X-Git-Url: https://git.lizzy.rs/?a=blobdiff_plain;f=src%2Flibrustc%2Ftraits%2Ferror_reporting.rs;h=65d08ab03aaaf699bd60872ff6d53a5ec4198609;hb=48b0fd2060614fc917616e5023a2b1af3158308a;hp=18f083e154a86eb523d22eefb95563452e9a76ad;hpb=614da98454984921142eb2059db7be953d2c855c;p=rust.git

diff --git a/src/librustc/traits/error_reporting.rs b/src/librustc/traits/error_reporting.rs
index 18f083e154a..65d08ab03aa 100644
--- a/src/librustc/traits/error_reporting.rs
+++ b/src/librustc/traits/error_reporting.rs
@@ -33,11 +33,12 @@
 use crate::ty::SubtypePredicate;
 use crate::util::nodemap::{FxHashMap, FxHashSet};
 
-use errors::{Applicability, DiagnosticBuilder, pluralize};
+use errors::{Applicability, DiagnosticBuilder, pluralize, Style};
 use std::fmt;
 use syntax::ast;
 use syntax::symbol::{sym, kw};
 use syntax_pos::{DUMMY_SP, Span, ExpnKind, MultiSpan};
+use rustc::hir::def_id::LOCAL_CRATE;
 
 use rustc_error_codes::*;
 
@@ -165,7 +166,7 @@ fn report_fulfillment_error(
         body_id: Option<hir::BodyId>,
         fallback_has_occurred: bool,
     ) {
-        debug!("report_fulfillment_errors({:?})", error);
+        debug!("report_fulfillment_error({:?})", error);
         match error.code {
             FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
                 self.report_selection_error(
@@ -713,20 +714,24 @@ pub fn report_selection_error(
                 }
                 match obligation.predicate {
                     ty::Predicate::Trait(ref trait_predicate) => {
-                        let trait_predicate =
-                            self.resolve_vars_if_possible(trait_predicate);
+                        let trait_predicate = self.resolve_vars_if_possible(trait_predicate);
 
                         if self.tcx.sess.has_errors() && trait_predicate.references_error() {
                             return;
                         }
                         let trait_ref = trait_predicate.to_poly_trait_ref();
-                        let (post_message, pre_message) =
-                            self.get_parent_trait_ref(&obligation.cause.code)
-                                .map(|t| (format!(" in `{}`", t), format!("within `{}`, ", t)))
+                        let (
+                            post_message,
+                            pre_message,
+                        ) = self.get_parent_trait_ref(&obligation.cause.code)
+                            .map(|t| (format!(" in `{}`", t), format!("within `{}`, ", t)))
                             .unwrap_or_default();
 
-                        let OnUnimplementedNote { message, label, note }
-                            = self.on_unimplemented_note(trait_ref, obligation);
+                        let OnUnimplementedNote {
+                            message,
+                            label,
+                            note,
+                        } = self.on_unimplemented_note(trait_ref, obligation);
                         let have_alt_message = message.is_some() || label.is_some();
                         let is_try = self.tcx.sess.source_map().span_to_snippet(span)
                             .map(|s| &s == "?")
@@ -767,6 +772,17 @@ pub fn report_selection_error(
                                 )
                             };
 
+                        if self.suggest_add_reference_to_arg(
+                            &obligation,
+                            &mut err,
+                            &trait_ref,
+                            points_at_arg,
+                            have_alt_message,
+                        ) {
+                            self.note_obligation_cause(&mut err, obligation);
+                            err.emit();
+                            return;
+                        }
                         if let Some(ref s) = label {
                             // If it has a custom `#[rustc_on_unimplemented]`
                             // error message, let's display it as the label!
@@ -784,6 +800,7 @@ pub fn report_selection_error(
                         self.suggest_fn_call(&obligation, &mut err, &trait_ref, points_at_arg);
                         self.suggest_remove_reference(&obligation, &mut err, &trait_ref);
                         self.suggest_semicolon_removal(&obligation, &mut err, span, &trait_ref);
+                        self.note_version_mismatch(&mut err, &trait_ref);
 
                         // Try to report a help message
                         if !trait_ref.has_infer_types() &&
@@ -1035,6 +1052,43 @@ pub fn report_selection_error(
         err.emit();
     }
 
