Support type inference for oneOf schemas

Support for type inference for non-shape types in oneOf constraints. Shapes are still unsupported, just as they are unsupported for anyOf. They're a fair bit of work to get right and will come later, if we deem that worthwhile.

Author: ianhoffman

src/Codegen/Constraints/UntypedBuilder.php

@@ -11,6 +11,7 @@
   HackBuilderKeys,
   HackBuilderValues,
 };
+use type Slack\Hack\JsonSchema\Sentinal;
 
 type TUntypedSchema = shape(
   ?'anyOf' => vec<TSchema>,
@@ -141,24 +142,35 @@ private function generateNotChecks(vec<TSchema> $schemas, HackBuilder $hb): void
 
   }
 
-  // TODO: Determine Lowest Upper Bound for oneOf constraint.
   private function generateOneOfChecks(vec<TSchema> $schemas, HackBuilder $hb): void {
     $constraints = vec[];
+    $types = vec[];
     foreach ($schemas as $index => $schema) {
       $schema_builder =
         new SchemaBuilder($this->ctx, $this->generateClassName($this->suffix, 'oneOf', (string)$index), $schema);
       $schema_builder->build();
       $constraints[] = "{$schema_builder->getClassName()}::check<>";
+      $types[] = $schema_builder->getTypeInfo();
     }
 
+    $type_info = Typing\TypeSystem::union($types);
+    // For now, keep upcasting nonnull to mixed.
+    // This is a temporary cludge to reduce the amount of code changed by generating unions.
+    // TODO: Stop doing the above.
+    if ($type_info is Typing\ConcreteType && $type_info->getConcreteTypeName() === Typing\ConcreteTypeName::NONNULL) {
+      $type_info = Typing\TypeSystem::mixed();
+    }
+    $this->type_info = $type_info;
+
     $hb
       ->addAssignment('$constraints', $constraints, HackBuilderValues::vec(HackBuilderValues::literal()))
       ->ensureEmptyLine();
 
     $hb
       ->addAssignment('$passed_any', false, HackBuilderValues::export())
       ->addAssignment('$passed_multi', false, HackBuilderValues::export())
-      ->addAssignment('$output', null, HackBuilderValues::export())
+      // Use `sentinal` rather than `null` so that it's obvious when we failed to match any constraint.
+      ->addAssignment('$output', Str\format('new \%s()', Sentinal::class), HackBuilderValues::literal())
       ->startForeachLoop('$constraints', null, '$constraint')
       ->startTryBlock()
       ->addMultilineCall('$output = $constraint', vec['$input', '$pointer'])
@@ -181,7 +193,7 @@ private function generateOneOfChecks(vec<TSchema> $schemas, HackBuilder $hb): vo
     );
 
     $hb
-      ->startIfBlock('$passed_multi || !$passed_any')
+      ->startIfBlockf('$passed_multi || !$passed_any || $output is \%s', Sentinal::class)
       ->addAssignment(
         '$error',
         $error,
@@ -452,7 +464,7 @@ private function getOptimizedAnyOfTypes(vec<SchemaBuilder> $schema_builders): ?T
 
               if ($property_type === TSchemaType::STRING_T && C\contains($required, $property_name)) {
                 $typed_property_schema =
-                  type_assert_shape($property_schema, 'Slack\Hack\JsonSchema\Codegen\TStringSchema');
+                  type_assert_type($property_schema, \Slack\Hack\JsonSchema\Codegen\TStringSchema::class);
 
                 $enum = $typed_property_schema['enum'] ?? null;
                 if ($enum is nonnull && C\count($enum) === 1) {

src/Sentinal.hack

@@ -0,0 +1,6 @@
+namespace Slack\Hack\JsonSchema;
+
+/**
+ * Represents an unset value.
+ */
+final class Sentinal {}

tests/DiscardAddititionalPropertiesValidatorTest.php

@@ -10,10 +10,7 @@ final class DiscardAddititionalPropertiesValidatorTest extends BaseCodegenTestCa
 
   <<__Override>>
   public static async function beforeFirstTestAsync(): Awaitable<void> {
-    $ret = self::getBuilder(
-      'discard-additional-properties-schema.json',
-      'DiscardAddititionalPropertiesValidator',
-    );
+    $ret = self::getBuilder('discard-additional-properties-schema.json', 'DiscardAddititionalPropertiesValidator');
     $ret['codegen']->build();
     require_once($ret['path']);
   }

tests/UntypedSchemaValidatorTest.php

@@ -202,4 +202,36 @@ public function testAnyOfOptimizedEnumCoercionInvalid(): void {
     expect($error['pointer'] ?? null)->toBeSame('/any_of_optimized_enum');
   }
 
+  public function testOneOfNullableString(): void {
+    $this->expectCases(
+      vec[
+        shape('input' => 'foo', 'output' => dict['one_of_nullable_string' => 'foo'], 'valid' => true),
+        shape('input' => null, 'output' => dict['one_of_nullable_string' => null], 'valid' => true),
+        shape('input' => true, 'valid' => false),
+      ],
+      $input ==> new UntypedSchemaValidator(dict['one_of_nullable_string' => $input]),
+    );
+  }
+
+  public function testOneOfStringAndInt(): void {
+    $this->expectCases(
+      vec[
+        shape('input' => 'foo', 'output' => dict['one_of_string_and_int' => 'foo'], 'valid' => true),
+        shape('input' => 3, 'output' => dict['one_of_string_and_int' => 3], 'valid' => true),
+        shape('input' => true, 'valid' => false),
+      ],
+      $input ==> new UntypedSchemaValidator(dict['one_of_string_and_int' => $input]),
+    );
+  }
+
+  public function testOneOfStringAndVec(): void {
+    $this->expectCases(
+      vec[
+        shape('input' => 'foo', 'output' => dict['one_of_string_and_vec' => 'foo'], 'valid' => true),
+        shape('input' => vec[3], 'output' => dict['one_of_string_and_vec' => vec[3]], 'valid' => true),
+        shape('input' => 3, 'valid' => false),
+      ],
+      $input ==> new UntypedSchemaValidator(dict['one_of_string_and_vec' => $input]),
+    );
+  }
 }

tests/examples/codegen/AddressSchemaValidator.php

@@ -5,7 +5,7 @@
  * To re-generate this file run `make test`
  *
  *
- * @generated SignedSource<<f55b7686ddc5695a203819aec8bb8742>>
+ * @generated SignedSource<<884da88463b70fac29468fab117c4e1b>>
  */
 namespace Slack\Hack\JsonSchema\Tests\Generated;
 use namespace Slack\Hack\JsonSchema;
@@ -23,7 +23,7 @@
 
 type TAddressSchemaValidatorPropertiesLongitude = mixed;
 
-type TAddressSchemaValidatorPropertiesLatitude = mixed;
+type TAddressSchemaValidatorPropertiesLatitude = num;
 
 type TAddressSchemaValidator = shape(
   ?'post-office-box' => string,
@@ -425,7 +425,7 @@ public static function check(
 
     $passed_any = false;
     $passed_multi = false;
-    $output = null;
+    $output = new \Slack\Hack\JsonSchema\Sentinal();
     foreach ($constraints as $constraint) {
       try {
         $output = $constraint($input, $pointer);
@@ -438,7 +438,7 @@ public static function check(
       }
     }
 
-    if ($passed_multi || !$passed_any) {
+    if ($passed_multi || !$passed_any || $output is \Slack\Hack\JsonSchema\Sentinal) {
       $error = shape(
         'code' => JsonSchema\FieldErrorCode::FAILED_CONSTRAINT,
         'constraint' => shape(