Write line number without allocation

Author: swsnr

glib/src/bridged_logging.rs

@@ -141,19 +141,28 @@ impl GlibLogger {
         func: Option<&str>,
         message: &str,
     ) {
-        let line = line.map(|l| l.to_string());
-        let line = line.as_deref();
+        // Write line number into a static array to avoid allocating its string
+        // represntation. 16 bytes allow 10^15 lines, which should be more than
+        // sufficient.
+        let mut line_buffer = [0u8; 16];
+        let line = {
+            use std::io::{Cursor, Write};
+            let mut c = Cursor::new(line_buffer.as_mut_slice());
+            match line {
+                Some(lineno) => write!(&mut c, "{lineno}").ok(),
+                None => write!(&mut c, "<unknown line>").ok(),
+            };
+            let pos = c.position() as usize;
+            &line_buffer[..pos]
+        };
         let glib_level = GlibLogger::level_to_glib(level);
         let fields = [
             LogField::new(gstr!("PRIORITY"), glib_level.priority().as_bytes()),
             LogField::new(
                 gstr!("CODE_FILE"),
                 file.unwrap_or("<unknown file>").as_bytes(),
             ),
-            LogField::new(
-                gstr!("CODE_LINE"),
-                line.unwrap_or("<unknown line>").as_bytes(),
-            ),
+            LogField::new(gstr!("CODE_LINE"), line),
             LogField::new(
                 gstr!("CODE_FUNC"),
                 func.unwrap_or("<unknown module path>").as_bytes(),