Increase verbosity when suggesting subtle code changes

src/librustc_infer/infer/error_reporting/need_type_info.rs

@@ -3,7 +3,7 @@ use crate::infer::InferCtxt;
 use rustc::hir::map::Map;
 use rustc::ty::print::Print;
 use rustc::ty::{self, DefIdTree, Infer, Ty, TyVar};
-use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
+use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Namespace};
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
@@ -462,24 +462,19 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         e: &Expr<'_>,
         err: &mut DiagnosticBuilder<'_>,
     ) {
-        if let (Ok(snippet), Some(tables), None) = (
-            self.tcx.sess.source_map().span_to_snippet(segment.ident.span),
-            self.in_progress_tables,
-            &segment.args,
-        ) {
+        if let (Some(tables), None) = (self.in_progress_tables, &segment.args) {
             let borrow = tables.borrow();
             if let Some((DefKind::AssocFn, did)) = borrow.type_dependent_def(e.hir_id) {
                 let generics = self.tcx.generics_of(did);
                 if !generics.params.is_empty() {
-                    err.span_suggestion(
-                        segment.ident.span,
+                    err.span_suggestion_verbose(
+                        segment.ident.span.shrink_to_hi(),
                         &format!(
                             "consider specifying the type argument{} in the method call",
-                            if generics.params.len() > 1 { "s" } else { "" },
+                            pluralize!(generics.params.len()),
                         ),
                         format!(
-                            "{}::<{}>",
-                            snippet,
+                            "::<{}>",
                             generics
                                 .params
                                 .iter()

src/librustc_privacy/lib.rs

@@ -1038,7 +1038,7 @@ impl<'a, 'tcx> NamePrivacyVisitor<'a, 'tcx> {
                 def.variant_descr(),
                 self.tcx.def_path_str(def.did)
             )
-            .span_label(span, format!("field `{}` is private", field.ident))
+            .span_label(span, "private field")
             .emit();
         }
     }
@@ -1180,7 +1180,11 @@ impl<'a, 'tcx> TypePrivacyVisitor<'a, 'tcx> {
     fn check_def_id(&mut self, def_id: DefId, kind: &str, descr: &dyn fmt::Display) -> bool {
         let is_error = !self.item_is_accessible(def_id);
         if is_error {
-            self.tcx.sess.span_err(self.span, &format!("{} `{}` is private", kind, descr));
+            self.tcx
+                .sess
+                .struct_span_err(self.span, &format!("{} `{}` is private", kind, descr))
+                .span_label(self.span, &format!("private {}", kind))
+                .emit();
         }
         is_error
     }
@@ -1313,8 +1317,12 @@ impl<'a, 'tcx> Visitor<'tcx> for TypePrivacyVisitor<'a, 'tcx> {
                     hir::QPath::Resolved(_, ref path) => path.to_string(),
                     hir::QPath::TypeRelative(_, ref segment) => segment.ident.to_string(),
                 };
-                let msg = format!("{} `{}` is private", kind.descr(def_id), name);
-                self.tcx.sess.span_err(span, &msg);
+                let kind = kind.descr(def_id);
+                self.tcx
+                    .sess
+                    .struct_span_err(span, &format!("{} `{}` is private", kind, name))
+                    .span_label(span, &format!("private {}", kind))
+                    .emit();
                 return;
             }
         }

src/librustc_resolve/diagnostics.rs

@@ -952,7 +952,7 @@ impl<'a> Resolver<'a> {
         let descr = get_descr(binding);
         let mut err =
             struct_span_err!(self.session, ident.span, E0603, "{} `{}` is private", descr, ident);
-        err.span_label(ident.span, &format!("this {} is private", descr));
+        err.span_label(ident.span, &format!("private {}", descr));
         if let Some(span) = ctor_fields_span {
             err.span_label(span, "a constructor is private if any of the fields is private");
         }

src/librustc_resolve/late/diagnostics.rs

@@ -506,10 +506,10 @@ impl<'a> LateResolutionVisitor<'a, '_, '_> {
 
         match (res, source) {
             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
-                err.span_suggestion(
-                    span,
+                err.span_suggestion_verbose(
+                    span.shrink_to_hi(),
                     "use `!` to invoke the macro",
-                    format!("{}!", path_str),
+                    "!".to_string(),
                     Applicability::MaybeIncorrect,
                 );
                 if path_str == "try" && span.rust_2015() {

