Add support for JTS Spatial queries with polygons via extending "location_rpt" field type attributes

I think that the smart way to allow jts is to create a new SearchApiBackend extending some existing one. Creating the relevant form checkbox to enable/disable the option as you said.
But also is possible to alter all backends schema.xml output...You can just do it using the hook hook_search_api_solr_config_files_alter as here:

/**                                                                                             
 * Alter the newly assembled Solr configuration files.                                          
 *                                                                                              
 * @param string[] $files                                                                       
 *   Array of config files keyed by file names.                                                 
 * @param string $lucene_match_version                                                          
 *   Lucene (Solr) minor version string.                                                        
 * @param string $server_id                                                                     
 *   Optional Search API server id. Will be set in most cases but might be                      
 *   empty when the config generation is triggered via UI or drush.                             
 */                                                                                             
function your_module_search_api_solr_config_files_alter(array &$files, string $lucene_match_version, string $server_id = '') {
  $jts_spatial = '<fieldType name="location_rpt" class="solr.SpatialRecursivePrefixTreeFieldType" spatialContextFactory="org.locationtech.spatial4j.context.jts.JtsSpatialContextFactory"          
autoIndex="true" validationRule="repairBuffer0" distErrPct="0.025" maxDistErr="0.001" distanceUnits="kilometers" />';                                                                              
  $files['schema.xml'] = preg_replace("@<fieldType\s+name=\"location_rpt\"\s+class=\"solr\.SpatialRecursivePrefixTreeFieldType\"\s+geo=\"true\"\s+distErrPct=\"0\.025\"\s+maxDistErr=\"0\.001\"\s+ 
distanceUnits=\"kilometers\"\s+/>@ms", $jts_spatial, $files['schema.xml']);
}                                                                                                                                                                                                  

I think that the smart way to allow jts is to create a new SearchApiBackend extending some existing one. Creating the relevant form checkbox to enable/disable the option as you said.
But also is possible to alter all backends schema.xml output...You can just do it using the hook hook_search_api_solr_config_files_alter as here:

I don't agree that extending SearchApiBackend would be a smart choice ;-)

The hook in #3 is the way to go unless we have all field types configurable like the text based field types.

oops... ok! So the patch I am attaching is not the way to go?... So do you think that it is better to use the hook as in #3 ?

In conjunction with a geofield it's working fine. So I'm able to store a polygon. And then with a given coordinates point I can search for the polygons that are containing that point.

thank's !

while not reviewing what I said in the previous patch.
I have created a module that adds the configuration as #3 explains, also, it adds more features such as a views filter plugin to do JTS queries , by now just "contains" predicate can be used. Also modifies the rpt datatype provided by search_api_location to allow index shape fields. So this way one can lookup for shapes that are containing a given lat,lon point.
I hope you can review and found it as useful as I do... it's in https://www.drupal.org/project/jts_solr_queries

The patch looks basically good. But it requires more work and will not pass the tests as it is!

1. +++ b/src/Plugin/SolrConnector/StandardSolrConnector.php
   @@ -50,5 +50,10 @@ class StandardSolrConnector extends SolrConnectorPluginBase {
   +      $files['schema.xml'] = preg_replace("@<fieldType\s+name=\"location_rpt\"\s+class=\"solr\.SpatialRecursivePrefixTreeFieldType\"\s+geo=\"true\"\s+distErrPct=\"0\.025\"\s+maxDistErr=\"0\.001\"\s+distanceUnits=\"kilometers\"\s+/>@ms", $jts_spatial, $files['schema.xml']);
   

   The regex should be less specific, for example
   <fieldType[^>]+name=\"location_rpt\"[^>]*/>

2. +++ b/src/SolrConnector/SolrConnectorPluginBase.php
   @@ -107,6 +107,7 @@ abstract class SolrConnectorPluginBase extends ConfigurablePluginBase implements
   +      'jts' => FALSE,
   

   "jts" needs to be added to config/schema/search_api_solr.connector.standard.schema.yml

3. The existing configs for the test servers need to be updated to contain the "jts" flag.
4. At least the config generator test has to be extended, following the pattern of "jmx".
5. An integration test would be nice. At least we should ensure that Solr starts without errors.
6. We need to verify which Solr versions can handle this. Maybe some adjustments to the search_api_solr_legacy module is required.

You should search the entire module for "jmx". This will give you a good orientation what needs to done!

Nice to see this issue ressurection :) Despite I am using an alter to carry on the jts support as we talk in previous comments( and everything is running fine). Will help with the above when I have time .

The patch in #10 looks much better :-)

@aleix If you find some time, it would be nice if you can complete the test part. Searching the tests folder for "jmx" will give you a good starting point.

I rebased the patch of #10 in a fresh issue fork from 4.x-dev. This will make it easier to rebase in the future if needed and to continue working on this.

As per #12 we still need tests :-)

Yes, I'll merge it as soon as there's a test. As mentioned in #12 it should be straight forward.

The patch contained some small errors as it altered the schema.xml only for those Connectors that inherit the StandardSolrConnector. But the config itself is part of SolrConnectorPluginBase.

I also added the test and took care of the Solr36Connector.

Good job @mkalkbrenner!