From 8b0e3170876168369a99a34e231a635d15d395a0 Mon Sep 17 00:00:00 2001
From: Sephyi <me@sephy.io>
Date: Sun, 19 Apr 2026 19:04:30 +0200
Subject: [PATCH] refactor(services): replace byte indexing with strip_prefix

Six diff-line processing sites used &line[1..] / &l[1..] to drop the
leading '+' or '-', which is safe here because the guards limit those
lines to ASCII prefixes, but strip_prefix expresses the intent directly
and removes the implicit byte-boundary assumption.

Sites updated:

- context.rs detect_import_changes: collapse the dual +/- branch into
  a single strip_prefix chain that picks the action label in one pass.
- context.rs detect_intents: swap the negated starts_with guard for a
  let-else over strip_prefix('+'), keeping the +++ header filter.
- context.rs detect_metadata_breaking: rewrite the is_added/is_removed
  dispatch around strip_prefix, then derive is_removed from is_added.
- splitter.rs diff_fingerprint: filter_map(strip_prefix) in the
  added/removed line builders.
- safety.rs scan_full_diff_with_patterns: let-chain strip_prefix('+')
  alongside the existing !starts_with("+++") header guard.

Behaviorally identical; zero new allocations. Verified with
cargo fmt --check, cargo clippy --all-targets --all-features -D warnings
(clean), and cargo test --all-targets (440 passed, 1 pre-existing
porcelain timeout flake also present on clean origin/development).

Closes audit entry F-011 from #3.
---
 src/services/context.rs  | 37 +++++++++++++++++++++----------------
 src/services/safety.rs   |  5 +++--
 src/services/splitter.rs |  8 ++++----
 3 files changed, 28 insertions(+), 22 deletions(-)

diff --git a/src/services/context.rs b/src/services/context.rs
index 8c59f91..24172ac 100644
--- a/src/services/context.rs
+++ b/src/services/context.rs
@@ -995,21 +995,20 @@ impl ContextBuilder {
                     continue;
                 }
                 // Detect added/removed import lines
-                if (line.starts_with('+') && Self::is_import_line(&line[1..]))
-                    || (line.starts_with('-') && Self::is_import_line(&line[1..]))
-                {
-                    let action = if line.starts_with('+') {
-                        "added"
-                    } else {
-                        "removed"
-                    };
+                let (action, content) = if let Some(rest) = line.strip_prefix('+') {
+                    ("added", rest)
+                } else if let Some(rest) = line.strip_prefix('-') {
+                    ("removed", rest)
+                } else {
+                    continue;
+                };
+                if Self::is_import_line(content) {
                     let stem = file
                         .path
                         .file_stem()
                         .and_then(|s| s.to_str())
                         .unwrap_or("?");
-                    let content = line[1..].trim();
-                    imports.push(format!("{}: {} {}", stem, action, content));
+                    imports.push(format!("{}: {} {}", stem, action, content.trim()));
                 }
             }
         }
@@ -1067,11 +1066,13 @@ impl ContextBuilder {
             let filename = file.path.file_name().and_then(|n| n.to_str()).unwrap_or("");
 
             for line in file.diff.lines() {
-                if !line.starts_with('+') || line.starts_with("+++") {
+                if line.starts_with("+++") {
                     continue;
                 }
+                let Some(content) = line.strip_prefix('+') else {
+                    continue;
+                };
                 total_added += 1;
-                let content = &line[1..];
                 let trimmed = content.trim();
 
                 // Error handling patterns
@@ -1207,13 +1208,17 @@ impl ContextBuilder {
             let name = file.path.file_name().and_then(|n| n.to_str()).unwrap_or("");
 
             for line in file.diff.lines() {
-                let is_removed = line.starts_with('-') && !line.starts_with("---");
-                let is_added = line.starts_with('+') && !line.starts_with("+++");
-                let content = if is_removed || is_added {
-                    &line[1..]
+                if line.starts_with("+++") || line.starts_with("---") {
+                    continue;
+                }
+                let (is_added, content) = if let Some(rest) = line.strip_prefix('+') {
+                    (true, rest)
+                } else if let Some(rest) = line.strip_prefix('-') {
+                    (false, rest)
                 } else {
                     continue;
                 };
+                let is_removed = !is_added;
 
                 match name {
                     "Cargo.toml" => {
diff --git a/src/services/safety.rs b/src/services/safety.rs
index a2f17b0..d9e4cff 100644
--- a/src/services/safety.rs
+++ b/src/services/safety.rs
@@ -314,8 +314,9 @@ pub fn scan_full_diff_with_patterns(
         }
 
         // Only check added lines
-        if line.starts_with('+') && !line.starts_with("+++") {
-            let content = &line[1..];
+        if !line.starts_with("+++")
+            && let Some(content) = line.strip_prefix('+')
+        {
             for pat in patterns {
                 if pat.regex.is_match(content) {
                     found.push(SecretMatch {
diff --git a/src/services/splitter.rs b/src/services/splitter.rs
index 4f546e1..5a7f3c6 100644
--- a/src/services/splitter.rs
+++ b/src/services/splitter.rs
@@ -197,13 +197,13 @@ impl CommitSplitter {
         let mut indent_only_changes = 0usize;
         let added_lines: Vec<&str> = lines
             .iter()
-            .filter(|l| l.starts_with('+') && !l.starts_with("+++"))
-            .map(|l| &l[1..])
+            .filter(|l| !l.starts_with("+++"))
+            .filter_map(|l| l.strip_prefix('+'))
             .collect();
         let removed_lines: Vec<&str> = lines
             .iter()
-            .filter(|l| l.starts_with('-') && !l.starts_with("---"))
-            .map(|l| &l[1..])
+            .filter(|l| !l.starts_with("---"))
+            .filter_map(|l| l.strip_prefix('-'))
             .collect();
 
         for added_line in &added_lines {