Optimize union handling with enum for all-literal unions and set additionalItems to false for array schemas

Author: antonmedv

src/Schema/JsonSchemaGenerator.php

@@ -132,13 +132,27 @@ private static function convert(SchemaType $schema): array
             return [
                 'type' => 'array',
                 'items' => \array_map(fn(SchemaType $s) => self::convert($s), $schema->elements),
+                'additionalItems' => false,
                 'minItems' => \count($schema->elements),
                 'maxItems' => \count($schema->elements),
             ];
         }
 
         // $schema is UnionType at this point
         /** @var UnionType $schema */
+        // Detect all-literal unions and emit compact "enum" keyword
+        $allLiterals = true;
+        foreach ($schema->branches as $branch) {
+            if (!($branch instanceof LiteralType)) {
+                $allLiterals = false;
+                break;
+            }
+        }
+        if ($allLiterals) {
+            return [
+                'enum' => \array_map(fn(SchemaType $s) => ($s instanceof LiteralType) ? $s->value : null, $schema->branches),
+            ];
+        }
         return [
             'oneOf' => \array_map(fn(SchemaType $s) => self::convert($s), $schema->branches),
         ];

tests/Schema/JsonSchemaTest.php

@@ -303,6 +303,7 @@ public function testTuple(): void
                     ['type' => 'string'],
                     ['type' => 'boolean'],
                 ],
+                'additionalItems' => false,
                 'minItems' => 3,
                 'maxItems' => 3,
             ],
@@ -324,10 +325,17 @@ public function testUnion(): void
     public function testEnum(): void
     {
         $this->assertJsonSchema(S::enum('fast', 'safe', 'auto'), [
+            'enum' => ['fast', 'safe', 'auto'],
+        ]);
+    }
+
+    public function testUnionMixedNotEnum(): void
+    {
+        // Union of non-literals still uses oneOf
+        $this->assertJsonSchema(S::union(S::string(), S::null()), [
             'oneOf' => [
-                ['const' => 'fast'],
-                ['const' => 'safe'],
-                ['const' => 'auto'],
+                ['type' => 'string'],
+                ['type' => 'null'],
             ],
         ]);
     }