+    /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
+    /// with the same path as `trait_ref`, a help message about
+    /// a probable version mismatch is added to `err`
+    fn note_version_mismatch(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        trait_ref: &ty::PolyTraitRef<'tcx>,
+    ) {
+        let get_trait_impl = |trait_def_id| {
+            let mut trait_impl = None;
+            self.tcx.for_each_relevant_impl(trait_def_id, trait_ref.self_ty(), |impl_def_id| {
+                if trait_impl.is_none() {
+                    trait_impl = Some(impl_def_id);
+                }
+            });
+            trait_impl
+        };
+        let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
+        let all_traits = self.tcx.all_traits(LOCAL_CRATE);
+        let traits_with_same_path: std::collections::BTreeSet<_> = all_traits
+            .iter()
+            .filter(|trait_def_id| **trait_def_id != trait_ref.def_id())
+            .filter(|trait_def_id| self.tcx.def_path_str(**trait_def_id) == required_trait_path)
+            .collect();
+        for trait_with_same_path in traits_with_same_path {
+            if let Some(impl_def_id) = get_trait_impl(*trait_with_same_path) {
+                let impl_span = self.tcx.def_span(impl_def_id);
+                err.span_help(impl_span, "trait impl with same name found");
+                let trait_crate = self.tcx.crate_name(trait_with_same_path.krate);
+                let crate_msg = format!(
+                    "Perhaps two different versions of crate `{}` are being used?",
+                    trait_crate
+                );
+                err.note(&crate_msg);
+            }
+        }
+    }
     fn suggest_restricting_param_bound(
         &self,
         err: &mut DiagnosticBuilder<'_>,
@@ -1371,6 +1425,73 @@ fn suggest_fn_call(
         }
     }
 
+    fn suggest_add_reference_to_arg(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+        err: &mut DiagnosticBuilder<'tcx>,
+        trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
+        points_at_arg: bool,
+        has_custom_message: bool,
+    ) -> bool {
+        if !points_at_arg {
+            return false;
+        }
+
+        let span = obligation.cause.span;
+        let param_env = obligation.param_env;
+        let trait_ref = trait_ref.skip_binder();
+
+        if let ObligationCauseCode::ImplDerivedObligation(obligation) = &obligation.cause.code {
+            // Try to apply the original trait binding obligation by borrowing.
+            let self_ty = trait_ref.self_ty();
+            let found = self_ty.to_string();
+            let new_self_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_static, self_ty);
+            let substs = self.tcx.mk_substs_trait(new_self_ty, &[]);
+            let new_trait_ref = ty::TraitRef::new(obligation.parent_trait_ref.def_id(), substs);
+            let new_obligation = Obligation::new(
+                ObligationCause::dummy(),
+                param_env,
+                new_trait_ref.to_predicate(),
+            );
+            if self.predicate_must_hold_modulo_regions(&new_obligation) {
+                if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
+                    // We have a very specific type of error, where just borrowing this argument
+                    // might solve the problem. In cases like this, the important part is the
+                    // original type obligation, not the last one that failed, which is arbitrary.
+                    // Because of this, we modify the error to refer to the original obligation and
+                    // return early in the caller.
+                    let msg = format!(
+                        "the trait bound `{}: {}` is not satisfied",
+                        found,
+                        obligation.parent_trait_ref.skip_binder(),
+                    );
+                    if has_custom_message {
+                        err.note(&msg);
+                    } else {
+                        err.message = vec![(msg, Style::NoStyle)];
+                    }
+                    if snippet.starts_with('&') {
+                        // This is already a literal borrow and the obligation is failing
+                        // somewhere else in the obligation chain. Do not suggest non-sense.
+                        return false;
+                    }
+                    err.span_label(span, &format!(
+                        "expected an implementor of trait `{}`",
+                        obligation.parent_trait_ref.skip_binder(),
+                    ));
+                    err.span_suggestion(
+                        span,
+                        "consider borrowing here",
+                        format!("&{}", snippet),
+                        Applicability::MaybeIncorrect,
+                    );
+                    return true;
+                }
+            }
+        }
+        false
+    }
+
     /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,
     /// suggest removing these references until we reach a type that implements the trait.
     fn suggest_remove_reference(