Auto merge of #111585 - matthiaskrgr:rollup-468pykj, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #102673 (Update doc for `PhantomData` to match code example)
 - #111531 (Fix ice caused by shorthand fields in NoFieldsForFnCall)
 - #111547 (Start node has no immediate dominator)
 - #111548 (add util function to TokenStream to eliminate some clones)
 - #111560 (Simplify find_width_of_character_at_span.)
 - #111569 (Appease lints)
 - #111581 (Fix some misleading and copy-pasted `Pattern` examples)
 - #111582 ((docs) Change "wanting" to "want")

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

2 files changed, 8 insertions, 24 deletions

diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index 7bbab34c69a..97cb734619e 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -20,6 +20,7 @@
 #![feature(min_specialization)]
 #![feature(rustc_attrs)]
 #![feature(let_chains)]
+#![feature(round_char_boundary)]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
 
diff --git a/compiler/rustc_span/src/source_map.rs b/compiler/rustc_span/src/source_map.rs
index 8238a16969d..11ea5fe4ddf 100644
--- a/compiler/rustc_span/src/source_map.rs
+++ b/compiler/rustc_span/src/source_map.rs
@@ -1019,36 +1019,19 @@ impl SourceMap {
 
         let src = local_begin.sf.external_src.borrow();
 
-        // We need to extend the snippet to the end of the src rather than to end_index so when
-        // searching forwards for boundaries we've got somewhere to search.
-        let snippet = if let Some(ref src) = local_begin.sf.src {
-            &src[start_index..]
+        let snippet = if let Some(src) = &local_begin.sf.src {
+            src
         } else if let Some(src) = src.get_source() {
-            &src[start_index..]
+            src
         } else {
             return 1;
         };
-        debug!("snippet=`{:?}`", snippet);
 
-        let mut target = if forwards { end_index + 1 } else { end_index - 1 };
-        debug!("initial target=`{:?}`", target);
-
-        while !snippet.is_char_boundary(target - start_index) && target < source_len {
-            target = if forwards {
-                target + 1
-            } else {
-                match target.checked_sub(1) {
-                    Some(target) => target,
-                    None => {
-                        break;
-                    }
-                }
-            };
-            debug!("target=`{:?}`", target);
+        if forwards {
+            (snippet.ceil_char_boundary(end_index + 1) - end_index) as u32
+        } else {
+            (end_index - snippet.floor_char_boundary(end_index - 1)) as u32
         }
-        debug!("final target=`{:?}`", target);
-
-        if forwards { (target - end_index) as u32 } else { (end_index - target) as u32 }
     }
 
     pub fn get_source_file(&self, filename: &FileName) -> Option<Lrc<SourceFile>> {