Add hook views_geojson_feature_alter

+++ b/views_geojson.module
@@ -221,6 +221,12 @@ function _views_geojson_render_fields($view, $row, $index) {
+  foreach (module_implements('views_geojson_render_fields_alter') as $module) {
+    $function = $module . '_views_geojson_render_fields_alter';

You should use module_invoke_all

+++ b/views_geojson.module
@@ -221,6 +221,12 @@ function _views_geojson_render_fields($view, $row, $index) {
+    $function($feature, $view, $row, $index);

Isn't there a more general hook_field_alter available in views context? Maybe I'm just garbling ;)

You could add some documentation just before the _alter call too.

@dasjo, Is this the only way to achieve this ? There are no cleaner way using views hook ?

I think the only applicable views hook here could be hook_views_post_render. But that will likely be slower in many cases because you're altering already rendered output and doing an extra iteration over the results to access individual rows.

Regarding the proposed solutions:

• I don't really like the foreach() either. It's cleaner to adhere to generic drupal altering patterns.
• The module_invoke_all passing by reference limitation is mainly a memory issue if implemented correctly I guess. You could just pass it and change the data once it returns.
• Drupal alter would be cleaner. Even with the limitation of only 2 arguments. Geocluster currently only alters one argument anyway (the row).

Finally there is #2370471: Make patching Views GeoJSON obsolete. That takes a different approach that looks pretty solid. But it probably also requires a rewrite of non-leaflet js to catch clustering properties.

Also related is #2578785: Large-scale location mapping in Drupal 8 (Views).

Here's a patch containing the drupal_alter implementation. I'm also submitting an issue at the geocluster issue queue to properly implement the alter hook.

As a side note: I think this hook should be named hook_views_geojson_feature_alter() instead, because we're altering a "$feature", not a "$render_fields", within the contexts $view and $row. That's why I renamed the hook. This'll break the already broken geocluster implementation. See: #2370471: Make patching Views GeoJSON obsolete and http://cgit.drupalcode.org/geocluster/tree/geocluster.module#n169

changed title to match patch in #7