Search span using *unnormalized* ident (#6073)

Fixes 6069

Calling `item.ident.as_str()` returns an NFC normalized ident, which
might not be what's written in the source code. To avoid panics when
calling `snippet_provider.span_after` use the ident from the source.

src/items.rs

@@ -1166,9 +1166,9 @@ pub(crate) fn format_trait(
 
     // FIXME(#2055): rustfmt fails to format when there are comments between trait bounds.
     if !bounds.is_empty() {
-        let ident_hi = context
-            .snippet_provider
-            .span_after(item.span, item.ident.as_str());
+        // Retrieve *unnormalized* ident (See #6069)
+        let source_ident = context.snippet(item.ident.span);
+        let ident_hi = context.snippet_provider.span_after(item.span, source_ident);
         let bound_hi = bounds.last().unwrap().span().hi();
         let snippet = context.snippet(mk_sp(ident_hi, bound_hi));
         if contains_comment(snippet) {

tests/rustfmt/main.rs

@@ -176,7 +176,7 @@ fn rustfmt_emits_error_on_line_overflow_true() {
 #[test]
 #[allow(non_snake_case)]
 fn dont_emit_ICE() {
-    let files = ["tests/target/issue_5728.rs", "tests/target/issue_5729.rs"];
+    let files = ["tests/target/issue_5728.rs", "tests/target/issue_5729.rs", "tests/target/issue_6069.rs"];
 
     for file in files {
         let args = [file];

tests/target/issue_6069.rs

@@ -0,0 +1,3 @@
+// `Foó` as written here ends with ASCII 6F `'o'` followed by `'\u{0301}'` COMBINING ACUTE ACCENT.
+// The compiler normalizes that combination to NFC form, `'\u{00F3}'` LATIN SMALL LETTER O WITH ACUTE.
+trait Foó: Bar {}