src/librustc_trait_selection/traits/error_reporting/mod.rs

@@ -815,11 +815,11 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             // For example, if `expected_args_length` is 2, suggest `|_, _|`.
             if found_args.is_empty() && is_closure {
                 let underscores = vec!["_"; expected_args.len()].join(", ");
-                err.span_suggestion(
+                err.span_suggestion_verbose(
                     pipe_span,
                     &format!(
                         "consider changing the closure to take and ignore the expected argument{}",
-                        if expected_args.len() < 2 { "" } else { "s" }
+                        pluralize!(expected_args.len())
                     ),
                     format!("|{}|", underscores),
                     Applicability::MachineApplicable,
@@ -833,7 +833,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         .map(|(name, _)| name.to_owned())
                         .collect::<Vec<String>>()
                         .join(", ");
-                    err.span_suggestion(
+                    err.span_suggestion_verbose(
                         found_span,
                         "change the closure to take multiple arguments instead of a single tuple",
                         format!("|{}|", sugg),
@@ -870,7 +870,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             String::new()
                         },
                     );
-                    err.span_suggestion(
+                    err.span_suggestion_verbose(
                         found_span,
                         "change the closure to accept a tuple instead of individual arguments",
                         sugg,
@@ -1420,15 +1420,14 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
                         //    |
                         //    = note: cannot resolve `_: Tt`
 
-                        err.span_suggestion(
-                            span,
+                        err.span_suggestion_verbose(
+                            span.shrink_to_hi(),
                             &format!(
                                 "consider specifying the type argument{} in the function call",
-                                if generics.params.len() > 1 { "s" } else { "" },
+                                pluralize!(generics.params.len()),
                             ),
                             format!(
-                                "{}::<{}>",
-                                snippet,
+                                "::<{}>",
                                 generics
                                     .params
                                     .iter()
@@ -1590,7 +1589,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
                             [] => (span.shrink_to_hi(), ":"),
                             [.., bound] => (bound.span().shrink_to_hi(), " + "),
                         };
-                        err.span_suggestion(
+                        err.span_suggestion_verbose(
                             span,
                             "consider relaxing the implicit `Sized` restriction",
                             format!("{} ?Sized", separator),

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -390,7 +390,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         }
         let hir = self.tcx.hir();
         // Get the name of the callable and the arguments to be used in the suggestion.
-        let snippet = match hir.get_if_local(def_id) {
+        let (snippet, sugg) = match hir.get_if_local(def_id) {
             Some(hir::Node::Expr(hir::Expr {
                 kind: hir::ExprKind::Closure(_, decl, _, span, ..),
                 ..
@@ -401,7 +401,8 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     None => return,
                 };
                 let args = decl.inputs.iter().map(|_| "_").collect::<Vec<_>>().join(", ");
-                format!("{}({})", name, args)
+                let sugg = format!("({})", args);
+                (format!("{}{}", name, sugg), sugg)
             }
             Some(hir::Node::Item(hir::Item {
                 ident,
@@ -422,7 +423,8 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     })
                     .collect::<Vec<_>>()
                     .join(", ");
-                format!("{}({})", ident, args)
+                let sugg = format!("({})", args);
+                (format!("{}{}", ident, sugg), sugg)
             }
             _ => return,
         };
@@ -431,10 +433,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             // an argument, the `obligation.cause.span` points at the expression
             // of the argument, so we can provide a suggestion. This is signaled
             // by `points_at_arg`. Otherwise, we give a more general note.
-            err.span_suggestion(
-                obligation.cause.span,
+            err.span_suggestion_verbose(
+                obligation.cause.span.shrink_to_hi(),
                 &msg,
-                snippet,
+                sugg,
                 Applicability::HasPlaceholders,
             );
         } else {
@@ -619,7 +621,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         .source_map()
                         .span_take_while(span, |c| c.is_whitespace() || *c == '&');
                     if points_at_arg && mutability == hir::Mutability::Not && refs_number > 0 {
-                        err.span_suggestion(
+                        err.span_suggestion_verbose(
                             sp,
                             "consider changing this borrow's mutability",
                             "&mut ".to_string(),

src/librustc_typeck/astconv.rs

@@ -1452,8 +1452,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             .expect("missing associated type");
 
         if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
-            let msg = format!("associated type `{}` is private", binding.item_name);
-            tcx.sess.span_err(binding.span, &msg);
+            tcx.sess
+                .struct_span_err(
+                    binding.span,
+                    &format!("associated type `{}` is private", binding.item_name),
+                )
+                .span_label(binding.span, "private associated type")
+                .emit();
         }
         tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
 
