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_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/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/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
     }

src/librustc_typeck/check/pat.rs

@@ -753,17 +753,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         res.descr(),
                     ),
                 );
-                let (msg, sugg) = match parent_pat {
-                    Some(Pat { kind: hir::PatKind::Struct(..), .. }) => (
-                        "bind the struct field to a different name instead",
-                        format!("{}: other_{}", ident, ident.as_str().to_lowercase()),
-                    ),
-                    _ => (
-                        "introduce a new binding instead",
-                        format!("other_{}", ident.as_str().to_lowercase()),
-                    ),
+                match parent_pat {
+                    Some(Pat { kind: hir::PatKind::Struct(..), .. }) => {
+                        e.span_suggestion_verbose(
+                            ident.span.shrink_to_hi(),
+                            "bind the struct field to a different name instead",
+                            format!(": other_{}", ident.as_str().to_lowercase()),
+                            Applicability::HasPlaceholders,
+                        );
+                    }
+                    _ => {
+                        let msg = "introduce a new binding instead";
+                        let sugg = format!("other_{}", ident.as_str().to_lowercase());
+                        e.span_suggestion(ident.span, msg, sugg, Applicability::HasPlaceholders);
+                    }
                 };
-                e.span_suggestion(ident.span, msg, sugg, Applicability::HasPlaceholders);
             }
         }
         e.emit();

src/test/ui/error-codes/E0615.stderr

@@ -2,7 +2,12 @@ error[E0615]: attempted to take value of method `method` on type `Foo`
   --> $DIR/E0615.rs:11:7
    |
 LL |     f.method;
-   |       ^^^^^^ help: use parentheses to call the method: `method()`
+   |       ^^^^^^
+   |
+help: use parentheses to call the method
+   |
+LL |     f.method();
+   |             ^^
 
 error: aborting due to previous error
 

src/test/ui/extern/extern-types-unsized.stderr

@@ -2,15 +2,17 @@ error[E0277]: the size for values of type `A` cannot be known at compilation tim
   --> $DIR/extern-types-unsized.rs:22:20
    |
 LL | fn assert_sized<T>() { }
-   |    ------------ -- help: consider relaxing the implicit `Sized` restriction: `: ?Sized`
-   |                 |
-   |                 required by this bound in `assert_sized`
+   |    ------------ - required by this bound in `assert_sized`
 ...
 LL |     assert_sized::<A>();
    |                    ^ doesn't have a size known at compile-time
    |
    = help: the trait `std::marker::Sized` is not implemented for `A`
    = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | fn assert_sized<T: ?Sized>() { }
+   |                  ^^^^^^^^
 
 error[E0277]: the size for values of type `A` cannot be known at compilation time
   --> $DIR/extern-types-unsized.rs:25:5

src/test/ui/implicit-method-bind.stderr

@@ -2,7 +2,12 @@ error[E0615]: attempted to take value of method `abs` on type `i32`
   --> $DIR/implicit-method-bind.rs:2:20
    |
 LL |     let _f = 10i32.abs;
-   |                    ^^^ help: use parentheses to call the method: `abs()`
+   |                    ^^^
+   |
+help: use parentheses to call the method
+   |
+LL |     let _f = 10i32.abs();
+   |                       ^^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-13853-2.stderr

@@ -2,7 +2,12 @@ error[E0615]: attempted to take value of method `get` on type `std::boxed::Box<(
   --> $DIR/issue-13853-2.rs:5:43
    |
 LL | fn foo(res : Box<dyn ResponseHook>) { res.get }
-   |                                           ^^^ help: use parentheses to call the method: `get()`
+   |                                           ^^^
+   |
+help: use parentheses to call the method
+   |
+LL | fn foo(res : Box<dyn ResponseHook>) { res.get() }
+   |                                              ^^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-26472.stderr

@@ -2,9 +2,12 @@ error[E0616]: field `len` of struct `sub::S` is private
   --> $DIR/issue-26472.rs:11:13
    |
 LL |     let v = s.len;
-   |             ^^---
-   |               |
-   |               help: a method `len` also exists, call it with parentheses: `len()`
+   |             ^^^^^
+   |
+help: a method `len` also exists, call it with parentheses
+   |
+LL |     let v = s.len();
+   |                  ^^
 
 error[E0616]: field `len` of struct `sub::S` is private
   --> $DIR/issue-26472.rs:12:5

src/test/ui/issues/issue-35241.stderr

@@ -5,14 +5,16 @@ LL | struct Foo(u32);
    | ---------------- fn(u32) -> Foo {Foo} defined here
 LL | 
 LL | fn test() -> Foo { Foo }
-   |              ---   ^^^
-   |              |     |
-   |              |     expected struct `Foo`, found fn item
-   |              |     help: use parentheses to instantiate this tuple struct: `Foo(_)`
+   |              ---   ^^^ expected struct `Foo`, found fn item
+   |              |
    |              expected `Foo` because of return type
    |
    = note: expected struct `Foo`
              found fn item `fn(u32) -> Foo {Foo}`
+help: use parentheses to instantiate this tuple struct
+   |
+LL | fn test() -> Foo { Foo(_) }
+   |                       ^^^
 
 error: aborting due to previous error
 

src/test/ui/methods/method-missing-call.stderr

@@ -2,13 +2,23 @@ error[E0615]: attempted to take value of method `get_x` on type `Point`
   --> $DIR/method-missing-call.rs:22:26
    |
 LL |                         .get_x;
-   |                          ^^^^^ help: use parentheses to call the method: `get_x()`
+   |                          ^^^^^
+   |
+help: use parentheses to call the method
+   |
+LL |                         .get_x();
+   |                               ^^
 
 error[E0615]: attempted to take value of method `filter_map` on type `std::iter::Filter<std::iter::Map<std::slice::Iter<'_, {integer}>, [closure@$DIR/method-missing-call.rs:27:20: 27:25]>, [closure@$DIR/method-missing-call.rs:28:23: 28:35]>`
   --> $DIR/method-missing-call.rs:29:16
    |
 LL |               .filter_map;
-   |                ^^^^^^^^^^ help: use parentheses to call the method: `filter_map(...)`
+   |                ^^^^^^^^^^
+   |
+help: use parentheses to call the method
+   |
+LL |               .filter_map(_);
+   |                          ^^^
 
 error: aborting due to 2 previous errors
 

src/test/ui/question-mark-type-infer.stderr

@@ -2,12 +2,13 @@ error[E0284]: type annotations needed
   --> $DIR/question-mark-type-infer.rs:12:21
    |
 LL |     l.iter().map(f).collect()?
-   |                     ^^^^^^^
-   |                     |
-   |                     cannot infer type
-   |                     help: consider specifying the type argument in the method call: `collect::<B>`
+   |                     ^^^^^^^ cannot infer type
    |
    = note: cannot resolve `<_ as std::ops::Try>::Ok == _`
+help: consider specifying the type argument in the method call
+   |
+LL |     l.iter().map(f).collect::<B>()?
+   |                            ^^^^^
 
 error: aborting due to previous error