From d393799d2aa6be734ac098d4576a3c44edc3c858 Mon Sep 17 00:00:00 2001
From: oddvalue <jim@oddvalue.co.uk>
Date: Fri, 12 Jun 2026 20:06:50 +0100
Subject: [PATCH] Optimize `buildFilterArgument` in `Shard` plugin for compact
 regex generation and add comprehensive tests (#1675)

---
 src/Plugins/Shard.php        | 33 ++++++++++++-
 tests/Unit/Plugins/Shard.php | 92 ++++++++++++++++++++++++++++++++++++
 2 files changed, 124 insertions(+), 1 deletion(-)

diff --git a/src/Plugins/Shard.php b/src/Plugins/Shard.php
index 92b782b6..b08dd1dd 100644
--- a/src/Plugins/Shard.php
+++ b/src/Plugins/Shard.php
@@ -225,7 +225,38 @@ final class Shard implements AddsOutput, HandlesArguments, Terminable
      */
     private function buildFilterArgument(array $testsToRun): string
     {
-        return addslashes(implode('|', $testsToRun));
+        if ($testsToRun === []) {
+            return '';
+        }
+
+        /** @var array<string, mixed> $tree */
+        $tree = [];
+        foreach ($testsToRun as $class) {
+            $parts = explode('\\', $class);
+            $current = &$tree;
+            foreach ($parts as $part) {
+                if (! isset($current[$part])) {
+                    $current[$part] = [];
+                }
+                $current = &$current[$part];
+            }
+        }
+
+        $buildRegex = function (array $tree) use (&$buildRegex): string {
+            $parts = [];
+            foreach ($tree as $key => $sub) {
+                $subRegex = $buildRegex($sub);
+                if ($subRegex === '') {
+                    $parts[] = preg_quote($key, '/');
+                } else {
+                    $parts[] = preg_quote($key, '/').'\\\\'.(count($sub) > 1 ? '('.$subRegex.')' : $subRegex);
+                }
+            }
+
+            return implode('|', $parts);
+        };
+
+        return $buildRegex($tree);
     }
 
     /**
diff --git a/tests/Unit/Plugins/Shard.php b/tests/Unit/Plugins/Shard.php
index f23e8581..bd5a5e06 100644
--- a/tests/Unit/Plugins/Shard.php
+++ b/tests/Unit/Plugins/Shard.php
@@ -50,6 +50,98 @@ describe('getShard', function () {
     ])->throws(InvalidOption::class);
 });
 
+describe('buildFilterArgument', function () {
+    it('generates compact filter for single test', function () {
+        $output = new BufferedOutput;
+        $shard = new Shard($output);
+
+        $reflection = new ReflectionClass($shard);
+        $method = $reflection->getMethod('buildFilterArgument');
+
+        $filter = $method->invoke($shard, ['Tests\\Unit\\ExampleTest']);
+
+        expect($filter)->toBe('Tests\\\\Unit\\\\ExampleTest');
+    });
+
+    it('generates compact filter for multiple tests with common prefix', function () {
+        $output = new BufferedOutput;
+        $shard = new Shard($output);
+
+        $reflection = new ReflectionClass($shard);
+        $method = $reflection->getMethod('buildFilterArgument');
+
+        $filter = $method->invoke($shard, [
+            'Tests\\Unit\\Foo\\BarTest',
+            'Tests\\Unit\\Foo\\BazTest',
+        ]);
+
+        expect($filter)->toBe('Tests\\\\Unit\\\\Foo\\\\(BarTest|BazTest)');
+    });
+
+    it('generates compact filter for tests with different namespaces', function () {
+        $output = new BufferedOutput;
+        $shard = new Shard($output);
+
+        $reflection = new ReflectionClass($shard);
+        $method = $reflection->getMethod('buildFilterArgument');
+
+        $filter = $method->invoke($shard, [
+            'Tests\\Unit\\FooTest',
+            'Tests\\Feature\\BarTest',
+        ]);
+
+        expect($filter)->toBe('Tests\\\\(Unit\\\\FooTest|Feature\\\\BarTest)');
+    });
+
+    it('returns empty string for empty test list', function () {
+        $output = new BufferedOutput;
+        $shard = new Shard($output);
+
+        $reflection = new ReflectionClass($shard);
+        $method = $reflection->getMethod('buildFilterArgument');
+
+        $filter = $method->invoke($shard, []);
+
+        expect($filter)->toBe('');
+    });
+
+    it('generates compact filter for deeply nested namespaces', function () {
+        $output = new BufferedOutput;
+        $shard = new Shard($output);
+
+        $reflection = new ReflectionClass($shard);
+        $method = $reflection->getMethod('buildFilterArgument');
+
+        $filter = $method->invoke($shard, [
+            'Tests\\Unit\\Plugins\\Concerns\\Foo',
+            'Tests\\Unit\\Plugins\\Concerns\\Bar',
+            'Tests\\Unit\\Plugins\\Concerns\\Baz',
+        ]);
+
+        expect($filter)->toBe('Tests\\\\Unit\\\\Plugins\\\\Concerns\\\\(Foo|Bar|Baz)');
+    });
+
+    it('handles mix of nested and flat namespaces', function () {
+        $output = new BufferedOutput;
+        $shard = new Shard($output);
+
+        $reflection = new ReflectionClass($shard);
+        $method = $reflection->getMethod('buildFilterArgument');
+
+        $tests = [
+            'Tests\\Unit\\SimpleTest',
+            'Tests\\Unit\\Plugins\\Concerns\\HandleArguments',
+            'Tests\\Unit\\Plugins\\Concerns\\Validation',
+            'Tests\\Unit\\Another\\Deep\\Nested\\Test',
+        ];
+
+        $filter = $method->invoke($shard, $tests);
+
+        expect($filter)
+            ->toBe(addslashes('Tests\\Unit\\(SimpleTest|Plugins\\Concerns\\(HandleArguments|Validation)|Another\\Deep\\Nested\\Test)'));
+    });
+});
+
 describe('ensureFilterLengthIsSafe', function () {
     it('accepts filter within length limit', function () {
         $output = new BufferedOutput;