Auto merge of #78429 - casey:doctest-attribute-splitting, r=jyn514

[rust.git] / compiler / rustc_errors / src / emitter.rs

diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index ea62e21523028e3223fde03bc4098feb14fbb9f2..42c3d5e48fe86f040e041389c932e83504234c59 100644 (file)
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -1713,7 +1713,18 @@ fn emit_messages_default(
         let max_line_num_len = if self.ui_testing {
             ANONYMIZED_LINE_NUM.len()
         } else {
-            self.get_max_line_num(span, children).to_string().len()
+            // Instead of using .to_string().len(), we iteratively count the
+            // number of digits to avoid allocation. This strategy has sizable
+            // performance gains over the old string strategy.
+            let mut n = self.get_max_line_num(span, children);
+            let mut num_digits = 0;
+            loop {
+                num_digits += 1;
+                n /= 10;
+                if n == 0 {
+                    break num_digits;
+                }
+            }
         };
 
         match self.emit_message_default(span, message, code, level, max_line_num_len, false) {