fix(index): read a stored index that covers a deleted attribute

src/Database/Index.php

@@ -132,12 +132,18 @@ public static function ttl(string $key, string $attribute, int $ttl): self
      */
     public static function fromDocument(Document $document): self
     {
-        return self::hydrate(
-            self::storedKey($document),
-            $document->getAttribute(self::TYPE, IndexType::Key->value),
+        [$attributes, $lengths, $orders] = self::withoutDroppedAttributes(
             $document->getAttribute(self::ATTRIBUTES, []),
             $document->getAttribute(self::LENGTHS, []),
             $document->getAttribute(self::ORDERS, []),
+        );
+
+        return self::hydrate(
+            self::storedKey($document),
+            $document->getAttribute(self::TYPE, IndexType::Key->value),
+            $attributes,
+            $lengths,
+            $orders,
             $document->getAttribute(self::TTL),
         );
     }
@@ -176,6 +182,27 @@ private static function storedKey(Document $document): mixed
         return \is_string($key) && $id === '_'.$key && \str_starts_with($id, '_index_') ? $id : $key;
     }
 
+    /**
+     * 7.x left null in a stored index's attributes when an attribute it covered was deleted, while the engine dropped
+     * that column from the index. Such an index is read as covering the attributes it still has, with the lengths and
+     * orders at their positions.
+     *
+     * @return array{mixed, mixed, mixed}
+     */
+    private static function withoutDroppedAttributes(mixed $attributes, mixed $lengths, mixed $orders): array
+    {
+        if (! \is_array($attributes) || ! \in_array(null, $attributes, true)) {
+            return [$attributes, $lengths, $orders];
+        }
+
+        $kept = \array_flip(\array_keys(\array_filter($attributes, static fn (mixed $attribute): bool => $attribute !== null)));
+        $alongside = static fn (mixed $values): mixed => \is_array($values) && \count($values) === \count($attributes)
+            ? \array_values(\array_intersect_key($values, $kept))
+            : $values;
+
+        return [\array_values(\array_intersect_key($attributes, $kept)), $alongside($lengths), $alongside($orders)];
+    }
+
     /**
      * @internal
      */

tests/unit/Indexes/LegacyDroppedAttributeIndexTest.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace Tests\Unit\Indexes;
+
+use PHPUnit\Framework\TestCase;
+use Utopia\Database\Attribute;
+use Utopia\Database\Collection;
+use Utopia\Database\Document;
+use Utopia\Database\Exception\Index as IndexException;
+use Utopia\Database\Index;
+use Utopia\Query\OrderDirection;
+
+final class LegacyDroppedAttributeIndexTest extends TestCase
+{
+    public function testAFulltextIndexWhoseOnlyAttributeWasDeletedIsReadWithNoAttributes(): void
+    {
+        $index = Index::fromDocument(new Document(['$id' => 'category', 'key' => 'category', 'type' => 'fulltext', 'attributes' => [null], 'orders' => ['ASC'], 'lengths' => [200]]));
+
+        $this->assertSame('category', $index->key);
+        $this->assertSame([], $index->attributes);
+        $this->assertSame([], $index->lengths);
+        $this->assertSame([], $index->orders);
+    }
+
+    public function testAUniqueIndexKeepsTheAttributesItStillCoversWithTheirLengthsAndOrders(): void
+    {
+        $index = Index::fromDocument(new Document(['$id' => 'index_2', 'key' => 'index_2', 'type' => 'unique', 'attributes' => ['playId', null], 'orders' => ['ASC', 'ASC'], 'lengths' => [null, null]]));
+
+        $this->assertSame(['playId'], $index->attributes);
+        $this->assertSame([null], $index->lengths);
+        $this->assertSame([OrderDirection::Asc], $index->orders);
+    }
+
+    public function testADroppedAttributeBetweenOthersKeepsEachLengthAndOrderAtItsAttribute(): void
+    {
+        $index = Index::fromDocument(new Document(['$id' => 'mixed', 'key' => 'mixed', 'type' => 'key', 'attributes' => ['a', null, 'c'], 'orders' => ['ASC', 'DESC', 'DESC'], 'lengths' => [10, 20, 30]]));
+
+        $this->assertSame(['a', 'c'], $index->attributes);
+        $this->assertSame([10, 30], $index->lengths);
+        $this->assertSame([OrderDirection::Asc, OrderDirection::Desc], $index->orders);
+    }
+
+    public function testACollectionHoldingSuchAnIndexIsRead(): void
+    {
+        $collection = Collection::fromDocument(new Document([
+            '$id' => 'plays',
+            'name' => 'plays',
+            'attributes' => [Attribute::string(key: 'playId', size: 36)->toDocument()],
+            'indexes' => [new Document(['$id' => 'index_2', 'key' => 'index_2', 'type' => 'unique', 'attributes' => ['playId', null], 'orders' => ['ASC', 'ASC'], 'lengths' => [null, null]])],
+        ]));
+
+        $this->assertSame(['playId'], $collection->indexes()[0]->attributes);
+    }
+
+    public function testAnIndexDefinedByACallerStillRefusesAnAttributeThatIsNotAString(): void
+    {
+        $this->expectException(IndexException::class);
+        $this->expectExceptionMessage('Index attributes must be strings');
+
+        Index::fromArray(['$id' => 'bad', 'type' => 'key', 'attributes' => ['playId', null]]);
+    }
+}