Merge pull request #15296 from jdaugherty/7.0.x

doc - #15293 - add warning about invokedynamic performance

Author: jdaugherty

grails-doc/src/en/guide/upgrading/upgrading60x.adoc

@@ -62,6 +62,16 @@ In your gradle file, you can force a dependency upgrade via this code:
   }
 ----
 
+5. By default, Groovy 4 switches away from callsite optimizations and uses invokedynamic instead. This can result in performance regressions compared to Grails 6. Groovy 5 will remove the ability to disable invokedynamic, but to disable it for Groovy 4, modify your `build.gradle` to include the following:
+
+[source,groovy]
+.build.gradle
+----
+  tasks.withType(GroovyCompile).configureEach {
+        groovyOptions.optimizationOptions.indy = false
+  }
+----
+
 ==== 3. Unified Project Version
 
 Grails 7 moved to a mono repository.