Fix optimize dropping only-last-event sub queries

src/Store/SubQuery.php

@@ -54,6 +54,15 @@ public function empty(): bool
 
     public function includes(SubQuery $other): bool
     {
+        // Only the last matching event is loaded. That event is only the last event
+        // of the other query as well, if both queries match exactly the same events.
+        if ($this->onlyLastEvent) {
+            return $other->onlyLastEvent
+                && $this->streamName === $other->streamName
+                && self::isSameSet($this->tags, $other->tags)
+                && self::isSameSet($this->events, $other->events);
+        }
+
         if ($this->streamName !== null && $this->streamName !== $other->streamName) {
             return false;
         }
@@ -65,11 +74,16 @@ public function includes(SubQuery $other): bool
         // events is an allow list: an empty list matches everything, so it is the
         // broadest filter. Otherwise this query only covers the other one when
         // every event the other query allows is also allowed here.
-        if ($this->events !== [] && ($other->events === [] || !self::isSubset($other->events, $this->events))) {
-            return false;
-        }
+        return $this->events === [] || ($other->events !== [] && self::isSubset($other->events, $this->events));
+    }
 
-        return !$this->onlyLastEvent || $other->onlyLastEvent;
+    /**
+     * @param list<string> $a
+     * @param list<string> $b
+     */
+    private static function isSameSet(array $a, array $b): bool
+    {
+        return self::isSubset($a, $b) && self::isSubset($b, $a);
     }
 
     /**

tests/Unit/DecisionModel/StoreDecisionModelBuilderTest.php

@@ -10,10 +10,12 @@
 use Patchlevel\EventSourcing\Store\AppendCondition;
 use Patchlevel\EventSourcing\Store\AppendStore;
 use Patchlevel\EventSourcing\Store\Header\TagsHeader;
+use Patchlevel\EventSourcing\Store\InMemoryStore;
 use Patchlevel\EventSourcing\Store\Query;
 use Patchlevel\EventSourcing\Store\SubQuery;
 use Patchlevel\EventSourcing\Tests\Unit\Fixture\Email;
 use Patchlevel\EventSourcing\Tests\Unit\Fixture\IncrementProjection;
+use Patchlevel\EventSourcing\Tests\Unit\Fixture\LastEmailProjection;
 use Patchlevel\EventSourcing\Tests\Unit\Fixture\ProfileCreated;
 use Patchlevel\EventSourcing\Tests\Unit\Fixture\ProfileId;
 use PHPUnit\Framework\Attributes\CoversClass;
@@ -67,6 +69,29 @@ public function testWithProjections(): void
         self::assertEquals(new AppendCondition($expectedQuery, 1), $state->appendCondition);
     }
 
+    public function testOnlyLastEventProjectionsWithOverlappingTags(): void
+    {
+        $store = new InMemoryStore();
+        $store->save(
+            Message::create(new ProfileCreated(ProfileId::fromString('1'), Email::fromString('first@patchlevel.de')))
+                ->withHeader(new TagsHeader(['a', 'b'])),
+            Message::create(new ProfileCreated(ProfileId::fromString('2'), Email::fromString('second@patchlevel.de')))
+                ->withHeader(new TagsHeader(['a'])),
+        );
+
+        $builder = new StoreDecisionModelBuilder($store);
+
+        $state = $builder->build([
+            'a' => new LastEmailProjection(['a']),
+            'ab' => new LastEmailProjection(['a', 'b']),
+        ]);
+
+        self::assertEquals(
+            ['a' => 'second@patchlevel.de', 'ab' => 'first@patchlevel.de'],
+            $state->state,
+        );
+    }
+
     public function testEmptyStream(): void
     {
         $store = $this->createMock(AppendStore::class);

tests/Unit/Fixture/LastEmailProjection.php

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\EventSourcing\Tests\Unit\Fixture;
+
+use Patchlevel\EventSourcing\Attribute\Apply;
+use Patchlevel\EventSourcing\Projection\BasicProjection;
+
+final class LastEmailProjection extends BasicProjection
+{
+    /** @param list<string> $tags */
+    public function __construct(
+        private readonly array $tags = [],
+    ) {
+    }
+
+    #[Apply]
+    public function applyProfileCreated(string|null $state, ProfileCreated $event): string
+    {
+        return $event->email->toString();
+    }
+
+    public function initialState(): string|null
+    {
+        return null;
+    }
+
+    /** @return list<string> */
+    public function tagFilter(): array
+    {
+        return $this->tags;
+    }
+
+    protected function lastEventIsEnough(): bool
+    {
+        return true;
+    }
+}

tests/Unit/Store/QueryTest.php

@@ -199,6 +199,48 @@ public static function providerForOptimize(): Generator
             new Query(),
         ];
 
