fix(diff+file): avoid filling defaults in config for kong

the previous logic was filling defaults in the configuration that was
passed to Kong. This was  problematic, especially where nils were
populated as defaults, e.g. if a shorthand_field was passed with some
value and the corresponding new field is auto-populated as `nil` by decK
, the auto-populated nil value would take precedence in Kong thus causing
the shorthand_field to be ignored
(https://konghq.atlassian.net/browse/KAG-5157).

This change applies the default values only to configurations used for
diff, the original configuration is always passed to Kong as is.

pkg/diff/diff.go

@@ -599,6 +599,32 @@ func (sc *Syncer) Solve(ctx context.Context, parallelism int, dry bool, isJSONOu
 		var err error
 		var result crud.Arg
 
+		// holds the original event with the unchanged configuration
+		// below the config may be updated, to render the diff correctly
+		originalE := e
+
+		// If the event is for a plugin, inject defaults in the plugin's Config
+		// This is required for computing a diff that takes defaults into account
+		// Defaults are populated by Kong Gateway when a plugin is created and
+		// values are not provided; the diff should not display these values as changes
+		if plugin, ok := e.Obj.(*state.Plugin); ok {
+			pluginCopy := &state.Plugin{
+				Plugin: *plugin.DeepCopy(),
+				Meta:   plugin.Meta,
+			}
+			e.Obj = pluginCopy
+
+			var schema map[string]interface{}
+			schema, err = sc.kongClient.Plugins.GetFullSchema(ctx, pluginCopy.Plugin.Name)
+			if err != nil {
+				return schema, err
+			}
+
+			if err := kong.FillPluginsDefaults(&pluginCopy.Plugin, schema); err != nil {
+				return nil, fmt.Errorf("failed filling plugin defaults: %w", err)
+			}
+		}
+
 		c := e.Obj.(state.ConsoleString)
 		objDiff := map[string]interface{}{
 			"old": e.OldObj,
@@ -679,8 +705,8 @@ func (sc *Syncer) Solve(ctx context.Context, parallelism int, dry bool, isJSONOu
 
 		if !dry {
 			// sync mode
-			// fire the request to Kong
-			result, err = sc.processor.Do(ctx, e.Kind, e.Op, e)
+			// fire the request to Kong; Pass the original event, with the unchanged configuration.
+			result, err = sc.processor.Do(ctx, originalE.Kind, originalE.Op, originalE)
 			// TODO https://github.com/Kong/go-database-reconciler/issues/22 this does not print, but is switched on
 			// sc.enableEntityActions because the existing behavior returns a result from the anon Run function.
 			// Refactoring should use only the channel and simplify the return, probably to just an error (all the other

pkg/file/builder.go

@@ -1467,20 +1467,6 @@ func (b *stateBuilder) getPluginSchema(pluginName string) (map[string]interface{
 	return schema, nil
 }
 
-func (b *stateBuilder) addPluginDefaults(plugin *FPlugin) error {
-	if b.client == nil {
-		return nil
-	}
-	schema, err := b.getPluginSchema(*plugin.Name)
-	if err != nil {
-		if errors.Is(err, ErrWorkspaceNotFound) {
-			return nil
-		}
-		return fmt.Errorf("retrieve schema for %v from Kong: %w", *plugin.Name, err)
-	}
-	return kong.FillPluginsDefaults(&plugin.Plugin, schema)
-}
-
 func (b *stateBuilder) ingestPlugins(plugins []FPlugin) error {
 	for _, p := range plugins {
 		p := p
@@ -1504,9 +1490,6 @@ func (b *stateBuilder) ingestPlugins(plugins []FPlugin) error {
 		if err != nil {
 			return err
 		}
-		if err := b.addPluginDefaults(&p); err != nil {
-			return fmt.Errorf("add defaults to plugin '%v': %w", *p.Name, err)
-		}
 		utils.MustMergeTags(&p, b.selectTags)
 		if plugin != nil {
 			p.Plugin.CreatedAt = plugin.CreatedAt