fix(mysql): bind get connection callback to active context

Signed-off-by: Simon Stone <simonstone1@gmail.com>

plugins/node/opentelemetry-instrumentation-mysql/src/instrumentation.ts

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { diag, Span, SpanKind, SpanStatusCode } from '@opentelemetry/api';
+import { context, diag, Span, SpanKind, SpanStatusCode, trace } from '@opentelemetry/api';
 import {
   InstrumentationBase,
   InstrumentationNodeModuleDefinition,
@@ -203,6 +203,13 @@ export class MySQLInstrumentation extends InstrumentationBase<
 
   private _getConnectionCallbackPatchFn(cb: Function, format: formatType) {
     const thisPlugin = this;
+    // If a parent span exists, bind the callback so that the parent span
+    // is still visible after we've gone through the MySQL pool code.
+    const activeContext = context.active();
+    const parentSpan = trace.getSpan(activeContext);
+    if (parentSpan && typeof cb === 'function') {
+      cb = context.bind(activeContext, cb);
+    }
     return function () {
       if (arguments[1]) {
         // this is the callback passed into a query