+        yield 'only last event with fewer tags keeps narrower only last event' => [
+            new Query(
+                new SubQuery(['a'], onlyLastEvent: true),
+                new SubQuery(['a', 'b'], onlyLastEvent: true),
+            ),
+            new Query(
+                new SubQuery(['a'], onlyLastEvent: true),
+                new SubQuery(['a', 'b'], onlyLastEvent: true),
+            ),
+        ];
+
+        yield 'only last event with more events keeps narrower only last event' => [
+            new Query(
+                new SubQuery(['a'], [ProfileCreated::class], onlyLastEvent: true),
+                new SubQuery(['a'], [ProfileCreated::class, ProfileVisited::class], onlyLastEvent: true),
+            ),
+            new Query(
+                new SubQuery(['a'], [ProfileCreated::class], onlyLastEvent: true),
+                new SubQuery(['a'], [ProfileCreated::class, ProfileVisited::class], onlyLastEvent: true),
+            ),
+        ];
+
+        yield 'equal only last event subqueries' => [
+            new Query(
+                new SubQuery(['a'], [ProfileCreated::class], onlyLastEvent: true),
+                new SubQuery(['a'], [ProfileCreated::class], onlyLastEvent: true),
+            ),
+            new Query(
+                new SubQuery(['a'], [ProfileCreated::class], onlyLastEvent: true),
+            ),
+        ];
+
+        yield 'full subquery absorbs narrower only last event' => [
+            new Query(
+                new SubQuery(['a']),
+                new SubQuery(['a', 'b'], onlyLastEvent: true),
+            ),
+            new Query(
+                new SubQuery(['a']),
+            ),
+        ];
+
         yield 'empty sub query with only last event' => [
             new Query(
                 new SubQuery(

tests/Unit/Store/SubQueryTest.php

@@ -236,6 +236,42 @@ public static function providerForIncludes(): Generator
             new SubQuery(onlyLastEvent: true),
             true,
         ];
+
+        yield 'only last event with same filters includes only last event' => [
+            new SubQuery(['tag1', 'tag2'], [ProfileCreated::class, ProfileVisited::class], 'foo', true),
+            new SubQuery(['tag2', 'tag1'], [ProfileVisited::class, ProfileCreated::class], 'foo', true),
+            true,
+        ];
+
+        yield 'only last event with fewer tags does not include only last event' => [
+            new SubQuery(['tag1'], onlyLastEvent: true),
+            new SubQuery(['tag1', 'tag2'], onlyLastEvent: true),
+            false,
+        ];
+
+        yield 'only last event with more events does not include only last event' => [
+            new SubQuery(['tag1'], [ProfileCreated::class, ProfileVisited::class], onlyLastEvent: true),
+            new SubQuery(['tag1'], [ProfileCreated::class], onlyLastEvent: true),
+            false,
+        ];
+
+        yield 'only last event with all events does not include only last event' => [
+            new SubQuery(['tag1'], onlyLastEvent: true),
+            new SubQuery(['tag1'], [ProfileCreated::class], onlyLastEvent: true),
+            false,
+        ];
+
+        yield 'only last event without stream name does not include only last event' => [
+            new SubQuery(['tag1'], onlyLastEvent: true),
+            new SubQuery(['tag1'], streamName: 'foo', onlyLastEvent: true),
+            false,
+        ];
+
+        yield 'empty only last event does not include only last event' => [
+            new SubQuery(onlyLastEvent: true),
+            new SubQuery(['tag1'], onlyLastEvent: true),
+            false,
+        ];
     }
 
     /**