From adaf2bf2828215c8c3525703a6850ea4b0ec61fd Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Tue, 15 Sep 2026 08:26:29 +0000
Subject: [PATCH] refactor: optimize string capacity allocation in lsp
 range_formatting

Co-authored-by: Tcode-Motion <188012755+Tcode-Motion@users.noreply.github.com>
---
 .jules/bolt.md       |  3 +++
 tools/lsp/src/lib.rs | 17 ++++++++++++-----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/.jules/bolt.md b/.jules/bolt.md
index 5034e016..110a0b82 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -20,3 +20,6 @@
 ## 2024-08-01 - Bytecode Disassembler String Allocation Optimization
 **Learning:** Formatting directly into a string buffer inside a tight loop with `write!(buffer, ...)` avoids unnecessary string heap allocations compared to `buffer.push_str(&format!(...))`.
 **Action:** Always prefer formatting directly into the target String buffer when concatenating strings in loops in performance-sensitive paths like debuggers or disassemblers.
+## 2024-05-19 - [Optimize string concatenation in LSP range_formatting]
+**Learning:** Temporary files created for testing performance locally, especially compiled executable binaries, will cause CI pollution and code review failure if not deleted before submitting a patch. String concatenation in a loop over slices can be highly optimized by pre-calculating capacity.
+**Action:** Always delete scratch benchmark files (e.g. `rm -f test_perf*`) immediately after use and before requesting code review. Always use `String::with_capacity` when iterating over slices to avoid intermediate reallocation overhead.
diff --git a/tools/lsp/src/lib.rs b/tools/lsp/src/lib.rs
index 9e8845d5..ce2cc4a5 100644
--- a/tools/lsp/src/lib.rs
+++ b/tools/lsp/src/lib.rs
@@ -1291,11 +1291,18 @@ impl LanguageServer for Backend {
         let start = range.start.line as usize;
         let end = (range.end.line as usize).min(lines.len() - 1);
 
-        let mut selection = String::new();
-        for i in start..=end {
-            selection.push_str(lines[i]);
-            selection.push('\n');
-        }
+        let selection = if start <= end {
+            let slice = &lines[start..=end];
+            let capacity: usize = slice.iter().map(|l| l.len() + 1).sum();
+            let mut s = String::with_capacity(capacity);
+            for line in slice {
+                s.push_str(line);
+                s.push('\n');
+            }
+            s
+        } else {
+            String::new()
+        };
 
         let formatted = self.format_source(&selection);
         Ok(Some(vec![TextEdit {