Intersection `non-empty-string&lowercase-string` rejected as "must be all objects" (used by laravel/framework Str::lower)

[alies-dev]

Summary

Psalm rejects the pseudo-type intersection non-empty-string&lowercase-string with:

InvalidDocblock: Intersection types must be all objects, Psalm\Type\Atomic\TNonEmptyString provided

The single-token equivalent non-empty-lowercase-string is accepted and works correctly, so the two forms are not interchangeable today.

This is closely related to #9628 (which covers literal-string&non-empty-string and friends), but I am filing this separately because it has a concrete real-world impact: laravel/framework's Illuminate\Support\Str::lower() docblock uses exactly this intersection.

Why it matters

Str::lower() in Laravel 13 ships with:

/**
 * Convert the given string to lower-case.
 *
 * @param  string  $value
 * @return ($value is '' ? '' : non-empty-string&lowercase-string)
 */
public static function lower($value)

Any Psalm user analysing a Laravel project therefore gets an InvalidDocblock out of the box on a widely used framework helper. Workarounds (stubbing the method to use non-empty-lowercase-string instead) exist but require plugin/stub-level overrides.

Reproduction

https://psalm.dev/r/b51da730d4

Output (Psalm 7.0.0-beta19):

ERROR: InvalidDocblock
Intersection types must be all objects, Psalm\Type\Atomic\TNonEmptyString provided
  @return ($value is '' ? '' : non-empty-string&lowercase-string)

ERROR: InvalidDocblock
Intersection types must be all objects, Psalm\Type\Atomic\TNonEmptyString provided
  @return non-empty-string&lowercase-string

Expected

non-empty-string&lowercase-string should be accepted and treated equivalently to the existing single-token pseudo-type non-empty-lowercase-string (which Psalm already supports). Ideally the same treatment would extend to the cases in #9628.

Environment

• Psalm 7.0.0-beta19
• PHP 8.5.5