Rollup merge of #87311 - oli-obk:nll_suggestion_span, r=estebank

Get back the more precise suggestion spans of old regionck

I noticed that when you turn on nll, the structured suggestion replaces a snippet instead of appending a snippet. It seems clearer to the user to only highlight the newly added characters instead of the entire `impl Trait` (and old regionck already does it this way).

r? ``@estebank``

compiler/rustc_mir/src/borrow_check/diagnostics/region_errors.rs

@@ -9,7 +9,7 @@ use rustc_middle::mir::{ConstraintCategory, ReturnConstraint};
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, RegionVid, Ty};
 use rustc_span::symbol::{kw, sym};
-use rustc_span::Span;
+use rustc_span::{BytePos, Span};
 
 use crate::util::borrowck_errors;
 
@@ -641,12 +641,14 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                         } else {
                             "'_".to_string()
                         };
-                        let suggestion = if snippet.ends_with(';') {
+                        let span = if snippet.ends_with(';') {
                             // `type X = impl Trait;`
-                            format!("{} + {};", &snippet[..snippet.len() - 1], suggestable_fr_name)
+                            span.with_hi(span.hi() - BytePos(1))
                         } else {
-                            format!("{} + {}", snippet, suggestable_fr_name)
+                            span
                         };
+                        let suggestion = format!(" + {}", suggestable_fr_name);
+                        let span = span.shrink_to_hi();
                         diag.span_suggestion(
                             span,
                             &format!(

src/test/ui/impl-trait/must_outlive_least_region_or_bound.nll.stderr

@@ -9,7 +9,7 @@ LL | fn elided(x: &i32) -> impl Copy { x }
 help: to allow this `impl Trait` to capture borrowed data with lifetime `'1`, add `'_` as a bound
    |
 LL | fn elided(x: &i32) -> impl Copy + '_ { x }
-   |                       ^^^^^^^^^^^^^^
+   |                                 ^^^^
 
 error: lifetime may not live long enough
   --> $DIR/must_outlive_least_region_or_bound.rs:5:32
@@ -23,7 +23,7 @@ LL | fn explicit<'a>(x: &'a i32) -> impl Copy { x }
 help: to allow this `impl Trait` to capture borrowed data with lifetime `'a`, add `'a` as a bound
    |
 LL | fn explicit<'a>(x: &'a i32) -> impl Copy + 'a { x }
-   |                                ^^^^^^^^^^^^^^
+   |                                          ^^^^
 
 error: lifetime may not live long enough
   --> $DIR/must_outlive_least_region_or_bound.rs:7:46

src/test/ui/impl-trait/static-return-lifetime-infered.nll.stderr

@@ -9,7 +9,7 @@ LL |     fn iter_values_anon(&self) -> impl Iterator<Item=u32> {
 help: to allow this `impl Trait` to capture borrowed data with lifetime `'1`, add `'_` as a bound
    |
 LL |     fn iter_values_anon(&self) -> impl Iterator<Item=u32> + '_ {
-   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                                           ^^^^
 
 error: lifetime may not live long enough
   --> $DIR/static-return-lifetime-infered.rs:9:37
@@ -23,7 +23,7 @@ LL |     fn iter_values<'a>(&'a self) -> impl Iterator<Item=u32> {
 help: to allow this `impl Trait` to capture borrowed data with lifetime `'a`, add `'a` as a bound
    |
 LL |     fn iter_values<'a>(&'a self) -> impl Iterator<Item=u32> + 'a {
-   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                                             ^^^^
 
 error: aborting due to 2 previous errors
 

src/test/ui/self/arbitrary_self_types_pin_lifetime_impl_trait-async.nll.stderr

@@ -9,7 +9,7 @@ LL |     async fn f(self: Pin<&Self>) -> impl Clone { self }
 help: to allow this `impl Trait` to capture borrowed data with lifetime `'1`, add `'_` as a bound
    |
 LL |     async fn f(self: Pin<&Self>) -> impl Clone + '_ { self }
-   |                                     ^^^^^^^^^^^^^^^
+   |                                                ^^^^
 
 error: aborting due to previous error
 

src/test/ui/self/arbitrary_self_types_pin_lifetime_impl_trait.nll.stderr

@@ -9,7 +9,7 @@ LL |     fn f(self: Pin<&Self>) -> impl Clone { self }
 help: to allow this `impl Trait` to capture borrowed data with lifetime `'1`, add `'_` as a bound
    |
 LL |     fn f(self: Pin<&Self>) -> impl Clone + '_ { self }
-   |                               ^^^^^^^^^^^^^^^
+   |                                          ^^^^
 
 error: aborting due to previous error
 

src/test/ui/suggestions/lifetimes/trait-object-nested-in-impl-trait.nll.stderr

@@ -9,7 +9,7 @@ LL |     fn iter(&self) -> impl Iterator<Item = Box<dyn Foo>> {
 help: to allow this `impl Trait` to capture borrowed data with lifetime `'1`, add `'_` as a bound
    |
 LL |     fn iter(&self) -> impl Iterator<Item = Box<dyn Foo>> + '_ {
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                                          ^^^^
 
 error: lifetime may not live long enough
   --> $DIR/trait-object-nested-in-impl-trait.rs:39:9
@@ -47,7 +47,7 @@ LL |     fn iter<'a>(&'a self) -> impl Iterator<Item = Box<dyn Foo>> {
 help: to allow this `impl Trait` to capture borrowed data with lifetime `'a`, add `'a` as a bound
    |
 LL |     fn iter<'a>(&'a self) -> impl Iterator<Item = Box<dyn Foo>> + 'a {
-   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                                                 ^^^^
 
 error: aborting due to 4 previous errors