perf: Avoid `Vec<&str>` allocation during line length checking

src/check_lines.rs

@@ -3,6 +3,22 @@ use rustpython_parser::ast::Location;
 use crate::checks::{Check, CheckKind};
 use crate::settings::Settings;
 
+/// Whether the given line is too long and should be reported.
+fn should_enforce_line_length(line: &str, limit: usize) -> bool {
+    if line.len() > limit {
+        let mut chunks = line.split_whitespace();
+        if let (Some(first), Some(_)) = (chunks.next(), chunks.next()) {
+            // Do not enforce the line length for commented lines with a single word
+            !(first == "#" && chunks.next().is_none())
+        } else {
+            // Single word / no printable chars - no way to make the line shorter
+            false
+        }
+    } else {
+        false
+    }
+}
+
 pub fn check_lines(checks: &mut Vec<Check>, contents: &str, settings: &Settings) {
     let enforce_line_too_ling = settings.select.contains(CheckKind::LineTooLong.code());
 
@@ -18,16 +34,13 @@ pub fn check_lines(checks: &mut Vec<Check>, contents: &str, settings: &Settings)
         }
 
         // Enforce line length.
-        if enforce_line_too_ling && line.len() > settings.line_length {
-            let chunks: Vec<&str> = line.split_whitespace().collect();
-            if !(chunks.len() == 1 || (chunks.len() == 2 && chunks[0] == "#")) {
-                let check = Check {
-                    kind: CheckKind::LineTooLong,
-                    location: Location::new(row + 1, settings.line_length + 1),
-                };
-                if !check.is_inline_ignored(line) {
-                    line_checks.push(check);
-                }
+        if enforce_line_too_ling && should_enforce_line_length(line, settings.line_length) {
+            let check = Check {
+                kind: CheckKind::LineTooLong,
+                location: Location::new(row + 1, settings.line_length + 1),
+            };
+            if !check.is_inline_ignored(line) {
+                line_checks.push(check);
             }
         }
     }