.
-    fn evaluate_obligation_no_overflow(
+    crate fn evaluate_obligation_no_overflow(
         &self,
         obligation: &PredicateObligation<'tcx>,
     ) -> EvaluationResult {

src/librustc/ty/sty.rs

@@ -1775,6 +1775,10 @@ impl<'tcx> TyS<'tcx> {
     #[inline]
     pub fn is_bool(&self) -> bool { self.kind == Bool }
 
+    /// Returns `true` if this type is a `str`.
+    #[inline]
+    pub fn is_str(&self) -> bool { self.kind == Str }
+
     #[inline]
     pub fn is_param(&self, index: u32) -> bool {
         match self.kind {

src/librustc_errors/styled_buffer.rs

@@ -111,7 +111,7 @@ impl StyledBuffer {
 
     pub fn prepend(&mut self, line: usize, string: &str, style: Style) {
         self.ensure_lines(line);
-        let string_len = string.len();
+        let string_len = string.chars().count();
 
         // Push the old content over to make room for new content
         for _ in 0..string_len {

src/librustc_typeck/check/demand.rs

@@ -349,7 +349,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // If the span is from a macro, then it's hard to extract the text
         // and make a good suggestion, so don't bother.
-        let is_macro = sp.from_expansion();
+        let is_desugaring = match sp.desugaring_kind() {
+            Some(k) => sp.is_desugaring(k),
+            None => false
+        };
+        let is_macro = sp.from_expansion() && !is_desugaring;
 
         match (&expr.kind, &expected.kind, &checked_ty.kind) {
             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {

src/librustc_typeck/check/expr.rs

@@ -87,6 +87,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
+            self.suggest_ref_or_into(&mut err, expr, expected_ty, ty);
+
             let expr = match &expr.kind {
                 ExprKind::DropTemps(expr) => expr,
                 _ => expr,

src/librustc_typeck/check/method/mod.rs

@@ -58,7 +58,7 @@ pub enum MethodError<'tcx> {
 
     // Found a `Self: Sized` bound where `Self` is a trait object, also the caller may have
     // forgotten to import a trait.
-    IllegalSizedBound(Vec<DefId>),
+    IllegalSizedBound(Vec<DefId>, bool),
 
     // Found a match, but the return type is wrong
     BadReturnType,
@@ -213,33 +213,49 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             segment,
         );
 
+        let mut needs_mut = false;
+        if let ty::Ref(region, t_type, mutability) = self_ty.kind {
+            let trait_type = self.tcx.mk_ref(region, ty::TypeAndMut {
+                ty: t_type,
+                mutbl: mutability.invert(),
+            });
+            match self.lookup_probe(
+                span,
+                segment.ident,
+                trait_type,
+                call_expr,
+                ProbeScope::TraitsInScope
+            ) {
+                Ok(ref new_pick) if *new_pick != pick => {
+                    needs_mut = true;
+                }
+                _ => {}
+            }
+        }
+
         if result.illegal_sized_bound {
             // We probe again, taking all traits into account (not only those in scope).
-            let 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()],
-                    Err(Ambiguity(ref sources)) => {
-                        sources.iter()
-                               .filter_map(|source| {
-                                   match *source {
-                                       // Note: this cannot come from an inherent impl,
-                                       // because the first probing succeeded.
-                                       ImplSource(def) => self.tcx.trait_id_of_impl(def),
-                                       TraitSource(_) => None,
-                                   }
-                               })
-                               .collect()
+            let 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()],
+                Err(Ambiguity(ref sources)) => sources.iter().filter_map(|source| {
+                    match *source {
+                        // Note: this cannot come from an inherent impl,
+                        // because the first probing succeeded.
+                        ImplSource(def) => self.tcx.trait_id_of_impl(def),
+                        TraitSource(_) => None,
                     }
-                    _ => Vec::new(),
-                };
+                }).collect(),
+                _ => Vec::new(),
+            };
 
-            return Err(IllegalSizedBound(candidates));
+            return Err(IllegalSizedBound(candidates, needs_mut));
         }
 
         Ok(result.callee)