Support specifying searchable columns for Select via callable

[ppmathis]

As of today, Filament\Forms\Components\Select supports specifying a static list of searchable columns as an array like this:

Select::make('example_id')
  ->relationship('example')
  ->getOptionLabelFromRecordUsing(fn (Model $record) => sprintf('%s (%s)', $record->name, $record->slug))
  ->searchable(['slug', 'name'])

This works like a charm and there are no issues with that. However in my scenario I have a use case where I would like to dynamically define the list of searchable columns. I first expected this to work out of the box, as searchable() also supports passing a callable that gets evaluated:

Select::make('example_id')
  ->relationship('example')
  ->getOptionLabelFromRecordUsing(fn (Model $record) => sprintf('%s (%s)', $record->name, $record->slug))
  ->searchable(function(): array|false {
    // Example of how the callable could still influence search to be disabled
    if($someLogicHere) { return false; }

    // Example of how columns are returned, this would be dynamic (e.g. from some model interface method)
    // As of today, these are ignored, and it only matters if this callable returns a truthy value to determine searchability
    return ['slug', 'name'];
  });

The current implementation correctly evaluates this callable during isSearchable(), and proceeds to make the Select field searchable. While this works, the actual searching is broken, never returning any results. This happens because getSearchResultsForJs() will call into getSearchResults(), which calls into the pre-defined getSearchResultsUsing() callable (automatically set when calling relationship()), which then calls getSearchColumns() while building the search query.

Said getSearchColumns() method however will always result in null / an empty list, as it no longer evaluates $this->isSearchable as set by calling searchable(), but instead directly uses $this->searchColumns:

filament/packages/forms/src/Components/Select.php

Lines 609 to 618 in bf8da41

	public function getSearchColumns(): ?array
	{
	$columns = $this->searchColumns;
	if ($this->hasRelationship() && (filled($relationshipTitleAttribute = $this->getRelationshipTitleAttribute()))) {
	$columns ??= [$relationshipTitleAttribute];
	}
	return $columns;
	}

Unfortunately this does not work, as passing a callable to searchable() will skip assigning $this->searchColumns due to lazy evaluation:

filament/packages/forms/src/Components/Select.php

Lines 537 to 548 in bf8da41

	public function searchable(bool | array | Closure $condition = true): static
	{
	if (is_array($condition)) {
	$this->isSearchable = true;
	$this->searchColumns = $condition;
	} else {
	$this->isSearchable = $condition;
	$this->searchColumns = null;
	}
	return $this;
	}

I think it would be neat if getSearchColumns() would also properly evaluate $this->isSearchable() and respect the returned columns. This would also match the behavior that I initially expected.

As of today, there exists no simple method on dynamically defining these columns, without either extending the actual class or redefining the complete logic of getSearchResultsUsing() within the relationship() method.

Note: This actually initially caused an exception to be thrown, as $this->getSearchColumns() returned null when undefined, which broke the foreach loop. I noticed though that the latest version no longer suffers from this thanks to 4331e16, but unfortunately this only fixed the symptom without making dynamic search columns feasible.