[review comments] modify test and clean up code

Co-Authored-By: estebank <esteban@kuber.com.ar>

Author: oli-obk

src/librustc/middle/resolve_lifetime.rs

@@ -2252,7 +2252,7 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
     fn suggest_lifetime(&self, db: &mut DiagnosticBuilder<'_>, span: Span, msg: &str) -> bool {
         match self.tcx.sess.source_map().span_to_snippet(span) {
             Ok(ref snippet) => {
-                let (sugg, applicability) = if &snippet[..] == "&" {
+                let (sugg, applicability) = if snippet == "&" {
                     ("&'static ".to_owned(), Applicability::MachineApplicable)
                 } else if snippet == "'_" {
                     ("'static".to_owned(), Applicability::MachineApplicable)

src/test/ui/lifetimes/lifetime-elision-return-type-trait.rs

@@ -8,3 +8,5 @@ use std::error::Error;
 fn foo() -> impl Future<Item=(), Error=Box<Error>> {
     Ok(())
 }
+
+fn main() {}

src/test/ui/lifetimes/lifetime-elision-return-type-trait.stderr

@@ -1,7 +1,3 @@
-error[E0601]: `main` function not found in crate `lifetime_elision_return_type_trait`
-   |
-   = note: consider adding a `main` function to `$DIR/lifetime-elision-return-type-trait.rs`
-
 error[E0106]: missing lifetime specifier
   --> $DIR/lifetime-elision-return-type-trait.rs:8:44
    |
@@ -10,7 +6,6 @@ LL | fn foo() -> impl Future<Item=(), Error=Box<Error>> {
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors occurred: E0106, E0601.
-For more information about an error, try `rustc --explain E0106`.
+For more information about this error, try `rustc --explain E0106`.