@@ -2316,8 +2321,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         let kind = DefKind::AssocTy;
         if !item.vis.is_accessible_from(def_scope, tcx) {
-            let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
-            tcx.sess.span_err(span, &msg);
+            let kind = kind.descr(item.def_id);
+            let msg = format!("{} `{}` is private", kind, assoc_ident);
+            tcx.sess
+                .struct_span_err(span, &msg)
+                .span_label(span, &format!("private {}", kind))
+                .emit();
         }
         tcx.check_stability(item.def_id, Some(hir_ref_id), span);
 

src/librustc_typeck/check/expr.rs

@@ -1583,13 +1583,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         };
         let mut err = struct_span_err!(
             self.tcx().sess,
-            expr.span,
+            field.span,
             E0616,
             "field `{}` of {} `{}` is private",
             field,
             kind_name,
             struct_path
         );
+        err.span_label(field.span, "private field");
         // Also check if an accessible method exists, which is often what is meant.
         if self.method_exists(field, expr_t, expr.hir_id, false) && !self.expr_in_place(expr.hir_id)
         {
@@ -1614,7 +1615,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             field,
             expr_t
         );
-
+        err.span_label(field.span, "method, not a field");
         if !self.expr_in_place(expr.hir_id) {
             self.suggest_method_call(
                 &mut err,

src/librustc_typeck/check/method/mod.rs

@@ -137,7 +137,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self_ty: Ty<'tcx>,
         call_expr: &hir::Expr<'_>,
     ) {
-        let has_params = self
+        let params = self
             .probe_for_name(
                 method_name.span,
                 probe::Mode::MethodCall,
@@ -147,26 +147,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 call_expr.hir_id,
                 ProbeScope::TraitsInScope,
             )
-            .and_then(|pick| {
+            .map(|pick| {
                 let sig = self.tcx.fn_sig(pick.item.def_id);
-                Ok(sig.inputs().skip_binder().len() > 1)
-            });
+                sig.inputs().skip_binder().len().saturating_sub(1)
+            })
+            .unwrap_or(0);
 
         // Account for `foo.bar<T>`;
-        let sugg_span = method_name.span.with_hi(call_expr.span.hi());
-        let snippet = self
-            .tcx
-            .sess
-            .source_map()
-            .span_to_snippet(sugg_span)
-            .unwrap_or_else(|_| method_name.to_string());
-        let (suggestion, applicability) = if has_params.unwrap_or_default() {
-            (format!("{}(...)", snippet), Applicability::HasPlaceholders)
-        } else {
-            (format!("{}()", snippet), Applicability::MaybeIncorrect)
-        };
+        let sugg_span = call_expr.span.shrink_to_hi();
+        let (suggestion, applicability) = (
+            format!("({})", (0..params).map(|_| "_").collect::<Vec<_>>().join(", ")),
+            if params > 0 { Applicability::HasPlaceholders } else { Applicability::MaybeIncorrect },
+        );
 
-        err.span_suggestion(sugg_span, msg, suggestion, applicability);
+        err.span_suggestion_verbose(sugg_span, msg, suggestion, applicability);
     }
 
     /// Performs method lookup. If lookup is successful, it will return the callee

src/librustc_typeck/check/method/suggest.rs

@@ -758,25 +758,27 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             MethodError::Ambiguity(sources) => {
                 let mut err = struct_span_err!(
                     self.sess(),
-                    span,
+                    item_name.span,
                     E0034,
                     "multiple applicable items in scope"
                 );
-                err.span_label(span, format!("multiple `{}` found", item_name));
+                err.span_label(item_name.span, format!("multiple `{}` found", item_name));
 
                 report_candidates(span, &mut err, sources, sugg_span);
                 err.emit();
             }
 
             MethodError::PrivateMatch(kind, def_id, out_of_scope_traits) => {
+                let kind = kind.descr(def_id);
                 let mut err = struct_span_err!(
                     self.tcx.sess,
-                    span,
+                    item_name.span,
                     E0624,
                     "{} `{}` is private",
-                    kind.descr(def_id),
+                    kind,
                     item_name
                 );
+                err.span_label(item_name.span, &format!("private {}", kind));
                 self.suggest_valid_traits(&mut err, out_of_scope_traits);
                 err.emit();
             }

src/librustc_typeck/check/mod.rs

@@ -4941,15 +4941,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
                 _ => {}
             }
-            if let Ok(code) = self.sess().source_map().span_to_snippet(expr.span) {
-                err.span_suggestion(
-                    expr.span,
-                    &format!("use parentheses to {}", msg),
-                    format!("{}({})", code, sugg_call),
-                    applicability,
-                );
-                return true;
-            }
+            err.span_suggestion_verbose(
+                expr.span.shrink_to_hi(),
+                &format!("use parentheses to {}", msg),
+                format!("({})", sugg_call),
+                applicability,
+            );
+            return true;
         }
         false
     }