perf(codegen): reduce memory allocations in generate_line_offset_tables (#13054)

Author: Boshen

crates/oxc_codegen/src/sourcemap_builder.rs

@@ -325,6 +325,7 @@ impl<'a> SourcemapBuilder<'a> {
                 column_offsets_id: None,
             });
 
+            let mut columns = vec![]; // Used as a buffer to reduce memory reallocations.
             let remaining = &content.as_bytes()[line_byte_offset as usize..];
             for (byte_offset_from_line_start, b) in remaining.iter().enumerate() {
                 #[expect(clippy::cast_possible_truncation)]
@@ -350,7 +351,7 @@ impl<'a> SourcemapBuilder<'a> {
                         line.column_offsets_id =
                             Some(ColumnOffsetsId::from_usize(column_offsets.len()));
 
-                        let mut columns = vec![];
+                        columns.clear();
 
                         // Loop through rest of line char-by-char.
                         // `chunk_byte_offset` in this loop is byte offset from start of this 1st
@@ -395,7 +396,7 @@ impl<'a> SourcemapBuilder<'a> {
                             // Record column offsets
                             column_offsets.push(ColumnOffsets {
                                 byte_offset_to_first: byte_offset_from_line_start,
-                                columns: columns.into_boxed_slice(),
+                                columns: columns.into_iter().collect(),
                             });
 
                             // Revert back to outer loop for next line
@@ -409,7 +410,7 @@ impl<'a> SourcemapBuilder<'a> {
                         // Record column offsets
                         column_offsets.push(ColumnOffsets {
                             byte_offset_to_first: byte_offset_from_line_start,
-                            columns: columns.into_boxed_slice(),
+                            columns: columns.into_iter().collect(),
                         });
 
                         break 'lines;