Count chars when creating SourceAnnotation

src/formatting.rs

@@ -359,15 +359,16 @@ impl FormattingError {
             | ErrorKind::DeprecatedAttr
             | ErrorKind::BadAttr
             | ErrorKind::LostComment => {
-                let trailing_ws_start = self
-                    .line_buffer
-                    .rfind(|c: char| !c.is_whitespace())
-                    .map(|pos| pos + 1)
-                    .unwrap_or(0);
-                (
-                    trailing_ws_start,
-                    self.line_buffer.len() - trailing_ws_start,
-                )
+                let mut last_non_whitespace = 0;
+                let mut end = 0;
+                // annotate-snippet uses char-length, this code needs to as well
+                for (ind, ch) in self.line_buffer.chars().enumerate() {
+                    if !ch.is_whitespace() {
+                        last_non_whitespace = ind + 1;
+                    }
+                    end = ind + 1;
+                }
+                (last_non_whitespace, end - last_non_whitespace)
             }
             _ => unreachable!(),
         }

tests/issue-6083/issue_6083.rs

@@ -0,0 +1,6 @@
+// rustfmt-error_on_unformatted: false
+fn dummy() {
+    let my_var = 5 /* öäåöäåöäåöäåöäåöå */ 
+         / m as f64
+        + 0f64;
+}

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", "tests/target/issue_6069.rs"];
+    let files = ["tests/target/issue_5728.rs", "tests/target/issue_5729.rs", "tests/target/issue_6069.rs", "tests/issue-6083/issue_6083.rs"];
 
     for file in files {
         let args = [file];