Move validation check to add_source_mapping_end

Move position validation from add_source_mapping() to add_source_mapping_end()
as suggested in code review. This is more precise since add_source_mapping_end()
is specifically where span.end is used, which is the position that can be beyond
source bounds when codegen adds punctuation.

Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

Author: Copilot

crates/oxc_codegen/src/lib.rs

@@ -889,6 +889,16 @@ impl<'a> Codegen<'a> {
         if let Some(sourcemap_builder) = self.sourcemap_builder.as_mut()
             && !span.is_empty()
         {
+            // Validate that span.end is within source content bounds.
+            // When oxc_codegen adds punctuation (semicolons, newlines) that don't exist in the
+            // original source, span.end may be at or beyond the source content length.
+            // We should not create sourcemap tokens for such positions as they would be invalid.
+            if let Some(source_text) = self.source_text {
+                #[expect(clippy::cast_possible_truncation)]
+                if span.end >= source_text.len() as u32 {
+                    return;
+                }
+            }
             sourcemap_builder.add_source_mapping(self.code.as_bytes(), span.end, None);
         }
     }

crates/oxc_codegen/src/sourcemap_builder.rs

@@ -105,17 +105,6 @@ impl<'a> SourcemapBuilder<'a> {
         if self.last_position == Some(position) {
             return;
         }
-
-        // Validate that position is within source content bounds.
-        // When oxc_codegen adds punctuation (semicolons, newlines) that don't exist in the
-        // original source, it may call this method with positions beyond the source content.
-        // We should not create sourcemap tokens for such positions as they would be invalid.
-        // Position must be < source.len() to be valid (position == source.len() is EOF, beyond content).
-        #[expect(clippy::cast_possible_truncation)]
-        if position >= self.original_source.len() as u32 {
-            return;
-        }
-
         let (original_line, original_column) = self.search_original_line_and_column(position);
         self.update_generated_line_and_column(output);
         let name_id = name.map(|s| self.sourcemap_builder.add_name(s));