Request for New Feature: Allow the Schema Builder instance to be set on the Connection

[kfriars]

In order to reliably and safely use a custom Schema Builder for an existing Connection, you need to create an entirely new thinly wrapped Connection. Furthermore, if you simply override the instance bound to the container it puts the instance resolved from the Schema Facade out of sync with the Schema Builder instance set on the Connection.

The reason this is the case, is that even if you set db.schema there are many places that use getSchemaBuilder() on the connection which ignores whatever is bound to the container. In that getSchemaBuilder() method it returns a hardcoded instance of the framework's Builder class.

I would propose an implementation which is already currently used with schemaGrammar in the Illuminate\Database\Connection class.

class Connection implements ConnectionInterface
{
   // ....
   
    /**
     * The schema builder implementation.
     *
     * @var \Illuminate\Database\Schema\Builder
     */
    protected $schemaBuilder;
        
    /**
     * Set the schema builder used by the connection.
     *
     * @param  \Illuminate\Database\Schema\Builder  $builder
     * @return $this
     */
     public function setSchemaBuilder(SchemaBuilder $builder)
     {
          $this->schemaBuilder = $builder;

          return $this;
     }

    /**
     * Get a schema builder instance for the connection.
     *
     * @return \Illuminate\Database\Schema\Builder
     */
    public function getSchemaBuilder()
    {
        if  ($this->schemaBuilder) {
            return $this->schemaBuilder;
        }

        if (is_null($this->schemaGrammar)) {
            $this->useDefaultSchemaGrammar();
        }

        return new SchemaBuilder($this);
    }
    
    // ....
}

It is not the end of the world to have to wrap the connection, and I doubt there are too many applications/packages that need to override the Schema Builder, so I can understand if this is deemed out-of-scope.

This came to light because our company created plank/snapshots as an approach to versioning content, which relies on a custom Schema Builder and Migrator.

Let me know if this could be supported and I will create a PR to be reviewed.