fix(compiler-core): fix scope var reference check for v-on expressions

fix #2564

packages/compiler-core/src/transforms/vOn.ts

@@ -79,7 +79,12 @@ export const transformOn: DirectiveTransform = (
     // process the expression since it's been skipped
     if (!__BROWSER__ && context.prefixIdentifiers) {
       isInlineStatement && context.addIdentifiers(`$event`)
-      exp = processExpression(exp, context, false, hasMultipleStatements)
+      exp = dir.exp = processExpression(
+        exp,
+        context,
+        false,
+        hasMultipleStatements
+      )
       isInlineStatement && context.removeIdentifiers(`$event`)
       // with scope analysis, the function is hoistable if it has no reference
       // to scope variables.