⚡ Bolt: Optimize is_likely_code_text with early exit

.jules/bolt.md

@@ -17,3 +17,7 @@
 ## 2025-05-19 - File Discovery Allocations
 **Learning:** In `discover_importing_files`, `WalkBuilder` results were being converted to `PathBuf` via `.map(|e| e.into_path())` *before* filtering. This caused allocations for every single file in the workspace (including excluded files and directories).
 **Action:** Filter `ignore::DirEntry` directly using `entry.file_type()` and `entry.path()` before mapping to `PathBuf`. This avoids allocations for non-matching files.
+
+## 2024-05-31 - is_likely_code_text Binary File Scanning Optimization
+**Learning:** In `is_likely_code_text` heuristic functions, counting non-printable characters across an entire buffer without an early exit caused a significant performance penalty when scanning binary files, forcing full 8KB scans even after the failure threshold was met. Furthermore, simple mathematical checks (`non_printable * 20 < sample_len`) without early bounds checks can be heavily optimized for mismatch cases.
+**Action:** When writing heuristics that iterate over buffers to classify data, always add an early exit condition as soon as a failure/success threshold is met.

crates/mill-services/src/services/reference_updater/detectors/generic.rs

@@ -519,12 +519,19 @@ fn is_likely_code_text(content: &str) -> bool {
     let sample = &content.as_bytes()[..sample_len];
     let mut non_printable = 0usize;
     for &b in sample {
-        let is_text = b == b'\n' || b == b'\r' || b == b'\t' || (b >= 0x20 && b <= 0x7e);
+        // Optimize range check to use .contains() to prevent clippy warnings.
+        let is_text = b == b'\n' || b == b'\r' || b == b'\t' || (0x20..=0x7e).contains(&b);
         if !is_text {
             non_printable += 1;
+            // Early exit optimization: abort scanning as soon as failure threshold is met
+            // avoiding full 8KB scan for large binary files.
+            if non_printable * 20 >= sample_len {
+                return false;
+            }
         }
     }
-    non_printable * 20 < sample_len
+    // Correctly handle zero-length inputs preserving original logic
+    sample_len > 0
 }
 
 fn is_obviously_irrelevant_extension(ext: &str) -> bool {