Auto merge of #41174 - estebank:issue-41155, r=nikomatsakis

Point at only one char on `Span::next_point`

Avoid pointing at two chars so the diagnostic output doesn't display a
multiline span when starting beyond a line end.

Fix #41155.

Instead of

```rust
error: expected one of `(`, `const`, `default`, `extern`, `fn`, `type`, or `unsafe`, found `}`
 --> <anon>:3:1
  |
1 |   impl S {	pub
  |  _____________- starting here...
2 | |
  | |  ...ending here: expected one of 7 possible tokens here
3 |   }
  |   ^ unexpected token
```

show

```rust
error: expected one of `(`, `const`, `default`, `extern`, `fn`, `type`, or `unsafe`, found `}`
  --> <anon>:13:1
   |
12 |     pub
   |        - expected one of 7 possible tokens here
13 | }
   | ^ unexpected token
```

1 files changed, 4 insertions, 2 deletions

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 43d21015a4f..58be43526fd 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -592,8 +592,10 @@ impl<'a> Parser<'a> {
             } else {
                 label_sp
             };
-            err.span_label(sp, &label_exp);
-            if !sp.source_equal(&self.span) {
+            if self.span.contains(sp) {
+                err.span_label(self.span, &label_exp);
+            } else {
+                err.span_label(sp, &label_exp);
                 err.span_label(self.span, &"unexpected token");
             }
             Err(err)