fix callable strings

Author: staabm

src/Type/CallableType.php

@@ -24,6 +24,7 @@
 use PHPStan\Reflection\Php\DummyParameter;
 use PHPStan\ShouldNotHappenException;
 use PHPStan\TrinaryLogic;
+use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
 use PHPStan\Type\Generic\TemplateType;
 use PHPStan\Type\Generic\TemplateTypeHelper;
 use PHPStan\Type\Generic\TemplateTypeMap;
@@ -331,7 +332,12 @@ public function toArrayKey(): Type
 
 	public function toCoercedArgumentType(bool $strictTypes): Type
 	{
-		return TypeCombinator::union($this, new StringType(), new ArrayType(new MixedType(true), new MixedType(true)), new ObjectType(Closure::class));
+		return TypeCombinator::union(
+			$this,
+			TypeCombinator::intersect(new StringType(), new AccessoryNonEmptyStringType()),
+			new ArrayType(new MixedType(true), new MixedType(true)),
+			new ObjectType(Closure::class),
+		);
 	}
 
 	public function isOffsetAccessLegal(): TrinaryLogic

tests/PHPStan/Analyser/nsrt/bug-12393b.php

@@ -584,7 +584,7 @@ class CallableString {
 
     public function doFoo(callable $foo): void {
         $this->foo = $foo;
-        assertType('string', $this->foo); // could be non-empty-string
+        assertType('callable-string|non-empty-string', $this->foo);
     }
 }