[5.7] Wrong bindings when calling whereHas on a relation that uses $withCount

[aocneanu]

• Laravel Version: 5.7.9
• PHP Version: 7.2.8
• Database Driver & Version: MySQL 5.7.23

Description:

I have a Project that hasMany Contracts while a Contract belongsTo a project. Contracts can be of many types.

Contract also has a morphMany relation to Document and uses protected $withCount="['documents']

The problem manifests when I try to query Projects that have Contracts of a certain type. In this case nothing is returned because of incorrect bindings.

Steps To Reproduce:

I'm using tinker with DB::enableQueryLog() / DB::getQueryLog()

The following query:

    Project::whereHas('contracts')->get()

returns the collection of projects that have at least one contract, even if the query log shows an extra binding:

     [
       "query" => "select * from `projects` where exists (select * from `contracts` where `projects`.`id` = `contracts`.`project_id`)",
       "bindings" => [
         "App\Contract", //notice this
       ],
       "time" => 1.39,
     ],

While this query:

    Project::whereHas('contracts', function($q) {
        $q->whereType(1);
     })->get()

returns an empty collection and the query log is:

    [
       "query" => "select * from `projects` where exists (select * from `contracts` where `projects`.`id` = `contracts`.`project_id` and `type` = ?)",
       "bindings" => [
         "App\Contract", //again
         1,
       ],
       "time" => 1.39,
     ]

The query as shown by the DebugBar:

select * from `projects` where exists (select * from `contracts` where `projects`.`id` = `contracts`.`project_id` and `type` = 'App\Contract')

I found many previous issues and PRs related to this problem but apparently the above scenario is still not covered:

ref #24240, #24865, #25280, #24240

#25997 will probably make possible at least a workaround